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Title: Characterization of the ITER model negative ion source during long pulse operation

Abstract

It is foreseen to operate the neutral beam system of the International Thermonuclear Experimental Reactor (ITER) for pulse lengths extending up to 1 h. The performance of the KAMABOKO III negative ion source, which is a model of the source designed for ITER, is being studied on the MANTIS test bed at Cadarache. This article reports the latest results from the characterization of the ion source, in particular electron energy distribution measurements and the comparison between positive ion and negative ion extraction from the source.

Authors:
; ; ; ; ; ;  [1];  [2];  [3];  [4]
  1. Association EURATOM-CEA, CEA Cadarache, F-13108, St. Paul lez Durance (France)
  2. (Ireland)
  3. (United Kingdom)
  4. (France)
Publication Date:
OSTI Identifier:
20778996
Resource Type:
Journal Article
Resource Relation:
Journal Name: Review of Scientific Instruments; Journal Volume: 77; Journal Issue: 3; Conference: 11. international conference on ion sources, Caen (France), 12-16 Sep 2005; Other Information: DOI: 10.1063/1.2164891; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; ANIONS; CATIONS; COLLIDING BEAMS; COMPARATIVE EVALUATIONS; DESIGN; ELECTRONS; ENERGY SPECTRA; EXPERIMENTAL REACTORS; ION SOURCES; ITER TOKAMAK; OPERATION; PERFORMANCE; PULSES

