Auxiliary ECR heating system for the gas dynamic trap

Abstract

Physics aspects of a new system for electron cyclotron resonance heating (ECRH) at the magnetic mirror device Gas Dynamic Trap (GDT, Budker Institute, Novosibirsk) are discussed. This system based on two 400 kW/54.5 GHz gyrotrons is aimed at increasing the electron temperature up to the range 250–350 eV for improved energy confinement of hot ions. The key physical issue of the GDT magnetic field topology is that conventional ECRH geometries are not accessible. The proposed solution is based on a peculiar effect of radiation trapping in inhomogeneous magnetized plasma. Under specific conditions, oblique launch of gyrotron radiation results in generation of right-hand-polarized (R) electromagnetic waves propagating with high N|| in the vicinity of the cyclotron resonance layer, which leads to effective single-pass absorption of the injected microwave power. In the present paper, we investigate numerically an optimized ECRH scenario based on the proposed mechanism of wave propagation and discuss the design of the ECRH system, which is currently under construction at the Budker Institute.

Electron cyclotron emission at the fundamental harmonic in GDT magnetic mirror

“…As microwave beam propagates towards the ECR layer, a magnitude of the magnetic field decreases what eventually leads to internal reflection of some part the beam from the plasma-vacuum boundary. The plasma column acts as a waveguide, inhomogeneous in transverse and longitudinal directions, whereby the radiation is delivered to the ECR surface [19][20][21] . As we detect ECE through the same ECRH port, Figure 3 illustrates not only the ECRH geometry, but also the received emission pattern and the plasma configuration near the ECE…”

“…Implementing effective microwave heating of dense plasma at GDT requires a rather unusual scheme based on radiation trapping by a non-uniform plasma column 19,20 ; see also Ref. 21 in which the same scheme is studied using a more advanced theoretical model.…”

Recent progress of plasma confinement and heating studies in the gas dynamic trap

“…Particle balance of the target plasma is sustained by fueling with a cold gas. The ECRH system is built upon two 54.5 GHz gyrotrons with total incident power of up to 0.7 MW, in addition to the main 5 MW heating power form the neutral beams [7].…”

Control of energy deposition profile for electron cyclotron resonance heating in open trap

“…It should be noted as well that the perturbation produced by this additional system is local. It introduces small perturbations to the main field of the trap, which is usually optimized from the viewpoint of plasma confinement and in some cases, from the viewpoint of transportation of the radiation to the resonance region as well [12]. …”