Search

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.

プラズマ計測におけるノイズ低減のため、3波長レーザー干渉計を新たに開発した。本干渉計はヘテロダイン検波のマッハツェンダー型１波長レーザー干渉計を３セットで構成されており、各干渉計のビームを同軸伝送している。原理的に、3波長レーザー干渉計は2波長レーザー干渉計と比較してS/N比を33％程度向上できる。テスト環境における試験では3波長レーザー干渉計は光路変化に対するノイズフロアを大幅に低減し、S/N比については最大で15%改善に成功した。, 第38回 プラズマ・核融合学会 年会

ITERダイバータ赤外サーモグラフィでは高い放射線環境下にミラー及びレンズを配置し光を伝送する。そのため、ITERでの全運転期間を通して顕著な光学特性の劣化がない光学材料の選定及び遮蔽設計が必要不可欠となる。本研究ではITERダイバータ赤外サーモグラフィで使用可能な光学素子の選定及びその遮蔽設計の指標の決定を目的とし、レンズ材料のガンマ線及び中性子照射を実施しその前後の光学特性の計測から中赤外領域における放射線耐性を評価した。今回はその中でもSi、ZnSe、ZnS、CaF2の主要材料に絞り各材料のガンマ線及び中性子照射特性の詳細を報告する。, 第38回プラズマ核融合学会・年会

本研究ではITERダイバータ領域用の紫外-近赤外域分光計測システム開発の一環として、タングステンダイバータ化したITERにおける燃料/壁材由来の中性粒子及びイオンの発光とそれに寄与する素過程について検討を行っている。現在設計中の分光システムで計測され得る各種発光強度分布に加え、これらを用いてイオン化フロント位置や粒子発生量等の物理量を評価するために重要な素過程であるイオン化/再結合の寄与等について、ITERのプラズマシミュレーションデータから計算した結果を報告した。, 第38回 プラズマ・核融合学会 年会

Hot spots on the divertor tiles at JET result in overestimation of the tile surface temperature which causes unnecessary termination of pulses. However, the appearance of hot spots can also indicate the condition of the divertor tile surfaces. To analyse the behaviour of the hot spots in the outer divertor tiles of JET, a simple image processing algorithm is developed. The algorithm isolates areas of bright pixels in the camera image and compares them to previously identified hot spots. The activity of the hot spots is then linked to values of other signals and parameters in the same time intervals. The operation of the detection algorithm was studied in a limited pulse range with high hot spot activity on the divertor tiles 5, 6 and 7. This allowed us to optimise the values of the controlling parameters. Then, the wider applicability of the method has been demonstrated by the analysis of the hot spot behaviour in a whole experimental campaign.

Elsevier社刊Encyclopedia of Nuclear Energyのうち、第12章、磁場閉じ込め核融合技術のうち「プラズマ工学」を執筆したものであり、プラズマ生成、着火、核融合反応の維持に必要な燃料供給、加熱、電流駆動、計測とプラズマ制御のカギとなる技術の概要を紹介する。主にこれまでの開発の経緯、核融合実験炉ITERに用いられた最新技術を紹介し、これらの技術の核融合原型炉における展開を議論した。

量研ITERプロジェクト部では、マイクロフィッションチェンバー(MFC)、ポロイダル偏光計(PoPola)、周辺トムソン散乱計測(ETS)、ダイバータ不純物モニター(DIM)、ダイバータ赤外線サーモグラフィー(IRTh)の５つのITER用計測装置の開発を進めている。ITERの計測装置の中で、高線量の真空容器内、真空境界と生体遮蔽の間のインタースペース(IS)と呼ばれる空間、生体遮蔽の外側のポートセル(PC)と呼ばれる部屋に設置する機器は、信頼性を担保するために、設計段階で放射線照射による動作試験等を実施し、その信頼性を示す必要がある。本研究では、2018年度より実験課題として、上記計測装置のうち放射線下で用いる光学部品等にガンマ線を照射し、その信頼性の評価を行っている。本報告では、これまでに行った実験結果、進捗状況及び今後の予定等に関して報告する。, QST高崎 サイエンスフェスタ 2020

Fiberform nanostructured tungsten (FN-W) samples were synthesized by helium plasma irradiation with different irradiation times. It is shown that the optical reflectivity decreases significantly with the increase of the irradiation time, even in a long-wavelength infrared range up to several dozen µm. These experimental results are of importance for the usage of retroflectors and will offer a promising direction for other practical applications.

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.

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.

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.

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.

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°.

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°.

