Extension of high power deuterium operation of negative ion based neutral beam injector in the large helical device

Ikeda, K.; Tsumori, K.; Nagaoka, K.; Nakano, H.; Kisaki, M.; Fujiwara, Y.; Kamio, S.; Haba, Y.; Masaki, S.; Osakabe, M.

doi:10.1063/1.5128529

Cited by 15 publications

(8 citation statements)

References 30 publications

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“…Alternative methods to reduce electrons need to be found. For the purpose of reducing the electron flux, three methods were proposed; they are (1) reduction of the plasma flux by expanding the distance between the centre plane of the filter magnets and the plane of PG facing to the source plasma, (2) enhancing the strength of the magnetic field, which is induced with the EDMs, penetrating into the source plasma near the PG apertures by shortening the PG-EG gap from 8 mm to 7 mm [14] and (3) installation of a device named the 'electron fence (EF)' to reduce electron density at the extraction region.…”

Section: − Acceleration and Co-extracted Electronsmentioning

confidence: 99%

“…It is observed that current ratio of electrons to deuterium negative ions (D − ions) extracted from ion source becomes larger than that in the extraction of hydrogen negative ions (H − ions) in the same magnetic configuration and strength. These problems induced with co-extracted electrons decrease injection stability and limit the injection power [6][7][8][9][10][11][12][13][14]. For those reasons above, reduction of co-extracted electrons is one of the main issues in the beam acceleration of n-NBI.…”

Section: Introductionmentioning

confidence: 99%

“…To keep the perveance matching, the extraction voltage needed to be reduced, and the acceleration voltage also had to be lowered in accordance with the reduction of extraction voltage to obtain optimum beamfocusing condition. The consequence was that the power to the LHD from the three n-NBIs increased to 7 MW at a beam energy of ∼175 keV [14].…”

Section: Introductionmentioning

confidence: 99%

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Challenges toward improvement of deuterium-injection power in the Large Helical Device negative-ion-based NBIs

et al. 2022

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Improvement of deuterium injection power in the negative-ion-based NBIs (n-NBIs) for the Large Helical Device (LHD) are reported. Co-extracted electron current at acceleration of deuterium negative ions (D− ions) limits the injection power. The electron current is reduced by decreasing the extraction gap, and the injected D− current evaluated from the injection power increased from 46 to 55 A. Greater electron reduction was achieved by installing a structure named an ‘electron fence’ (EF), with which D− beam power was successfully improved from 2.0 MW to 3.0 MW. The injection power in three configurations − without EF, with EF of 5 mm and 7 mm distance from the plasma grid (PG) surface − have been compared in both cases of hydrogen and deuterium operations, and it was found that the configuration with the EF of 5 mm distance was the best to satisfy the performance for both of hydrogen and deuterium injections. Although the co-extracted electron current is reduced in the negative ion sources applied for JT-60SA and ITER by utilizing the PG filter, it is possible to achieve more effective electron reduction by combining the PG filter and the EF.

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Section: − Acceleration and Co-extracted Electronsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Challenges toward improvement of deuterium-injection power in the Large Helical Device negative-ion-based NBIs

et al. 2022

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“…Up to now, most negative ion source test facilities for fusion operate in hydrogen and only little experience is available on operation in deuterium [5,6]. In order to close this gap in knowledge and experience, the current experimental program at ELISE is focussed on developing advanced operational scenarios for long pulse operation in deuterium.…”

Section: Introductionmentioning

confidence: 99%

NNBI for ITER: status of long pulses in deuterium at the test facilities BATMAN Upgrade and ELISE

