Development of frequency modulation reflectometer for Korea Superconducting Tokamak Advanced Research tokamak

Abstract

Frequency modulation reflectometer has been developed to measure the plasma density profile of the Korea Superconducting Tokamak Advanced Research tokamak. Three reflectometers are operating in extraordinary polarization mode in the frequency range of Q band (33.6-54 GHz), V band (48-72 GHz), and W band (72-108 GHz) to measure the density up to 7 × 10(19) m(-3) when the toroidal magnetic field is 2 T on axis. The antenna is installed inside of the vacuum vessel. A new vacuum window is developed by using 50 μm thick mica film and 0.1 mm thick gold gasket. The filter bank of low pass filter, notch filter, and Faraday isolator is used to reject the electron cyclotron heating high power at attenuation of 60 dB. The full frequency band is swept in 20 μs. The mixer output is directly digitized with sampling rate of 100 MSamples/s. The phase is obtained by using wavelet transform. The whole hardware and software system is described in detail and the measured density profile is presented as a result.

Line integrated density measurements on the Versatile Experiment Spherical Torus (VEST) using frequency sweep interferometer

“…In reflectometer, the microwaves reflect at the cutoff density because the microwave frequency range belongs to the plasma frequency range. Q, V, and W band frequency modulated continuous wave reflectometers [27] operating in X-mode polarization have been operated in the KSTAR tokamak since 2013.…”

Overview and recent progress of KSTAR diagnostics

“…The reflectometer system [13] is composed of Q (33-50 GHz), V (50-75 GHz), and W (75-110 GHz) band frequency modulation continuous wave (FMCW) radars. The reflectometer is operating in two different modes.…”

Microwave Reflectometry to Characterize the Time-Varying Plasma Generated in the Shock Tube

“…To verify the effectiveness of time-dependent r reconstruction algorithm to eliminate the effects of multiple solutions, the numerical analysis based on the calculated Γ r (t) from the preset r (t) is conducted. Two functions, as illustrated in (18) and (19), are utilized to describe r (t) = r (t) + j r (t) of time-varying plasma.…”

“…Microwave reflectometry is often employed for the purpose of diagnosis and monitoring [13]. For the application of plasma diagnostics, most microwave reflectometries are related to the radar techniques in the time-domain and dedicated to the fusion plasma with various techniques such as amplitude modulation (AM) reflectometry [14]- [17], frequency modulation (FM) reflectometry [18], [19], and pulsed reflectometry [20]- [22]. However, the plasma generated in the shock tube is about a few hundred microseconds, making it hard to implement the modulation techniques.…”