This study solves the Grad-Shafranov equation with a fixed plasma boundary by utilizing a meshless method for the first time. Previous studies have utilized a finite element method (FEM) to solve an equilibrium inside the fixed separatrix. In order to avoid difficulties of FEM (such as mesh problem, difficulty of coding, expensive calculation cost), this study focuses on the meshless methods, especially RBF-MFS and KANSA's method to solve the fixed boundary problem. The results showed that CPU time of the meshless methods was ten to one hundred times shorter than that of FEM to obtain the same accuracy.

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.

The JT-60SA tokamak, being built under the Broader Approach agreement jointly by Europe and Japan, is due to start operation in 2020 and is expected to give substantial contributions to both ITER and DEMO scenario optimisation. A broad set of preparation activities for an efficient start of the experiments on JT-60SA is being carried out, involving elaboration of the Research Plan, advanced modelling in various domains, feasibility and conception studies of diagnostics and other sub-systems in connection with the priorities of the scientific programme, development and validation of operation tools. The logic and coherence of this approach, as well as the most significant results of the main activities undertaken are presented and summarised. EURATOM 633053

New results from MAST are presented that focus on validating models in order to extrapolate to future devices. Measurements during start-up experiments have shown how the bulk ion temperature rise scales with the square of the reconnecting field. During the current ramp up models are not able to correctly predict the current diffusion. Experiments have been performed looking at edge and core turbulence. At the edge detailed studies have revealed how filament characteristic are responsible for determining the near and far SOL density profiles. In the core the intrinsic rotation and electron scale turbulence have been measured. The role that the fast ion gradient has on redistributing fast ions through fishbone modes has led to a redesign of the neutral beam injector on MAST Upgrade. In H-mode the turbulence at the pedestal top has been shown to be consistent with being due to electron temperature gradient modes. A reconnection process appears to occur during ELMs and the number of filaments released determines the power profile at the divertor. Resonant magnetic perturbations can mitigate ELMs provided the edge peeling response is maximised and the core kink response minimised. The mitigation of intrinsic error fields with toroidal mode number n>1 has been shown to be important for plasma performance., 34 pages, 10 figures. This is an author-created, un-copyedited version of an article submitted for publication in Nuclear Fusion. IoP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it

Helium is widely used as a fuel or minority gas in laboratory fusion experiments, and will be present as ash in DT thermonuclear plasmas. It is therefore essential to have a good understanding of its atomic physics. To this end He II population modelling has been undertaken for the spectroscopic levels arising from shells with principal quantum number n = 1–5. This paper focuses on a collisional excitation model; ionisation and recombination will be considered in a subsequent article. Heavy particle collisional excitation rate coefficients have been generated to supplement the currently-available atomic data for He II, and are presented for proton, deuteron, triton and α-particle projectiles. The widely-used criterion for levels within an n shell being populated in proportion to their statistical weights is reassessed with the most recent atomic data, and found not to apply to the He II levels at tokamak densities (1018–1021 m−3). Consequences of this and other likely sources of errors are quantified, as is the effect of differing electron and ion temperatures. Line intensity ratios, including the so-called 'branching ratios' and the fine-structure β 1, β 2, β 3 and γ ratios, are discussed, the latter with regard to their possible use as diagnostics.

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.

We successfully generated two spherical tokamaks (ST) at two null points by using ex-vessel poloidal field (PF) coils only and succeeded in merging them. This scheme is called a double null merging (DNM) scheme. First, two pairs of ex-vessel PF coils generate two null points where the poloidal field is zero at the upper and lower regions inside the vacuum vessel. Then a poloidal flux swing generates two STs at two null points, because the distance to the wall along the magnetic field is long at the null points. Finally, the coil currents push two STs toward the mid-plane and merge them into a single ST. Since a magnetic reconnection during merging transforms magnetic energy into thermal energy, this merged ST plasma is expected to have a high beta. It must be noted that the DNM scheme generates an ST without a center solenoid coil. The DNM scheme was demonstrated on the TS-3/4 (Japan) and MAST (UKAEA). However, these devices have all PF coils inside the vacuum vessels, and the initial plasmas were generated around the PF coils, not the null points. Since internal coils are not feasible in a fusion reactor due to high neutron flux, it is important to demonstrate the DNM scheme by using ex-vessel PF coils. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 179(4): 18–24, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21254

