Study of seed plasma generation for NBI plasma start-up using non-resonant microwave launch in Heliotron J
- 11 May 2020
- journal article
- research article
- Published by IOP Publishing in Plasma Physics and Controlled Fusion
- Vol. 62 (6), 065009
- https://doi.org/10.1088/1361-6587/ab877e
Abstract
Here, we report on a study of seed plasmas produced by non-resonant 2.45 GHz microwave heating in Heliotron J, which is useful for plasma start-up by neutral beam injection (NBI) under the conditions of low beam power (<1 MW), low accerelation voltage (<30 kV) and small device size (similar to 1 m). The pre-ionization technique using the non-resonant heating produced the electron density in the order of 10(17)-10(18) m(-3) with the energy exceeds the CII ionization potential (30 eV). The existence of the relativistic electrons, which was essential to produce the seed plasmas, was confirmed experimentally during the pre-ionization phase by the synchrotron radiation and the hard x-ray emission measurements. The production mechanism of the relativistic electrons was considered to be stochastic interactions between the electrons and the microwave-frequency field. By optimizing the additional gas fueling during the microwave launch, a higher seed-plasma density more than 4 x 10(18) m(-3) was obtained, resulting that a rapid density evolution after NBI turn-on was successful even in the low NBI power (0.3 MW) condition. The seed plasmas produced by the pre-ionization method is useful to realize the plasma start-up under low absorption power condition in larger heliotron/stellarator devices such as perpendicular NBI in W7-X or deuterium NBI in LHD.Keywords
This publication has 14 references indexed in Scilit:
- Assessment of the plasma start-up in Wendelstein 7-X with neutral beam injectionNuclear Fusion, 2015
- Stochastic acceleration of relativistic electrons and plasma heating and current drive with 2.45 GHz frequency at the WEGA stellaratorPlasma Physics and Controlled Fusion, 2014
- Plasma startup using neutral beam injection assisted by 2.45 GHz microwaves in Heliotron JNuclear Fusion, 2011
- Electron cyclotron heating assisted startup in JT-60UNuclear Fusion, 2005
- Experimental study of plasma breakdown by second harmonic electron cyclotron waves in Heliotron JNuclear Fusion, 2004
- Plasma build-up in stellarators by neutral beams aloneNuclear Fusion, 2002
- Analysis of plasma initiation by neutral beams in the Large Helical DeviceNuclear Fusion, 2002
- Plasma startup by neutral beam injection in the Large Helical DeviceNuclear Fusion, 1999
- ECRH-assisted start-up in ITERPlasma Physics and Controlled Fusion, 1996
- Low voltage Ohmic and electron cyclotron heating assisted startup in DIII-DNuclear Fusion, 1991