R&D progress of the high power negative ion accelerator for the ITER NB system at JAEA
Identifieur interne : 000E41 ( Istex/Corpus ); précédent : 000E40; suivant : 000E42R&D progress of the high power negative ion accelerator for the ITER NB system at JAEA
Auteurs : M. Kashiwagi ; M. Taniguchi ; M. Dairaku ; H. P. L. De Esch ; L. R. Grisham ; L. Svensson ; H. Tobari ; N. Umeda ; K. Watanabe ; K. Sakamoto ; T. InoueSource :
- Nuclear Fusion [ 0029-5515 ] ; 2009.
Abstract
At JAEA, as the Japan Domestic Agency (JADA) for ITER, a MAMuG (multi-aperture multi-grid) accelerator has been developed to perform the required R&D for the ITER neutral beam (NB) system. As a result of countermeasures to handle excess heat load to the ion source by backstreaming positive ions, H ion beam current was increased to 0.32A (the ion current density of 140Am2) at a beam energy of 796keV. This high power beam acceleration simulated the ITER operation condition maintaining the perveance (H ion current density/beam energy3/2) of the ITER accelerator. After the high power beam operation, the pulse length was successfully extended from 0.2 to 5s at 550keV, which yielded a 131mA H ion beam as an initial test of the long pulse operation. A test of a single-aperture single-gap (SINGAP) accelerator was performed at JAEA under an ITER R&D task agreement. The objective of this test was to compare two different accelerator concepts (SINGAP and MAMuG) at the same test facility. As a result, the MAMuG accelerator was defined as the baseline design for ITER, due to advantages in its better voltage holding and less electron acceleration. In three-dimensional beam trajectory analyses, the aperture offset at the bottom of the extractor was found to be effective for compensation of beamlet deflection due to their own space charge. It has been analytically demonstrated that these compensated beamlets can be focused at a focal point by adopting the aperture offset at the final grid of the accelerator.
Url:
DOI: 10.1088/0029-5515/49/6/065008
Links to Exploration step
ISTEX:6742B0FA9A751F7C6C9DEF4D6C0F471082BB2376Le document en format XML
<record><TEI wicri:istexFullTextTei="biblStruct"><teiHeader><fileDesc><titleStmt><title>R&D progress of the high power negative ion accelerator for the ITER NB system at JAEA</title><author><name sortKey="Kashiwagi, M" sort="Kashiwagi, M" uniqKey="Kashiwagi M" first="M." last="Kashiwagi">M. Kashiwagi</name><affiliation><mods:affiliation>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</mods:affiliation></affiliation><affiliation><mods:affiliation>E-mail:kashiwagi.mieko@jaea.go.jp</mods:affiliation></affiliation></author><author><name sortKey="Taniguchi, M" sort="Taniguchi, M" uniqKey="Taniguchi M" first="M." last="Taniguchi">M. Taniguchi</name><affiliation><mods:affiliation>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</mods:affiliation></affiliation></author><author><name sortKey="Dairaku, M" sort="Dairaku, M" uniqKey="Dairaku M" first="M." last="Dairaku">M. Dairaku</name><affiliation><mods:affiliation>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</mods:affiliation></affiliation></author><author><name sortKey="De Esch, H P L" sort="De Esch, H P L" uniqKey="De Esch H" first="H. P. L." last="De Esch">H. P. L. De Esch</name><affiliation><mods:affiliation>CEA Cadarache, F-13108, St Paul-lez-Durance, CEDEX, France</mods:affiliation></affiliation></author><author><name sortKey="Grisham, L R" sort="Grisham, L R" uniqKey="Grisham L" first="L. R." last="Grisham">L. R. Grisham</name><affiliation><mods:affiliation>Plasma Physics Laboratory, Princeton University, PO Box 451, Princeton, NJ 08543, USA</mods:affiliation></affiliation></author><author><name sortKey="Svensson, L" sort="Svensson, L" uniqKey="Svensson L" first="L." last="Svensson">L. Svensson</name><affiliation><mods:affiliation>CEA Cadarache, F-13108, St Paul-lez-Durance, CEDEX, France</mods:affiliation></affiliation></author><author><name sortKey="Tobari, H" sort="Tobari, H" uniqKey="Tobari H" first="H." last="Tobari">H. Tobari</name><affiliation><mods:affiliation>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</mods:affiliation></affiliation></author><author><name sortKey="Umeda, N" sort="Umeda, N" uniqKey="Umeda N" first="N." last="Umeda">N. Umeda</name><affiliation><mods:affiliation>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</mods:affiliation></affiliation></author><author><name sortKey="Watanabe, K" sort="Watanabe, K" uniqKey="Watanabe K" first="K." last="Watanabe">K. Watanabe</name><affiliation><mods:affiliation>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</mods:affiliation></affiliation></author><author><name sortKey="Sakamoto, K" sort="Sakamoto, K" uniqKey="Sakamoto K" first="K." last="Sakamoto">K. Sakamoto</name><affiliation><mods:affiliation>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</mods:affiliation></affiliation></author><author><name sortKey="Inoue, T" sort="Inoue, T" uniqKey="Inoue T" first="T." last="Inoue">T. Inoue</name><affiliation><mods:affiliation>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</mods:affiliation></affiliation></author></titleStmt><publicationStmt><idno type="wicri:source">ISTEX</idno><idno type="RBID">ISTEX:6742B0FA9A751F7C6C9DEF4D6C0F471082BB2376</idno><date when="2009" year="2009">2009</date><idno type="doi">10.1088/0029-5515/49/6/065008</idno><idno type="url">https://api.istex.fr/document/6742B0FA9A751F7C6C9DEF4D6C0F471082BB2376/fulltext/pdf</idno><idno type="wicri:Area/Istex/Corpus">000E41</idno></publicationStmt><sourceDesc><biblStruct><analytic><title level="a">R&D progress of the high power negative ion accelerator for the ITER NB system at JAEA</title><author><name sortKey="Kashiwagi, M" sort="Kashiwagi, M" uniqKey="Kashiwagi M" first="M." last="Kashiwagi">M. Kashiwagi</name><affiliation><mods:affiliation>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</mods:affiliation></affiliation><affiliation><mods:affiliation>E-mail:kashiwagi.mieko@jaea.go.jp</mods:affiliation></affiliation></author><author><name sortKey="Taniguchi, M" sort="Taniguchi, M" uniqKey="Taniguchi M" first="M." last="Taniguchi">M. Taniguchi</name><affiliation><mods:affiliation>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</mods:affiliation></affiliation></author><author><name sortKey="Dairaku, M" sort="Dairaku, M" uniqKey="Dairaku M" first="M." last="Dairaku">M. Dairaku</name><affiliation><mods:affiliation>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</mods:affiliation></affiliation></author><author><name sortKey="De Esch, H P L" sort="De Esch, H P L" uniqKey="De Esch H" first="H. P. L." last="De Esch">H. P. L. De Esch</name><affiliation><mods:affiliation>CEA Cadarache, F-13108, St Paul-lez-Durance, CEDEX, France</mods:affiliation></affiliation></author><author><name sortKey="Grisham, L R" sort="Grisham, L R" uniqKey="Grisham L" first="L. R." last="Grisham">L. R. Grisham</name><affiliation><mods:affiliation>Plasma Physics Laboratory, Princeton University, PO Box 451, Princeton, NJ 08543, USA</mods:affiliation></affiliation></author><author><name sortKey="Svensson, L" sort="Svensson, L" uniqKey="Svensson L" first="L." last="Svensson">L. Svensson</name><affiliation><mods:affiliation>CEA Cadarache, F-13108, St Paul-lez-Durance, CEDEX, France</mods:affiliation></affiliation></author><author><name sortKey="Tobari, H" sort="Tobari, H" uniqKey="Tobari H" first="H." last="Tobari">H. Tobari</name><affiliation><mods:affiliation>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</mods:affiliation></affiliation></author><author><name sortKey="Umeda, N" sort="Umeda, N" uniqKey="Umeda N" first="N." last="Umeda">N. Umeda</name><affiliation><mods:affiliation>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</mods:affiliation></affiliation></author><author><name sortKey="Watanabe, K" sort="Watanabe, K" uniqKey="Watanabe K" first="K." last="Watanabe">K. Watanabe</name><affiliation><mods:affiliation>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</mods:affiliation></affiliation></author><author><name sortKey="Sakamoto, K" sort="Sakamoto, K" uniqKey="Sakamoto K" first="K." last="Sakamoto">K. Sakamoto</name><affiliation><mods:affiliation>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</mods:affiliation></affiliation></author><author><name sortKey="Inoue, T" sort="Inoue, T" uniqKey="Inoue T" first="T." last="Inoue">T. Inoue</name><affiliation><mods:affiliation>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</mods:affiliation></affiliation></author></analytic><monogr></monogr><series><title level="j">Nuclear Fusion</title><title level="j" type="abbrev">Nucl. Fusion</title><idno type="ISSN">0029-5515</idno><idno type="eISSN">1741-4326</idno><imprint><publisher>IOP Publishing and International Atomic Energy Agency</publisher><date type="published" when="2009">2009</date><biblScope unit="volume">49</biblScope><biblScope unit="issue">6</biblScope><biblScope unit="page" from="1">1</biblScope><biblScope unit="page" to="7">7</biblScope><biblScope unit="production">Printed in the UK</biblScope></imprint><idno type="ISSN">0029-5515</idno></series><idno type="istex">6742B0FA9A751F7C6C9DEF4D6C0F471082BB2376</idno><idno type="DOI">10.1088/0029-5515/49/6/065008</idno><idno type="PII">S0029-5515(09)03675-8</idno><idno type="articleID">303675</idno><idno type="articleNumber">065008</idno></biblStruct></sourceDesc><seriesStmt><idno type="ISSN">0029-5515</idno></seriesStmt></fileDesc><profileDesc><textClass></textClass><langUsage><language ident="en">en</language></langUsage></profileDesc></teiHeader><front><div type="abstract">At JAEA, as the Japan Domestic Agency (JADA) for ITER, a MAMuG (multi-aperture multi-grid) accelerator has been developed to perform the required R&D for the ITER neutral beam (NB) system. As a result of countermeasures to handle excess heat load to the ion source by backstreaming positive ions, H ion beam current was increased to 0.32A (the ion current density of 140Am2) at a beam energy of 796keV. This high power beam acceleration simulated the ITER operation condition maintaining the perveance (H ion current density/beam energy3/2) of the ITER accelerator. After the high power beam operation, the pulse length was successfully extended from 0.2 to 5s at 550keV, which yielded a 131mA H ion beam as an initial test of the long pulse operation. A test of a single-aperture single-gap (SINGAP) accelerator was performed at JAEA under an ITER R&D task agreement. The objective of this test was to compare two different accelerator concepts (SINGAP and MAMuG) at the same test facility. As a result, the MAMuG accelerator was defined as the baseline design for ITER, due to advantages in its better voltage holding and less electron acceleration. In three-dimensional beam trajectory analyses, the aperture offset at the bottom of the extractor was found to be effective for compensation of beamlet deflection due to their own space charge. It has been analytically demonstrated that these compensated beamlets can be focused at a focal point by adopting the aperture offset at the final grid of the accelerator.