Five-channel tunable W-band Doppler backscattering system in the experimental advanced superconducting tokamak

Abstract

A 5-channel Doppler backscattering system has been designed and installed in the Experimental Advanced Superconducting Tokamak (EAST). Through an I/Q-type double sideband modulator and a frequency multiplier, an array of finely spaced (Δf = 400 MHz) frequencies that span 1.6 GHz has been created. The center of the array bandwidth is tunable within the range of 75-97.8 GHz, which covers most of the W band (75-110 GHz). The incident angle can be adjusted from −4° to 12°, and the wavenumber range is 4-15 cm−1 with a wavenumber resolution of Δk/k ≤ 0.35. Ray tracing is used to calculate the scattering location and the scattering wavenumber. This article details the hardware design, the ray tracing, and the preliminary experimental results from EAST plasmas.

The simulation of ELMs mitigation by pedestal coherent mode in EAST using BOUT++

“…Figure 1(d) gives a time trace of the D α signal, which can characterize the edge radiation emission and the activity of the instabilities in the pedestal. Figure 1(e) shows the spectrum of the density fluctuations in the pedestal measured by the Doppler backscattering (DBS) [35,36]. There is a CM with frequency about 15-20 kHz.…”

Interplay among turbulence, flow and impurities for sustaining magnetic island

“…Here, for the first time, we report the experimental observations that strong turbulence and flows (measured by the Doppler reflectometry (DR) [16]) can be generated as the impurity concentration inside a large MI (measured by the absolute extreme ultraviolet (XUV) arrays [17]) with an electron temperature dip in the vicinity of the O-point (measured by the electron cyclotron emission (ECE) [18]). The turbulence is probably driven by the non-monotonic electron temperature caused by the localized impurity radiation.…”

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].…”