Heat wave propagation experiments have been carried out on the Wendelstein 7-AS stellarator. The deposition of electron cyclotron resonance heating power is highly localized in the plasma centre, so that power modulation produces heat waves which propagate away from the deposition volume. Radiometry of the electron cyclotron emission is used to measure the generated temperature perturbation. The propagation time delay of the temperature perturbation as a function of distance to the power deposition region is used to determine the electron thermal conductivity χe. This value is then compared with the value determined by global power balance. In contrast to sawtooth propagation experiments in tokamaks, it is found that the value of χe from heat wave propagation is comparable to that calculated by power balance. In addition, inward propagating waves were produced by choosing a power deposition region away from the plasma centre. Experiments were carried out at 70 GHz in the ordinary mode and at 140 GHz in the extraordinary mode. Variations of the modulation power amplitude have demonstrated that the inferred value of χe is independent of the amplitude of the induced temperature perturbations

In W 7-AS the H mode has been observed for the first time in a currentless stellarator plasma. H modes are achieved with 0.4 MW electron cyclotron resonance heating at 140 GHz at high density. The H phases display all characteristics known from tokamak H modes including edge localized modes (ELMs). The achievement of the H mode in a shear-free stellarator without toroidal current has consequences on //-mode transition and ELM theories.

Dispersion curves are plotted for the extraordinary branch of the electron- and ion-cyclotron harmonic waves propagating perpendicularly to the static magnetic field in a non-relativistic, hot Maxwellian plasma, without invoking the electrostatic approximation. It is found that, except in the vicinity of the cyclotron harmonics and the hybrid resonances, either the cold-plasma or the electrostatic approximation are accurate representations of the exact solution. The hybrid resonances of the cold-plasma model become monotonically shrinking regions of low group velocity as the temperature is increased, till all discernible evidence of these resonances disappears as the parameters corresponding to the thermonuclear plasmas are approached.

The first plasma experiments on the W7AS advanced stellarator were conjuctea in October 1988, after magnetic surface mapping. The characteristics of the device &re described. During the first phase of operation, 70 GHz ECF was used to geneTate and heat a "currentless" plasma which was maintained in quasi-steady state for typically 0.5 s. Effects of the magnetic configuration on the confinement and measures to deal with the observed plasma current (bootstrap current and ECF-driven current) were investigated. Preliminary results of transport analysis are presented and compared with predictions of transport models.

An upper bound for the local electron heat coefficient χ(r) in electron cyclotron heated (ECH) discharges is determined experimentally. The method applied uses power modulation of the ECH and measures the time delay of the electron temperature response as a function of radius by means of a multi-channel radiometer for second-harmonic electron cyclotron emission (ECE). The evaluation is restricted to plasma radii between 3 and 6.5 cm, where the pre-conditions of the method are best verified experimentally. The theoretical transport model considers only processes related to the electron temperature gradient and neglects the dependence of χ on Te.