</div></front></TEI><istex><corpusName>iop</corpusName><author><json:item><name>M. Kashiwagi</name><affiliations><json:string>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</json:string><json:string>E-mail:kashiwagi.mieko@jaea.go.jp</json:string></affiliations></json:item><json:item><name>M. Taniguchi</name><affiliations><json:string>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</json:string></affiliations></json:item><json:item><name>M. Dairaku</name><affiliations><json:string>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</json:string></affiliations></json:item><json:item><name>H.P.L. de Esch</name><affiliations><json:string>CEA Cadarache, F-13108, St Paul-lez-Durance, CEDEX, France</json:string></affiliations></json:item><json:item><name>L.R. Grisham</name><affiliations><json:string>Plasma Physics Laboratory, Princeton University, PO Box 451, Princeton, NJ 08543, USA</json:string></affiliations></json:item><json:item><name>L. Svensson</name><affiliations><json:string>CEA Cadarache, F-13108, St Paul-lez-Durance, CEDEX, France</json:string></affiliations></json:item><json:item><name>H. Tobari</name><affiliations><json:string>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</json:string></affiliations></json:item><json:item><name>N. Umeda</name><affiliations><json:string>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</json:string></affiliations></json:item><json:item><name>K. Watanabe</name><affiliations><json:string>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</json:string></affiliations></json:item><json:item><name>K. Sakamoto</name><affiliations><json:string>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</json:string></affiliations></json:item><json:item><name>T. Inoue</name><affiliations><json:string>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</json:string></affiliations></json:item></author><language><json:string>eng</json:string></language><abstract>At JAEA, as the Japan Domestic Agency (JADA) for ITER, a MAMuG (multi-aperture multi-grid) accelerator has been developed to perform the required R&D for the ITER neutral beam (NB) system. As a result of countermeasures to handle excess heat load to the ion source by backstreaming positive ions, H ion beam current was increased to 0.32A (the ion current density of 140Am2) at a beam energy of 796keV. This high power beam acceleration simulated the ITER operation condition maintaining the perveance (H ion current density/beam energy3/2) of the ITER accelerator. After the high power beam operation, the pulse length was successfully extended from 0.2 to 5s at 550keV, which yielded a 131mA H ion beam as an initial test of the long pulse operation. A test of a single-aperture single-gap (SINGAP) accelerator was performed at JAEA under an ITER R&D task agreement. The objective of this test was to compare two different accelerator concepts (SINGAP and MAMuG) at the same test facility. As a result, the MAMuG accelerator was defined as the baseline design for ITER, due to advantages in its better voltage holding and less electron acceleration. In three-dimensional beam trajectory analyses, the aperture offset at the bottom of the extractor was found to be effective for compensation of beamlet deflection due to their own space charge. It has been analytically demonstrated that these compensated beamlets can be focused at a focal point by adopting the aperture offset at the final grid of the accelerator.</abstract><qualityIndicators><score>7.877</score><pdfVersion>1.4</pdfVersion><pdfPageSize>595 x 841 pts</pdfPageSize><refBibsNative>true</refBibsNative><keywordCount>0</keywordCount><abstractCharCount>1517</abstractCharCount><pdfWordCount>4425</pdfWordCount><pdfCharCount>24344</pdfCharCount><pdfPageCount>7</pdfPageCount><abstractWordCount>246</abstractWordCount></qualityIndicators><title>R&D progress of the high power negative ion accelerator for the ITER NB system at JAEA</title><pii><json:string>S0029-5515(09)03675-8</json:string></pii><genre><json:string>article</json:string></genre><host><volume>49</volume><pages><total>7</total><last>7</last><first>1</first></pages><issn><json:string>0029-5515</json:string></issn><issue>6</issue><genre></genre><language><json:string>unknown</json:string></language><eissn><json:string>1741-4326</json:string></eissn><title>Nuclear Fusion</title></host><publicationDate>2009</publicationDate><copyrightDate>2009</copyrightDate><doi><json:string>10.1088/0029-5515/49/6/065008</json:string></doi><id>6742B0FA9A751F7C6C9DEF4D6C0F471082BB2376</id><fulltext><json:item><original>true</original><mimetype>application/pdf</mimetype><extension>pdf</extension><uri>https://api.istex.fr/document/6742B0FA9A751F7C6C9DEF4D6C0F471082BB2376/fulltext/pdf</uri></json:item><json:item><original>false</original><mimetype>application/zip</mimetype><extension>zip</extension><uri>https://api.istex.fr/document/6742B0FA9A751F7C6C9DEF4D6C0F471082BB2376/fulltext/zip</uri></json:item><istex:fulltextTEI uri="https://api.istex.fr/document/6742B0FA9A751F7C6C9DEF4D6C0F471082BB2376/fulltext/tei"><teiHeader><fileDesc><titleStmt><title level="a">R&D progress of the high power negative ion accelerator for the ITER NB system at JAEA</title></titleStmt><publicationStmt><authority>ISTEX</authority><publisher>IOP Publishing and International Atomic Energy Agency</publisher><availability><p>IOP</p></availability><date>2009</date></publicationStmt><sourceDesc><biblStruct type="inbook"><analytic><title level="a">R&D progress of the high power negative ion accelerator for the ITER NB system at JAEA</title><author><persName><forename type="first">M.</forename><surname>Kashiwagi</surname></persName><affiliation>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</affiliation><affiliation>E-mail:kashiwagi.mieko@jaea.go.jp</affiliation></author><author><persName><forename type="first">M.</forename><surname>Taniguchi</surname></persName><affiliation>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</affiliation></author><author><persName><forename type="first">M.</forename><surname>Dairaku</surname></persName><affiliation>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</affiliation></author><author><persName><forename type="first">H.P.L.</forename><surname>de Esch</surname></persName><affiliation>CEA Cadarache, F-13108, St Paul-lez-Durance, CEDEX, France</affiliation></author><author><persName><forename type="first">L.R.</forename><surname>Grisham</surname></persName><affiliation>Plasma Physics Laboratory, Princeton University, PO Box 451, Princeton, NJ 08543, USA</affiliation></author><author><persName><forename type="first">L.</forename><surname>Svensson</surname></persName><affiliation>CEA Cadarache, F-13108, St Paul-lez-Durance, CEDEX, France</affiliation></author><author><persName><forename type="first">H.</forename><surname>Tobari</surname></persName><affiliation>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</affiliation></author><author><persName><forename type="first">N.</forename><surname>Umeda</surname></persName><affiliation>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</affiliation></author><author><persName><forename type="first">K.</forename><surname>Watanabe</surname></persName><affiliation>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</affiliation></author><author><persName><forename type="first">K.</forename><surname>Sakamoto</surname></persName><affiliation>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</affiliation></author><author><persName><forename type="first">T.