Heating and current drive by electron cyclotron waves

Abstract

The physics model of electron cyclotron heating (ECH) and current drive (ECCD) is becoming well validated through systematic comparisons of theory and experiment. This work has shown that ECH and ECCD can be highly localized and robustly controlled in toroidal plasma confinement systems, leading to applications including stabilization of magnetohydrodynamic instabilities like neoclassical tearing modes, control and sustainment of desired profiles of current density and plasma pressure, and studies of localized transport in laboratory plasmas. The experimental work was supported by a broad base of theory based on first principles which is now well encapsulated in linear ray tracing codes describing wave propagation, absorption, and current drive and in fully relativistic quasilinear Fokker–Planck codes describing in detail the response of the electrons to the energy transferred from the wave. The subtle balance between wave-induced diffusion and Coulomb relaxation in velocity space provides an understanding of the effects of trapping of current-carrying electrons in the magnetic well. Strong quasilinear effects and radial transport of electrons, which may broaden the driven current profile, have also been observed under some conditions and appear to be consistent with theory, but in large devices these are usually insignificant. The agreement of theory and experiment, the wide range of established applications, and the technical advantages of ECH support the application of ECH in next-step tokamaks and stellarators.

Validation metrics for turbulent plasma transport

“…Verification and validation of the various codes and models used in these power balance calculations are challenging exercises in their own right, and it is essential to always bear in mind that the lack of direct measurements of local fluxes is a significant constraint on the validation of these tools. However, through combinations of extensive verification exercises, 95 global cross-checks (e.g., comparisons of predicted and measured neutron production rates to constrain fast ion densities injected by neutral beams [96][97][98] or hard X-ray emissions associated with interactions between fast electrons and lower hybrid, electron cyclotron, and ion cyclotron waves [99][100][101] ) and comparisons with both measured changes in equilibrium profiles [102][103][104][105][106] and core fluctuations, 107,108 quantitative confidence in these models to a fairly high level has been established for many operating conditions of interest. Nonetheless, power balance analyses are still subject to significant aleatory (i.e., statistical) and systematic uncertainties.…”

Avoiding Tokamak Disruptions by Applying Static Magnetic Fields That Align Locked Modes with Stabilizing Wave-Driven Currents

“…To this end, it is more efficient to use the available wave power to drive maximum current. This is obtained for injection at an appropriate oblique angle relative to the magnetic field [26]. If, instead, injection is perpendicular or nearly perpendicular to the field, the main effect is some heating but little or no current, which typically is insufficient for complete stabilization (Fig.2c).…”

Design of a steerable launcher for the ECH system on KSTAR

“…Electron cyclotron heating (ECH) and electron cyclotron current drive (ECCD) launcher system has installed on the KSTAR tokamak. An ECH/ECCD system is required for localized plasma heating, plasma startup for large superconducting tokamak device, preionization for low voltage startup, non-inductive current drive, and discharge cleaning of a vacuum vessel [1][2][3]. Recently, ECH/ECCD system is used in MHD instability modes control such as suppression of neoclassical tearing mode (NTM), control of sawtooth and internal transport barriers for high-performance and stability of the plasma [4][5][6].…”