Fully non-inductive second harmonic electron cyclotron plasma ramp-up in the QUEST spherical tokamak

Abstract

Fully non-inductive second (2nd) harmonic electron cyclotron (EC) plasma current ramp-up was demonstrated with a newlly developed 28 GHz system in the QUEST spherical tokamak. A high plasma current of 54 kA was non-inductively ramped up and sustained stably for 0.9 s with a 270 kW 28 GHz wave. A higher plasma current of 66 kA was also non-inductively achieved with a slow ramp-up of the vertical field. We have achieved a significantly higher plasma current than those achieved previously with the 2nd harmonic EC waves. This fully non-inductive 2nd harmonic EC plasma ramp-up method might be useful for future burning plasma devices and fusion reactors, in particular for operations at half magnetic field with the same EC heating equipment.

Fast Tangentially Viewed Soft X-Ray Imaging System Based on Image Intensifier with Microchannel Plate Detector on QUEST

“…All of the QUEST discharges discussed in this paper were produced in an inboard limiter (IL) configuration [12]. Two electron cyclotron wave (ECW) systems operating at 8.2 and 28 GHz are used for current start-up and current driving, respectively [13][14][15]. A center solenoid (CS) coil is used for Ohmic heating [16].…”

“…Non-inductive current ramp-up has previously been obtained in QUEST through the use of ECW [13,14], and the generation and confinement of energetic electrons has been shown to play an important role in driving plasma current [12]. Normally, the presence of energetic electrons is indicated by the hard X-rays produced when the electrons hit a wall.…”

High-Field-Side RF Injection for Excitation of Electron Bernstein Waves

“…Non-inductive current drive is one of the crucial topics in regard to spherical tokamak (ST), where space for the central solenoid is technically limited [1]. Radiofrequency (RF) waves in the range of the electron cyclotron frequency are commonly used in heating and current drive in STs [2][3][4][5]. In the initial phase of plasma build-up, the first pass absorption at the electron cyclotron resonance (ECR) layer is very small because the electron temperature T e and density n e are low, and multiple reflections of RF waves inside the vessel enable RF-induced breakdown [6][7][8].…”

TSC Simulation of Transient CHI in New Electrode Configuration on QUEST

“…ECH is a very powerful tool for heating low-temperature plasmas. Demonstrating electron heating of a transient CHI target using the high power 28 GHz ECH system on QUEST is an important objective [8].…”