</forename><surname>Inoue</surname></persName><affiliation>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</affiliation></author></analytic><monogr><title level="j">Nuclear Fusion</title><title level="j" type="abbrev">Nucl. Fusion</title><idno type="pISSN">0029-5515</idno><idno type="eISSN">1741-4326</idno><imprint><publisher>IOP Publishing and International Atomic Energy Agency</publisher><date type="published" when="2009"></date><biblScope unit="volume">49</biblScope><biblScope unit="issue">6</biblScope><biblScope unit="page" from="1">1</biblScope><biblScope unit="page" to="7">7</biblScope><biblScope unit="production">Printed in the UK</biblScope></imprint></monogr><idno type="istex">6742B0FA9A751F7C6C9DEF4D6C0F471082BB2376</idno><idno type="DOI">10.1088/0029-5515/49/6/065008</idno><idno type="PII">S0029-5515(09)03675-8</idno><idno type="articleID">303675</idno><idno type="articleNumber">065008</idno></biblStruct></sourceDesc></fileDesc><profileDesc><creation><date>2009</date></creation><langUsage><language ident="en">en</language></langUsage><abstract><p>At JAEA, as the Japan Domestic Agency (JADA) for ITER, a MAMuG (multi-aperture multi-grid) accelerator has been developed to perform the required R&D for the ITER neutral beam (NB) system. As a result of countermeasures to handle excess heat load to the ion source by backstreaming positive ions, H ion beam current was increased to 0.32A (the ion current density of 140Am2) at a beam energy of 796keV. This high power beam acceleration simulated the ITER operation condition maintaining the perveance (H ion current density/beam energy3/2) of the ITER accelerator. After the high power beam operation, the pulse length was successfully extended from 0.2 to 5s at 550keV, which yielded a 131mA H ion beam as an initial test of the long pulse operation. A test of a single-aperture single-gap (SINGAP) accelerator was performed at JAEA under an ITER R&D task agreement. The objective of this test was to compare two different accelerator concepts (SINGAP and MAMuG) at the same test facility. As a result, the MAMuG accelerator was defined as the baseline design for ITER, due to advantages in its better voltage holding and less electron acceleration. In three-dimensional beam trajectory analyses, the aperture offset at the bottom of the extractor was found to be effective for compensation of beamlet deflection due to their own space charge. It has been analytically demonstrated that these compensated beamlets can be focused at a focal point by adopting the aperture offset at the final grid of the accelerator.</p></abstract><textClass><classCode scheme="">41.75.Cn</classCode><classCode scheme="">41.85.Lc</classCode></textClass></profileDesc><revisionDesc><change when="2009">Published</change></revisionDesc></teiHeader></istex:fulltextTEI><json:item><original>false</original><mimetype>text/plain</mimetype><extension>txt</extension><uri>https://api.istex.fr/document/6742B0FA9A751F7C6C9DEF4D6C0F471082BB2376/fulltext/txt</uri></json:item></fulltext><metadata><istex:metadataXml wicri:clean="corpus iop not found" wicri:toSee="no header"><istex:xmlDeclaration>version="1.0" encoding="ISO-8859-1"</istex:xmlDeclaration><istex:docType SYSTEM="http://ej.iop.org/dtd/iopv1_5_2.dtd" name="istex:docType"></istex:docType><istex:document><article artid="nf303675"><article-metadata><jnl-data jnlid="nf"><jnl-fullname>Nuclear Fusion</jnl-fullname><jnl-abbreviation>Nucl. Fusion</jnl-abbreviation><jnl-shortname>NF</jnl-shortname><jnl-issn>0029-5515</jnl-issn><jnl-coden>NUFUAU</jnl-coden><jnl-imprint>IOP Publishing and International Atomic Energy Agency</jnl-imprint><jnl-web-address>stacks.iop.org/NF</jnl-web-address></jnl-data><volume-data><year-publication>2009</year-publication><volume-number>49</volume-number></volume-data><issue-data><issue-number>6</issue-number><coverdate>June 2009</coverdate></issue-data><article-data><article-type type="paper" sort="regular"></article-type><type-number type="paper" numbering="article" artnum="065008"></type-number><article-number>303675</article-number><first-page>1</first-page><last-page>7</last-page><length>7</length><pii>S0029-5515(09)03675-8</pii><doi>10.1088/0029-5515/49/6/065008</doi><copyright>2009 IAEA, Vienna</copyright><ccc>0029-5515/09/065008+07$30.00</ccc><printed>Printed in the UK</printed><features colour="global" mmedia="no" suppdata="no"></features></article-data></article-metadata><header><title-group><title>R&D progress of the high power negative ion accelerator for the ITER NB system at JAEA</title><short-title>R&D progress of the high power negative ion accelerator for the ITER NB system at JAEA</short-title><ej-title>R&D progress of the high power negative ion accelerator for the ITER NB system at JAEA</ej-title></title-group><author-group><author address="nf303675ad1" email="nf303675ea1"><first-names>M.</first-names><second-name>Kashiwagi</second-name></author><author address="nf303675ad1"><first-names>M.</first-names><second-name>Taniguchi</second-name></author><author address="nf303675ad1"><first-names>M.</first-names><second-name>Dairaku</second-name></author><author address="nf303675ad2"><first-names>H.P.L.</first-names><second-name>de Esch</second-name></author><author address="nf303675ad3"><first-names>L.R.</first-names><second-name>Grisham</second-name></author><author address="nf303675ad2"><first-names>L.</first-names><second-name>Svensson</second-name></author><author address="nf303675ad1"><first-names>H.</first-names><second-name>Tobari</second-name></author><author address="nf303675ad1"><first-names>N.</first-names><second-name>Umeda</second-name></author><author address="nf303675ad1"><first-names>K.</first-names><second-name>Watanabe</second-name></author><author address="nf303675ad1"><first-names>K.</first-names><second-name>Sakamoto</second-name></author><author address="nf303675ad1"><first-names>T.</first-names><second-name>Inoue</second-name></author></author-group><address-group><address id="nf303675ad1"><orgname>Japan Atomic Energy Agency (JAEA)</orgname>, 801-1 Mukouyama, Naka 311-0193, <country>Japan</country></address><address id="nf303675ad2"><orgname>CEA Cadarache</orgname>, F-13108, St Paul-lez-Durance, CEDEX, <country>France</country></address><address id="nf303675ad3"><orgname>Plasma Physics Laboratory, Princeton University</orgname>, PO Box 451, Princeton, NJ 08543, <country>USA</country></address><e-address id="nf303675ea1"><email mailto="kashiwagi.mieko@jaea.go.jp">kashiwagi.mieko@jaea.go.jp</email></e-address></address-group><history received="30 December 2008" accepted="8 April 2009" online="6 May 2009"></history><abstract-group><abstract><heading>Abstract</heading><p indent="no">At JAEA, as the Japan Domestic Agency (JADA) for ITER, a MAMuG (multi-aperture multi-grid) accelerator has been developed to perform the required R&D for the ITER neutral beam (NB) system. As a result of countermeasures to handle excess heat load to the ion source by backstreaming positive ions, H<sup>−</sup> ion beam current was increased to 0.32 A (the ion current density of 140 A m<sup>−2</sup>) at a beam energy of 796 keV. This high power beam acceleration simulated the ITER operation condition maintaining the perveance (H<sup>−</sup> ion current density/beam energy<sup>3/2</sup>) of the ITER accelerator. After the high power beam operation, the pulse length was successfully extended from 0.2 to 5 s at 550 keV, which yielded a 131 mA H<sup>−</sup> ion beam as an initial test of the long pulse operation. A test of a single-aperture single-gap (SINGAP) accelerator was performed at JAEA under an ITER R&D task agreement. The objective of this test was to compare two different accelerator concepts (SINGAP and MAMuG) at the same test facility. As a result, the MAMuG accelerator was defined as the baseline design for ITER, due to advantages in its better voltage holding and less electron acceleration. In three-dimensional beam trajectory analyses, the aperture offset at the bottom of the extractor was found to be effective for compensation of beamlet deflection due to their own space charge. It has been analytically demonstrated that these compensated beamlets can be focused at a focal point by adopting the aperture offset at the final grid of the accelerator.</p></abstract></abstract-group><classifications><class-codes scheme="pacs" print="yes"><code>41.75.Cn</code><code>41.85.Lc</code></class-codes></classifications></header><body numbering="bysection"><sec-level1 id="nf303675s1" label="1"><heading>Introduction</heading><p indent="no">In a negative ion accelerator for the ITER neutral beam (NB) system, it is required to produce D<sup>−</sup> ion beams of ion current density of 200 A m<sup>−2</sup> and beam energy at 1 MeV for 3600 s [<cite linkend="nf303675bib01">1</cite>, <cite linkend="nf303675bib02">2</cite>]. At JAEA, as the Japan Domestic Agency (JADA), R&D of the high power negative ion accelerator is in progress utilizing the MeV Test Facility (MTF) [<cite linkend="nf303675bib03">3</cite>] that is capable of 0.5 A H<sup>−</sup> ion acceleration up to 1 MeV. To meet the ITER requirement, a five stage MAMuG (multi-aperture multi-grid) accelerator has been developed at the MTF. After sustaining 1 MV for 8500 s stably [<cite linkend="nf303675bib04">4</cite>], H<sup>−</sup> ion beam current and beam energy have been progressed year by year [<cite linkend="nf303675bib05">5</cite>, <cite linkend="nf303675bib06">6</cite>].</p><p>An option of the ITER accelerator, a single-aperture single-gap (SINGAP) has been developed at CEA Cadarache, France [<cite linkend="nf303675bib07">7</cite>]. To assess the SINGAP and the MAMuG concepts at the same test facility with the same diagnostics, a collaborative R&D was performed between JAEA and CEA Cadarache under an ITER task agreement. For this purpose, the SINGAP accelerator was installed and tested at the MTF [<cite linkend="nf303675bib08">8</cite>].