A detailed analysis of the spectra of synchrotron radiation emitted by runaway electrons, and an analysis of synchrotron radiation spot shapes are presented for EAST runaway cases. Conditions required for the asymptotic expressions of synchrotron radiation spectra to be valid are studied for these EAST parameters. We provide the correct synchrotron radiation spectra in typical EAST discharges, and we show results of calculations of the shape of the synchrotron radiation spots emitted by runaway electrons. These shapes are detected by a visible light camera in EAST. Safety factor q(r), the horizontal displacement of electron drift surfaces with respect to the magnetic surfaces δe, pitch angle θp, and the position of the camera were taken into account. Our results indicate that the θp and q profiles can significantly affect the synchrotron radiation spot shape; it is simpler to record all synchrotron radiation if the camera is placed far from the plasma. An asymmetrical synchrotron radiation spot shape can be deduced when the effect of the drift orbit shift is taken into account. Our results can explain the asymmetrical ring-like synchrotron radiation spot shape from runaway electron beams in EAST experiments.

ITER as a superconducting fusion machine needs efficient wall conditioning techniques for application in the presence of the permanent high toroidal magnetic field for (i) reducing the in-vessel impurity content, (ii) controlling the surface hydrogen isotopic ratio and (iii) mitigating the in-vessel long-term tritium inventory build-up. Encouraging results recently obtained with ion-cyclotron wall conditioning (ICWC) in the present-day tokamaks and stellarators have raised ICWC to the status of one of the most promising techniques available to ITER for routine inter-pulse and overnight conditioning with the ITER main ICRF heating system in the presence of the permanent high toroidal magnetic field. This paper is dedicated to a milestone experiment in ICWC research: the first simulation of ICWC operation in an equivalent ITER full-field scenario and the assessment of the wall conditioning effect on the carbon wall in the largest present-day tokamak JET. In addition, we address in this paper the following topics: (i) an analysis of the radio frequency (RF) physics of ICWC discharges, (ii) the optimization of the operation of ICRF antennas for plasma startup and (iii) an outlook for the performance of ICWC in ITER using the ICRF heating system. Important operational aspects of the conventional ICRF heating system in JET (the so-called A2 antenna system) for use in the ICWC mode are highlighted: (i) the ability of the antenna to ignite the cleaning discharge safely and reliably in different gases, (ii) the capacity of the antennas to couple a large fraction of the RF generator power (>50%) to low-density (≈10 16 -10 18 m −3 ) plasmas and (iii) the ICRF absorption schemes aimed at improved RF plasma homogeneity and enhanced conditioning effect. Successful optimization of the JET-ICWC discharge parameters

The paper studies the distribution function of a runaway electron beam with allowance for close collisions of fast tail electrons with thermal ones, as a result of which momentum is imparted to the latter sufficient for escape into a continuous acceleration regime. It is shown that a beam is formed which is not in equilibrium with respect to transverse momenta; it may excite electromagnetic plasma instabilities under the conditions of linear and non-linear electron cyclotron resonance.

The plasma response influence on the penetration of an external low frequency helical perturbation into a tokamak edge plasma has been studied on the basis of the two-fluid MHD equations in the linear approximation for the cylindrical model. Components of the penetrating field, the plasma flows, the perturbation current density distribution and the radial profile of the poloidal driven force density are found in the resonant region and investigated for the parameters of the TEXTOR-DED, CSTN-IV and HYBTOK-II tokamaks. Preliminary comparisons with the CSTN-IV and HYBTOK-II experiments are made and a good qualitative agreement has been found.

In the Uragan‐3M (U‐3M) and Uragan‐2M (U‐2M) torsatrons possibilities and prospects of Alfvén method utilization for wall conditioning, plasma production and heating are studied. In U‐3M the effect of fast ion loss on H‐like mode formation is investigated. In U‐2M the wall conditioning associated with the chemical reactivity of the atomic hydrogen to create volatile substances is used. A compact four‐strap antenna is proposed for Alfvén resonance heating in U‐2M (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)