[en] A positive limiter biasing on the CT-6B tokamak resulted in a slight increase of edge density and an obvious drop of electron temperature, which is in the temperature range where the rate coefficients for ionization processes are strongly temperature dependent. Concomitantly, edge fluctuations are enhanced, suggesting that the presence of neutral particles may play an important role in modifying edge turbulence

[en] Langmuir probes and a Mach probe were used for measuring edge fluctuations and parallel plasma flow, respectively, on the CT-6B tokamak. A maximum radial gradient in parallel flow was observed to be located roughly at the maximum E_r shear layer (or, namely, the poloidal velocity shear layer). E_r shear is found to be very possibly consistent with a regulating effect on edge turbulence features. Non-linear analysis indicates that non-linear phase coupling in turbulence may be influenced by E_r shear, or that there exist coherent structures induced by strong E_r shear, and the phase coupling processes show an intermittent character. The results provide some new observations for a better understanding of the basic mechanisms of edge turbulence. (author)

[en] Core and edge turbulences were measured by Langmuir probe arrays in the KT-5C tokamak plasma. The radial wavenumber spectra show a quasimode like structure which results in a net radial outward propagation of the turbulent fluctuations. The measured fluctuation levels and wave action fluxes are in good agreement with model predictions by Mattor et al., suggesting that drift wave propagation could be a source of edge turbulence

[en] Features of a low frequency ion mode were observed together with the electron drift wave type fluctuations by a Langmuir probe array in the bulk plasma inside the velocity shear layer in the KT-5C tokamak. The measured ion mode wavenumber, scaling of the ion mode with chord-average density, and the estimated η_i value suggest that the observed ion mode may be the theoretically predicted η_i mode driven by ion temperature gradient

[en] The experiment for controlling the plasma edge radial electric field using a set of biased limiters which can be easily reconnected has been carried out on the KT-5C tokamak for the first time. It is found that positive biasing is more effective than the negative in modifying the edge electric field. The collecting area of the limiter (perpendicular to the toroidal magnetic field), the strength of toroidal field and the value of the applied biasing voltage can affect the experiment results sensitively. The edge potential will finally be saturated by increasing the collecting area or the biasing voltage (either positively or negatively). It is shown that the relative position of biased limiter to the plasma column can be very important for modifying the edge electric field

[en] The experiment on improving the plasma edge parameters and the studying of its mechanism had been carried out on KT-5C Tokamak, in which a set of biasing limiters that can be multiply combined are used to control the edge plasma radial electric field. The result of the experiment shows that both the positive and the negative biasing can change the plasma potential, but the positive biasing is more effective to establish a steep radial electric field to control the edge fluctuation and thus improve the confinement of the plasma. The profile of the measured edge electron temperature, electron density and the space potential by a moveable Langmuir probe became more slanted during the period of positive biasing and this correspond to the calculation results of the decrement of the edge particles flux and the increment of the particle confine time

[en] The present design concept for the ITER low-field-side reflectometer transmission line (TL) consists of an ~40 m long, 6.35 cm diameter helically corrugated waveguide (WG) together with ten 90° miter bends. This paper presents an evaluation of the TL performance at low frequencies (33-50 GHz) where the predicted HE11 mode ohmic and mode conversion losses start to increase significantly. Quasi-optical techniques were used to form a near Gaussian beam to efficiently couple radiation in this frequency range into the WG. We observed that the output beams from the guide remained linearly polarized with cross-polarization power levels of ~1.5%-3%. The polarization rotation due to the helical corrugations was in the range ~1°-3°. The radiated beam power profiles typically show excellent Gaussian propagation characteristics at distances >20 cm from the final exit aperture. The round trip propagation loss was found to be ~2.5 dB at 50 GHz and ~6.5 dB at 35 GHz, showing an inverse increase with frequency. This was consistent with updated calculations of miter bend and ohmic losses. At low frequencies (33-50 GHz), the mode purity remained very good at the exit of the waveguide, and the losses are perfectly acceptable for operation in ITER. Finally, the primary challenge may come from the future addition of a Gaussian telescope and other filter components within the corrugated guide, which will likely introduce additional perturbations to the beam profile and an increase in mode-conversion loss.