</p><p>The design study of the accelerator has been progressed. One of the issues for long pulse operation in the JT-60U negative ion source is to suppress power loads to the accelerator grids and the beamline components by deflected beamlets due to their mutual space charge repulsion [<cite linkend="nf303675bib09">9</cite>, <cite linkend="nf303675bib10">10</cite>]. At present, metal bars were attached around the aperture area at the exit of the electron suppression grid (ESG, 3rd grid) [<cite linkend="nf303675bib11">11</cite>]. By forming electric field distortion, beamlets from the outermost apertures are steered to counteract the space-charge-induced beamlet deflection. However, the beamlet steering by the metal bar is only effective to the outermost beamlets since the field distortion does not propagate far into the inner beam region. In order to steer all beamlets properly, beamlet steering by an aperture offset in the ESG has been simulated in a three-dimensional (3D) beam analysis [<cite linkend="nf303675bib12">12</cite>] utilizing the OPERA-3d code [<cite linkend="nf303675bib13">13</cite>]. After the compensation of beamlet deflection, the beamlet focusing towards a focal point was examined utilizing the aperture offset in the grounded grid (GRG).</p><p>In this paper, the progress of high power negative ion acceleration and the initial result of pulse length extension in the MAMuG accelerator are described in section <secref linkend="nf303675s2">2</secref>. A comparison of the MAMuG and the SINGAP accelerators is reported in section <secref linkend="nf303675s3">3</secref>. The design of the aperture offset steering is discussed in section <secref linkend="nf303675s4">4</secref> and a summary of the progress follows.</p></sec-level1><sec-level1 id="nf303675s2" label="2"><heading>Progress of high power negative ion acceleration in the MAMuG accelerator</heading><sec-level2 id="nf303675s2-1" label="2.1"><heading>MAMuG accelerator at MTF</heading><p indent="no">Figure <figref linkend="nf303675fig01">1</figref> shows a cross-sectional illustration of the five stage MAMuG accelerator, called a MeV accelerator, at the MTF. Although the ITER accelerator is required to accelerate 40 A of D<sup>−</sup> ion beams, the accelerated beam current at the MTF is limited by the power supply capability, 0.5 A. The accelerator development at JAEA was mainly dedicated to the acceleration of high current density beams equivalent to the ITER requirement, 200 A m<sup>−2</sup>, up to 1 MeV. To demonstrate a vacuum insulation of the accelerator required for ITER, the main structure of the MAMuG accelerator is immersed in a vacuum, surrounded by a stack of five insulator columns made of fibre reinforced plastic (FRP). The FRP insulators as a bushing and the power supply at the MTF are contained in SF<sub>6</sub> insulation gas at 0.6 MPa. On the top of the accelerator, a negative ion source called ‘KAMABOKO source [<cite linkend="nf303675bib14">14</cite>]’ is mounted to produce high density H<sup>−</sup> ions. In order to enhance the negative ion production, a small amount of Cs is seeded in the KAMABOKO source. The accelerator consists of four intermediate acceleration grids (A1G, A2G, A3G and A4G) and a GRG. The apertures for beam acceleration are arranged in a lattice pattern of 3 × 5. The diameter of apertures in the acceleration grids and the GRG is 16 mm. The acceleration grids and the GRG are insulated by cylindrical post insulators made of Al<sub>2</sub>O<sub>3</sub>. The negative ions are accelerated electrostatically by the potential difference of 200 kV at the maximum between each grid and up to 1 MeV in total. The potential of the acceleration grids and the GRG are provided through metal rods penetrating the flanges of the FRP bushing to each grid support of the accelerator. The H<sub>2</sub> gas is fed for plasma production from the top of the KAMABOKO source and flows through not only the apertures in the accelerator but also the large space between the accelerator and the FRP insulator column. The gas pressure is almost uniform in the beamline (the accelerator and that behind) due to large gas conductance around the accelerator. The beam divergence was evaluated from a profile of light emission from the beam path utilizing a CCD camera and a beam footprint observed on a one-dimensional carbon fibre composite (CFC) plate utilizing an infrared (IR) camera. The accelerated H<sup>−</sup> ion beam current was measured by a calorimeter. The power supply drain current (<italic>I</italic><sub>acc</sub>) and the intermediate grid currents (<italic>I</italic><sub>A1G</sub>, <italic>I</italic><sub>A2G</sub>, <italic>I</italic><sub>A3G</sub>, <italic>I</italic><sub>A4G</sub>) were measured electrically by series resistors in the power supply lines.
<figure id="nf303675fig01" pageposition="top"><graphic><graphic-file version="print" format="EPS" align="middle" filename="images/nf303675fig01.eps" width="XXX"></graphic-file><graphic-file version="ej" format="JPEG" align="middle" filename="images/nf303675fig01.jpg"></graphic-file></graphic><caption id="nf303675fc01" label="Figure 1"><p indent="no">A cross-sectional illustration of the five stage MAMuG accelerator at the MTF.</p></caption></figure></p></sec-level2><sec-level2 id="nf303675s2-2" label="2.2"><heading>High power negative ion acceleration in the MAMuG accelerator</heading><p indent="no">Up to 2005, 836 keV, 146 A m<sup>−2</sup> H<sup>−</sup> beam (total H<sup>−</sup> current; 206 mA from 9 apertures) was successfully accelerated [<cite linkend="nf303675bib04">4</cite>, <cite linkend="nf303675bib08">8</cite>]. In a wide range of the operation window between 450 and 750 keV in the beam energy but maintaining the perveance (H<sup>−</sup> ion current density/(beam energy)<sup>3/2</sup>), a beam divergence angle of about 5 mrad was attained, which fulfilled the ITER requirement (⩽7 mrad) [<cite linkend="nf303675bib04">4</cite>, <cite linkend="nf303675bib08">8</cite>, <cite linkend="nf303675bib15">15</cite>]. However, such a high power H<sup>−</sup> ion beam degraded rapidly due to air leak from an uncooled port plug (made of SS) located at the top of the KAMABOKO source [<cite linkend="nf303675bib15">15</cite>]. The port plug and its Viton O-ring used for the vacuum seal of the port plug were partially melted. It indicated excess temperature rise as a consequence of high heat load input due to backstreaming positive ions. Due to the air leak, enhancement of negative ion production by Cs was degraded. To protect the port plug from the heat load by the backstreaming positive ions, a water-cooled beam dump was equipped on top of the ion source. After mounting the beam dump, high current beam production lasted for more than 1 month, and high current H<sup>−</sup> ion beams of 0.32 A have been extracted from 15 apertures (140 A m<sup>−2</sup>) and accelerated up to 796 keV [<cite linkend="nf303675bib08">8</cite>]. The drain current (H<sup>−</sup> ion plus co-accelerated electrons) reached 0.42 A, which was close to the limit of the power supply.</p><p>Our target is now directed to extend the pulse length with a high power H<sup>−</sup> ion beam. Figure <figref linkend="nf303675fig02">2</figref> shows the energy of the H<sup>−</sup> ion beam ((beam energy) × (ion beam current) × (pulse length), in kJ) as a function of the beam energy (keV). In the high energy beam acceleration as described above, the pulse length has been limited to 0.2–1.0 s. As the first campaign for long pulse operation at the MTF, the pulse length was extended to 5 s. The beam energy was limited to about 500 keV to avoid excess damages on the uncooled acceleration grids. The maximum beam parameter attained so far was 131 mA (57 A m<sup>−2</sup>) as the negative ion current and 550 keV as the beam energy. For 5 s, stable beam acceleration was achieved without breakdown and beam current degradation. The energy of the H<sup>−</sup> ion beam for 5 s operation (squares in the figure) was 370 kJ at the maximum, which was about four times larger than the past experiment (95 kJ at the maximum, circles in the figure). As alternatives to present non-water-cooled grids, the water-cooled acceleration grids and the GRG are now ready for the coming long pulse test aimed at extending the pulse length with a higher power H<sup>−</sup> ion beam.
<figure id="nf303675fig02" pageposition="top"><graphic><graphic-file version="print" format="EPS" align="middle" filename="images/nf303675fig02.eps" width="XXX"></graphic-file><graphic-file version="ej" format="JPEG" align="middle" filename="images/nf303675fig02.jpg"></graphic-file></graphic><caption id="nf303675fc02" label="Figure 2"><p indent="no">Energy of the beam (kJ) as a function of beam energy (keV). The energy of the beam (kJ) was the product of beam energy, ion beam current and pulse length.</p></caption></figure></p></sec-level2></sec-level1><sec-level1 id="nf303675s3" label="3"><heading>Comparison test of MAMuG and SINGAP accelerators at the MTF</heading><sec-level2 id="nf303675s3-1" label="3.1"><heading>SINGAP accelerator at the MTF</heading><p indent="no">Figure <figref linkend="nf303675fig03">3</figref> shows the SINGAP accelerator installed in the FRP bushing at the MTF. The SINGAP consists of only two grids, that is, a pre-acceleration grid with the same aperture array as the MAMuG and the GRG with a single large opening of 114 mm × 106 mm. Thus, there are no intermediate grids. The advantage of the SINGAP is its simple geometry. For this test, the pre-acceleration grid, the GRG and their support frames were newly manufactured. To obtain a large gas conductance as much as that of the MAMuG accelerator, large openings are provided at the grid support frame. The pre-acceleration voltage was originally designed to be 60 kV [<cite linkend="nf303675bib07">7</cite>] and was changed to 200 kV [<cite linkend="nf303675bib16">16</cite>] in the present test to use the A1G voltage as the pre-acceleration voltage at the MTF. The SINGAP accelerator was designed to apply 200 kV to the pre-acceleration and 800 kV between the pre-acceleration grid and the GRG to accelerate the negative ions up to 1 MeV. The optimum gap length between the pre-acceleration grid and the GRG was determined to be 307 mm from a 3D beam trajectory simulation at CEA.
