Overview of first Wendelstein 7-X high-performance operation

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A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
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Date
2019-11
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Mcode
Degree programme
Language
en
Pages
11
1-11
Series
Nuclear Fusion, Volume 59, issue 11
Abstract
The optimized superconducting stellarator device Wendelstein 7-X (with major radius R = 5.5 m, minor radius a = 0.5 m, and 30 m(3) plasma volume) restarted operation after the assembly of a graphite heat shield and 10 inertially cooled island divertor modules. This paper reports on the results from the first high-performance plasma operation. Glow discharge conditioning and ECRH conditioning discharges in helium turned out to be important for density and edge radiation control. Plasma densities of 1-4.5 x 10(19) m(-3) with central electron temperatures 5-10 keV were routinely achieved with hydrogen gas fueling, frequently terminated by a radiative collapse. In a first stage, plasma densities up to 1.4 x 10(20) m(-3) were reached with hydrogen pellet injection and helium gas fueling. Here, the ions are indirectly heated, and at a central density of 8 . 10(19 )m(-3) a temperature of 3.4 keV with T-e/T-i = 1 was transiently accomplished, which corresponds to nT(i)(0)tau(E) = 6.4 x 10(19) keV s m(-3) with a peak diamagnetic energy of 1.1 MJ and volume-averaged normalized plasma pressure = 1.2%. The routine access to high plasma densities was opened with boronization of the first wall. After boronization, the oxygen impurity content was reduced by a factor of 10, the carbon impurity content by a factor of 5. The reduced (edge) plasma radiation level gives routinely access to higher densities without radiation collapse, e.g. well above 1 x 10(20) m(-2) line integrated density and T-e = T-i = 2 keV central temperatures at moderate ECRH power. Both X2 and O2 mode ECRH schemes were successfully applied. Core turbulence was measured with a phase contrast imaging diagnostic and suppression of turbulence during pellet injection was observed.
Description
| openaire: EC/H2020/633053/EU//EUROfusion
Keywords
stellarator, divertor, ECR heating, NBI heating, plasma performance, turbulence, impurities, DENSITY LIMIT, PHYSICS, CONFINEMENT, STELLARATOR, SYSTEM, W7-X
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Klinger , T , Andreeva , T , Bozhenkov , S , Brandt , C , Burhenn , R , Buttenschoen , B , Fuchert , G , Geiger , B , Grulke , O , Laqua , H P , Pablant , N , Rahbarnia , K , Stange , T , von Stechow , A , Tamura , N , Thomsen , H , Turkin , Y , Wegner , T , Abramovic , I , Aekaeslompolo , S , Alcuson , J , Aleynikov , P , Aleynikova , K , Ali , A , Alonso , A , Anda , G , Ascasibar , E , Baehner , J P , Baek , S G , Balden , M , Baldzuhn , J , Banduch , M , Barbui , T , Behr , W , Beidler , C , Benndorf , A , Biedermann , C , Biel , W , Blackwell , B , Blanco , E , Blatzheim , M , Ballinger , S , Bluhm , T , Boeckenhoff , D , Boeswirth , B , Boettger , L-G , Borchardt , M , Borsuk , M , Boscary , J , Bosch , H-S , Beurskens , M , Brakel , R , Brand , H , Braeuer , T , Braune , H , Brezinsek , S , Brunner , K-J , Bussiahn , R , Bykov , I , Cai , J , Calvo , I , Cannas , B , Cappa , A , Carls , A , Carralero , D , Carraro , L , Carvalho , B , Castejon , F , Charl , A , Chaudhary , N , Chauvin , D , Chernyshev , F , Cianciosa , M , Citarella , R , Claps , G , Coenen , J , Cole , M J , Cole , M J , Cordella , F , Cseh , G , Czarnecka , A , Czerski , K , Czerwinski , M , Czymek , G , da Molin , A , da Silva , A , Damm , H , de la Pena , A , Degenkolbe , S , Dhard , C P , Dibon , M , Dinklage , A , Dittmar , T , Drevlak , M , Drewelow , P , Drews , P , Durodie , F , Edlund , E , van Eeten , P , Effenberg , F , Ehrke , G , Elgeti , S , Endler , M , Ennis , D , Esteban , H , Estrada , T , Fellinger , J , Feng , Y , Flom , E , Fernandes , H , Fietz , W H , Figacz , W , Fontdecaba , J , Ford , O , Fornal , T , Frerichs , H , Freund , A , Funaba , T , Galkowski , A , Gantenbein , G , Gao , Y , Garcia Regana , J , Gates , D , Geiger , J , Giannella , R , Gogoleva , A , Goncalves , B , Goriaev , A , Gradic , D , Grahl , M , Green , J , Greuner , H , Grosman , A , Grote , H , Gruca , M , Guerard , C , Hacker , P , Han , X , Harris , J H , Hartmann , D , Hathiramani , D , Hein , 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