A microwave reflectometry system operating in the V-band frequency with extraordinary mode polarization has been developed on the EAST tokamak. The reflectometry system, using a voltage-controlled oscillator (VCO) source driven by an arbitrary waveform generator with high temporal resolution, can operate for the density profile measurement. The result of the bench test shows that the output frequency of the VCO has a linear dependence on time. The dispersion of reflectometry system is determined and reported in this paper. The evolution of a pedestal density profile during the L-H transition is observed by the reflectometry in H-mode discharges on EAST tokamak. A frequency synthesizer is used to replace the VCO as microwave source for density fluctuation measurements. The level of density fluctuation in the pedestal shows an abrupt decrease when the plasma enters into H-mode. A coherent mode with a frequency of about 100 kHz is observed and the mode frequency decreases gradually as the pedestal evolves.
Density modulation experiments are successfully conducted on HT-7
ohmic discharge to investigate particle transport coefficients:
diffusion coefficients D and convection velocity V. The particle
transport is studied at low (1.5×1019 m−3)
and high (3×1019 m−3) density regimes. The
clear differences are observed that D is 0.42 m2 /s and
0.17 m2/s, V is 4.7 m/s (outward) and 1.6 m/s (inward) for
low and high density plasmas respectively, where spatially constant D
and V(r) = (r/a)V
0 were assumed for the analysis.
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