<figure id="nf303675fig03" pageposition="top"><graphic><graphic-file version="print" format="EPS" align="middle" filename="images/nf303675fig03.eps" width="XXX"></graphic-file><graphic-file version="ej" format="JPEG" align="middle" filename="images/nf303675fig03.jpg"></graphic-file></graphic><caption id="nf303675fc03" label="Figure 3"><p indent="no">SINGAP accelerator at the MTF.</p></caption></figure></p></sec-level2><sec-level2 id="nf303675s3-2" label="3.2"><heading>Voltage holding capability</heading><p indent="no">Figure <figref linkend="nf303675fig04">4</figref> shows the high voltage conditioning history of the MAMuG in April 2007 and the SINGAP for two test campaigns (August 2007 and January 2008). All plots in the figure show sustained voltage. In the case of the MAMuG, initial breakdown started from about 400 kV. Then, 757 kV has been sustained after 60 h of conditioning. The voltage was increased up to 1 MV by adding H<sub>2</sub> gas of 0.2 Pa in the beamline. The conditioning histories of the SINGAP were almost the same for two test campaigns. However, the conditioning curve started from a relatively lower voltage than that in the MAMuG. The progress of the conditioning for the SINGAP was much slower compared with that of the MAMuG. In the SINGAP case, the maximum voltage holding was 572 kV after 120 h of conditioning and seemed to be saturated at the level below 600 kV. By adding H<sub>2</sub> gas to the accelerator (0.25 Pa in the beamline), voltage holding was increased to 787 kV but could not sustain the required voltage of 1 MV.
<figure id="nf303675fig04" pageposition="top"><graphic><graphic-file version="print" format="EPS" align="middle" filename="images/nf303675fig04.eps" width="XXX"></graphic-file><graphic-file version="ej" format="JPEG" align="middle" filename="images/nf303675fig04.jpg"></graphic-file></graphic><caption id="nf303675fc04" label="Figure 4"><p indent="no">Conditioning history of high voltage holding. Voltage without and with H<sub>2</sub> gas feeding shown by opened and closed symbols, respectively.</p></caption></figure></p><p>Figure <figref linkend="nf303675fig05">5</figref> shows the sustained voltage (<italic>V</italic>) as a function of gap length (<italic>d</italic>) in the MAMuG and the SINGAP tests at the MTF. When the H<sub>2</sub> gas was fed, the sustained voltage between the pre-acceleration grid and the GRG (307 mm in the gap length) was 630 kV (4/5 of 787 kV) in the SINGAP test though the required voltage was 800 kV in this gap. In the MAMuG test, the required voltage in each stage (each gap length: 104 mm/94 mm/87 mm/78 mm/72 mm), 200 kV, was successfully achieved. The curve of voltage holding capability according to Clump theory (<italic>V</italic> = <italic>V</italic><sub>0</sub><italic>d</italic><sup>0.5</sup>) was shown by a dotted line, which was obtained in an experiment done in the past utilizing a gap length of 10–50 mm [<cite linkend="nf303675bib17">17</cite>]. This dotted line indicates that the voltage holding capability is expected to be about 300 kV at a gap length of the MAMuG. This is high enough for the MAMuG requirements. On the other hand, the voltage holding capability is about 600 kV at the gap length of the SINGAP. This was lower than the SINGAP requirement and almost similar to the sustained voltage in the SINGAP test. The results of the voltage holding tests indicated that the SINGAP cannot satisfy the ITER requirement in voltage holding.
<figure id="nf303675fig05" pageposition="top"><graphic><graphic-file version="print" format="EPS" align="middle" filename="images/nf303675fig05.eps" width="XXX"></graphic-file><graphic-file version="ej" format="JPEG" align="middle" filename="images/nf303675fig05.jpg"></graphic-file></graphic><caption id="nf303675fc05" label="Figure 5"><p indent="no">Voltage as a function of gap length in MAMuG (squares) and SINGAP (circle) tests at the MTF.</p></caption></figure></p></sec-level2><sec-level2 id="nf303675s3-3" label="3.3"><heading>Negative ion beam acceleration</heading><p indent="no">Following the high voltage conditioning, beam acceleration tests were performed. Figure <figref linkend="nf303675fig06">6</figref> shows the H<sup>−</sup> negative ion current density as a function of the beam energy. The perveance matched condition for the ITER operation is expressed by a line. The results of the SINGAP and the MAMuG are shown by triangles and circles, respectively. At the SINGAP first campaign, it was impossible to measure the negative ion current accurately due to co-acceleration of many electrons to the calorimeter. In the second campaign, a pair of magnets were installed to generate a transverse magnetic field downstream of the GRG for suppression of the electrons from the beam path. At the perveance matched condition, 626 keV, 225 mA (97 A m<sup>−2</sup>), the beam was successfully accelerated at the beamline gas pressure of 0.08 Pa. The drain current of acceleration power supply (<italic>I</italic><sub>acc</sub>) was 462 mA. The beam divergence of the perveance matched condition was evaluated to be 4.5 mrad [<cite linkend="nf303675bib16">16</cite>] from the beam footprint observed on the 1D CFC target. At the underperveance condition, 672 keV, a 220 mA beam was obtained. The higher acceleration current at above 700 keV could not be attained due to the poor voltage holding. The maximum voltage with the H<sup>−</sup> ion beam was 775 keV, but the current was limited to only 75 mA at this voltage. The amount of co-accelerated electrons
<inline-eqn></inline-eqn>) was estimated as the difference between the power supply drain current (<italic>I</italic><sub>acc</sub> and the H<sup>−</sup> ion current
<inline-eqn></inline-eqn>, such as
<inline-eqn></inline-eqn> was 237 mA (=462–225 mA) at the perveance matched condition. As a result, the ratio of the electron to the H<sup>−</sup> ion
<inline-eqn></inline-eqn> for the SINGAP was estimated to be 1.05. This is three times larger than that of the MAMuG
<inline-eqn></inline-eqn> at the same gas pressure of 0.08 Pa. Note that the pressure was about three times higher than the designed value of the ITER NB, <0.03 Pa [<cite linkend="nf303675bib18">18</cite>]. Though the gas pressure was high in the experiments at the MTF, these results indicate that the SINGAP configuration permits acceleration of many electrons easily up to the high energy.
<figure id="nf303675fig06" pageposition="top"><graphic><graphic-file version="print" format="EPS" align="middle" filename="images/nf303675fig06.eps" width="XXX"></graphic-file><graphic-file version="ej" format="JPEG" align="middle" filename="images/nf303675fig06.jpg"></graphic-file></graphic><caption id="nf303675fc06" label="Figure 6"><p indent="no">H<sup>−</sup> ion current density as a function of beam energy in MAMuG (circles) and SINGAP (triangles) tests at the MTF.</p></caption></figure></p><p>The acceleration of many electrons causes excess power loading to the beamline component and degradation of acceleration efficiency. The electron currents in both accelerators at the ITER relevant gas pressure were estimated by Fubiani and de Esch <italic>et al</italic> utilizing the EAMCC code [<cite linkend="nf303675bib19">19</cite>, <cite linkend="nf303675bib20">20</cite>]. The results showed that electron power of 7.3 MW was transmitted from the large openings of the grids in the SINGAP accelerator [<cite linkend="nf303675bib19">19</cite>]. By contrast in the ITER MAMuG, electron power transmitted out of the accelerator was only 0.8 MW because most of the electrons were intercepted on the intermediate grids [<cite linkend="nf303675bib20">20</cite>]. The small amount of electron acceleration is an advantage of the MAMuG accelerator.</p><p>In 2008, the ITER organization decided to utilize the MAMuG accelerator as a baseline design for the ITER NB system as a result of its better voltage holding and less electron acceleration.</p></sec-level2></sec-level1><sec-level1 id="nf303675s4" label="4"><heading>Design study of the aperture offset for beamlet steering</heading><sec-level2 id="nf303675s4-1" label="4.1"><heading>Calculation model and aperture offset design</heading><p indent="no">Figure <figref linkend="nf303675fig07">7</figref> shows the calculation model. The aperture shape and the gap length of the JT-60U negative ion accelerator was modelled, which was almost identical to those of the MAMuG accelerator for ITER. The accelerator consisted of a plasma grid (PG), an extraction grid (EXG) and an ESG as well as three acceleration grids (A1G, A2G and GRG). One-third of the acceleration voltage was applied equally to each acceleration grid. The aperture array was simplified from the original of 9 × 24 to 5 × 10. The diameters of the aperture are 14 mm in the PG, 11 mm in the EXG, 14 mm in the ESG and 16 mm in the acceleration grids.
<figure id="nf303675fig07" pageposition="top"><graphic><graphic-file version="print" format="EPS" align="middle" filename="images/nf303675fig07.eps" width="XXX"></graphic-file><graphic-file version="ej" format="JPEG" align="middle" filename="images/nf303675fig07.jpg"></graphic-file></graphic><caption id="nf303675fc07" label="Figure 7"><p indent="no">Schematic view of the calculation domain of multi-beamlets analysis.</p></caption></figure></p><p>In the OPERA-3d code, the trajectories of fifty beamlets extracted from 5 × 10 apertures were calculated including their space charge simultaneously. Each beamlet consisted of about 400 beam particles. OPERA-3d cannot handle extraction of negative ions from the plasma. Therefore, the initial position and velocity of the negative ions were determined according to the physics law of the positive ion extraction (Child–Langmuir law) utilizing a 2D beam trajectory code, ‘BEAMORBT’ [<cite linkend="nf303675bib21">21</cite>]. Here, the following were assumed: (1) uniform distribution of the negative ions over the aperture area and (2) that the space charge given by the electrons is negligibly small. The space charge effect is proportional to the product of the current and the square root of mass. It was experimentally confirmed that the extracted negative ion current and electron current were comparable under enhancement of negative ion production by Cs seeding [<cite linkend="nf303675bib22">22</cite>]. Then the space charge effect by the electron is expected to be negligibly small, that is, about one-sixtieth of that by D<sup>−</sup> negative ions. Therefore, this assumption would be applicable to the present negative ion extraction and acceleration analyses.</p><p>The required aperture offset to compensate for the beamlet deflection was examined according to the thin lens theory [<cite linkend="nf303675bib23" range="bib23,bib24,bib25,bib26">23–26</cite>]. A focal length <italic>F</italic> is expressed as follows.
