Non-linear temperature oscillations in the plasma centre on Tore Supra and their interplay with MHD

Regular oscillations of the central electron temperature have been observed by means of ECE and SXR diagnostics during non-inductively driven discharges on Tore Supra. These oscillations are sustained by LHCD, do not have a helical structure and, therefore, cannot be ascribed as MHD phenomena. The most probable explanation of this oscillating regime (O-regime) is the assumption that the plasma current density (and, thus, the q-profile) and the electron temperature evolve as a non-linearly coupled predator-pray system. The integrated modelling code CRONOS has been used to demonstrate that the coupled heat transport and resistive diffusion equations admit solutions for the electron temperature and the current density which have a cyclic behaviour. Recent experimental results in which the O-regime co-exists with MHD modes will be presented. Because both phenomena are linked to details of the q-profile, some interplay between MHD and oscillations may occur. The localisation of magnetic islands allows to obtain an accurate picture of the q-profile in the plasma core. In some case, MHD-driven reconnection helps in maintaining a weakly inverted q-profile that is found to be, in the CRONOS simulations, a necessary condition to trigger the oscillations.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004, Nice (France

Present status and future plans for Tore Supra

Tore Supra is a limiter tokamak with circular plasma cross-section. The superconducting toroidal magnet is a unique feature which allows very long pulse discharges. Tore Supra has ion cyclotron resonance heating and an electron cyclotron system is being installed. Noninductive currents are driven by lower hybrid and by the bootstrap effect. Highlights of previous results include long pulses lasting up to 2 minutes with 280 MJ coupled into the plasma and fully non-inductive discharges lasting up to 75 seconds. Tore Supra is presently in the middle of a major shutdown for the installation of a new toroidal pumped limiter. This will be actively cooled with capability for steady state operation at total power levels around 20 MW. Future plans include upgrades to the ion cyclotron heating and lower hybrid current drive systems and a new pellet injector

Magnetic Fusion Basics

At the core of the sun and stars, light nuclei combine - or fuse - to create heavier nuclei. This process releases a significant quantity of energy and is the source of the heat and light that we receive. Harnessing this type of reaction on earth for the purpose of generating energy would open the way to almost unlimited resources. This is the aim of fusion research undertaken by the leading industrial nations. The main principles for mastering fusion energy on earth will be described in this paper. After a reminder of the main fusion reactions and the conditions to obtain fusion, this document will focus on the magnetic fusion based concepts. The magnetic confinement principles (particle trajectories, confinement time, Q factor, particles and heat transport, confinement methods, stability limits …) will be exposed with a special emphasis on the Tokamak configuration. The role of the main components of such device will be described: magnetic system, plasma facing components including divertor, fuel injection, heating systems, diagnostics … Methods for creating, heating and mastering plasma inside a tokamak will be explained and specifi cities due to long plasma duration capabilities will be pointed out (plasma wall interactions…)

Discharges with high bootstrap current fraction on Tore Supra

Bootstrap current is regarded as a serious candidate for non-inductively driving a significant fraction of the total current. High bootstrap fraction discharges have already been achieved and analysed in several tokamaks, including JT-60, DIII-D and TFTR. Tore Supra (R=2. 36 m, a=0.80 m) is particularly suited for the study of non-inductive discharges and long pulse operation. It is equipped with several of non-inductive current drive/heating systems including Lower Hybrid Current Drive (LHCD), Fast Wave Electron Heating (FWEH), and in the future Electron Cyclotron Heating. Fully non-inductive discharges with enhanced confinement (LHEP mode) have already been obtained in Tore Supra with LHCD. High {Beta}p ({le}1.6) regimes current nave also been achieved in the presence of FWEH. In particular, a discharge with 70% of the total current generated by the bootstrap current was observed. In this context, non-inductive current density profile determination is essential for understanding current drive experiments and ultimately for implementing current profile control. This paper briefly describes two methods developed on Tore Supra to determine the non-inductive current density profiles. The agreement between the two methods has been tested by applying them to ohmic discharges. These methods are then applied to the high bootstrap fraction discharges heated by FWEH. The non-inductive current density profile of these discharges are carried out. and the results are finally compared to several models of bootstrap current including Hirsman`s with low collisionality, matrix formulation and both Kessel and Houlberg matrix formulation

XUV SPECTROSCOPY IN JET

The 2m extreme grazing incidence XW Schwob-Fraenkel spectrometer has been described in detail [1]. Its use on the TFR tokamak is presented in a parallel paper [2]. The instrument installed on JET differs in that it has two microchannel plates scanning independently two portions of the spectral range from 10 to 335Å. A full scan takes 164 ms, due to the low number of photons. 127 spectra may be taken during a 20s tokamak discharge. The calculated and measured spectral resolution (FWHM) with a 600g/mm Bausch and Lomb grating and 20 µm entrance slit is shown in Fig. 1 for detector positions, y, between 200 and 390 mm (corresponding wavelengths of the central pixels are 85 and 310 Å, respectively)