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A new temperature measurement method—the dual two-color method—was developed to accurately measure the temperature over an ultra-wide temperature range (200–3600 °C) for ITER divertor infrared thermography. This novel method introduces a third wavelength filter to the conventional two-color method by replacing the shorter single wavelength bandpass filter with a customized dual-bandpass filter having two transmission bands, without having to add a third infrared camera. The dominant wavelength band of the total radiance through the dual-band filter changes automatically as the temperature increases and, consequently, either the shorter or longer wavelength band of the dual-bandpass filter is used to establish the two-color combination at both low and high temperatures. The dual two-color method increased the acceptable measurement error of the two-color radiance ratio for the temperature measurement requirement of the ITER divertor infrared thermography to 9.45% from that of 4.3% when using the conventional two-color method.

This study developed a new heat flux reconstruction code based on the dual reciprocity boundary element method for the International Thermonuclear Experimental Reactor (ITER) divertor infrared (IR) thermography system. To use divertor heat flux reconstruction in ITER, we modeled the boundary condition between the coolant pipe inner wall and the coolant based on the temperature-dependent heat transfer coefficient and also considered the temperature dependence of tungsten thermal properties. Using this reconstruction code, we evaluated the sensitivity of the input data errors, divertor coolant temperature, and surface temperature errors on the accuracy of heat flux reconstruction by using simplified heat flux profiles, which are spatially uniform on the top surface of the monoblocks. This heat flux reconstruction method demonstrated that highly accurate heat flux reconstruction can be achieved for high heat flux cases in ITER; however, further studies are needed for low heat flux reconstruction.

In the KSTAR Tokamak, a “Tangential Thomson Scattering” (TTS) diagnostic system has been designed and installed to measure electron density and temperature profiles. In the edge system, TTS has 12 optical fiber bundles to measure the edge profiles with 10–15 mm spatial resolution. These 12 optical fibers and their spatial resolution are not enough to measure the pedestal width with a high accuracy but allow observations of L-H transition or H-L transitions at the edge. For these measurements, the prototype ITER edge Thomson Nd:YAG laser system manufactured by JAEA in Japan is installed. In this paper, the KSTAR TTS system is briefly described and some TTS edge profiles are presented and compared against the KSTAR Charge Exchange Spectroscopy and other diagnostics. The future upgrade plan of the system is also discussed in this paper.

This paper provides a novel method for evaluating signal intensities in incoherent Thomson scattering diagnostics. A double-pass Thomson scattering system, where a laser passes through the plasma twice, generates two scattering pulses from the plasma. Evaluations of the signal intensities in the spectrometer are sometimes difficult due to noise and stray light. We apply the singular value decomposition method to Thomson scattering data with strong noise components. Results show that the average accuracy of the measured electron temperature (Te) is superior to that of temperature obtained using a low-pass filter (

A new high speed Nd:YAG Thomson scattering AD Convertor (HYADC) that can directly convert the detected scattered light signal into a digital signal is under development. The HYADC is expected to improve a signal to noise ratio of the Nd:YAG Thomson scattering measurement. The data storage of the HYADC which is required for the direct conversion of whole plasma discharge is drastically reduced by a ring buffer memory and a stop trigger system. Data transfer of the HYADC is performed by the SiTCP. The HYADC is easily expandable to a multi-channel system by the distributed data processing, and is very compact and easy to implement as a built-in system of the polychromators.

A compact and two dimensional detector has been developed for the JT-60U Thomson scattering system, that consists mainly of a proximity focused image intensifier, a 20×12 spatially and spectrally arrayed silicon photodiode, and a data processing unit enabling high repetitive measurement at 1 kHz. To secure a wide spectral bandwidth for an effective detection of the Thomson scattering spectrum, we have introduced a spectrometer and lens systems with enhanced transmission in a longer wavelength, which can compensate for the decreasing characteristic of quantum efficiency of a transmission-mode photocathode used in the image intensifier. The spectral divide of the photodiode array is designed to give its full performance in a wide electron temperature (Te) range of 0.2–15 keV with 12 spectral channels. The application of this newly developed detector to the JT-60U core plasma measurement is also presented.

