Development of KSTAR ECE imaging system for measurement of temperature fluctuations and edge density fluctuations

Abstract

The ECE imaging ͑ECEI͒ diagnostic tested on the TEXTOR tokamak revealed the sawtooth reconnection physics in unprecedented detail, including the first observation of high-field-side crash and collective heat transport ͓H. K. Park, N. C. Luhmann, Jr., A. J. H. Donné et al., Phys. Rev. Lett. 96, 195003 ͑2006͔͒. An improved ECEI system capable of visualizing both high-and low-field sides simultaneously with considerably better spatial coverage has been developed for the KSTAR tokamak in order to capture the full picture of core MHD dynamics. Direct 2D imaging of other MHD phenomena such as tearing modes, edge localized modes, and even Alfvén eigenmodes is expected to be feasible. Use of ECE images of the optically thin edge region to recover 2D electron density changes during L/H mode transitions is also envisioned, providing powerful information about the underlying physics. The influence of density fluctuations on optically thin ECE is discussed.

Two-dimensional imaging of edge-localized modes in KSTAR plasmas unperturbed and perturbed by n=1 external magnetic fields

“…2,4 Combined with the observed coherent rotation of the entire filaments in the poloidal direction, this supports the validity of the ECE local measurement for all filament regions. On the other hand, the fluctuation dT rad =hT rad i will contain the finite density effect in the case of marginal optical depth, 12,13 i.e.,dT rad =hT rad i ¼ ð1 þ A 2 ÞdT e =hT e i þ A 2 dn e =hn e i, where A 2 ¼ ð1 À rÞse Às =ð1 À e Às Þð1 À re Às Þ and r is the wall reflection coefficient. For example, A 2 % 0:3 using s ¼ 1 and r ¼ 0.6, and the n e fluctuation of $30% will result in the T rad fluctuation of $9%.…”

“…During recent experiments in the KSTAR tokamak, 11 the details of the entire ELM evolution process have been observed in real-time 2D images via a 2D electron cyclotron emission imaging (ECEI) system, 12 revealing nonlinear and nonuniform nature of the ELM growth and burst process with sufficient temporal and spatial resolutions. 13 This paper summarizes the ELM dynamics observed in typical KSTAR H-mode plasmas and reports new observations on altered ELM dynamics under external magnetic perturbations following a brief introduction of the KSTAR ECEI system.…”

Visualization of core and edge MHD instabilities in 2D using ECEI

“…The radiative transfer equation in the slab geometry indicates that the density fluctuation (n e ) effect could be substantial on the ECE intensity (T ECE ) of the ELM filaments, , where A() is a function of the optical depth  [16]. The contributions of n e and T e on T ECE are unknown at present 03002-p. 6 due to the lack of the edge profile diagnostics. A simultaneous 2D measurement of X2 and O1 waves [10] is planned to resolve the effects of n e and T e utilizing the large difference in the optical depths or A() between X2 and O1 (see Fig.9).…”

“…The KSTAR ECEI system [6] is schematically shown in Fig.2a. The operation frequency and radial ranges are illustrated in Fig.2b.…”

Role of Radio Frequency and Microwaves in Magnetic Fusion Plasma Research

“…This combination of an almost-perfect symmetric magnetic field and perturbation tool allows for the systematic testing of stability and confinement physics. The last unique feature of the KSTAR is its state-of-the-art 2D microwave imaging system-which employs microwave imaging reflectometry (MIR) and a 2D/3D electron cyclotron emission imaging (ECEI) system-which can visualize the MHD and turbulence physics at excellent spatial and temporal resolutions [13,14]. These diagnostic systems have demonstrated new physics not available in the past with 1D diagnostic systems.…”