Search

This study developed a new correction method to reduce errors in temperature measurement caused by temperature-dependent emissivity for ITER divertor infrared (IR) thermography. In order to develop the method, we measured the spectral emissivity of tungsten from 200 °C to 1900 °C in the wavelength range of 1.5 μm to 4.5 μm and evaluated temperature measurement error of the two-color method. The results indicate that temperature-dependent emissivity is a major factor in temperature measurement errors, which suggests that accurately measuring temperature by using the conventional two-color method would prove difficult. The new correction method uses two emissivity inputs at different temperature points, in contrast to the conventional method, which uses emissivity measured at a single temperature point. Using this new correction method with a suitable wavelength combination for the two-color method, temperature measurement error was reduced to less than 5% at 1900 °C.

The ITER poloidal polarimeter will install optical components, corner cube retro-reflectors, into the slot of the first wall (FW) panels. The issues of designing the retro-reflector were (i) to achieve good thermal contact between the retro-reflector assembly and the FW and (ii) to accommodate the different thermal expansion of the retro-reflector made of tungsten and the FW made of stainless steel. In order to solve the issues, the CuCrZr filler was employed. A coupled mechanical-thermal analysis was carried out to confirm that the required contact pressure of 60 MPa persists during plasma operation. The highest predicted temperature of the retro-reflector was 673 °C, which is acceptable for tungsten. Electromagnetic analysis was carried out to confirm that the retro-reflector assembly will not move during plasma disruption. A maximum force of 3.06 kN is predicted on the retro-reflector during disruption and is much less than the static friction of 136 kN. In addition, the manufacturability of the retro-reflector assembly was successfully demonstrated. The roughness (Ra) and the flatness (root mean square) achieved for the mirror surface were 0.43 nm and 0.068 μm, respectively. The angle between the assembled mirrors was 90 ± 0.03°, better than the requirement of 90 ± 0.05°.

Magnification of a polarization angle with Littrow layout gratings has been developed. High magnification with a factor of 7.7 using two gratings in Littrow layout was experimentally proved. The magnification range was investigated by calculation at a wavelength of 10.6 μm. The method can be applied for a high magnification factor >30. Larger groove numbers and smaller blaze angles are suitable for the large magnification. Statistical fluctuation of the diffracted polarization angle is compared with that of the incident polarization angle.

This study evaluated an effect of an coupling between the Faraday and Cotton-Mouton effect to a measurement signal of the Dodel-Kunz method which uses counter-circular-polarized probing-laser for measuring the Faraday effect. When the coupling is small (the Faraday effect is dominant and the characteristic eigenmodes are approximately circularly polarized), the measurement signal can be algebraically expressed and it is shown that the finite effect of the coupling is still significant. When the Faraday effect is not dominant, a numerical calculation is necessary. The numerical calculation under an ITER-like condition (Bt = 5.3 T, Ip = 15 MA, a = 2 m, ne = 10(20) m(-3) and λ = 119 μm) showed that difference between the pure Faraday rotation and the measurement signal of the Dodel-Kunz method was an order of one degree, which exceeds allowable error of ITER poloidal polarimeter. In conclusion, similar to other polarimeter techniques, the Dodel-Kunz method is not free from the coupling between the Faraday and Cotton-Mouton effect.

The rotating waveplate Stokes polarimeter was developed for ITER (International Thermonuclear Experimental Reactor) poloidal polarimeter. The generalized model of the rotating waveplate Stokes polarimeter and the algorithm suitable for real-time field-programmable gate array (FPGA) processing were proposed. Since the generalized model takes into account each component associated with the rotation of the waveplate, the Stokes parameters can be accurately measured even in unideal condition such as non-uniformity of the waveplate retardation. Experiments using a He-Ne laser showed that the maximum error and the precision of the Stokes parameter were 3.5% and 1.2%, respectively. The rotation speed of waveplate was 20 000 rpm and time resolution of measuring the Stokes parameter was 3.3 ms. Software emulation showed that the real-time measurement of the Stokes parameter with time resolution of less than 10 ms is possible by using several FPGA boards. Evaluation of measurement capability using a far-infrared laser which ITER poloidal polarimeter will use concluded that measurement error will be reduced by a factor of nine.

The authors have made the basic and applied research on the polarimeter for plasma diagnostics. Recently, the authors have proposed an application of multiparameter measurement (magnetic field, B, electron density, ne, electron temperature, Te, and total plasma current, Ip) utilizing polarimeter to future fusion reactors. In this proceedings, the brief review of the polarimeter, the principle of the multiparameter measurement and the progress of the research on the multiparameter measurement are explained. The measurement method that the authors have proposed is suitable for the reactor for the following reasons; multiparameters can be obtained from a small number of diagnostics, the proposed method does not depend on time-history, and far-infrared light utilized by the polarimeter is less sensitive to degradation of of optical components. Taking into account the measuring error, performance assessment of the proposed method was carried. Assuming that the error of Δθ and Δe were 0.1° and 0.6°, respectivel...