<display-eqn id="nf303675eq001" eqnnum="1"></display-eqn>
Here <italic>V</italic><sub>BE</sub> is the beam energy and <italic>E</italic><sub>1</sub> and <italic>E</italic><sub>2</sub> are the electric field strength before and after the grid. δ<sub>0</sub> is the distance of the aperture offset. &thetas;<sub>0</sub> is the steering angle. The EXG is thick enough and therefore <italic>E</italic><sub>1</sub> can be negligible [<cite linkend="nf303675bib12">12</cite>, <cite linkend="nf303675bib27">27</cite>, <cite linkend="nf303675bib28">28</cite>] in equation (<eqnref linkend="nf303675eq001">1</eqnref>). When the aperture offset δ<sub>ESG</sub> is applied to the ESG, the steering angle &thetas;<sub>ESG</sub> at the ESG is expressed as
<display-eqn id="nf303675eq002" eqnnum="2"></display-eqn>
Equation (<eqnref linkend="nf303675eq002">2</eqnref>) indicates that the steering angle is proportional to the distance of the aperture offset. The steering angle does not vary with the beam energy when the ratio of extraction voltage and acceleration voltage is maintained [<cite linkend="nf303675bib12">12</cite>, <cite linkend="nf303675bib28">28</cite>]. When the aperture offset δ<sub>GRG</sub> is applied to the GRG, <italic>E</italic><sub>2</sub> can be neglected in equation (<eqnref linkend="nf303675eq001">1</eqnref>). Then, the deflection angle &thetas;<sub>GRG</sub> at the GRG is expressed as [<cite linkend="nf303675bib29">29</cite>],
<display-eqn id="nf303675eq003" eqnnum="3"></display-eqn></p></sec-level2><sec-level2 id="nf303675s4-2" label="4.2"><heading>Deflection compensation and focusing of beamlets</heading><p indent="no">Figure <figref linkend="nf303675fig08">8</figref> shows the calculated beam footprints. The beam condition was 340 keV, 110 A m<sup>−2</sup> D<sup>−</sup> ion beam, which was a typical operation condition of the JT-60U negative ion accelerator. The extraction voltage was set to be 5.4 kV so as to adjust the optimum beam optics. The open circles represent the positions of the apertures at the plasma grid drilled in a lattice pattern of 5 × 10. The calculated beamlet centre is plotted by the closed points. Figure <figref linkend="nf303675fig08">8(<italic>a</italic>)</figref> shows the calculated beam footprint at 3.5 m downstream from the GRG without the aperture offset. The aperture centres in the peripheral apertures were connected by lines to form a rectangular shape, whilst the beamlet centres in the beam footprint were connected by a dotted line. The arrows represent the movement of the beamlet due to the space charge repulsion. As shown in the figure, the beamlet footprint inflated out of the aperture area due to their mutual space charge repulsions. The deflection angle at the centre of the peripheral beamlets was 6 mrad, and the deflection angle at the corner of the peripheral beamlets was 4 mrad in both the <italic>X</italic> and <italic>Y</italic> directions. Thus, the deflection angle is dependent on the aperture position. Therefore, the proper aperture offset should be applied to each aperture. Figure <figref linkend="nf303675fig08">8(<italic>b</italic>)</figref> shows the calculated beam footprints at 3.5 m downstream from the GRG with a proper aperture offset in the ESG. The proper aperture offset was obtained from equation (<eqnref linkend="nf303675eq002">2</eqnref>). The details of the aperture offset are shown in figure <figref linkend="nf303675fig09">9(<italic>a</italic>)</figref>. It was clearly shown that the beamlets went straight to the corresponding positions with the aperture positions even at 3.5 m downstream as a result of the compensation with a proper aperture offset for each aperture. In order to focus the beamlets, the aperture offset in the GRG, as shown in figure <figref linkend="nf303675fig09">9(<italic>b</italic>)</figref>, was applied in addition to that in the ESG. The aperture offset in the GRG was obtained from equation (<eqnref linkend="nf303675eq003">3</eqnref>). Figure <figref linkend="nf303675fig08">8(<italic>c</italic>)</figref> shows the calculated beam footprints at the focal point, the exit of the residual ion dump (RID). As an example, the focal length and the focal direction were adjusted to the ITER requirement, that is, 7.2 m downstream from the GRG and focusing in the <italic>Y</italic> direction of the figures. The arrows indicate the movement of the beamlets from the GRG to the focal position in the <italic>Y</italic> direction. All beamlets were steered in the <italic>Y</italic> direction and concentrated on the <italic>X</italic> axis at the focal point. It was shown numerically that the beamlet deflection due to the space charge repulsion could be compensated for by the aperture offset in the ESG, and then the beamlets were focused successfully by the aperture offset in the GRG.
<figure id="nf303675fig08" pageposition="top"><graphic><graphic-file version="print" format="EPS" align="middle" filename="images/nf303675fig08.eps" width="XXX"></graphic-file><graphic-file version="ej" format="JPEG" align="middle" filename="images/nf303675fig08.jpg"></graphic-file></graphic><caption id="nf303675fc08" label="Figure 8"><p indent="no">Calculated beam footprints without the aperture offset (<italic>a</italic>) with the ESG aperture offset (<italic>b</italic>) with the ESG and (<italic>c</italic>) the GRG aperture offsets.</p></caption></figure><figure id="nf303675fig09" pageposition="top"><graphic><graphic-file version="print" format="EPS" align="middle" filename="images/nf303675fig09.eps" width="XXX"></graphic-file><graphic-file version="ej" format="JPEG" align="middle" filename="images/nf303675fig09.jpg"></graphic-file></graphic><caption id="nf303675fc09" label="Figure 9"><p indent="no">The aperture offset in a quarter of the aperture area. Aperture positions after the aperture offset are shown by dotted line circles. Such a aperture offset was symmetrically applied. Results of the aperture offset were shown in figure <figref linkend="nf303675fig08">8(<italic>b</italic>)</figref> with the ESG offset of (<italic>a</italic>) above and figure <figref linkend="nf303675fig08">8(<italic>c</italic>)</figref> with the GRG offset of (<italic>b</italic>).</p></caption></figure></p></sec-level2></sec-level1><sec-level1 id="nf303675s5" label="5"><heading>Summary</heading><p indent="no">The development of the high energy, high current MAMuG accelerator is in progress at JADA towards the ITER NB system. The accelerated H<sup>−</sup> ion current obtained at the MAMuG accelerator was increased to 0.32 A at a beam energy of 796 keV with maintaining the perveance matched conditions of the ITER operation. The SINGAP accelerator was tested at the JAEA MTF for comparison with the MAMuG accelerator. As a result, the MAMuG showed better performance than the SINGAP, and it has been decided to choose the MAMuG as the baseline design for the ITER accelerator. The grid design study was progressed utilizing the 3D beam analysis code. It was analytically demonstrated that the beamlet deflection due to the space charge repulsion was compensated for by the aperture offset in the ESG, and then the beamlets were focused at the focal point by adopting the aperture offset at the final grid of the accelerator.</p></sec-level1><sec-level1 id="nf303675s6"><heading>Disclaimer</heading><p indent="no">Part of this report was prepared as an account of work by or for the ITER Organization. The members of the organization are the People's Republic of China, the European Atomic Energy Community, the Republic of India, Japan, the Republic of Korea, the Russian Federation and the United States of America. The views and opinions expressed herein do not necessarily reflect those of the members or any agency thereof. Dissemination of the information in this paper is governed by the applicable terms of the ITER Joint Implementation Agreement.</p></sec-level1></body><back><references><heading>References</heading><reference-list type="numeric"><misc-ref id="nf303675bib01" num="1"><misc-text>ITER EDA Final Design Report</misc-text><year>2002</year><misc-title>ITER Technical Basis, Plant Description Document (PDD)</misc-title><misc-text>G A0 FDR 1 01-07-13 R1.0, IAEA EDA documentation No 24</misc-text></misc-ref><journal-ref id="nf303675bib02" num="2"><authors><au><second-name>Inoue</second-name><first-names>T.</first-names></au><others><italic>et al</italic></others></authors><year>2001</year><art-title>Design of neutral beam system for ITER-FEAT</art-title><jnl-title>Fusion Eng. Des.</jnl-title><volume>56–57</volume><pages>517–21</pages><crossref><cr_doi>http://dx.doi.org/10.1016/S0920-3796(01)00339-8</cr_doi><cr_issn type="print">09203796</cr_issn></crossref></journal-ref><journal-ref id="nf303675bib03" num="3"><authors><au><second-name>Watanabe</second-name><first-names>K.</first-names></au><others><italic>et al</italic></others></authors><year>2002</year><art-title>Development of a large volume negative-ion source for ITER neutral beam injector</art-title><jnl-title>Rev. Sci. Instrum.</jnl-title><volume>73</volume><pages>1090–2</pages><crossref><cr_doi>http://dx.doi.org/10.1063/1.1431422</cr_doi><cr_issn type="print">00346748</cr_issn></crossref></journal-ref><journal-ref id="nf303675bib04" num="4"><authors><au><second-name>Taniguchi</second-name><first-names>M.