The UTST (University of Tokyo Spherical Tokamak) device was constructed for the purpose of exploring the formation of ultrahigh-beta ST (spherical tokamak) plasma using the double null plasma merging method. When two plasmas merge together to form a single plasma, magnetic field lines reconnect, and magnetic field energy is converted to plasma kinetic energy, increasing the plasma beta. Merging start-up has been demonstrated in the TS-3/4, START, and MAST devices using coils inside the vacuum vessel, and the TS-3 plasma obtained a 50% beta. In order to demonstrate start-up in a more reactor-relevant situation, UTST has all poloidal field (PF) coils outside the vacuum vessel. The first plasma experiment on the UTST was begun in December 2007. In the results, the plasma obtained 10 kA by using only the outer PF coils and a single ST was generated in the lower area (z = –0.3 to –1.0 m) close to a washer gun. This result suggests that another washer gun on the top of the UTST can allow the generation of ST in the upper area and merging start-up by using outer PF coils. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 179(2): 20–26, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21216

Electron and ion heating characteristics during merging reconnection start-up on the MAST spherical tokamak have been revealed in detail using a 130 channel yttrium aluminum garnet (YAG) and a 300 channel Ruby-Thomson scattering system and a new 32 chord ion Doppler tomography diagnostic. Detailed 2D profile measurements of electron and ion temperature together with electron density have been achieved for the first time and it is found that electron temperature forms a highly localized hot spot at the X point and ion temperature globally increases downstream. For the push merging experiment when the guide field is more than 3 times the reconnecting field, a thick layer of a closed flux surface form by the reconnected field sustains the temperature profile for longer than the electron and ion energy relaxation time ~4-10 ms, both characteristic profiles finally forming a triple peak structure at the X point and downstream. An increase in the toroidal guide field results in a more peaked electron temperature profile at the X point, and also produces higher ion temperatures at this point, but the ion temperature profile in the downstream region is unaffected.

The nuclear heating rates of the optical mirrors of the poloidal polarimeter installed in the equatorial port plug of ITER are calculated. Since the system cannot have a sufficiently labyrinthine structure and the second mirrors are located closer to the plasma than the first mirrors due to limited space, the nuclear heating rate of the second mirrors is as high as that of the first mirrors. However, it is possible to reduce the nuclear heating rates more than 1 order if the blanket shield module provides a sufficient degree of neutron shielding. The effect of the neutron shield on the peripheral region of the upper port plug, in which the optical system of the poloidal polarimeter is installed, is also evaluated. The gamma-ray dose rate 10 6 s after shutdown of operations in the back flange region has been estimated to be ∼60 μSv/h when the neutron shield is filled in the port plug, which is below the design threshold for the ITER maintenance phase. Further, the nuclear heating rate of the Poloidal field coil near the same upper port has been evaluated to be more than 2 orders lower than the allowable value of 1 mW/cc.

This paper addresses a basic equilibrium/confinement question whether a field reversed configuration (FRC) with a balanced amount of magnetic and thermal energies is sustained solely by inductive magnetic flux (magnetic energy) injection of a centre solenoid coil. A new finding is that preferential injection of magnetic energy causes a significant increase in thermal energy of the FRC to maintain high-beta equilibrium. The FRC plasma is concluded to have the robustness needed to self-adjust the plasma heating power depending on the magnetic energy injection. In the flux ramped-up phase, i.e. in the phase where the applied inductive electric field did not penetrate into the core of the plasma, theJ×Bcompression (pinch effect) was considered to be dominant for heating the FRC. On the other hand, after the applied inductive electric field penetrated into the core region the resistivity of the FRC increased up to 10–20 times larger than the classical spitzer resistivity. This anomalous heating was the most probable cause for sustainment of the high-beta FRC in this phase. A quasi-steady state of the high-beta (volume averaged beta ∼0.6–0.7) FRC for 0.15 ms (∼energy confinement time of conventional FRCs) was achieved by the use of the present low power centre solenoid current drive. This successful result leads us to the next stage steady sustainment experiment of an FRC by increased capacitor bank energy.

In the last three years, magnetic reconnection research in the MAST spherical tokamak achieved major progress by the use of new 32 chord ion Doppler tomography and 130 channel YAG and 300 channel Ruby Thomson scattering diagnostics. In addition to the previously achieved high power plasma heating during merging, detailed full temperature profile measurements including the diffusion region have been achieved for the first time. 2D imaging measurements of ion and electron temperature profiles have revealed that magnetic reconnection mostly heats ions globally in the downstream region of outflow jet and electrons locally around the X-point. The toroidal field in MAST “over 0.3T” strongly inhibits cross-field thermal transport, and the characteristic peaked electron temperature profile around the X-point is sustained on a millisecond time scale. In contrast, ions are mostly heated in the downstream region of outflow acceleration and around the stagnation point formed by reconnected flux mostly by viscosity di...