Development of the CO2 interferometer/polarimeter system for line averaged electron density measurement in JT-60SA was progressed significantly. For the measurement, two viewing lines were selected, i.e. a tangential line and a vertical line. Two beam convertors were designed to optimize the beam size for long-distance transmission up to ~ 240 m. A CO2 laser spectral beam axis/profile monitoring system and a beam axis stabilizing system were newly developed. By use of blue light for fluorescence of targets of the monitoring system, instead of conventionally used ultra-violet light, monitoring stability was significantly improved. Practical characteristics of a high power RF discharge laser for JT-60SA such as wavelength stability and beam quality were investigated by the monitoring system. Beam axis deviation was controlled by the stabilizing system within 1% of the beam diameter. By a performance test of the RF discharge laser using a single-color table-top interferometer, a good linearity of phase difference is confirmed in whole of the fringe range by a plasma (~ 6 fringes) in JT-60SA. Obtained resolution of the phase difference (statistical error/5 μ s) is within 10°, which is promising to satisfy the target resolution of 1% for the line averaged electron density measurement.

A new reconstruction technique for Doppler spectroscopy has been developed using spatial and wavelength profiles of line spectrums. Unlike conventional deconvolution techniquies, maximum entropy method was applied to combined reconstruction of these two profiles. Our simulation and experimental results indicate its improved significantly accuracy and robustness against measurements noise.

Using an 8 × 8 channel photomultiplier tube assembly and a single Czerny-Turner monochromator, we have developed a novel Doppler spectroscopic system which can measure the time evolutions of spectral distribution of plasma emission from eight different lines of sight simultaneously. An optical lens system is employed to couple the output of the monochromator with the detector assembly, resulting in small cross-talks less than 5% in spatial distribution together with large magnification of up to 50 in wavelength direction. The suggested system yields cost-effective polychromatic measurements of eight spatial channels with uniform optical and electrical characteristics.

We have proposed a new approach for equilibrium reconstruction that can be applied to ITER-like burning plasmas. In this study, we have focused on carrying out equilibrium reconstruction using polarimetry, which is feasible for ITER-like burning plasmas. Polarimetry in burning plasmas is different from that in the existing tokamaks in two regards: (1) increased importance of the relativistic effects and (2) significant coupling with the Faraday and Cotton–Mouton effects. We found that when polarimetric data (orientation angle, θ, and ellipticity angle, ϵ, of a polarization state) are used as the constraints in the equilibrium reconstruction, the optimum weighting factors for θ and ϵ depend on the magnetic surfaces through which the viewing chord of polarimetry passes. We applied our approach to the operation scenarios II (S2) and IV (S4) in ITER. In the case where the viewing chords are via both the equatorial and upper ports, the measurement requirements for the accuracy of the q-profile in ITER (±10%) were satisfied in S2 and S4 when the measuring errors of θ and ϵ were less than 0.5° and 3°, respectively.

This paper describes results from the first integrated analysis of the feasibility of a retro-reflector (RR) installed in the ITER vacuum vessel. We have carried out thermal and structural analyses of a passively-cooled RR and a terrace retro-reflector array (TERRA) using heat load conditions expected in ITER. In the case of the RR, the maximum temperature is approximately 620°C, and flatness of the deformed mirror surface of the RR is approximately 80 µm. Although maximal displacement of the mirror surface is large, 69% of the incident-laser power returns to the diagnostic room (89.9% returns when the RR is not deformed), phase disturbance is π/4 and the rotation angle of the polarization plane is less than 0.06°. On the other hand, the maximum temperature of TERRA is approximately 350°C, and flatness of the deformed mirror surface is less than 10 µm. The flatness of the mirror surface of a deformed TERRA is much smaller compared to the laser wavelength (118 µm), but the global shape curves in a manner which disrupts the coherent phase of laser light. The curvature radius of TERRA is 21 m, and 49% of the incident-laser power returns to the diagnostic room (88.6% returns when TERRA is flat), phase disturbance is π/5 and the rotation angle of the polarization plane is less than 0.06°. Since the optimized incident angles of a flat and curved TERRA are different, real-time feedback control of the incident angle is necessary for applying TERRA to the ITER poloidal polarimeter.

A tangential viewing phase contrast imaging system is being designed for the JT-60SA tokamak to investigate microturbulence. In order to obtain localized information on the turbulence, a spatial-filtering technique is applied, based on magnetic shearing. The tangential viewing geometry enhances the radial localization. The probing laser beam is injected tangentially and traverses the entire plasma region including both low and high field sides. The spatial resolution for an Internal Transport Barrier discharge is estimated at 30%-70% of the minor radius at k = 5 cm(-1), which is the typical expected wave number of ion scale turbulence such as ion temperature gradient/trapped electron mode. Published by AIP Publishing.