</first-names></au><others><italic>et al</italic></others></authors><year>2006</year><art-title>Acceleration of MeV-class energy, high-current-density H<sup>−</sup>-ion beams for ITER neutral beam system</art-title><jnl-title>Rev. Sci. Instrum.</jnl-title><volume>77</volume><pages>03A514</pages><crossref><cr_doi>http://dx.doi.org/10.1063/1.2165748</cr_doi><cr_issn type="print">00346748</cr_issn></crossref></journal-ref><conf-ref id="nf303675bib05" num="5"><authors><au><second-name>Kashiwagi</second-name><first-names>M.</first-names></au><others><italic>et al</italic></others></authors><year>2008</year><art-title>High energy, high current accelerator development for ITER NBI at JADA</art-title><conf-title>Proc. 22nd Int. Conf. on Fusion Energy 2008</conf-title><conf-place>Geneva, Switzerland, 2008</conf-place><publication><place>Vienna</place><publisher>IAEA</publisher></publication><misc-text>CD-ROM file IT/P7-4 and <webref url="http://www.naweb.iaea.org/napc/physics/FEC/FEC2008/htm/index.htm">http://www.naweb.iaea.org/napc/physics/FEC/FEC2008/htm/index.htm</webref></misc-text></conf-ref><journal-ref id="nf303675bib06" num="6"><authors><au><second-name>Inoue</second-name><first-names>T.</first-names></au><others><italic>et al</italic></others></authors><year>2006</year><art-title>1 MeV, ampere class accelerator R&D for ITER</art-title><jnl-title>Nucl. Fusion</jnl-title><volume>46</volume><pages>S379–385</pages><crossref><cr_doi>http://dx.doi.org/10.1088/0029-5515/46/6/S20</cr_doi><cr_issn type="print">00295515</cr_issn><cr_issn type="electronic">17414326</cr_issn></crossref></journal-ref><journal-ref id="nf303675bib07" num="7"><authors><au><second-name>De Esch</second-name><first-names>H.P.L.</first-names></au><others><italic>et al</italic></others></authors><year>2005</year><art-title>Updated physics design ITER-SINGAP accelerator</art-title><jnl-title>Fusion Eng. Des.</jnl-title><volume>73</volume><pages>329</pages><crossref><cr_doi>http://dx.doi.org/10.1016/j.fusengdes.2005.07.003</cr_doi><cr_issn type="print">09203796</cr_issn></crossref></journal-ref><journal-ref id="nf303675bib08" num="8"><authors><au><second-name>Taniguchi</second-name><first-names>M.</first-names></au><others><italic>et al</italic></others></authors><year>2008</year><art-title>Development of 1 MeV H- accelerator at JAEA for ITER NB</art-title><jnl-title>Conf. Proc. Am. Inst. Phys.</jnl-title><volume>CP1097</volume><pages>335–43</pages></journal-ref><journal-ref id="nf303675bib09" num="9"><authors><au><second-name>Umeda</second-name><first-names>N.</first-names></au><others><italic>et al</italic></others></authors><year>2003</year><art-title>Improvement of beam performance in the negative-ion based NBI system for JT-60U</art-title><jnl-title>Nucl. Fusion</jnl-title><volume>43</volume><pages>522–6</pages><crossref><cr_doi>http://dx.doi.org/10.1088/0029-5515/43/7/302</cr_doi><cr_issn type="print">00295515</cr_issn><cr_issn type="electronic">17414326</cr_issn></crossref></journal-ref><journal-ref id="nf303675bib10" num="10"><authors><au><second-name>Ikeda</second-name><first-names>Y.</first-names></au><others><italic>et al</italic></others></authors><year>2006</year><art-title>Present status of the negative ion based NBI system for long pulse operation on JT-60U</art-title><jnl-title>Nucl. Fusion</jnl-title><volume>46</volume><pages>S211–9</pages><crossref><cr_doi>http://dx.doi.org/10.1088/0029-5515/46/6/S02</cr_doi><cr_issn type="print">00295515</cr_issn><cr_issn type="electronic">17414326</cr_issn></crossref></journal-ref><journal-ref id="nf303675bib11" num="11"><authors><au><second-name>Kamada</second-name><first-names>M.</first-names></au><others><italic>et al</italic></others></authors><year>2008</year><art-title>Beamlet deflection due to beamlet–beamlet interaction in a large-area multiaperture negative ion source for JT-60U</art-title><jnl-title>Rev. Sci. Instrum.</jnl-title><volume>79</volume><pages>02C114</pages><crossref><cr_doi>http://dx.doi.org/10.1063/1.2819333</cr_doi><cr_issn type="print">00346748</cr_issn></crossref></journal-ref><journal-ref id="nf303675bib12" num="12"><authors><au><second-name>Kashiwagi</second-name><first-names>M.</first-names></au><others><italic>et al</italic></others></authors><year>2008</year><art-title>Compensation of beamlet repulsion in a large negative ion source with a multi-aperture accelerator</art-title><jnl-title>Conf. Proc. Am. Inst. Phys.</jnl-title><volume>CP1097</volume><pages>421–30</pages></journal-ref><misc-ref id="nf303675bib13" num="13"><misc-text>OPERA-3d</misc-text><source>Vector Fields Co. Ltd.</source><misc-text><webref url="http://www.vectorfields.com/">http://www.vectorfields.com/</webref></misc-text></misc-ref><journal-ref id="nf303675bib14" num="14"><authors><au><second-name>Inoue</second-name><first-names>T.</first-names></au><others><italic>et al</italic></others></authors><year>2001</year><art-title>ITER R&D: auxiliary systems: neutral beam heating and current drive system</art-title><jnl-title>Fusion Eng. Des.</jnl-title><volume>55</volume><pages>291–301</pages><crossref><cr_doi>http://dx.doi.org/10.1016/S0920-3796(01)00202-2</cr_doi><cr_issn type="print">09203796</cr_issn></crossref></journal-ref><journal-ref id="nf303675bib15" num="15"><authors><au><second-name>Taniguchi</second-name><first-names>M.</first-names></au><others><italic>et al</italic></others></authors><year>2008</year><art-title>Acceleration of ampere class H<sup>−</sup> ion beam by MeV accelerator</art-title><jnl-title>Rev. Sci. Instrum.</jnl-title><volume>79</volume><pages>02C110</pages><crossref><cr_doi>http://dx.doi.org/10.1063/1.2816839</cr_doi><cr_issn type="print">00346748</cr_issn></crossref></journal-ref><journal-ref id="nf303675bib16" num="16"><authors><au><second-name>De Esch</second-name><first-names>H.P.L</first-names></au><others><italic>et al</italic></others></authors><year>2009</year><art-title>Results of the SINGAP neutral beam accelerator experiment at JAEA</art-title><jnl-title>Fusion Eng. Des.</jnl-title><misc-text>at press</misc-text></journal-ref><journal-ref id="nf303675bib17" num="17"><authors><au><second-name>Watanabe</second-name><first-names>K.</first-names></au><others><italic>et al</italic></others></authors><year>1992</year><art-title>Dc voltage holding experiments of vacuum gap for high-energy ion sources</art-title><jnl-title>J. Appl. Phys.</jnl-title><volume>72</volume><pages>3949–56</pages><crossref><cr_doi>http://dx.doi.org/10.1063/1.352247</cr_doi><cr_issn type="print">00218979</cr_issn></crossref></journal-ref><misc-ref id="nf303675bib18" num="18"><misc-text>ITER EDA Final Design Report</misc-text><year>2002</year><misc-title>Design Description Document (DDD)</misc-title><misc-text>WBS 5.3: Neutral Beam Heating and Current Drive System N53 DDD 29 01-07-03 R 0.1</misc-text></misc-ref><journal-ref id="nf303675bib19" num="19"><authors><au><second-name>Fubiani</second-name><first-names>G.</first-names></au><others><italic>et al</italic></others></authors><year>2008</year><art-title>Modeling of secondary emission processes in the negative ion based electrostatic accelerator of the international thermonuclear experimental reactor</art-title><jnl-title>Phys. Rev. ST Accel. Beams</jnl-title><volume>11</volume><pages>014202</pages><crossref><cr_doi>http://dx.doi.org/10.1103/PhysRevSTAB.11.014202</cr_doi><cr_issn type="electronic">10984402</cr_issn></crossref></journal-ref><journal-ref id="nf303675bib20" num="20"><authors><au><second-name>Fubiani</second-name><first-names>G.</first-names></au><others><italic>et al</italic></others></authors><art-title>Analysis of the two accelerator concepts foreseen for the neutral beam injector of the international thermonuclear experimental reactor</art-title><jnl-title>Phys. Rev. ST Accel. Beams</jnl-title><misc-text>submitted</misc-text></journal-ref><misc-ref id="nf303675bib21" num="21"><authors><au><second-name>Ohara</second-name><first-names>Y.</first-names></au></authors><year>1976</year><art-title>Simulation code for beam trajectories in an ion source</art-title><misc-title>JAERI-M 6757</misc-title><misc-text><webref url="http://jolissrch-inter.tokai-sc.jaea.go.jp/common/eindex.html">http://jolissrch-inter.tokai-sc.jaea.go.jp/common/eindex.html</webref></misc-text></misc-ref><conf-ref id="nf303675bib22" num="22"><authors><au><second-name>Okumura</second-name><first-names>Y.</first-names></au><others><italic>et al</italic></others></authors><year>1990</year><art-title>Cesium mixing in the multi-ampere volume H- ion source</art-title><conf-title>Proc. 50th Int. Symp.</conf-title><conf-place>Brookhaven, NY</conf-place><pages>pp 169–83</pages></conf-ref><journal-ref id="nf303675bib23" num="23"><authors><au><second-name>Whealton</second-name><first-names>J.H.</first-names></au></authors><year>1977</year><art-title>Linear optics theory of beamlet steering</art-title><jnl-title>Rev. Sci. Instrum.</jnl-title><volume>48</volume><pages>1428–9</pages><crossref><cr_doi>http://dx.doi.org/10.1063/1.1134911</cr_doi><cr_issn type="print">00346748</cr_issn></crossref></journal-ref><journal-ref id="nf303675bib24" num="24"><authors><au><second-name>Gardner</second-name><first-names>W.L.