The design and operation performance of the latest ruby Thomson scattering system for the JT-60U are described, which includes many novel approaches to attain the repetitive measurement of 60 spatial points with high resolution (8 mm), precision, and reliability especially for a high temperature and large size tokamak device. A beam combiner composed of a polarizer and a Faraday rotator for two ruby lasers has provided the transient measurement with the minimum time interval of 2 ms in burst operation and the multitime-slice measurement with the repetition rate of 0.5 Hz in normal operation. A newly developed photodiode array detector with high repetitive ability of 1 ms has been used for the high temperature core plasma measurement. A quantitative alignment of collection fiber object field has been utilized for the reliable ne profile measurement. By using Rayleigh scattering light, an in situ inferring method for a coated viewing window transmission has been found to have an effect on the precise correc...

A YAG laser Thomson scattering system has been developed to measure the time evolution of electron temperature (Te) and density (ne) profiles in the JT-60U. Presently this system provides Te and ne periodically every 100 ms (20 ms at the minimum) at 15 spatial channels. A six spectrum channel polychromator, which is a successive interference filter type, was designed to measure a wide Te range (20 eV–20 keV) by using five channels. The sixth channel is used for calibration by Rayleigh scattering. However, we also used the Rayleigh channel to measure Te and ne since the stray light level was very low. As a result, we were able to measure temperatures below 20 eV. The temperature of the silicon avalanche photodiode (APD) is stabilized by a Peltier element so that the gain is kept constant within ±0.5%. The stable performance of the APD enables accurate Te and ne measurement. During plasma operation, the electron temperature is measured over a wide range from the low temperature plasmas in the runaway plasma...

The design concept and operation performance of a novel alignment system for accurate electron density profile measurement is presented, which has been developed on the basis of the original method for adjusting quantitatively and actively an object field of collection fiber optics to a laser-beam axis. The quantitative expression needed for an appropriate alignment was able to be formulated using the beam width measured in situ by this alignment system and the four laser scattering intensity signals from special alignment fiber bundles. The effectiveness of this alignment system for precise and reliable measurement of electron density has been successfully demonstrated in the JT-60U Thomson scattering diagnostic through direct monitoring and quick restoration of alignment. The important and distinctive feature of this alignment system is to attain compatibility between a stable and accurate maintenance of alignment and an improvement of the signal-to-noise ratio of Thomson scattering to plasma light acco...

A new CO2 laser interferometer has been developed to measure the electron density of tokamak plasmas. Two different wavelength oscillators of 10.6 and 9.27 μm are utilized for simultaneous measurement of the density component and the optical path length change. A new technique using a common frequency shifter for two color lasers improves the stability of the system by a complete matching of both beat frequencies. The system provides advantages for practical problems of large tokmaks related to window darkening and large mechanical vibrations of reflection mirrors and offers improved laser beam monitoring and a simplified optical layout by using closer wavelengths. The electron density of JT‐60U is successfully measured for a plasma current of up to 3 MA. The density behavior during a fast major disruption is also diagnosed without a fringe loss. An effective density resolution is observed to be 2×1019 m−2, which corresponds to about 1/10 of a fringe. A very high resolution (1/104 fringe) phase comparator...

This paper focuses on a method for measuring the electron temperature (T(e)) without knowing the transmissivity using Thomson scattering diagnostic with a double-pass scattering system. Application of this method for measuring the anisotropic T(e), i.e., the T(e) in the directions parallel (T(eparallel)) and perpendicular (T(eperpendicular)) to the magnetic field, is proposed. Simulations based on the designed parameters for a JT-60SA indicate the feasibility of the measurements except in certain T(e) ranges, e.g., T(eparallel) ~ 3.5T(eperpendicular) at 120° of the scattering angle.

A prototype YAG laser system for the edge Thomson scattering system in ITER has been newly developed. Performance of the laser amplifier was improved by using flow tubes made of samarium-doped glass; the small signal gain reached 20 at its maximum. As a result, an output energy of 7.66 J at 100 Hz was successfully achieved, and the performance exceeded the target performance (5 J, 100 Hz).

This paper evaluates the accuracy of electron temperature measurements and relative transmissivities of double-pass Thomson scattering diagnostics. The electron temperature (Te) is obtained from the ratio of signals from a double-pass scattering system, then relative transmissivities are calculated from the measured Te and intensity of the signals. How accurate the values are depends on the electron temperature (Te) and scattering angle (θ), and therefore the accuracy of the values was evaluated experimentally using the Large Helical Device (LHD) and the Tokyo spherical tokamak-2 (TST-2). Analyzing the data from the TST-2 indicates that a high Te and a large scattering angle (θ) yield accurate values. Indeed, the errors for scattering angle θ = 135° are approximately half of those for θ = 115°. The method of determining the Te in a wide Te range spanning over two orders of magnitude (0.01-1.5 keV) was validated using the experimental results of the LHD and TST-2. A simple method to provide relative transmissivities, which include inputs from collection optics, vacuum window, optical fibers, and polychromators, is also presented. The relative errors were less than approximately 10%. Numerical simulations also indicate that the Te measurements are valid under harsh radiation conditions. This method to obtain Te can be considered for the design of Thomson scattering systems where there is high-performance plasma that generates harsh radiation environments.

