High-frequency heating of plasma with two ion species

Abstract

The authors consider the penetration of electromagnetic waves with a frequency of the order of the ion cyclotron frequencies and with a fixed longitudinal wave number k||, so that N|| = k||c/w » 1 deep into an inhomogeneous plasma with two ion species. The propagation of two kinds of waves (fast and slow) with widely differing polarization and transverse refraction index is possible. For both types of waves there is an evanesence region at the plasma periphery.The evanescence region is narrow for slow waves and they easily penetrate the plasma. In a dense plasma they become electrostatic and can reach the ion-ion hybrid resonance region. However, the damping of these waves due to Cherenkov interaction with electrons in a high-temperature plasma is strong and therefore they are not suitable for heating plasma of large dimensions, as they are absorbed at the plasma periphery.The fast waves have a wider evanescence region and can be excited effectively only if N 2 is not too high. These waves can be completely absorbed in the plasma (due to Cherenkov interaction with electrons) if £ ~(vjj/v^)Z e (ii)pja/c)exp(-Z e ) > 1, where a is the plasma radius and Z e = UJ/(^2 k|| v T e ) . Fast waves can also reach the region where they are transformed into slow waves. In this region their damping increases considerably. It is shown that the transformation region in an inhomogeneous plasma with two ion species in a non-uniform magnetic field may be at the centre of the plasma. Fast waves can be used effectively for heating plasma of large dimensions.

The Theory of Radio Frequency Plasma Heating

“…Mode conversion to ion Bernstein waves can occur for the fast wave with small k.. approaching this 'two-ion* hybrid resonance, which is also pre dicted to become strongly absorbing on the high-field side, (Klima et al 1975;Swanson, 1976), at temperatures above 2 keV in larger experiments. Thus, if it is desired to excite high-3 eigenmodes, mode conversion must be avoided.…”

Quantum electronics and the R V Khokhlov–S A Akhmanov school of coherent and nonlinear optics at Moscow State University

“…Taking into account the terms (e,/|e 3 |) 1 4) and, consequently, to a shift of the LH wave absorption region to the plasma periphery.…”

“…In the stellarator regime, a current of 13 kA was generated by injection of PRF « 40 kW. The current drive efficiency in this regime, T7 C D = 0-3 kA-kW' 1 , was somewhat lower than in the tokamak regime, where rj CD = 1 kA-kW" 1 . As noted previously [8], significant bootstrap currents can flow in stellarators and can degrade confinement through current driven instabilities.…”

“…The possibility of developing a tokamak that would operate in steady state, with the current sustained by lower hybrid (LH) waves [1,2], provides a strong stimulus for the study of high frequency (HF) plasma heating in the LH frequency range in tokamaks [3][4][5]. In 1987, a 2 MA current was sustained in the JT-60 tokamak at a low plasma density, rig = 3.2 x 10 n cm" 3 [3]; in the Alcator-C tokamak [4], a 200 kA current was sustained in a plasma with a density of Hg = 7 X 10 13 cm" 3 .…”

Magnetoacoustic Oscillations of a Plasma Containing Two Species of Ions

“…Klima et al [8,9] consider the propagation of magnetoacoustic waves perpendicular to the magnetic field in tokama ks.…”