The investigation of fluctuation phenomena in plasmas often necessitates the analysis of spatiotemporal signals. It is shown how such signals can be analyzed using the biorthogonal decomposition, which splits them into orthogonal spatial and temporal modes. The method, also referred to as the singular value decomposition, allows complex spatiotemporal patterns to be decomposed into a few coherent modes that are often easier to interpret. This is illustrated with two applications to fluctuating soft x-ray and magnetic signals, as measured in a tokamak. Emphasis is given to the physical interpretation of the biorthogonal components and their link with known physical models is discussed. It is shown how new insight can be gained in the interpretation of spatiotemporal plasma dynamics.

A new low noise miniaturized multichannel bolometer module for absolute measurements in the VUV and soft x spectral ranges is described. Highly integrated four-channel modules (2×3.3×1.5 cm3) each comprising four independent ac-excited (50 kHz) metal resistor bolometer bridges were successfully tested on a large tokamak (Tore Supra in Cadarache) and on an electron synchrotron (BESSY in Berlin). The bolometer system features a linear response to the absorbed radiation power, a low detection limit (≤1.0×10−6 W cm−2 on Tore Supra with an integration time of τint=10×10−3 s) and a low NEP (≤10×10−9 W on BESSY). The thermal cross-talk between adjacent detectors is negligible (<0.003) and a low thermal drift ΔUBr/ΔT < 10−4 V °C−1 is achieved. It can be operated at a maximum temperature of 150 °C, at high magnetic fields (tested up to B=4.5 T in the laboratory) and survives high nuclear radiation doses. The system offers the possibility of detecting low-power VUV and soft x-radiation with sampling rates of up to 10 kHz on plasma machines and of absolutely calibrating VUV and soft x instruments. Effective suppression of electric, thermal and nuclear radiation interferences is characteristic of the bolometer system.Strain gauge effects, which could affect the behavior of the bolometers at high magnetic fields, are suppressed by the ac-excitation technique.

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The toroidal field coils in Tore Supra are supra-conducting, and their number is restricted to 18. As a result, the ripple is fairly large, about 7% at the plasma boundary. Tore Supra has consequently been equipped with dedicated ripple loss diagnostics, which has allowed ripple loss studies. This paper reports on the measurements made with these diagnostics and provides an analysis of the experimental results, comparing them with theoretical expectations whenever possible. Furthermore, the main heating source accelerating ions in Tore Supra is ion cyclotron resonance range of frequency (ICRF) heating, and the paper provides new information on the ripple losses of ICRF accelerated ions.

Tore Supra experiments are at present devoted to the study of high density regimes with radiofrequency heating. Recently, an improved L mode confinement regime has been observed in plasmas heated by ion cyclotron hydrogen minority heating, at relatively high densities up to 80% of the Greenwald limit. The quality of energy confinement is as good as that of ELMy H mode. The main physical mechanism of this regime has not been clearly identified. However, some features very similar to those of previous improved confinement modes using neutral beam heating in other tokamaks have been observed.

The global energy confinement of combined ohmic and lower hybrid driven TORE SUPRA plasmas has been analysed at various densities. In contradiction to the L mode ITER scaling law, this analysis indicates that the global energy confinement time depends strongly on the plasma density. Furthermore, the thermal electron energy content of steady state discharges is found to be in good agreement with the global Rebut-Lallia-Watkins (RLW) scaling law. Current ramp experiments show an enhancement of the global energy confinement with the internal inductance, I,. These results have been extended to steady state regimes with lower hybrid current drive. Improved confinement has been obtained in a high I, steady state plasma ( I , = 1.7), where the modification of the current profile by lower hybrid waves leads to an increase in the central value of the safety factor (q$(O) 2: 2). In this case, the global confinement time is shown to exceed the value predicted by the RLW scaling law by 40%.

Preliminary experiments in the TORE SUPRA tokamak using the ergodic divertor configuration have shown a strong effect on plasma impurities. The result is a decontamination of the central plasma which is due to a decreased carbon content. This is the consequence of a screening effect of the peripheral ergodic layer which is due to an important increase of the recycling impurity flux, as well as of a modification of the impurity source terms.