Speaker
Braj Shukla
(ECRH)
Description
SST-1 Tokamak employs Electron Cyclotron Resonance (ECR) assisted pre-ionization as an effective support towards low loop-voltage plasma start-up at fundamental (O-mode) and second harmonic (X-mode). A 42GHz 500KW 500ms ECR source is used for this purpose. In recent experimental campaigns in SST-1, several experiments have been carried out on ECR assisted pre-ionization, plasma start-up, possible EC assisted current drives and ECR discharge cleaning.
In the EC-assisted start-up experiments, ~175kW power in fundamental O-mode is launched from the low field side that resulted in successful plasma start-up. With the available loop voltages, plasma current more than 100kA have been achieved with EC-assisted pre-ionization. The EC power is restricted to avoid the runaway electron generation. The EC pulse duration is varied from 80ms to 125ms. It is observed that in the initial phase of breakdown the hard X-rays appears and it subsequently reduces as the pulse progresses. This confirms good absorption of EC power at fundamental harmonic at higher density and temperature in the current ramp-up phase. The EC current drive (ECCD) effect is also observed in SST-1 as a SS304L, reflector is installed at the inboard side of tokamak to reflect the ECR beam in electron direction to assist the plasma current. The plasma discharges show around 10% contribution of ECCD.
The ECR discharge cleaning is also carried out with 42GHz ECRH system at a field of 1.3T bringing the ECR layer close to inboard side near the wall. The EC power (~100kW) has been launched with pulse duration of 100 to 200ms with pulse repetition rate of 1 Hz. The H2 pressure is 1x10-5-5mbar. The RGA scan shows increase of hydrogen and oxygen with ECR pulses in helium plasma confirming the wall conditioning. After the ECR cleaning, better plasma discharges are observed with higher current and duration.
Co-author
Braj Shukla
(ECRH, Institute for Plasma Research, Gandhinagar, India)