et al. 2021

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For the D-T operational phase of the international fusion experiment ITER, starting in 2035, pulses are planned with Q > 10 and a duration of 400 s and pulses with Q = 5 for up to 3600 s. The two neutral beam injection (NBI) systems will deliver 33.3 MW of heating power to the plasma and will also be an important source for non-inductive current drive. An essential part of the NBI systems is a large RF driven source for negative hydrogen or deuterium ions. In order to fulfil the requirements imposed to the NBI system, the ion source has to deliver an intense, stable and homogeneous large negative ion beam over pulse lengths of 400 s or 3600 s. Till now, long pulses in deuterium at the extracted negative ion current density required for ITER could not be demonstrated. The achievable performance is limited by a high current and a pronounced vertical asymmetry of the co-extracted electrons, both strongly increasing with time, whereas the stability of the negative deuterium ions is not an issue. For reduced performance, i.e. reduced negative ion current, lower and more stable co-extracted electron currents are observed, making possible pulses up to 3600 s (using pulsed extraction). One main aim of ongoing investigations at the two test facilities BATMAN Upgrade (Bavarian test machine for negative ions) and ELISE (extraction from a large ion source experiment) is the development of scenarios stabilizing and symmetrizing the co-extracted electron current in deuterium. These investigations are discussed and the current status of hardware upgrades ongoing at BATMAN Upgrade and ELISE towards the ITER scenario of one-hour steady state extraction is presented.

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“…On LHD, two negative ion injectors with arc sources were firstly operated in 1998 and the third injector was on service in 2001, and each injector has two negative hydrogen ion sources with the design parameters of 180 kV/80 A/5 MW. The totally actual beam power of 7 MW was achieved with the extraction parameters of 180 kV/55.4 A/1.6 s for 3 negative deuterium ion injectors [9]. However, the NBI system with the RF ion source has only been used to ASDEX upgrade tokamak [10].…”

Section: Introductionmentioning

confidence: 99%

Development of megawatt radiofrequency ion source for the neutral beam injector on HL-2A tokamak

et al. 2021

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A radiofrequency (RF) ion source with a megawatt power extraction, thunder I, has been developed for the neutral beam injector (NBI) on HL-2A tokamak. A full solid-state RF generator with output power of 80 kW and frequency of 2 MHz was built by an RF combiner using 8 modules of solid-state RF generator with power of P RF = 10 kW. The line electric efficiency of whole RF generator reaches 92% and its voltage standing wave ratio (VSWR) is 1.01, thus no water-cooling system is supplied. A quartz vessel with the inner diameter of 250 mm is directly adopted for resisting atmospheric pressure, which can dramatically simplify source structure. Nowadays, the extracted beam parameters of RF hydrogen ion source are 32 kV/20 A/0.1 s on a test bed, while the design parameters are 50 kV/20 A/3 s. The beam density profile measured by the infrared imaging technique at 1.3 m downstream from the grounded grid obeys a Gaussian distribution, and the corresponding half width of 1/e power decay at the matched condition is about 80 mm. Plasma homogeneity is over 90% at low RF power. The beam divergence angle meets the requirement of NBI system on HL-2A tokamak. The extractable current density increases almost linearly with the RF power. It reaches 2400 A m−2 at P RF = 32 kW. The ion density in front of plasma grid is about 1 × 1018 m−3, corresponding to an ionized fraction of about 1% at the gas pressure of 0.5 Pa. Single hydrogen ion fraction reaches 79% at the beam current of 12.4 A. Some improvements have been considered for optimizing ion source performance on next experimental campaign. One smaller auxiliary RF discharge chamber equipped with a gas feed path, driven by 13.56 MHz/3.5 kW generator, is connected to main discharge chamber driven by 2 MHz/40 kW generator. By this dual-driven configuration, the innovative RF plasma source with high-pressure density gradient solves the initial ignition problem of powerful RF ion source even if the gas pressure below 0.1 Pa. In addition, the RF negative hydrogen ion source of 200 kV/20 A/3600 s is also developed at SWIP for the China fusion engineering test reactor.

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Extension of high power deuterium operation of negative ion based neutral beam injector in the large helical device

Cited by 15 publications

References 30 publications

Challenges toward improvement of deuterium-injection power in the Large Helical Device negative-ion-based NBIs

Challenges toward improvement of deuterium-injection power in the Large Helical Device negative-ion-based NBIs

NNBI for ITER: status of long pulses in deuterium at the test facilities BATMAN Upgrade and ELISE

Development of megawatt radiofrequency ion source for the neutral beam injector on HL-2A tokamak

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