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.

Studies of fast ion outflow to the helical divertor of the U-3M torsatron

“…In addition, with specifics of the Alfven wave excitation and absorption in the ω ω ci range of frequencies in a radially non-uniform plasma [9] and magnetic field taken into account, one may expect substantial non-uniformities in heating power deposition and intensity of FI generation both along the torus and over the minor azimuth.…”

“…The plasma is produced and heated by RF fields in the frequency range ω ω ci (0) in the multi-mode Alfven resonance regime [9] with the working gas (hydrogen) continuously intake into the vacuum chamber. The RF power is injected into the plasma by the so-called frame-like antenna [9] embracing the plasma under the helical coils I and III within one field period (period 1 in Figure 1).…”

“…The RF power is injected into the plasma by the so-called frame-like antenna [9] embracing the plasma under the helical coils I and III within one field period (period 1 in Figure 1). The power fed to the antenna can attain ∼200 kW in the 50 ms pulse.…”

Results of localized Alfvén wave heating in TCABR

“…When v T e < c A , a slow quasi-electrostatic Alfvén wave (SQEAW) is excited with mainly collision damping and propagates towards the plasma boundary. The detailed picture of resonant absorption was established by subsequent theoretical work carried out by different investigators (see, for example, [8]- [13]) and experimentally confirmed in tokamaks [14]- [17] and stellarator [1,18].…”

Behavior of RF Discharge Plasmas in the Uragan‐3M and Uragan‐2M Torsatrons

“…The working gas (hydrogen) is admitted into the chamber continuously at the pressure of 10 −6 − 10 −4 Torr. The plasma is produced and heated by RF fields (frame-type antenna) at the frequency 8.8 MHz (ω ω ci ) in the multi-mode Alfvén resonance regime [1]. The RF power P fed in the antenna attains 200 kW.…”