Wave characteristics of electron cyclotron range of frequency in dipole confined plasmas

報告番号: 甲25000 ; 学位授与年月日: 2009-03-23 ; 学位の種別: 課程博士 ; 学位の種類: 博士(科学) ; 学位記番号: 博創域第418号 ; 研究科・専攻: 新領域創成科学研究科先端エネルギー工学専

ダイポール閉じ込めプラズマ中の電子サイクロトロン周波数帯波動の特性

University of Tokyo (東京大学

Gamma-ray irradiation effects on optical coatings and polarizers for edge Thomson scattering system in ITER

This paper reports the gamma-ray irradiation effects on optical coatings and polarizers to be used in the ITERedge Thomson scattering system (ETS). Outside a diagnostic port-plug, in the Interspace, a total dose of the orderof 1 MGy is expected through 20 years of ITER operation. In this study, gamma-ray irradiation experiments wereperformed up to 10 MGy. A high peak power laser beam, i.e. a pulse energy of 5 J and a pulse duration of∼4 ns,is needed for a Thomson scattering measurement in ITER. Laser-induced damage threshold (LIDT) of anti-re-flection (AR) and high-reflection (HR) coatings at the laser wavelengths after gamma-ray irradiation were in-vestigated. LIDT of AR coating for 0° injections was more likely higher for the irradiated samples at a wavelengthof 1064 nm. Regarding HR coatings, LIDT was not noticeably degraded by gamma-ray irradiation. Regardingpolarizers, no degradation of transmission and extinction ratio was observed at visible and near infrared wa-velength ranges when a wire-grid polarizer substrate is made of fused silica. Since a signal of ETS is almostlinearly polarized, a wire-grid polarizer enables to improve signal to noise ratio of electron temperature anddensity measurements by Thomson scattering in ITER

Note: Lossless laser beam combiner employing a high-speed rotating half-wave plate

We have developed a laser beam combiner employing a high-speed rotating half-wave plate based on the specific requirements of the Thomson scattering measurement systems in the ITER. The polarization extinction ratio of the output beam may exceed 1000 and was maintained for more than 1 h via feedback control of the half-wave plate rotation speed. The pointing fluctuations introduced by rotating the half-wave plate were in the order of microradians. The high-speed rotating half-wave plate provides a lossless means of combining laser beams together with stable beam pointing

Verification of in-situ calibration on spectral transmission of Thomson scattering measurement system under radiological environment in ITER

The ITER radiological environment will not allow operators to calibrate the optics near the vacuum vessel. An in-situ calibration of spectral transmission from the collection optics to the detector by analyzing two Thomson scattering spectra resulting from two laser beams having different wavelengths was investigated experimentally in the large helical device (LHD). We can measure electron temperature accurately and calibrate spectral transmission at the same time even when spectral transmission degrades during the experimental campaign

Fast signal modeling for Thomson scattering diagnostics and effects on electron temperature evaluation

As a signal processing method for fast digitizers of the switched-capacitor-type in the Thomson scattering diagnostics, the ”mode fitting” method is proposed. An ideal shape of the signal is estimated in this method by averaging many Thomson scattering signals. After applying this method to a relatively low density LHD plasma, the scattering of electron temperature profiles becomes small. The magnitude of error is also reduced by 1/2 at some positions. Simulations of signals with some noises based on the JT-60SA Thomson scattering system enables showing expected error in electron temperature. The error can be suppressed by the ”model fitting” method