Thomson scattering (TS) is a proven diagnostic technique that will be implemented in ITER in three independent systems. The Edge TS will measure electron temperature Te and electron density ne profiles at high resolution in the region with r/a>0.8 (with a the minor radius). The Core TS will cover the region r/a

This paper focuses on the design and development of the laser injection system for the ITER Edge Thomson Scattering system (ETS). The ITER ETS achieves a temporal resolution of 100 Hz by firing two 50 Hz laser beams alternatively. The use of dual lasers enables us to perform the Thomson scattering measurements at a temporal resolution of 50 Hz in case that one of the laser systems stops functioning. A new type of beam combiner was developed to obtain a single beam that is collinear and fixed linearly polarized from two laser beams using a motor-driven rotating half-wave plate. The rotating half-wave plate method does not induce misalignment even if the rotating mechanism malfunctions. The combined beam is relayed from the diagnostic hall to the plasma using mirror optics and is absorbed at the beam dump integrated on the inner blanket. The beam alignment system was designed to direct the laser beam onto the center of the beam dump head. The beam position at the beam dump is monitored by four alignment laser beams which propagate parallel to the diagnostic Nd:YAG laser beam and imaging systems installed outside the diagnostic port.

This paper presents an experimental demonstration to determine electron temperature (T(e)) with unknown spectral sensitivity (transmissivity) in a Thomson scattering system. In this method, a double-pass scattering configuration is used and the scattered lights from each pass (with different scattering angles) are measured separately. T(e) can be determined from the ratio of the signal intensities without knowing a real chromatic dependence in the sensitivity. Note that the wavelength range for each spectral channel must be known. This method was applied to the TST-2 Thomson scattering system. As a result, T(e) measured from the ratio (T(e,r)) and T(e) measured from a standard method (T(e,s)) showed a good agreement with∣T(e,r) - T(e,s)∣∕T(e,s)= 7.3%.

Neutron and gamma-ray irradiation complicates the design of the edge Thomson scattering (TS) system in ITER. The TS light is relayed through the relaying optics with labyrinth and fiber coupling optics. Electron density of 2×10(19) m(-3) is sufficient to measure T(e) and n(e) within a 10% and 5% margin of error, respectively, with a spatial resolution of 5 mm. This system can cover from 0.85 to 1 of the normalized minor radius. The time resolution is 10 ms, which is determined by the repetition rate of the laser device. A super-Gaussian is the ideal laser profile for the laser injection optics to avoid a breakdown of the filling gas used in density calibration through Raman scattering.

Polarization interferometers have some potential efficiency advantages for imaging Thomson scattering spectral analysis. In this article we present a number of designs for high-efficiency imaging polarization interferometers for Thomson scattering spectral analysis. The use of high-efficiency crystal polarizing beamsplitters (both displacement and angle) results in low-loss complementary passbands (no edge losses), simple imaging systems, and wide field of view. The efficiency and relative merits of both multiple-filter and dispersive-type configurations are being assessed before installation on the JT-60U ruby-laser Thomson scattering system. Light is transferred from the viewing port via a linear array of optical fiber bundles which will be imaged through the interferometer onto the photocathode of an intensified charge coupled device camera. Because of the broadband nature of the Thomson light, the optical delays required to Fourier analyze the spectrum are quite small. This leads to compact multicolor or dispersive systems based on combinations of Wollaston and Savart splitters and traditional waveplates.

For the satellite tokamak JT-60 Super Advanced (JT-60SA), a divertor Thomson scattering measurement system is planning to be installed. In this study, we improved the design of the collection optics based on the previous one, in which it was found that the solid angle of the collection optics became very small, mainly because of poor accessibility to the measurement region. By improvement, the solid angle was increased by up to approximately five times. To accurately assess the measurement performance, background noise was assessed using the plasma parameters in two typical discharges in JT-60SA calculated from the SONIC code. Moreover, the influence of the reflection of bremsstrahlung radiation by the wall is simulated by using a ray tracing simulation. The errors in the temperature and the density are assessed based on the simulation results for three typical field of views.

