Speaker
Ondrej Bogar
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1013.pdf
Density fluctuations measurement from fixed and sweeping microwave
reflectometer during L-H transition on the COMPASS tokamak
O. Bogar1,2 , J. Zajac1 , M. Varavin1
1 Institute of Plasma Physics, The Czech Academy of Sciences, Prague, Czech Republic
2 Faculty of Mathematics, Physics and Informatics, Comenius University, Bratislava, Slovakia
Microwave reflectometry is a versatile diagnostics that allows to perform both density profile
and density fluctuation measurement. Fast sweeping reflectometry uses the O-mode polarization
in frequency range 18-54 GHz. The sweeping time 6 µs followed by 1.5 µs of recovery time
allows the density profile reconstruction from the frequency spectra with high temporal and spa-
tial resolution. Fixed frequency measurement records the time evolution of the phase fluctuation
at the plasma density layer given by probing frequency. IQ detection separates measurements
of phase and amplitude of the reflected signal. IQ signal as well as IF signal is recorded at
200 Msamples/s. New dynamic calibration based on frequency marker and delay line tech-
nigue was performed in order to suppress the frequency non-linearity at high sweeping rates.
We investigate both the density fluctuation spectra and the fast density profile dynamics dur-
ing the L-H transitions with varying discharge parameters. This contribution presents radial
dependence of frequency spectra and radial profile of density fluctuation level from these two
technigues.