</first-names></au><others><italic>et al</italic></others></authors><year>1978</year><art-title>Ion beamlet steering by aperture displacement for a tetrode accelerating structure</art-title><jnl-title>Rev. Sci. Instrum.</jnl-title><volume>49</volume><pages>1214–5</pages><crossref><cr_doi>http://dx.doi.org/10.1063/1.1135553</cr_doi><cr_issn type="print">00346748</cr_issn></crossref></journal-ref><journal-ref id="nf303675bib25" num="25"><authors><au><second-name>Ohara</second-name><first-names>Y.</first-names></au></authors><year>1979</year><art-title>Beam focusing by aperture displacement in two-stage acceleration system</art-title><jnl-title>Japan. J. Appl. Phys.</jnl-title><volume>18</volume><pages>351–6</pages><crossref><cr_doi>http://dx.doi.org/10.1143/JJAP.18.351</cr_doi><cr_issn type="print">00214922</cr_issn></crossref></journal-ref><journal-ref id="nf303675bib26" num="26"><authors><au><second-name>Okumura</second-name><first-names>Y.</first-names></au><others><italic>et al</italic></others></authors><year>1980</year><art-title>Experimental study of ion beamlet steering by aperture displacement in two stage-accelerator</art-title><jnl-title>Rev. Sci. Instrum.</jnl-title><volume>51</volume><pages>471–3</pages><crossref><cr_doi>http://dx.doi.org/10.1063/1.1136248</cr_doi><cr_issn type="print">00346748</cr_issn></crossref></journal-ref><journal-ref id="nf303675bib27" num="27"><authors><au><second-name>Fujiwara</second-name><first-names>Y.</first-names></au><others><italic>et al</italic></others></authors><year>2000</year><art-title>Beamlet–beamlet interaction in a multi-aperture negative ion source</art-title><jnl-title>Rev. Sci. Instrum.</jnl-title><volume>71</volume><pages>3059–64</pages><crossref><cr_doi>http://dx.doi.org/10.1063/1.1305515</cr_doi><cr_issn type="print">00346748</cr_issn></crossref></journal-ref><misc-ref id="nf303675bib28" num="28"><authors><au><second-name>Inoue</second-name><first-names>T.</first-names></au><others><italic>et al</italic></others></authors><year>2000</year><art-title>Steering of high energy negative ion beam and design of beam forcing/deflection compensation for JT-60U large negative ion source</art-title><misc-title>JAERI-Tech 2000-023</misc-title><misc-text><webref url="http://jolissrch-inter.tokai-sc.jaea.go.jp/common/eindex.html">http://jolissrch-inter.tokai-sc.jaea.go.jp/common/eindex.html</webref></misc-text></misc-ref><misc-ref id="nf303675bib29" num="29"><authors><au><second-name>Inoue</second-name><first-names>T.</first-names></au><others><italic>et al</italic></others></authors><year>2000</year><art-title>Steering of H<sup>−</sup> ion beamlet by aperture displacement</art-title><misc-title>JAERI-Tech 2000-051</misc-title><misc-text><webref url="http://jolissrch-inter.tokai-sc.jaea.go.jp/common/eindex.html">http://jolissrch-inter.tokai-sc.jaea.go.jp/common/eindex.html</webref></misc-text></misc-ref></reference-list></references></back></article></istex:document></istex:metadataXml><mods version="3.6"><titleInfo><title>R&D progress of the high power negative ion accelerator for the ITER NB system at JAEA</title></titleInfo><titleInfo type="abbreviated"><title>R&D progress of the high power negative ion accelerator for the ITER NB system at JAEA</title></titleInfo><titleInfo type="alternative"><title>R&D progress of the high power negative ion accelerator for the ITER NB system at JAEA</title></titleInfo><name type="personal"><namePart type="given">M.</namePart><namePart type="family">Kashiwagi</namePart><affiliation>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</affiliation><affiliation>E-mail:kashiwagi.mieko@jaea.go.jp</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="given">M.</namePart><namePart type="family">Taniguchi</namePart><affiliation>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="given">M.</namePart><namePart type="family">Dairaku</namePart><affiliation>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="given">H.P.L.</namePart><namePart type="family">de Esch</namePart><affiliation>CEA Cadarache, F-13108, St Paul-lez-Durance, CEDEX, France</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="given">L.R.</namePart><namePart type="family">Grisham</namePart><affiliation>Plasma Physics Laboratory, Princeton University, PO Box 451, Princeton, NJ 08543, USA</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="given">L.</namePart><namePart type="family">Svensson</namePart><affiliation>CEA Cadarache, F-13108, St Paul-lez-Durance, CEDEX, France</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="given">H.</namePart><namePart type="family">Tobari</namePart><affiliation>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="given">N.</namePart><namePart type="family">Umeda</namePart><affiliation>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="given">K.</namePart><namePart type="family">Watanabe</namePart><affiliation>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="given">K.</namePart><namePart type="family">Sakamoto</namePart><affiliation>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="given">T.</namePart><namePart type="family">Inoue</namePart><affiliation>Japan Atomic Energy Agency (JAEA), 801-1 Mukouyama, Naka 311-0193, Japan</affiliation><role><roleTerm type="text">author</roleTerm></role></name><typeOfResource>text</typeOfResource><genre type="research-article" displayLabel="paper"></genre><originInfo><publisher>IOP Publishing and International Atomic Energy Agency</publisher><dateIssued encoding="w3cdtf">2009</dateIssued><copyrightDate encoding="w3cdtf">2009</copyrightDate></originInfo><language><languageTerm type="code" authority="iso639-2b">eng</languageTerm><languageTerm type="code" authority="rfc3066">en</languageTerm></language><physicalDescription><internetMediaType>text/html</internetMediaType><note type="production">Printed in the UK</note></physicalDescription><abstract>At JAEA, as the Japan Domestic Agency (JADA) for ITER, a MAMuG (multi-aperture multi-grid) accelerator has been developed to perform the required R&D for the ITER neutral beam (NB) system. As a result of countermeasures to handle excess heat load to the ion source by backstreaming positive ions, H ion beam current was increased to 0.32A (the ion current density of 140Am2) at a beam energy of 796keV. This high power beam acceleration simulated the ITER operation condition maintaining the perveance (H ion current density/beam energy3/2) of the ITER accelerator. After the high power beam operation, the pulse length was successfully extended from 0.2 to 5s at 550keV, which yielded a 131mA H ion beam as an initial test of the long pulse operation. A test of a single-aperture single-gap (SINGAP) accelerator was performed at JAEA under an ITER R&D task agreement. The objective of this test was to compare two different accelerator concepts (SINGAP and MAMuG) at the same test facility. As a result, the MAMuG accelerator was defined as the baseline design for ITER, due to advantages in its better voltage holding and less electron acceleration. In three-dimensional beam trajectory analyses, the aperture offset at the bottom of the extractor was found to be effective for compensation of beamlet deflection due to their own space charge. It has been analytically demonstrated that these compensated beamlets can be focused at a focal point by adopting the aperture offset at the final grid of the accelerator.</abstract><classification authority="pacs">41.75.Cn</classification><classification authority="pacs">41.85.Lc</classification><relatedItem type="host"><titleInfo><title>Nuclear Fusion</title></titleInfo><titleInfo type="abbreviated"><title>Nucl. Fusion</title></titleInfo><genre type="Journal">journal</genre><identifier type="ISSN">0029-5515</identifier><identifier type="eISSN">1741-4326</identifier><identifier type="PublisherID">NF</identifier><identifier type="CODEN">NUFUAU</identifier><identifier type="URL">stacks.iop.org/NF</identifier><part><date>2009</date><detail type="volume"><caption>vol.</caption><number>49</number></detail><detail type="issue"><caption>no.</caption><number>6</number></detail><extent unit="pages"><start>1</start><end>7</end><total>7</total></extent></part></relatedItem><identifier type="istex">6742B0FA9A751F7C6C9DEF4D6C0F471082BB2376</identifier><identifier type="DOI">10.1088/0029-5515/49/6/065008</identifier><identifier type="PII">S0029-5515(09)03675-8</identifier><identifier type="articleID">303675</identifier><identifier type="articleNumber">065008</identifier><accessCondition type="use and reproduction" contentType="copyright">2009 IAEA, Vienna</accessCondition><recordInfo><recordContentSource>IOP</recordContentSource><recordOrigin>2009 IAEA, Vienna</recordOrigin></recordInfo></mods></metadata><serie></serie></istex></record>Pour manipuler ce document sous Unix (Dilib)
EXPLOR_STEP=$WICRI_ROOT/Wicri/Musique/explor/OperaV1/Data/Istex/Corpus
HfdSelect -h $EXPLOR_STEP/biblio.hfd -nk 000E41 | SxmlIndent | more
Ou
HfdSelect -h $EXPLOR_AREA/Data/Istex/Corpus/biblio.hfd -nk 000E41 | SxmlIndent | more
Pour mettre un lien sur cette page dans le réseau Wicri
{{Explor lien
|wiki= Wicri/Musique
|area= OperaV1
|flux= Istex
|étape= Corpus
|type= RBID
|clé= ISTEX:6742B0FA9A751F7C6C9DEF4D6C0F471082BB2376
|texte= R&D progress of the high power negative ion accelerator for the ITER NB system at JAEA
}}
| This area was generated with Dilib version V0.6.21. |  |