Articles you may be interested inDesign of an X-mode fast-scanning reflectometry for edge density profile measurement on HT-7 tokamak Rev. Sci. Instrum. 74, 1522 (2003; 10.1063/1.1527253 Ultrashort pulse reflectometry for electron density profile measurements Rev. Sci. Instrum. 70, 1038 (1999); 10.1063/1.1149530Broadband reflectometry for the density profile and fluctuation measurements in the JT60 tokamak (abstract) Rev. Sci.The use of an ordinary mode refiectometer has already proved to be a good means for determining the density profile of a plasma, but the fact that this mode reflects where its frequency equals the local plasma frequency restricts its use to the region of the density gradient. The extraordinary mode refiectometry investigated here permits the observation of the scrape-off layer as well as the near-axis region and in certain conditions also the high magnetic field side of the density profile. It is also shown that this mode requires a range of frequency sweep for measuring a given density profile smaller than the ordinary mode. On the Petula-B tokamak, the density profile has been measured in 200 ps, its evolution when applying the lower hybrid current drive could be also followed. Since the measurement is particularly sensitive near the reflection point of the wave, it could be used to determine precisely the position of magnetic islands and the fluctuation amplitudes. In addition, the access and place occupied in the vacuum chamber being very small, this diagnostic should be compatible with reactor conditions. 539

The effects of the RF current drive on a hybrid RF-OH discharge, in which more than 70% of the plasma current is driven by the RF, have been extensively studied in the Petula-B tokamak. Observations of MHD activity indicate that the presence of RF-driven current cuppresses the growth of the MHD modes and allows stable low-q(a) (as low as 2) discharges with electron density and temperature profiles similar to those of the OH case.

Previously obtained data on the Wega tokamak by lower hybrid heating (f = 500 MHz; PHF = 130 kW) are re-visited in the light of recent theories on ion stochastic heating and quasi-linear electron Landau damping. It is possible, with the help of these theories, to correctly estimate the fast-ion mean energy, the HF power density coupled to the ions and that coupled to the electrons. The values of the parallel index of refraction, N‖, which are necessary to obtain a good quantitative agreement between experiment and theoretical estimates, are the same for ions and electrons, although higher than expected.