Microwave-assisted pre-ionization experiments on GLAST-Ⅲ |
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作者姓名: | Riaz KHAN Sehrish SHAKIR Ahmad ALI Muhammad Khawar AYUB Moazzam NAZIR Zia UR-REHMAN Abdul QAYYUM Muhammad Athar NAVEED Sarfraz AHMAD Zahoor AHMAD Rafaqat ALI Shahid HUSSAIN |
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作者单位: | Pakistan Tokamak Plasma Research Institute,P.O.Nilore,Islamabad 44000,Pakistan;Theoretical Physics Division,PINSTECH,P.O.Nilore,Islamabad 44000,Pakistan |
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摘 要: | GLAss Spherical Tokamak(GLAST-Ⅲ) is a spherical tokamak with an insulating vacuum vessel that has a unique single-passage capability for incident microwaves.In this work,electron cyclotron resonance heating(ECRH)-assisted plasma pre-ionization in GLAST-Ⅲ is explored for three radio-frequency(RF) polarizations(the O-,X-,and M-modes) at different toroidal-field(TF) strengths and filled gas pressures.The optimum hydrogen pressure is identified for efficient plasma pre-ionization.A comparison of the plasma pre-ionizations initiated by the O-,X-,and M-modes shows prominent differences in the breakdown time,location,and wave absorption.In the case of O-mode polarization,microwave absorption occurs for a relatively shorter duration,resulting in a bell-shaped electron-temperature(T_e) temporal profile.Microwave absorption is dominant in the case of the X-mode,leading to a broader T_e temporal profile.The M-mode discharge contains features of both the X-and O-modes.Efficient plasma pre-ionization is achieved in the X-mode polarization for the intermediate TF strengths(with a central toroidal magnetic field B_0=0.075 T).Traces of the electron-number density show a similar tendency,as revealed by T_e.These results suggest that the X-mode is the best candidate for efficient plasma pre-ionization at low filled gas pressures(~10~(-2) Pa) in small tokamaks.
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