Fully off-axis ECCD driven plasmas in TCV
Fully non-inductive TCV discharges with current profiles sustained only by off-axis Electron Cyclotron Current Drive (ECCD) (Ip~100kA, ne19> 0.6 1019m-3) have extended the range of TCV scenarios. The existence of a reverse shear profile is tested with additional on-axis heating (ECH). Modelling shows that the effect of radial transport on ECCD can lead to centrally peaked current density profile even without on-axis deposition. With the ECH/ECCD system of the TCV tokamak, steady state, non-inductive discharges, limited only by the pulse length of the gyrotrons, were previously sustained with a component of on-axis current drive. The modelling is performed with the CQL3D Fokker-Planck code, which includes a model for radial particle transport, and the TORAY-GA ray-tracing code. In addition, discharges with combined off-axis co-ECCD and on-axis counter-ECCD are analysed; in particular the contribution of the latter to both the current profile and the total plasma current is studied. The comparison of the calculated X-ray emission by supra-thermal electrons with results from a hard X-ray diagnostic provides further information on the hot electron tail profile. The motivation of the work is twofold. It gives a test of the quasi-linear wave absorption model for TCV since, in the plasmas concerned, the current will be carried entirely by non-thermal electrons. Secondly, the modification of the current profile is expected to have a favourable effect on the energy confinement time. This scenario is sensitive to the current density profile shape which, in TCV, depends greatly on the level of transport in the power deposition volume.
Bibliographic Reference: An oral report given at: 12th Joint Workshop on Electron Cyclotron Emission and Electron Cyclotron Resonance Heating Organised by: Association Euratom-CEA, Cadarache Held at: Aix-en-Provence (FR) May 13-16, 2002
Availability: Workshop papers are available online at: http://wshop.free.fr/ec12/ This paper is also published in report LRP 726/02, available free of charge from: École Polytechnique Fédérale de Lausanne, Ecublens, CH-1015 Lausanne Fax +41-21-69347
Record Number: 200215133 / Last updated on: 2002-08-07
Original language: en
Available languages: en