An eight-channel Doppler backscattering system in the experimental advanced superconducting tokamak

Abstract

Doppler backscattering system can measure the perpendicular velocity and fluctuation amplitude of the density turbulence with intermediate wavenumber. An eight-channel Doppler backscattering system has been installed in the Experimental Advanced Superconducting Tokamak (EAST), which can probe eight different radial locations simultaneously by launching eight fixed frequencies (55, 57.5, 60, 62.5, 67.5, 70, 72.5, 75 GHz) into plasma. The quasi-optical system consists of circular corrugated waveguide transmission, a fixed parabolic mirror, and a rotatable parabolic mirror which are integrated with quasi-optics front-end of the profile reflectometer inside the vacuum vessel. The incidence angle can be chosen from 5° to 12°, and the wavenumber range is 2-15/cm with the wavenumber resolution Δk/k≤0.21. Ray tracing simulations are used to calculate the scattering locations and the perpendicular wavenumber. The dynamic range of this new eight-channel Doppler backscattering system can be as large as 40 dB in the EAST. In this article, the hardware design, the ray tracing, and the preliminary experimental results in the EAST will be presented.

First Results of the Implementation of the Doppler Backscattering Diagnostic for the Investigation of the Transition to H-Mode in the Spherical Tokamak Globus-M2

“…This method has been used on a variety of tokamaks and has garnered results regarding the rotation velocity and radial electric field of the plasma [ 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 ]. On Globus-M, this diagnostic has also been successfully utilized but only for the study of plasma oscillatory processes, not to investigate the transition to H-mode [ 20 ].…”

Beam model of Doppler backscattering

“…(A. 14) We do not need to keep higher order terms because (c 2 /Ω 2 )K×(K×E) ∼ (c 2 K 2 /Ω 2 )E ∼ N 2 E and • E ∼ N 2 E, where N is the refractive index. For convenience, we use the notation D(q, K) = c 2 Ω 2 (KK − K 2 1) + (q), (A.…”

“…Here, k ⊥ is the wavenumber of turbulent fluctuations perpendicular to the magnetic field, and ρ i is the ion gyroradius. Consequently, it is a widely used diagnostic for both tokamaks and stellarators [8,9,10,11,12,13,14,15,16,17,18]. Moreover, since DBS is a microwave diagnostic, it is one of the few diagnostics that can be used in burning plasma because they are resilient to high neutron fluxes [19,20].…”

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].…”