Citation Formats

Hemsworth, R.S., Boilson, D., Crowley, B., Homfray, D., Esch, H.P.L. de, Krylov, A., Svensson, L., Association EURATOM-DCU, PRL/NCPST, Glasnevin, Dublin 13, Euratom/UKAEA Fusion Association, Culham Science Centre, Abingdon, OX14 3DB, and Association EURATOM-CEA, CEA Cadarache, F-13108, St. Paul lez Durance. Characterization of the ITER model negative ion source during long pulse operation. United States: N. p., 2006. Web. doi:10.1063/1.2164891.
Hemsworth, R.S., Boilson, D., Crowley, B., Homfray, D., Esch, H.P.L. de, Krylov, A., Svensson, L., Association EURATOM-DCU, PRL/NCPST, Glasnevin, Dublin 13, Euratom/UKAEA Fusion Association, Culham Science Centre, Abingdon, OX14 3DB, & Association EURATOM-CEA, CEA Cadarache, F-13108, St. Paul lez Durance. Characterization of the ITER model negative ion source during long pulse operation. United States. doi:10.1063/1.2164891.
Hemsworth, R.S., Boilson, D., Crowley, B., Homfray, D., Esch, H.P.L. de, Krylov, A., Svensson, L., Association EURATOM-DCU, PRL/NCPST, Glasnevin, Dublin 13, Euratom/UKAEA Fusion Association, Culham Science Centre, Abingdon, OX14 3DB, and Association EURATOM-CEA, CEA Cadarache, F-13108, St. Paul lez Durance. Wed . "Characterization of the ITER model negative ion source during long pulse operation". United States. doi:10.1063/1.2164891.
@article{osti_20778996,
title = {Characterization of the ITER model negative ion source during long pulse operation},
author = {Hemsworth, R.S. and Boilson, D. and Crowley, B. and Homfray, D. and Esch, H.P.L. de and Krylov, A. and Svensson, L. and Association EURATOM-DCU, PRL/NCPST, Glasnevin, Dublin 13 and Euratom/UKAEA Fusion Association, Culham Science Centre, Abingdon, OX14 3DB and Association EURATOM-CEA, CEA Cadarache, F-13108, St. Paul lez Durance},
abstractNote = {It is foreseen to operate the neutral beam system of the International Thermonuclear Experimental Reactor (ITER) for pulse lengths extending up to 1 h. The performance of the KAMABOKO III negative ion source, which is a model of the source designed for ITER, is being studied on the MANTIS test bed at Cadarache. This article reports the latest results from the characterization of the ion source, in particular electron energy distribution measurements and the comparison between positive ion and negative ion extraction from the source.},
doi = {10.1063/1.2164891},
journal = {Review of Scientific Instruments},
number = 3,
volume = 77,
place = {United States},
year = {Wed Mar 15 00:00:00 EST 2006},
month = {Wed Mar 15 00:00:00 EST 2006}
}
  • A model of the ion source designed for the neutral beam injectors of the International Thermonuclear Experimental Reactor (ITER), the KAMABOKO III ion source, is being tested on the MANTIS test stand at the DRFC Cadarache in collaboration with JAERI, Japan, who designed and supplied the ion source. The ion source is attached to a 3 grid 30 keV accelerator (also supplied by JAERI) and the accelerated negative ion current is determined from the energy deposited on a calorimeter located 1.6 m from the source.During experiments on MANTIS three adverse effects of long pulse operation were found: The negative ionmore » current to the calorimeter is {approx_equal}50% of that obtained from short pulse operation Increasing the plasma grid (PG) temperature results in {<=}40% enhancement in negative ion yield, substantially below that reported for short pulse operation, {>=}100%. The caesium 'consumption' is up to 1500 times that expected.Results presented here indicate that each of these is, at least partially, explained by thermal effects. Additionally presented are the results of a detailed characterisation of the source, which enable the most efficient mode of operation to be identified.« less
  • A high-power large negative ion source has been operated for a long pulse duration. A three-grid single-stage accelerator is used, where the extraction grid is shaped so that the secondary electrons generated on the extraction grid would be prevented from leaking into the acceleration gap. A stable long-pulse arc discharge with an arc power of 100 kW has been obtained over 15 s by balancing an individual arc current flowing through each filament. The cesium-seeded operation is not influenced by a temperature rise over 100{degree}C of the plasma grid during the long-pulse arc discharge. As a result, 330 kW (91more » keV{endash}3.6 A) of the negative ion beam was produced stably for 10 s from an area of 25cm{times}26cm, where the current density was 21mA/cm{sup 2} and the negative ion power density was 1.9kW/cm{sup 2}. The neutralization efficiency of accelerated negative ions has been measured including the residual positive and negative ion ratios by the water calorimetry of the beam dumps. The result agrees well with the calculation result. {copyright} {ital 1997 American Institute of Physics.}« less
  • Advanced Tokamak concepts and steady state plasma scenarios require external plasma heating and current drive for extended time periods. This poses several problems for the neutral beam injection systems that are currently in use. The power loading of the ion source and accelerator are especially problematic. The Kamaboko negative ion source, a small scale model of the ITER arc source, is being prepared for extended operation of deuterium beams for up to 1000 seconds. The operating conditions of the plasma grid prove to be important for reducing electron power loading of the accelerator. Operation of deuterium beams for extended periodsmore » also poses radiation safety risks which must be addressed.« less
  • R and D of high power density negative ion beam acceleration has been carried out at MeV test facility in JAEA to realize ITER neutral beam accelerator. The main target is H{sup −} ion beam acceleration up to 1 MeV with 200 A/m{sup 2} for 60 s whose pulse length is the present facility limit. For long pulse acceleration at high power density, new extraction grid (EXG) has been developed with high cooling capability, which electron suppression magnet is placed under cooling channel similar to ITER. In addition, aperture size of electron suppression grid (ESG) is enlarged from 14 mmmore » to 16 mm to reduce direct interception on the ESG and emission of secondary electron which leads to high heat load on the upstream acceleration grid. By enlarging ESG aperture, beam current increased 10 % at high current beam and total acceleration grid heat load reduced from 13 % to 10 % of input power at long pulse beam. In addition, heat load by back stream positive ion into the EXG is measured for the first time and is estimated as 0.3 % of beam power, while heat load by back stream ion into the source chamber is estimated as 3.5 ~ 4.0 % of beam power. Beam acceleration up to 60 s which is the facility limit, has achieved at 683 keV, 100 A/m{sup 2} of negative ion beam, whose energy density increases two orders of magnitude since 2011.« less
  • High power and long-pulse negative ion extractor, which is composed of the plasma grid (PG) and the extraction grid (EXG), is newly developed toward the neutral beam injector for heating and current drive of future fusion machines such as ITER, JT-60 Super Advanced and DEMO reactor. The PG is designed to enhance surface production of negative ions efficiently by applying the chamfered aperture. The efficiency of the negative ion production for the discharge power increased by a factor of 1.3 against that of the conventional PG. The EXG is also designed with the thermal analysis to upgrade the cooling capabilitymore » for the long pulse operation of >1000 s required in ITER. Though the magnetic field for electron suppression is reduced to 0.75 of that in the conventional EXG due to this upgrade, it was experimentally confirmed that the extracted electron current can be suppressed to the allowable level for the long pulse operation. These results show that newly developed extractor has the high potential for the long pulse extraction of the negative ions.« less