Achievement of high power and long pulse negative ion beam acceleration for JT-60SA NBI

Hoshino, Junichi; Kashiwagi, M.; Ichikawa, Masahiro; Umeda, N.; Saquilayan, G. Q.; Tobari, H.; Watanabe, K.; Kojima, Akira; Yoshida, Masafumi

doi:10.1063/1.5131302

Cited by 17 publications

(14 citation statements)

References 11 publications

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“…It was found that the PG temperature strongly affects the measured cesium density, which, during plasma pulses, increases by a factor of 3 when decreasing T PG from 140 • C to 80 • C. If the cesium density before the grid surface is associated with the cesium coverage on the surface, this suggests that, within this range, the lower temperature would be more suitable for negative ion production, as it was also shown by the negative ion current. This result appears different from the findings in filament-based sources, which instead operate at significantly higher temperatures [23]. However, it should be mentioned that the temperature of the PG mask, which is not temperature-controlled, is unknown, yet certainly higher than the PG one; so the effective PG temperature might be higher than indicated.…”

Section: First Cesium Campaign In Spidercontrasting

confidence: 74%

SPIDER, the Negative Ion Source Prototype for ITER: Overview of Operations and Cesium Injection

Serianni¹,

Sartori²,

Agnello³

et al. 2023

IEEE Trans. Plasma Sci.

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Section: First Cesium Campaign In Spidercontrasting

confidence: 74%

SPIDER, the Negative Ion Source Prototype for ITER: Overview of Operations and Cesium Injection

Serianni¹,

Sartori²,

Agnello³

et al. 2023

IEEE Trans. Plasma Sci.

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“…Although the ITER targets were not demonstrated up to now, the achieved combination of CW extraction pulse length and current density represents a huge step forward compared to previous results and to the results of other test facilities (see for example [18]).…”

Section: Upgrade Of Elise To Cw Extraction and First Resultsmentioning

confidence: 91%

Paving the road towards ITER relevant long deuterium pulses at ELISE by investigating improved operational scenarios

Wünderlich,

Yordanov,

Riedl

et al. 2023

J. Inst.

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Hydrogen plasma pulses of 1000 s with an extracted current density of over 90 % of the ITER target value (while also fulfilling the requirements for the electron-ion ratio and the global top/bottom beam homogeneity) were demonstrated at the ELISE test facility with its half ITER-size negative hydrogen ion source in pulsed extraction mode, i.e. short beam extraction phases of ≈10 s each ≈150 s, and using the so-called potential rods. In deuterium roughly 67 % of the ITER target for the extracted current density has been achieved for pulses longer than 45 minutes, limited by a pronounced vertical asymmetry and increase with time in the co-extracted electron current. In order to stabilize the co-extracted electron current during long pulses, particularly in deuterium, improved operational scenarios have to be developed. At ELISE, it was investigated the possibility to remove the potential rods and instead to set the bias plate to a positive voltage with respect to the source vessel. In this operational scenario short pulses in deuterium can be achieved with an extracted negative ion current density of up to 90 % of the ITER target value. In order to improve the physics insight, a 2D fluid code is applied. The first general result is that the modified potentials of surfaces close to the extraction system strongly affect the fluxes of charged particles towards different surfaces and consequently can result in a reduction of the co-extracted electron current. The temporal behaviour during long pulses with pulsed extraction, in particular of the co-extracted electrons, demonstrates a significant impact of the beam extraction on the caesium dynamics. Thus, CW extraction is mandatory for developing fully ITER relevant operational scenarios. After an extensive upgrade, ELISE is now capable of performing CW pulses, i.e. long-pulse beam extraction.

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“…Then, the gap length was changed from 75/65/55 mm in the original to all 85 mm. (B) Suppression of generation of the diverged beam and secondary electrons inside the EXG [8,9,15]: these are the cause of the grid heat load. In the beam analysis carried out to understand these issues, the negative ions extracted from the PG with a diameter of 14 mm are converged between the PG and the EXG due to the extraction voltage, and then they spread inside the 17 mm thick EXG.…”

Section: Accelerator and Modification Pointsmentioning

confidence: 99%

“…In section 4, the filament break and its protection are reported. Section 5 shows a demonstration of the beam acceleration toward 500 keV, 130 A m −2 for 100 s [15]. Through this beam acceleration test, influences of the Cs leaked to the accelerator are also investigated and discussed.…”

Section: Introductionmentioning

confidence: 99%

100 s negative ion accelerations for the JT-60SA negative-ion-based neutral beam injector

Kashiwagi¹,

Hoshino²,

Ichikawa³

et al. 2021

Nucl. Fusion

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In the negative-ion-based neutral beam injector (N-NBI) of JT-60SA, a hydrogen negative ion beam with energy of 500 keV and a current density of 154 A m−2 for 118 s has been successfully demonstrated. This achievement exceeds the requirements (500 keV, 130 A m−2, 100 s) for the first time. To maintain stable negative ion production for a long pulse, the optimal temperatures of the chamber wall and plasma grid were analytically examined and were experimentally demonstrated. It was confirmed that the temperature during the beam pulse should be <50 °C for the chamber wall and >200 °C for the plasma grid. Damage to the filament cathode due to an abnormal discharge, so-called arcing, has been mitigated by developing a fast cut-off system of the arc current for around 100 μs after the arcing. To maintain sufficient voltage holding capability and to reduce the grid heat load due to the beam in the accelerator, techniques developed for the beam acceleration have been applied to this test. As a result of the integration of these techniques, a stable beam over 100 s has been demonstrated successfully. This is the first achievement over a 100 s stable beam with intensity of >75 MW m−2, which is the required practical level in the N-NBI. These results contribute to the coming NBI system for ITER and DEMO.

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Achievement of high power and long pulse negative ion beam acceleration for JT-60SA NBI

Cited by 17 publications

References 11 publications

SPIDER, the Negative Ion Source Prototype for ITER: Overview of Operations and Cesium Injection

SPIDER, the Negative Ion Source Prototype for ITER: Overview of Operations and Cesium Injection

Paving the road towards ITER relevant long deuterium pulses at ELISE by investigating improved operational scenarios

100 s negative ion accelerations for the JT-60SA negative-ion-based neutral beam injector

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