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

Abstract

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.

Numerical study of stripping and stray particles for the one-RF-driver NBI negative ion source prototype of CFETR

“…The under-plan China Fusion Engineering Test Reactor (CFETR) [1] employs the negative-ion-based NBI because of the retaining high neutralization efficiency of negative ions with the energy up to 1 MeV. The prototype of CFETR NBI negative hydrogen ion source is being developed in Southwest Institute of Physics [2]. For now, the first setup is equipped with only one RF plasma driver.…”

Progress of the RF negative hydrogen ion source for fusion at HUST

“…The development of negative ion sources for long-pulse and high-power beam extraction is pursued in fusion research institutes worldwide, e.g. IPP Garching (Germany), Consorzio RFX (Italy), JAEA, QST, NIFS (Japan), ASIPP and SWIP (China) [2][3][4][5][6][7].…”

“…Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP) has developed a high current negative ion source test facility, called 'HUNTER', with main design parameters of 100 kW RF power and 6 kV extraction voltage [16][17][18]. An RF negative hydrogen ion source of 200 kV/20 A/3600 s is under development at Southwestern Institute of Physics (SWIP) [7].…”

Stress-driven surface swell and exfoliation of copper as the plasma-facing materials in NBI ICP source

“…FS and GG (thermal loads up to 10 MW m −2 [19]) are proved to be critical components of the RF source from thermo-hydraulic viewpoint. In addition, Lie et al [20] applied infrared imaging technology to study the profile of beam energy density. The results indicate that the plasma density near PG increases almost linearly with the RF power.…”