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Instrumentation for a multichord motional Stark effect diagnostic in KSTAR.
Chung, J,Ko, J,De Bock, M F M,Jaspers, R J E American Institute of Physics 2014 Review of scientific instruments Vol.85 No.11
<P>The motional Stark effect (MSE) diagnostic is used to measure the radial magnetic pitch angle profile in neutral beam heated plasmas. This information is used to calculate the safety factor, q, with magnetic equilibrium reconstruction codes such as EFIT. The MSE diagnostic is important during active shaping of the q profile to optimize confinement and stability, and it has become a key diagnostic in high performance tokamaks. A multichord photo-elastic modulator (PEM) based MSE system is being developed for a real-time plasma current profile control in Korea Superconducting Tokamak Advanced Research (KSTAR). The PEM-based approach is a standard method that measures the polarization direction of a single Stark line with narrow tunable bandpass filters. A tangential view of the heating beam provides good spatial resolution of 1-3 cm, which provides an opportunity to install 25 spatial channels spanning the major radius from 1.74 m to 2.84 m. Application of real-time control is a long-term technical goal after commissioning the diagnostic in KSTAR, which is expected in 2015. In this paper, we describe the design of this newly-constructed multichord MSE diagnostic in KSTAR.</P>
Status of PEM-based Polarimetric MSE Development at KSTAR
고진석,정진일,Seung Tae Oh,고원하,Maarten de Bock,Henry Ong,Guido Lange 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.65 No.8
A multi-chord PEM (photo elastic modulator)-based polarimetric motional Stark effect (MSE)system is under development for the KSTAR tokamak. The conceptual design for the front opticswas optimized to preserve not only the polarization state of the input light for the MSE measurementsbut also the signal intensity of the existing charge exchange spectroscopy (CES) system thatwill share the front optics with the MSE. The optics design incorporates how to determine thenumber of channels and the number of fibers for each channel. A dielectric coating will be appliedon the mirror to minimize the relative reflectivity and the phase shift between the two orthogonalpolarization components of the incident light. Lenses with low stress-birefringence constants will beadopted to minimize non-linear and random changes in the polarization through the lenses, whichis a trade-off with the rather high Faraday rotation in the lenses because the latter effect is linearand can be relatively easily calibrated out. Intensive spectrum measurements and their comparisonswith the simulated spectra are done to assist the design of the bandpass filter system that will alsouse tilting stages to remotely control the passband. Following the system installation in 2014, theMSE measurements are expected to be performed during the 2015 KSTAR campaign.
Motional Stark Effect Diagnostics for KSTAR
J. Chung,고진석,J. Howard,C. Michael,G. von Nessi,A. Thorman,M. F. M. De Bock 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.65 No.8
The motional Stark effect (MSE) diagnostic is used to measure the radial magnetic pitch-angleprofile in neutral-beam-heated plasmas. The diagnostic relies upon the measurement of the polarizationdirection of Stark-split D-alpha emission from injected fast neutral atoms in a magnetic field. Measurements of the magnetic pitch angle are used with magnetic equilibrium reconstruction codessuch as EFIT to calculate the safety factor in shaped plasmas. The MSE diagnostic is importantfor determining the shape of the q profile to optimize confinement and stability, and it has becomea key element in high-performance tokamaks. For the purpose of achieving the high-performanceoperating region in the Korea Superconducting Tokamak Advanced Research KSTAR device, twotypes of methods are being studied. In KSTAR, a multichord PEM (photo-elastic modulator)-basedMSE system is being developed, and an imaging MSE polarimetry system using the coherence imagingtechnique has been showing promising initial results during the last two KSTAR experimentalcampaigns in 2012 and 2013, respectively. In this paper, we describe the progress of the KSTARMSE diagnostics.