Observation on fundamental and second harmonic mode ECRH assisted plasma startup in SST-1 experiments

Abstract

In SST-1, successful plasma startup has been achieved at very low loop voltage with the help of ECRH pre-ionization. ECRH is operated in both O mode and X mode for the purpose of pre-ionization at the pre fill pressure of 1×10−5mbar. A delay in breakdown has been observed in case of second harmonic ECRH pre-ionization; where in case of fundamental mode of ECRH pre-ionization, the instant breakdown has been observed. This work has attempted at explaining the non-linear interaction of the seed electrons with the electromagnetic field of the incident ECRH wave that has led to break down of the plasma. The delay in the break down attributes to the time differential between the applications of the ECRH pulse to that of the appearance of the H-alpha signal in SST-1. The observed experimental results have been discussed in this paper from the first principles and numerically solving the electron-ECRH field interactions resulting in energy gains of the electrons leading to plasma break down in SST-1 specific discharge conditions.