Quasi-optical theory of microwave plasma heating in open magnetic trap

Abstract

Microwave heating of a high-temperature plasma confined in a large-scale open magnetic trap, including all important wave effects like diffraction, absorption, dispersion and wave beam aberrations, is described for the first time within the first-principle technique based on consistent Maxwell's equations. With this purpose, the quasi-optical approach is generalized over weakly inhomogeneous gyrotrotropic media with resonant absorption and spatial dispersion, and a new form of the integral quasi-optical equation is proposed. An effective numerical technique for this equation's solution is developed and realized in a new code QOOT, which is verified with the simulations of realistic electron cyclotron heating scenarios at the Gas Dynamic Trap at the Budker Institute of Nuclear Physics (Novosibirsk, Russia).

Electron cyclotron emission at the fundamental harmonic in GDT magnetic mirror

“…In this way, any ECRH code that calculates radial power deposition profile may be easily adopted for calculation of ECE of thermal plasma. In this paper, the power deposition is provided by the available ECRH ray-tracing code, which has been recently benchmarked against the more accurate quasi-optical code QOOT 21 .…”

“…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…”

Quasi-optical approach to reconstruction of plasma fluctuations using amplitude distribution of transmitted microwave beam

“…The code is able to model the propagation and the electron cyclotron absorption of wave beams in weakly relativistic plasma in electromagnetically large devices (with typical size of few thousands of wavelengths) in a reasonable time. Calculations using LAQO proved the importance of taking into account these effects to describe correctly the RF power deposition profile in tokamak plasmas [3,4] and in open magnetic trap [5,6]. A small solution time for the direct problem of wave beam propagation allows the use of LAQO to solve the inverse problem, such as reconstruction of distributions of fluctuating plasma parameters using the amplitude profile of the transmitted beam.…”

Quasi-optical approach for inhomogeneous dissipative media with high-order spatial dispersion

“…Its generalization to the case of anisotropic and gyrotropic media with spatial dispersion and dissipation [3] was used to simulate the propagation of quasi-optical wave beams in tokamaks and showed much higher accuracy for resonance absorption in comparison to the previously used approaches [4]. In this paper, we discuss the further generalization of the quasi-optical approach [5] and the features of its application in media of a special kind.A quasi-optical equation [3] is the equation for the scalar complex amplitude U of the wave beam corresponding to selected electromagnetic mode in smoothly inhomogeneous mediaHere the momentum operatoris defined as the differentiation operator in the coordinate space normalized on the vacuum wave number k 0 = Ȧ/c. The simplification of this equation is possible for paraxial wave beams (broad in the wavelength scale) with parameters varying slowly along some curve r 0 (the reference ray).…”

“…Its generalization to the case of anisotropic and gyrotropic media with spatial dispersion and dissipation [3] was used to simulate the propagation of quasi-optical wave beams in tokamaks and showed much higher accuracy for resonance absorption in comparison to the previously used approaches [4]. In this paper, we discuss the further generalization of the quasi-optical approach [5] and the features of its application in media of a special kind.…”