Poloidal rotation velocity measurement with an MIR system on KSTAR

Review of Scientific Instruments

Choi

et al. 2014

A second electron cyclotron emission imaging (ECEI) system has been installed on the KSTAR tokamak, toroidally separated by 1/16th of the torus from the first ECEI system. For the first time, the dynamical evolutions of MHD instabilities from the plasma core to the edge have been visualized in quasi-3D for a wide range of the KSTAR operation (B0 = 1.7∼3.5 T). This flexible diagnostic capability has been realized by substantial improvements in large-aperture quasi-optical microwave components including the development of broad-band polarization rotators for imaging of the fundamental ordinary ECE as well as the usual 2nd harmonic extraordinary ECE.

Section: Ecei Systems On the Kstarmentioning

confidence: 99%

Quasi 3D ECE imaging system for study of MHD instabilities in KSTAR

Yun

Review of Scientific Instruments

Choi

et al. 2014

“…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.…”

Section: Introductionmentioning

confidence: 99%

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

Kwon

et al. 2018

Physics of Plasmas

Quasi-coherent (QC) modes, known as a type of the trapped electron mode (TEM) turbulence, have been measured in the outboard core region of low-density electron cyclotron resonant heating (ECH) injected and ohmically heated L-mode plasmas on the Korea Superconducting Tokamak Advanced Research (KSTAR) device. It appears that QC modes of 20-60 kHz occur or strengthen with an increase of the electron temperature to ion temperature ratio, but weaken or are fully suppressed by increased density/collisionality. Toroidal rotation shear, which is strongly related to the density/collisionality, also seems to stabilize the QC modes. Linear gyrokinetic simulations indicate that TEM is the most unstable mode at low densities where the QC modes are observed for both the ECH and ohmic plasmas. At high densities where the QC modes are suppressed, the most unstable mode is the ion temperature gradient (ITG) mode for the ECH plasmas but still TEM for the ohmic plasmas. In the ECH plasmas, it is found that the direction of the core toroidal intrinsic rotation is gradually reversed from the co-current to counter-current direction and the QC mode is suppressed as the line-averaged density increases, which can be explained by the transition of dominant micro-turbulence (TEM to ITG). However, in the ohmically heated plasmas, the acceleration of the core toroidal rotation is not fully explained by the TEM-ITG transition since the direction of the core toroidal rotation is counter-current direction when the QC mode is observed. Furthermore, the core toroidal rotation is accelerated to the counter-current direction even the line-averaged density decreases. Published by AIP Publishing. https://doi.

“…The MIR system is the primary diagnostic tool among the turbulence diagnostic systems in KSTAR. Note that the data used in this paper is from the system [4,5] prior the upgrade [6]. Spatially resolved fluctuation measurements in semi-2D (16 by 2 in the poloidal and radial directions) were obtained using an array of vertically aligned 16 detectors, twofrequency extraordinary mode (X-mode) probe beams, and a large-aperture quasi-optical system.…”

Section: Microwave Imaging Reflectometer On Kstarmentioning

confidence: 99%

“…In a recent study for the L-mode discharges heated by neutral beam injection (NBI) in KSTAR [3], ion-gyroscale fluctuations in the electron density (n e ) were measured and characterized using a microwave imaging reflectometer (MIR) [4,5]. Spatial scale in poloidal direction ( θ /ρ i = 5 -10) and temporal scale (τ c = 2-6 μs) of the measured fluctuations were found to be linearly dependent on the local equilibrium parameters relevant to ion-gyroscale turbulence, where θ is the poloidal correlation length, ρ i = √ m i T i /eB is the ion gyroradius Nuclear Fusion…”

Section: Introductionmentioning

confidence: 99%

Study of ion-gyroscale fluctuations in low-density L-mode plasmas heated by NBI on KSTAR

Leem

et al. 2018

Nucl. Fusion

Broadband density fluctuations with peak frequency ranging from 150 to 400 kHz were measured using a multichannel microwave imaging reflectometer in core region of the low-density L-mode plasmas heated by neutral beam injection on KSTAR. These fluctuations have been studied by comparing the dominant mode scales estimated from the measurement with those predicted from linear gyrokinetic simulation. The measured poloidal wavenumbers are qualitatively comparable to those of the ‘fastest growing modes’ from simulations, whereas they are larger than those of the ‘transport-dominant modes’ by about a factor of three. The agreement on wavenumbers between the measurement and linear simulation (for the fastest growing modes) is probably due to sufficiently weak flow shear compared to the maximum linear growth rate. Meanwhile, the transport-dominant modes seem to be related to the fluctuations in lower frequencies (∼80–150 kHz) observed in some of the measurement.