A. Heym

Effect of Rf Heating on Edge Parameters in the Tca Tokamak

Abstract Detailed scrape-off measurements during Alfven wave heating experiments ( P RF ~ 200 kW) in TCA are presented. The Measurements are performed by means of electrical probes and by deposition probes fixed onto the antennae. It is shown that different antenna designs strongly influence the behaviour of the boundary plasma. Even during low power RF heating experiments is it found that the plasma-antenna interaction leads to a non-Maxwellian plasma. Low frequency density fluctuations are associated with changes of the density and temperature profiles during RF. High frequency fluctuations at the driving frequency and their harmonics are observed.

Recent results from the TCV Tokamak

During the first two years of operation, the TCV tokamak has produced a large variety of plasma shapes and magnetic configurations, with 1.0≤Btor≤1.46T,Ip≤800kA,k≤2.05, −0.7≤δ≤1. A new shape control algorithm, based on a finite element reconstruction of the plasma current in real time, has been implemented. Vertical growth rates up to 1000s−1 have been stabilized using the external coil system. Ohmic H-modes with Troyon factors (βtoraB/Ip) up to two and densities up to 2.25×1020m−3, corresponding to the Greenwald limit, have been obtained in diverted discharges. Limiter H-modes with line averaged electron densities up to 1.7×1020m−3 have been obtained in elongated D-shaped plasmas with 360 kA≤IP≤600 kA.

Recent Alfven-Wave Heating Results on the Tca Tokamak

In this paper, we present the most recent results obtained during the Alfven wave Heating experiments being carried out on the TCA Tokamak. We have obtained both significant electron heating and some ion heating using rf powers up to 230 kW, greater than the value of the ohmic heating power in the target plasma. Firstly, we shall describe the AWH method as applied to TCA and then briefly cover some of the low power experiments carried out during the last year. The higher power experiments will then be discussed, along with some of the problems we have encountered.

Observation of slowly varying magnetic induction in a rotating magnetic field pinch

Recent measurements on a rotating magnetic field pinch reveal in the plasma core large magnetic fields which change slowly in time. Computations based on MHD theory show qualitatively that such fields should be expected, but they fail to reproduce the observed spatial extent and magnitude. Trapping and compression of the induction generated by the first half cycle of the rotating field is apparently a primary cause of the phenomenon.