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

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

doi:10.1088/1741-4326/ac388a

Cited by 14 publications

(4 citation statements)

References 14 publications

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“…In R & D of the negative ion source for the NB injector of JT-60SA, a hydrogen negative ion (H − ) beam with 500 keV, 156 A m −2 for 118 s has been successfully demonstrated, which exceeds the requirement of 500 keV, 130 A m −2 for 100 s in JT-60SA (figure 8) [15]. This test was performed by using a cesium (Cs)-seeded negative ion source and a threestage accelerator with multi-apertures.…”

Section: Nbimentioning

confidence: 99%

Completion of JT-60SA construction and contribution to ITER

et al. 2022

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Construction of the JT-60SA tokamak was completed on schedule in March 2020. Manufacture and assembly of all the main tokamak components satisfied technical requirements, including dimensional accuracy and functional performances. Development of the plasma heating systems and diagnostics have also progressed, including the demonstration of the favourable electron cyclotron range of frequency (ECRF) transmission at multiple frequencies and the achievement of long sustainment of a high-energy intense negative ion beam. Development of all the tokamak operation control systems has been completed, together with an improved plasma equilibrium control scheme suitable for superconducting tokamaks including ITER. For preparation of the tokamak operation, plasma discharge scenarios have been established using this advanced equilibrium controller. Individual commissioning of the cryogenic system and the power supply system confirmed that these systems satisfy design requirements including operational schemes contributing directly to ITER, such as active control of heat load fluctuation of the cryoplant, which is essential for dynamic operation in superconducting tokamaks. The integrated commissioning (IC) is started by vacuum pumping of the vacuum vessel and cryostat, and then moved to cool-down of the tokamak and coil excitation tests. Transition to the super-conducting state was confirmed for all the TF, EF and CS coils. The TF coil current successfully reached 25.7 kA, which is the nominal operating current of the TF coil. For this nominal toroidal field of 2.25 T, ECRF was applied and an ECRF plasma was created. The IC was, however, suspended by an incident of over current of one of the superconducting equilibrium field coil and He leakage caused by insufficient voltage holding capability at a terminal joint of the coil. The unique importance of JT-60SA for H-mode and high-β steady-state plasma research has been confirmed using advanced integrated modellings. These experiences of assembly, IC and plasma operation of JT-60SA contribute to ITER risk mitigation and efficient implementation of ITER operation.

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Section: Nbimentioning

confidence: 99%

Completion of JT-60SA construction and contribution to ITER

et al. 2022

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“…Other important test facilities for ITER are located in Japan [8]. In particular, the National Institutes for Quantum and Radiological Science and Technology (QST) in Naka, Japan, hosts a massive negative ion source producing high power negative ion beams, with energy of 500 keV, current of 22 A (130 A m −2 in the current density) and beam-on time of 100 s [9]. A large negative ion source with a 1.2 m long arc discharge chamber and a multi-aperture three-stage accelerator have been built to reach the goal values.…”

Section: Introduction: Diagnostics In Nbi Negative Ion Sourcesmentioning

confidence: 99%

Study and development of diagnostic systems to characterise the extraction region in SPIDER

Segalini,

Candeloro,

Poggi

et al. 2024

J. Inst.

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SPIDER, an RF-driven negative ion source in the Neutral Beam Test Facility (NBTF), serves as the prototype for ITER's neutral beam injector (NBI). It is composed of 8 drivers powered by 4 RF generators, aiming to accelerate 50 A of negative hydrogen ions to 100 KeV with a beam uniformity target of 10%. The experiment, launched in 2018, tested negative ion production using caesium. Results match those of similar facilities, but SPIDER faces challenges due to its size, multiple drivers, and non-uniform plasma expansion. These issues impact beam uniformity, preventing the machine from reaching expected performance. To address this, SPIDER initiated a significant shutdown at the end of 2021 for improvements. One the most important aspects studied during the first experimental campaign is source uniformity, addressed both in terms of plasma and of caesium distribution. The latter is particularly relevant since its quality is directly related to the beam uniformity and divergence. To have more insight about these issues, monitoring the plasma properties in the extraction region is crucial, hence in the present contribution, the design and development of two new diagnostic systems are described: a movable Langmuir probe and a Retarding Field Energy Analyser (RFEA). The first can provide a vertical scan of the main plasma parameters close to the plasma grid. The spatial resolution would improve with respect to the already installed set of fixed Langmuir probes embedded in the grid system, and the newly installed diagnostic could interact with other sensors to produce complementary measurements (namely, electron photo-detachment). The latter, instead, allows the monitoring of the positive ion energy distribution: positive ions, in fact, can be precursors of the negative ones produced at the caesiated surface, but also influence the energy of negative ion and their extraction probability and thus collecting information about their energy distribution allows inferring details about the extracted negative ion beam. The two diagnostics are designed focusing on the experimental constraint of integrating the diagnostics in a harsh and complex environment such as SPIDER plasma: a preliminary study of the placement inside the source is carried out, then the electrode of the movable probe and the RFEA sensor are sized according to the spatial and energy resolution requested by the system.

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“…Comprehensive Research Facility for Fusion Technology (CRAFT) is one of the national large research infrastructures in China, which aim to overcome a series of key technologies for the construction and operation of a fusion reactor. Based on the experience of the routine operating NNBI systems of JT-60U [12] and LHD [13], the NNBI system is much more demanding and complex than a PNBI system. Thus, a NNBI test facility is included and under construction in the CRAFT.…”

Section: Introductionmentioning

confidence: 99%

Study on stray electrons ejecting from a long-pulse negative ion source for fusion

Yang,

Wei,

et al. 2024

Plasma Phys. Control. Fusion

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The negative ion based neutral beam injection (NNBI) is a desirable plasma heating and current drive method for the large-scale magnetic fusion devices. Due to the strict requirements and difficult development of the negative ion source for fusion, a long-pulse negative ion source has been developed under the framework of the Comprehensive Research Facility for Fusion Technology (CRAFT) in China. This negative ion source consists of a single RF driver plasma source and a three-electrode accelerator. The typical extraction and acceleration voltage are 4~8 kV and 40~50 kV, respectively.During one shot of the long-pulse (~100 s) beam extraction, the gas pressure in the vacuum vessel increased sharply and the temperature of the cryopump rise from 8 K to 20 K. Moreover, the vessel wall appeared a high temperature after several long-pulse shots. A self-consistent simulation of beam-gas interaction revealed that the heat loads on the vessel wall should be caused by the stray electrons ejecting from the accelerator. Those stray electrons are mainly generated via the stripping or ionization collisions and strongly deflected by the downstream side of the deflection magnetic field for the co-extracted electron. The location of hot spots measured by infrared thermography is consistent with the simulation results. To solve this problem, a series of electron dumps are designed to avoid the direct impinging of the ejecting electrons on the cryopump and the vessel wall. And the results suggest that the hot spots are almost eliminated.

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

Cited by 14 publications

References 14 publications

Completion of JT-60SA construction and contribution to ITER

Completion of JT-60SA construction and contribution to ITER

Study and development of diagnostic systems to characterise the extraction region in SPIDER

Study on stray electrons ejecting from a long-pulse negative ion source for fusion

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