This paper presents the design of a collection optics used for the Thomson scattering diagnostic in JT-60SA. Good spatial resolution ( ~ 10mm) is necessary for the optics to measure detailed profiles of electron temperature (Te) and density (ne) in the plasma edge region. Six lenses forming a Petzval-like lens are employed in this design. The use of an anomalous dispersion glass material for two lenses suppresses severe chromatic aberration; two flat mirrors prevent interference with the port plug in which the collection optics is to be installed. The resultant spot radius (resolution) at the image for the peripheral region is approximately 0.2 mm. When another collection optics previously designed for core measurements is used simultaneously, the angle of laser polarization must be considered because the two collection optics are to be installed in different port-plugs accessing the vacuum vessel from the cryostat. Otherwise, the measured signal would be degraded, and the scattered spectra would be different from the expected ones. This paper evaluates the scattered spectra with relativistic effects without any approximations. This paper also provides a means to optimize the polarization angle by considering a simulated profile in JT-60SA and contributes to future devices that have limited space for collection optics.

This paper includes discussions of spatial resolution and accuracy of the edge Thomson scattering system in ITER (ITER ETS). In the present design, the dominant factor for spatial resolution degradation relative to the scattering length is aberrations of the collection optics. A scattering length of approximately 4 mm is acceptable to obtain a spatial resolution of 5 mm. Statistical errors were evaluated according to measurement accuracy. Since the background light during ITER plasma discharge is much stronger than the Thomson scattering, the laser pulse duration is one of the most crucial specifications to obtain accurate measurements. The impact of fast sampling relative to current integration was also investigated. It is expected that the measurement accuracy improves when the waveform of the scattered light is sampled directly particularly for low density measurement.

This paper contains the design of the beam dump for the ITER edge Thomson scattering system and mainly concerns its lifetime under the harsh thermal and electromagnetic loads as well as tight space allocation. The lifetime was estimated from the multi-pulse laser-induced damage threshold. In order to extend its lifetime, the structure of the beam dump was optimized. A number of bent sheets aligned parallel in the beam dump form a shape called a chevron which enables it to avoid the concentration of the incident laser pulse energy. The chevron beam dump is expected to withstand thermal loads due to nuclear heating, radiation from the plasma, and numerous incident laser pulses throughout the entire ITER project with a reasonable margin for the peak factor of the beam profile. Structural analysis was also carried out in case of electromagnetic loads during a disruption. Moreover, detailed issues for more accurate assessments of the beam dump's lifetime are clarified. Variation of the bi-directional reflection distribution function (BRDF) due to erosion by or contamination of neutral particles derived from the plasma is one of the most critical issues that needs to be resolved. In this paper, the BRDF was assumed, and the total amount of stray light and the absorbed laser energy profile on the beam dump were evaluated.

Collection optics for core measurements in a JT-60SA Thomson scattering system were designed. The collection optics will be installed in a limited space and have a wide field of view and wide wavelength range. Two types of the optics are therefore suggested: refraction and reflection types. The reflection system, with a large primary mirror, avoids large chromatic aberrations. Because the size limit of the primary mirror and vignetting due to the secondary mirror affect the total collection throughput, conditions that provide the high throughput are found through an optimization. A refraction system with four lenses forming an Ernostar system is also employed. The use of high-refractive-index glass materials enhances the freedom of the lens curvatures, resulting in suppression of the spherical and coma aberration. Moreover, sufficient throughput can be achieved, even with smaller lenses than that of a previous design given in [H. Tojo, T. Hatae, T. Sakuma, T. Hamano, K. Itami, Y. Aida, S. Suitoh, and D. Fujie, Rev. Sci. Instrum. 81, 10D539 (2010)]. The optical resolutions of the reflection and refraction systems are both sufficient for understanding the spatial structures in plasma. In particular, the spot sizes at the image of the optics are evaluated as ~0.3 mm and ~0.4 mm, respectively. The throughput for the two systems, including the pupil size and transmissivity, are also compared. The results show that good measurement accuracy (10%) even at high electron temperatures (30 keV) can be expected in the refraction system.

A new type polychromator has been designed for the edge Thomson scattering system in ITER. Signal light is parallelly dispersed into two parts at the first interference filter. Spectral transmissivities for some spectral channels may enhance better than the conventional type polychromator. In the new type polychromator, the misalignment due to the machine accuracy is expected to be within the margin of APD area. In order to calibrate the spectral transmissivity using the dual-laser injection method during the plasma discharge, it is preferred that the spectral channels are separated at the geometric mean of the injected two wavelengths.

