Absorption of Alfvén waves and plasma production in the OMEGA and URAGAN-3 toroidal devices

Abstract

The paper describes a theoretical and experimental study of the structure of local Alfvén resonance (AR) and absorption of Alfvén waves (AWs) in an inhomogeneous toroidal plasma. An analysis is made of expressions for the RF field distribution in the AR region and for the power absorbed by the plasma, taking into account finite ion Larmor radius, inertia of electrons, the gyrotropy effect and Cherenkov absorption of waves by electrons. The dispersion characteristics of the AWs excited have been studied in the currentless regime on the OMEGA toroidal device. Amplitude and phase space-time measurements of the Ẽ and B̃ components of the RF field in the AR region for travelling and standing AWs have been made. AW absorption in the AR region and the dynamics of plasma production using AWs have been studied on the OMEGA device and on the URAGAN-3 torsatron. With an input of about 500 kW of RF power in the frequency region ω < ωci. in the U-3 torsatron, a dense hydrogen plasma which had a clearly defined boundary and divertor layers was produced with the following parameters: n̄e = 1.1 × 1013, T̄e ≈ T̄i ≈100 eV. In these experiments, which were performed with weak magnetic fields (Bo ≤ 4.2 kG), the beta achieved (≈0.5%) is comparable with the theoretical maximum equilibrium value for the device.