A novel, tunable, multimodal microwave system for microwave reflectometry system

Abstract

Based on a new technique, a tunable, multi-channel system that covers the Q–band (33–55 GHz) is presented in this article. It has a potential use of the Doppler backscattering system diagnostic that can measure the turbulence radial correlation and the perpendicular velocity of turbulence by changing the incident angle. The system consists primarily of a double-sideband (DSB) modulation and a multiplier, which creates four probing frequencies. The probing frequency enables the simultaneous analysis of the density fluctuations and flows at four distinct radial regions in tokamak plasma. The amplitude of the probing frequency can be adjusted by the initial phase of the intermediate frequency (IF) input from the double-sideband, and the typical flatness is less than 10 dB. The system was tested in the lab with a rotating grating, and the results show that the system can operate in the frequency range of 33–55 GHz with a Q-band multitude and that the power of each channel can be adjusted by the phase of the IF input of DSB.

Design of a variable frequency comb reflectometer system for the ASDEX Upgrade tokamak

“…The comb will consist of  f nf 6 LO IF , with n=1...3. It should be noted that for this concept, the power of individual comb frequencies is particularly sensitive to relative input power levels, as discussed in detail in reference [13]. Hence, careful system calibration and configuration will be necessary to obtain optimum results across the full W-band of frequencies.…”

“…A somewhat different concept is based on the launch of several probing frequencies simultaneously into the plasma and their simultaneous detection [4][5][6][7][8][9][10][11][12][13][14]. In this way, the information of several radial positions is obtained at the same time.…”

Application of Dual Frequency Comb Method as an Approach to Improve the Performance of Multi-Frequency Simultaneous Radiation Doppler Radar for High Temperature Plasma Diagnostics

“…Since electromagnetic waves in the millimeter-wave range can be used in relation to the electron plasma frequency and the electron cyclotron frequency range, the system is expected to be used as a stable and robust measurement method, and is also expected to be used in future nuclear burning fusion reactors. In fusion plasma research, this Doppler radar is called a Doppler reflectometer or a Doppler back-scattering and has been applied to various experimental devices around the world, such as helical/stellarators (Wendelstein 7-AS [1,2], 7-X [3], TJ-II [4], LHD [5][6][7][8]), tokamaks (Tuman-3M [9], ASDEX Upgrade [10][11][12][13], Tore Supra [14,15], DIII-D [16,17], JT-60U [18], MAST [19], JET [20], HL-2A [21], TCV [22], EAST [23][24][25]), and linear machines (C-2 FRC [26], GAMMA-10 [27]). In particular, in recent years, systems capable of simultaneous multi-frequency observation have been developed with the aim of understanding the instantaneous spatial structure of turbulence [6][7][8]13,17,[21][22][23][24][25].…”

“…In fusion plasma research, this Doppler radar is called a Doppler reflectometer or a Doppler back-scattering and has been applied to various experimental devices around the world, such as helical/stellarators (Wendelstein 7-AS [1,2], 7-X [3], TJ-II [4], LHD [5][6][7][8]), tokamaks (Tuman-3M [9], ASDEX Upgrade [10][11][12][13], Tore Supra [14,15], DIII-D [16,17], JT-60U [18], MAST [19], JET [20], HL-2A [21], TCV [22], EAST [23][24][25]), and linear machines (C-2 FRC [26], GAMMA-10 [27]). In particular, in recent years, systems capable of simultaneous multi-frequency observation have been developed with the aim of understanding the instantaneous spatial structure of turbulence [6][7][8]13,17,[21][22][23][24][25]. When observing turbulence in torus plasmas with this Doppler reflectometer, an ordinary or extraordinary wave is injected into the magnetic confined plasma, and the back-scattered wave from the vicinity of the cut-off position corresponding to the injecting frequency is observed, so the measurement position can be changed by changing the frequency.…”

“…In other words, a simple measurement system using a single source can extract a broad frequency component and achieve high spatial and temporal resolution at the same time. A frequency comb is a signal with periodic peak frequency components and utilizes oscillation from a single source such as a non-linear transmission line (NLTL) or step recovery diode (SRD), as shown in Figure 2, or comb-like frequency component radiation using a multiplier [13,[21][22][23][24][25].…”