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AbstractMeasurements of electron temperature fluctuations by means of correlation electron cyclotron emission (ECE) diagnostics aid in understanding the nature of the turbulent transport in fusion plasmas. On Tore Supra tokamak, a 32-channel heterodyne ECE radiometer has been upgraded to include two channels for temperature fluctuation measurements. The central frequency of the yttrium iron garnet filter on each channel is remotely monitored by a driver, allowing one to shift the observation volume in the plasma radially. To resolve the fluctuation amplitude of 0.1%, integration times of ~3 s at 1 MHz sampling rate are required for the statistical error level of 0.05%. Together with the 32-channel profile radiometer, correlation ECE is a powerful and unique tool for simultaneous observation of the magnetohydrodynamic phenomena and studies of the plasma transport properties in various heating regimes during long-shot multimegawatt operation. First measurements of temperature fluctuations, of various origins, on Tore Supra (including the observation of the toroidicity-induced Alfvén eigenmodes), as well as a description of the analysis methods used in the data evaluation, are reported in this paper.

To shed some light on the development of the fast m/n = 1/1 precursor to the sawtooth crash and its influence on plasma transport properties in the vicinity of the q = 1 surface, series of dedicated experiments have been conducted on the Tore Supra and TEXTOR tokamaks. It has been concluded that, before a crash, the hot core gets displaced with respect to the magnetic axis, drifts outwards by as much as 8–10 cm and may change its shape. Observation of the magnetic reconnection process has been made by means of electron cyclotron emission diagnostics. The heat pulse is seen far outside the inversion radius. The colder plasma develops a magnetic island on the former magnetic axis, after the hot core expulsion. Different kinds of behaviour of the m = 1 precursor before the crash, with respect to the displacement of the hot core and the duration of the oscillating phase, have been observed. An ideal kink model alone cannot be used for explanation; therefore, resistive effects play an important role in the mode development. Possible mechanisms that lead an m = 1 mode to such behaviour, and their links to the change in the central q-profile, are discussed. Results have been discussed in the light of various theoretical models of the sawtooth.

The deuterium Dα line emitted in front of an equatorial neutraliser plate in Ergodic Divertor Tore Supra plasmas is a common diagnostic of recycling particles in present Tokamaks. First, the possible perturbation of the Dα spectral lineshape by the nearby HeII line Brβ has been studied. Although its effect on the Dα line profile shape is evaluated to be non negligible in plasmas with large Helium contents, it is concluded that it should be of no influence in usual fusion plasmas. Second, a detailed study of the Dα spectral lineshape has been performed to obtain temperatures and densities of the different neutral deuterium species. A synthetic profile method taking into account Zeeman and Doppler effects has been used. This shows that two deuterium populations with specific behaviours have to be considered: the first one (‘cold atoms’) is composed of atomic deuterium coming from D2 desorbed from the neutraliser plate, while the second one (‘warm atoms’) is composed of charge exchange (CX) and reflected deuterium. The Doppler temperature of cold atoms increases with the edge electron density, n^edgee (1.4 eV < T^cD < 2.5 eV). The possible heating of cold atoms by D⁺ ions is evaluated to explain this effect. Molecular and atomic deuterium densities behaviour versus edge electron temperature Te are analysed with the use of the warm and cold Dα brightnesses coupled to a collisional radiative deuterium model. The results are compared to the numerical code EDCOLL. An important molecular density (> 10¹⁸ m^-3) is found for the whole range of edge electron temperature (10 eV < Te < 40 eV) while the ratio of the atomic to the molecular densities is around 1.8. The density of atoms coming from molecular dissociation is ~ 0.8 times the density of atoms created by charge exchange or re.ection of deuterons on the neutraliser.