The large helical device (LHD) Thomson scattering system measures electron temperature (Te) and density (ne) profiles of LHD plasmas, along the LHD major radius (R). The total length of plasma measured is 3 m (R = 2.325?5.386 m), the number of observation points is 144, and the spatial resolution is 12?25 mm. The sampling frequency is 10?100 msec (10?100 Hz). The measurable temperature and density ranges have been estimated to be 5 eV?20 keV and 1018?1022 m?3, respectively. The LHD Thomson scattering system consists of several subsystems, yttrium-aluminum-garnet (YAG) lasers, light collection optics, polychromators, and data acquisition system. In usual plasma experiments, we use three types of YAG lasers: 2 J/10 Hz, 1.6 J/30 Hz, and newly developed 1.2/50 Hz YAG lasers. Thomson scattering signals are analyzed with the FASTBUS-based data acquisition system. Recently, a hardware technique and three data analysis methods have been tested to improve data quality. By using these methods, the data quality has been increased by more than an order of magnitude in high-Te, low-ne plasma experiments. In the paper, we describe the current status of the LHD Thomson scattering system.

In this paper, we present the experimental results of an in-situ calibration method for Thomson scattering diagnostics in the TST-2 spherical tokamak. A double-pass scattering configuration was able to find the ratio of the output signal from the first (back scattering) pass to that from the second (forward scattering) pass; this ratio can be treated as an independent function of electron temperature. The electron temperature obtained by this new method was in good agreement with that obtained by a standard method (single pass). Relative sensitivities among spectral channels can be estimated by the new method without accessing the machines. The relative sensitivities obtained by the new method corresponded to the values obtained by direct calibration within an error of 5%, except for a spectral channel with a wide band-pass range. These results demonstrate the feasibility of applying this new in-situ calibration method to Thomson scattering diagnostics in severe radiation conditions.

This paper presents designs of collection optics for a JT-60SA Thomson scattering system. By using tangential (to the toroidal direction) YAG laser injection, three collection optics without strong chromatic aberration generated by the wide viewing angle and small design volume were found to measure almost all the radial space. For edge plasma measurements, the authors optimized the channel number and wavelength ranges of band-pass filters in a polychromator to reduce the relative error in T(e) by considering all spatial channels and a double-pass laser system with different geometric parameters.

In this study, we investigate designs for polychromators of the ITER edge Thomson scattering system by means of numerical calculations. For this purpose, we discuss the optimum transmission wavelength ranges of the optical filters and the optimum number of filters. Five different filter arrangements, including those with an optical notch filter to eliminate D(alpha) emission, are compared with each other. The measurement accuracy when using a polychromator is evaluated for midplane port configuration. It is found that the optimum filter number keeping in mind the cost performance cost is 5 or 6. Moreover, the use of an optical notch filter increases the measurement accuracy by approximately 5%.

A high performance phase conjugate mirror based on stimulated Brillouin scattering (SBS-PCM) has been applied to the Thomson scattering system in the JT-60U tokamak for the first time in order to improve the measurement performance. A SBS-PCM realized a high reflectivity of 95% at a high input power of 145W (2.9J, 50Hz). Using the SBS-PCM, two methods have been developed to increase the intensity of scattered light. For the first method, we have developed a new optical design to provide a double-pass scattering method with the SBS-PCM. A laser beam passing through the plasma is reflected by the SBS-PCM. The reflected beam passes the plasma again along the same path by means of the phase conjugation of the optically nonlinear stimulated Brillouin scattering process. The double-pass Thomson scattering method using the SBS-PCM has demonstrated an increase of the scattered light by a factor of 1.6 compared with the single-pass scattering method in JT-60U. A multipass Thomson scattering method in which the las...

For solving a window coating problem, an in situ window transmission monitoring by inferring it precisely from a known attenuation of the deposited film has been developed in the JT-60U Thomson scattering system. Also the practicability of an in situ window cleaning based on a laser blow-off technique has been investigated extensively. The coated film composition could be guessed to be a resin such as polyacrylonitrile with a small amount of metals. The existence of chromatic upper limit has been found in the recovered transmission after the blow-off cleaning, which gives systematic errors only of less than 3% to an apparent measurement of both electron density and temperature at 10 keV or less. The attenuation itself is unchanged before and after the laser blow-off cleaning. A complementary use of both methods will provide the Thomson scattering measurement of high Te plasmas with durable reliability and sufficient precision in the existing tokamaks and the International Thermonuclear Experimental Reactor.