Ion gyroscale fluctuation measurement with microwave imaging reflectometer on KSTAR

Abstract

Ion gyroscale turbulent fluctuations with the poloidal wavenumber k ∼ 3 cm have been measured in the core region of the neutral beam (NB) injected low confinement (L-mode) plasmas on Korea superconducting tokamak advanced research. The turbulence poloidal wavenumbers are deduced from the frequencies and poloidal rotation velocities in the laboratory frame, measured by the multichannel microwave imaging reflectometer. Linear and nonlinear gyrokinetic simulations also predict the unstable modes with the normalized wavenumber kρ ∼ 0.4, consistent with the measurement. Comparison of the measured frequencies with the intrinsic mode frequencies from the linear simulations indicates that the measured ones are primarily due to the E × B flow velocity in the NB-injected fast rotating plasmas.

Observation of electron driven quasi-coherent modes and their connection with core intrinsic rotation in KSTAR ECH and ohmic L-mode plasmas

“…In this paper, we focus on the properties of QC modes measured by the microwave imaging reflectometer (MIR) system [20][21][22] and the connection between QC modes and intrinsic rotations in ohmically heated and electron cyclotron resonant heating (ECH) plasmas. In order to explain the mechanism of intrinsic rotation, a theoretical model, which is based on TEM-ITG transition, was proposed.…”

Quasi-coherent fluctuation measurement with the upgraded microwave imaging reflectometer in KSTAR

“…Here, R 0 =1.79 m, a=0.46 m, and q(2.02 m)=1. 4. These values were obtained from the profiles in figure 14.…”

“…The spatial and temporal scales of the ion-gyroscale turbulence for the L-mode plasmas heated by NBI were estimated from the time-delayed cross-correlation between signals of the multiple poloidal channels, and compared to the parameters associated with the ion-gyroscale turbulence such as ion temperature gradient mode and trapped electron mode (TEM) [3]. The poloidal wavenumbers of the most unstable modes for the L-mode plasmas were deduced from peak frequencies (determined from cross-coherence spectra) and effective poloidal velocities of fluctuations, and they were compared to those predicted from linear and nonlinear gyrokinetic simulations [4,5]. Recently, characteristics of quasi-coherent modes (QCMs) known as a kind of TEM [6][7][8][9][10][11][12][13][14] were investigated for the ohmically heated or electron cyclotron resonant heating (ECH) assisted L-mode plasmas [15].…”

“…a) shows the radial profiles of U f from the charge exchange recombination spectroscopy (CES), α from EFIT reconstruction, and v θ for a low-field and high-current H-mode discharge heated by 4.4 MW NBI (shot #18674 with the magnetic field = B peak effective poloidal velocity is ∼33 km s −1 and the expected maximum frequency of the mode with = q k cm −1 is ∼1.8 MHz from a simple relationship[4] …”

Development and application of radar reflectometer using micro to infrared waves

“…It is seen that a clear correlation is observed in the poloidal direction in the H-mode plasma. MIR systems have been applied to various magnetically confined plasmas in the world such as DIII-D, LHD, KSTAR, ASDEX-U, and EAST, and produces useful information regarding fluctuations [48][49][50][51].…”