[en] A set of preliminary experimental results of the investigation of fast density variations in Pulsator by means of interferometric measurements shows the presence of internal modes in the electron density as well as in soft X-ry emission. (orig.)

[en] The problem of determining neutron emissivity from neutron brightness measurements in magnetic fusion plasmas is addressed. In the case of two-dimensional measurements with two orthogonal cameras, a complete, tomographic analysis of the data can in principle be performed. The results depend critically on the accuracy of the measurements and alternative solutions can be sought under the assumption of a known emissivity topology (Generalized Abel Inversion). In this work, neutron brightness data from the JET tokamak have been studied with both methods. We find that with the present experimental uncertainty (levels 10-20%) the Abel inversion method works best, while two-dimensional information cannot in general be deduced. This is confirmed by studies of the error propagation in the inversion using artificial data, which are also presented here. An important application of emissivity profile information is the determination of the plasma deuterium temperature profile, T_D(R). Results are presented here from the analysis of JET data and the errors in T_D(R) are discussed in some detail. It is found that, for typical JET plasma conditions, the dominant source of uncertainty arises from the high plasma impurity level and the fact that it is poorly known; these problems can be expected to be remedied and neutron brightness measurements would be expected to be very effective (especially in high density plasmas) as a T_D(R) diagnostics. (author)

[en] The experimental data reported indicate that even the small variations, from shot to shot, of the gas influx due to wall recycling lead to a deviation from the programmed discharge conditions and hence to disruption. (orig.)

[en] Electron density fluctuations measured with lambda = 2 mm waves radiating the plasma through several limiter chords of the Pulsator Tokamak have been correlated with sawtooth fluctuations of soft X-rays emitted along crossing chords. These studies and the similar sawtooth relaxation behaviour of other parameters during external disruption of off-centered discharges reveal that the observed fluctuations arise from relaxing plasma-limiter interactions, i.e. they are not caused by kink-mode oscillations as previously reported. (orig.)

[en] This report describes a fast, unmodulated interferometer with a bandwidth exceeding 1 MHz which delivers two separate signals for the continuously represented amplitude and phase. (orig.)

[en] A computer program was developed to calculate eddy currents in electrically conducting structures of general geometry in order to determine their magnetic fields. The program is based on the finite element network method (FEN), in which the structure considered is divided into directed, finite elements. Each element is then treated as a branch of a three-dimensional RL network. After R and L in all of the network branches have been calculated, the network differential equations represented in matrix form is solved. The time behaviour and distribution of the eddy currents then follow directly from the solution vector of the transient branch currents. The FEN is tested in the case of vertical field diffusion through the toroidal field coils of ZEPHYR. For this purpose an electrical model of the coil configurations was constructed on a scale of 1:5. The scaling laws applied are described. A detailed description of the measuring method used is given. The results of the calculations and measurements are compared for various frequencies of the vertical field. (orig./HT)

[en] A novel class of functions is discussed, which is particularly suited to describe hollow and peaked density profiles in JET (Joint European Torus) plasmas. Each function is determined through three parameters that are obtained by a least squares fitting technique to the line-of-sight integrals. A comparison of this new technique is made with the present Abel inversion and with LIDAR density profile measurements in JET. (author)

[en] Bolometrically measured asymmetries of emissivity for some characteristic JET discharges are presented and are in good agreement with theoretical results of calculations worked out in the frame of neoclassical theory. Application of theory to the case of strong toroidal rotation as induced with neutral injection shows a sensitive dependance of the impurity transport perpendicular to the magnetic surfaces from the parameter of poloidal rotation. The main result is the existence of a classical flow reversal. Without any poloidal rotation of the background ions, a large inward flow of impurities for co- and counter-injection is always predicted, while poloidal rotation in the direction of the ion diamagnetic drift motion leads to a strong outward drift. (author)

[en] Obtaining electron density profiles from integrated measurements (e.g., those made with a multichannel interferometer) in the case of asymmetrical plasma distributions often entails serious difficulties. Here we describe a method applicable when the profiles are shifted along the equatorial plane and also when the relation between phase shift and electron density may not be considered as linear

[en] JET has now been operated with an evaporated layer of beryllium on carbon and with beryllium as a limiter material. A principal objective of the experiment was to investigate the effect of beryllium as a first wall material would have on the operational space of JET. The results of this investigation are presented and contrasted with data obtained during the all carbon phase. The gettered phase showed no increase in the gas fuelled density limit except with RF heating. The limit had, however, changed in character, with the formation of a MARFE preventing any further increase in density. There was a disruption in only a few cases. In the beryllium limiter phase chlorine was a mjaor contributor to the radiated power, initially radiating 70% of the total radiated power. In these circumstances the density limit changed little from the gettered phase. However, as the chlorine diminished the limit was extended substantially beyond the level obtained with gettering alone, while still maintaining its soft character. The density at which the soft limit occured is shown to be a function of input power and plasma contamination with a weak dependence on q, and is described well by a scaling law based on a radiation model. Helium and pellet fuelled discharges have exceeded the deuterium gas fuelled limits, but we present evidence showing an overall consistency when the edge density is considered. (author) 7 refs., 5 figs