[en] An analysis is given of the first experimental data from a sin-cos reflectometer used at the CASTOR tokamak for the measurement of density fluctuations. The reflectometer operates at frequencies of 8.5 GHz and 10.26 GHz. Discrete Fourier transformation, fast Fourier transformation and autocorrelation analysis were used to obtain frequency spectra of density fluctuations and the time evolution of the Δτ parameter. The character of the spectra is shown to depend on the frequency used. The content of higher frequencies in the spectrum increases for density fluctuations at the plasma periphery. The correlation of fluctuations increases for the fluctuation at layers near to the plasma centrum. (J.B.) 8 figs., 5 refs

[en] Short communication

[en] The first microwave reflectometric device is described used at the CASTOR tokamak to measure fast density fluctuations. The device operates at the frequency of 10.26 GHz which makes it possible to detect fluctuations near the plasma periphery. The device was proved to work properly during the whole tokamak discharge despite the fact that the reflected signal level varied strongly. The construction of the reflectometric device is described as is its use of the so-called sin-cosin detection system, and the results obtained are discussed. (Z.S.) 8 figs., 3 refs

[en] An enhancement of line average electron density was observed in the CASTOR tokamak when lower-hybrid power was launched into ohmic plasma. A broadening of the density radial profile was also found. Such behavior of density in lower hybrid current drive (LHCD) discharges can be attributed to an improvement of particle confinement. The dependence was investigated of the global particle confinement time on the plasma density and the position in the plasma. A simple model was used to evaluate the total number of particles in the plasma volume. The global particle confinement improved by a factor of 2-2.5 during LHCD. Further improvement of the global particle confinement was found in the plasma closer to the optimum. (author) 5 figs., 5 refs

[en] A diagnostic pulsed arc source of a beam of lithium atoms was used for the measurement of the electron density profile in front of the lower hybrid grill at the CASTOR tokamak. It was shown that the profile is significantly modified during lower hybrid wave application if the regime with improved particle confinement is achieved. (author) 6 figs., 13 refs

[en] Feasibility studies of a new diffraction structure for launching lower hybrid waves into a tokamak plasma - of the microwave quasi-optical grill - are reported. The main parameters of the grill designed for the CASTOR tokamak are summarized, and results of preliminary radiation pattern measurements of a non-optimized model antenna are presented. The influence of a relatively great curvature of the plasma surface in the CASTOR tokamak is discussed and the ray tracing of the launched lower-hybrid wave in the actual CASTOR plasma is shown. Finally, the results of probe measurements of the CASTOR plasma core are given. (J.U.) 17 figs., 9 refs

[en] An effect of lower hybrid current drive on the turbulent parameters of the tokamak CASTOR periphery is reported. Suppression of the density fluctuations is correlated with the changes of the radial electric field, an increase of poloidal rotation velocity and the improvement of the global particle confinement time. (author) 10 refs., 4 figs

[en] A link between the level of electrostatic fluctuations and particle confinement is investigated experimentally in two regimes with an improved global particle confinement: Lower Hybrid Current Drive regime (LHCD). Edge Plasma Polarization regime (EPP). It has been found that the edge fluctuations are reduced and their character changes at LHCD. Preliminary results of the spectral analysis of the fluctuations at EPP regime are presented. (author) 4 refs.,4 figs

[en] A diagnostic pulsed arc source of a Li beam was used to measure the electron density profile in front of the lower hybrid grill on the CASTOR tokamak. It was shown that this profile is modified significantly during lower hybrid wave application if the regime with improved particle confinement is achieved. (author) 4 figs., 8 refs

[en] The role in the global confinement in tokamaks of turbulent electrostatic fluctuations in the tokamak edge region is presently well recognized despite the fact that there is still no adequate model describing all the measured dependences. Nevertheless, the poloidal velocity and its shear existing in the vicinity of the last closed flux surface seem to play an important role in the fluctuation driven radial particle fluxes. The paper presents some features of the density fluctuations and their poloidal velocity observed on the CASTOR tokamak in regimes with LHCD and with edge plasma polarization. (author). 10 refs, 5 figs