The Alfvén wave spectrum as measured on a tokamak

Abstract

The detailed experimental data obtained on the TCA tokamak [Proceedings of the 11th Symposium on Fusion Technology (CEC, Luxembourg, 1981), Vol. I, p. 601] concerning the antenna loading and wave fields as a function of the Alfvén wave spectrum are presented. The plasma density, plasma current, working gas, toroidal magnetic field, and frequency were varied systematically and the detailed results are compiled and discussed. In addition the phasing of the antenna currents was varied systematically, thereby exciting different combinations of modes, including pure traveling waves. The conclusions relevant to the design of an antenna system have been stressed.

Discrete spectrum of Alfvén ion–ion hybrid waves

“…The measured peak and minimum of the vacuum k z spectrum were k z Ϸ0.2 and 0.0 cm Ϫ1 , respectively. This experiment was very similar to a frequency sweep experiment carried out on TEXTOR, 13 where they identified a discrete MHD Alfvén spectrum.…”

“…This is similar to the well-known discrete spectrum for Alfvén waves in nominally one species plasmas, as measured on many devices, including PRETEXT, 12 Tokamak de Chauffage Alfvén TCA, 13 Torus of the University of Sydney TORTUS, 14 Tokamak Experiment for Technically Oriented Research ͑TEXTOR͒. 15 The discrete Alfvén spectrum follows from many theoretical treatments of Alfvén waves, which include boundary conditions.…”

“…The Phaedrus-T experiments presented here along with the heating and current drive results have been carried out in a significantly different regime than the TCA experiments 13,16 that defined the genre of Alfvén heating experiments. Our wave frequency was near the cyclotron frequency / cH (r ϭ 0) Ϸ 0.7 Շ 1, and our toroidal mode numbers were large ͉n͉ӷ1.…”

“…2 and 3. The swept frequency data coincide with the dispersion relation associated with the lower Alfvén continuum edge and high-density core, and not the calculated discrete surface modes associated with the low-density edge ͑sometimes called surface quasielectrostatic modes 13,16 ͒.…”

“…It is well known that near an Alfvén resonance zone, the wave group speed slows down and the B wave energy ''piles up'' and swells. Historically the experimental signature of Alfvén waves, even at the core of a largely inaccessible plasma, has been observed to be the edge B wave field, [12][13][14]29 so our use of edge B-dot probes to measure core wave properties has some tradition behind it.…”