Application of dynamic calibration and control waveform optimization techniques in the fast sweeping reflectometer upgrade on the HL-2A tokamak

Abstract

High temporal-spatial density profiles, measured by the frequency modulated continuous wave (FMCW) reflectometer, are crucial for the study of particle transport and confinement, especially for the transient events. However, the conventional calibration methods and control waveform of the voltage controlled oscillator (VCO) source constraint the increase of the sweeping frequency (time resolution) and the accuracy of the probed location of the FMCW. In this work, two methods of dynamic calibration of the VCO are proposed to reduce the measurement error due to the high sweep rate, and the results are found to be consistent with each other. In addition, the control waveform of VCOs are re-designed considering the VCO calibration results and dispersions of the waveguide and cables. Therefore, the sweep/dead time has been shortened to be 10 μs/50 ns from 25 μs/5 μs and the accuracy of the detection location has been improved significantly. The density profiles and density fluctuations during the tearing modes are presented which demonstrate the capability of the upgraded reflectometer.