24A03
World-wide Progress on Real Time 2-D ECE Imaging Programs
H.K. PARK1, N.C. LUHMANN JR.2 and A.J.H. DONNÉ3
1 POSTECH, Pohang, Korea
2 University of California at Davis, California, U.S.A
3 FOM Institute for Plasma Physics Rijnhuizen, Nieuwegein, The Netherlands
Abstract
Based on well established fundamentals of the electron cyclotron emission (ECE)process [1] in fusion plasmas, a unique and ambitious real time 2-D ECE Imaging (ECEI)
system on TEXTOR [2] was developed which demonstrated the advantage of hightemporal and spatial resolution 2-D images over the conventional 1-D data in studies ofthe physics of the sawtooth crash. Here, the measured real-time 2-D images of theinternal m/n=1/1 kink mode (sawtooth oscillation) common in tokamak plasmas weredirectly compared with those from various theoretical models from which the validity ofeach model was assessed [3]. The collection of a vast array of data provided the basis forthe random 3-D local reconnection model for the sawtooth crash phenomenon [4]. An
upgraded ECEI imaging system [5] utilizing newly developed microwave devicetechnology including a “mini-lens” based collection system and optimized lens based
optical system was tested. During commission of this new system, the study on sawtoothphenomena was focused on reconfirmation of the previous measurements, theidentification of post crash patterns, and multiple reconnection processes which areclosely tied with those from space plasma.
In the AUG imaging system [6] which is based on the improved detection systemfrom TEXTOR and newly designed optics, measurements have been conducted on a wide
variety of plasma instabilities, which include the edge localized mode (ELM) [7],neoclassical tearing modes (NTM), the sawtooth instability, and Alfvén waves [6]. To
overcome the thermal noise inherent in ECE data, the data have been filtered by both
singular value decomposition (SVD) and Fourier frequency filtering (see [6] for details).
These ECE-Imaging data are the first local 2-D temperature measurements of RSAEs,and represent a valuable extension to previous 1-D temperature measurements [8].
On the DIII-D ECEI system [9], a capability of simultaneous measurement of twoimages is implemented with the zooming capability based on a two lens system as shownin Fig.1. Further studies on the sawtooth instability and Alfvén waves at DIII-D [10] havemade use of improved image clarity to identify features which distinguish ideal MHD
and non-perturbative predictions [10].
Subsequently, an advanced ECEI system was designed and implemented on
KSTAR [11]. The generous access to the plasma and relatively modest constraints
imposed by KSTAR on the optical elements, facilitated a new optical system based on
triplet was designed for more versatility. Major improvements in the optical coupling
schemes of ECEI diagnostics have allowed for the implementation of a wide range ofvertical zoom capability with a maximum magnification of 3:1, and image focusing fromthe plasma edge to regions well to the inboard side of the core. Each of these features is
implemented while meeting an appropriate wavelength dependent compromise between
small viewing beam widths for adequate channel resolution and long confocal lengths for1uniformity over the radial extent of the imaged plasma. The DIII-D system makes use of
a doublet zoom lens configuration while the KSTAR system implements a uniqueadaptation of the Cooke triplet lens [8, 19], which has only a single moving element andyet minimal optical aberration due to a carefully optimized parabolic correction of theplasma facing lens. For two KSTAR experimental campaigns (2010 and 2011), various
studies were made including the detailed process of the ELM growth and burst [12] in theH-mode phase in KSTAR. In the 2011 campaign, the detailed images demonstratingchange of the ELM characteristics in response to the n=1 magnetic perturbation as shownin the right hand side of the Fig.1.
In summary, visualization of the dynamics of instabilities such as the sawtoothoscillation (internal m/n=1/1 kink mode), NTMs, ELMs and wave dynamics isdemonstrated through high resolution (spatial and temporal) ECEI systems. The ECE
imaging system is fast becoming a standard tool for many existing tokamaks and has
already produced extremely valuable physics results from TEXTOR, AUG, DIII-D andKSTAR. A new, wider coverage ECEI system has been developed for on EAST and iscurrently being installed and Tore Supra system is under design for the future.
This work is supported by the NRF, Korea, US DOE contract No. DE-FG02-99ER54531
and EURATOM.

Fig.1. Schematic of the ECEI system (simultaneous measurement of two images athigh and low field sides) and the structure of ELMs at the edge of the KSTAR
plasma is shown.
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