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...

Significant increase in the plasma temperature above 1 keV was measured during the kilogauss magnetic field reconnection of two merging toroidal plasmas under the high-guide field and collision-less conditions. The electron temperature was observed to peak significantly at the X-point inside the current sheet, indicating Joule heating caused by the toroidal electric field along the X-line. This peaked temperature increases significantly with the guide field, in agreement with the electron mean-free path calculation. The slow electron heating in the downstream suggests energy conversion from ions to electrons through ion-electron collisions in the bulk plasma as the second electron heating mechanism in the bulk plasma. The electron density profile clearly reveals the electron density pile-up / fast shock structures in the downstream of reconnection, suggesting energy conversion from ion flow energy to ion thermal energy as well as significant ion heating by reconnection outflow.

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 centre-solenoid-free merging start-up scheme for spherical tokamak plasmas was developed in a University of Tokyo spherical tokamak (UTST) experiment by using outer poloidal field coils. Torus breakdown was initiated at null points and two spherical tokamak plasmas with a total current up to 80 kA were generated inductively. Their merging process provided substantial ion and electron heating by magnetic reconnection. The obtained dependence of heating on plasma current suggests that high-temperature and high-current plasma suitable for neutral beam injection is attainable under the realistic conditions in the merging start-up method.

We developed a new application of the electric double layer capacitor (EDLC) as a sec-order quasi-DC power supply like flying-wheel motor-generators. We constructed the power supply using IGBT switching circuit and successfully demonstrated its initial operation whose current and duration time are 100A and 3sec, respectively, indicating a new potential of EDLC.

This paper proposes a new method to calculate a safety factor, q, profile from gridded data of a poloidal flux, ?, efficiently and accurately. Difficulties of calculating q are derived from a difficulty of specifying a contour line of ? and a singularity at a magnetic axis. In order to solve the first difficulty, the proposed method interpolates knots, which are located on a target ?, by utilizing a normalized arc length and constraints expressed by a magnetic field. Regarding the second difficulty, the proposed method identifies q0 by extrapolating a q profile around a magnetic axis with a constraint of dq/d??=?0 at the magnetic axis. Accuracy assessments of the proposed method are carried out by utilizing the Solov'ev-type equilibrium. The results show the validity and high performance of the proposed method.

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.

This study demonstrates the separation of the finite electron temperature on the plasma polarimetry in the magnetic confined fusion plasma for the first time. Approximate solutions of the transformed Stokes equation, including the relativistic effect, suggest that the orientation angle, θ, and ellipticity angle, ε, of polarization state have different dependency on the electron density, n(e), and the electron temperature, T(e), and that the separation of n(e) and T(e) from θ and ε is possible in principle. We carry out the equilibrium and kinetic reconstruction of tokamak plasma when the central electron density was 10(20) m(-3), and the central electron temperatures were 5, 10, 20, and 30 keV. For both cases when a total plasma current, I(p), is known and when I(p) is unknown, the profiles of plasma current density, j(φ), n(e), and T(e) are successfully reconstructed. The reconstruction of j(φ) without the information of I(p) indicates the new method of I(p) measurement applicable to steady state operation of tokamak.

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.

The temporal evolution of ion temperature and flow was observed to investigate the heating effect of plasma merging in the UTST device by using a multipoint Doppler spectroscopy measurement system. The bulk plasma ion temperature measured by a carbon impurity line was about 15-20 eV after plasma merging. In addition, anomalous broadening of the carbon line width was observed only in the early phase of plasma merging. Since carbon impurity emission comes mainly from the X-point and the vicinity of the center stack, the broad spectrum is considered to consist of a radially bi-directional outflow component from the X-point and a stationary component near the center stack. The outflow velocity estimated from the spectroscopy was about 24 km/s, which agreed well with both an Alfven velocity of 22 km/s and a velocity of the reconnected field line motion of 35 km/s.

The spatial distribution of the radiofrequency (RF) magnetic field associated with a high harmonic fast wave (HHFW) was measured using an array of magnetic probes in the plasma inside the University of Tokyo Spherical Tokamak (UTST). Data obtained from 25 probes (19 locations for toroidal polarization and 6 locations for vertical polarization) distributed along the poloidal cross section were analyzed. The RF magnetic field is polarized in the toroidal direction, indicating that the HHFW is excited in the plasma. The RF field is weak on the inboard side. Analysis of the group delay suggests that the waves travel long distances in the plasma, probably because of poor absorption. No indication of parametric decay was observed up to 80 kW of injected RF power.

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.