Modeling of solenoid-free start-up using 2nd harmonic electron cyclotron heating and current drive in QUEST

Abstract

A grid-based ECH ST/Tokamak start-up model is being developed where plasma parameters, generated plasma currents, and resulting poloidal magnetic fields are evolved from the vacuum fields. Initially, the current generated is purely pressure driven since the electron temperature is too low for ECCD. The grad-B drift driven current together with the processional currents can then create a closed flux surface configuration and then the bootstrap current in a closed configuration can further enhance the plasma current. After the flux closure, the 2nd harmonic ECH heating efficiency increases with plasma current since the confinement is increased and resulting electron temperature rise would further increase the ECH absorption and plasma current. Once the temperature of hot minority component becomes sufficiently high ~ 1 keV, the ECCD becomes significant for full current ramp-up.