Electron loss cross sections of Au⁺ and Au²⁺ by electron and proton impact are calculated by using respectively the Lotz formula and the LOSS and CAPTURE computer codes. The corresponding rate coefficients have also been calculated. Using this information, the signal levels of heavy ion beam probe in the Large Helical Device are estimated. The calculated beam currents at the detector position are compared with the detected beam currents in the MeV energy range for a plasma electron density of 1 × 10¹⁹ m^-3 and electron temperature of 1.5 keV. The obtained cross section / rate coefficient data can also be used for reconstruction of electron density and temperature profiles.

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The sizes of sample volumes, which determine the spatial resolution, are estimated by trajectory calculation for the heavy ion beam probe on LHD. The beam width, the divergence, and the beam energy difference are taken into account. From the points of view of the spatial resolution and the signal intensity, parallel beam is suitable for the injection beam. The size of the sample volume by the parallel beam with 10mm diameter is 42 mm. It is sufficient to measure the potential profile in the internal transport barrier in the LHD plasma. Taking into account the spatial profile of the beam, the spatial resolution will be better than 42 mm.

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Intermittent turbulent potential fluctuations in ion-cyclotron wave heated plasmas and effects of their suppression due to strongly sheared plasma rotation with electron-cyclotron heating (ECH) for potential formation are observed in GAMMA 10. Such a shear effect on the central-cell potential data is demonstrated by the use of a heavy ion beam probe (HIBP) for the first time in GAMMA 10. The HIBP system with a gold neutral beam is employed for measuring profiles of radially formed potential as well as the associated radially sheared E_r in the central cell. During the application of ECH, the produced stronger E_r shear results in reduction of the turbulent fluctuations. The results are consistent with reported X-ray tomography data on the effect of E_r shear on turbulence suppression.

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A neutral lithium beam probe (LiBP) for the Compact Helical System (CHS) has been extended to a two-dimensional imaging diagnostic (2-D-LiBP). Two-dimensional image of the plasma structure in the edge and separatrix region of the l = 2 helical device is obtained by changing the beam injection angle mechanically, shot-to-shot. The 2-D image has shown the asymmetric plasma structure in the edge separatrix region, suggesting that 2-D diagnostic is essential in the chaotic magnetic field region where magnetic surfaces are not defined by a flux function.

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Two dimensional lithium beam imaging technique has been applied in the spherical tokamak, CPD (Compact Plasma wall interaction experimental Device), to study the effects of various magnetic field configurations on RF plasma confinement topology. The performance of the lithium sheet beam is absolutely calibrated by a quartz crystal monitor. Experimental results show that plasma initiation takes place at the electron cyclotron resonance layer in a simple torus configuration and then it expands quickly to the low magnetic field side. Different magnetic field configurations critically affect the RF plasma confinement topology. A sharp lower boundary exists for the RF plasma in magnetic null configuration. Magnetic connection length plays the key role in defining plasma boundary and the critical value of connection length for plasma to exist in CPD is found to be ∼ 5-6 meter for a given pressure condition.

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A lithium ion gun is under construction for a lithium beam Zeeman polarimetry on JT-60U. The performance of the prototype ion gun has been estimated by the numerical simulation taking the space charge effects into account. The target values of the ion gun are the beam energy of 30 keV, the beam current of 10 mA and the beam divergence angle within 0.13 degrees. The low divergence of 0.13 degrees is required for the geometry of the Zeeman polarimetry on JT-60U where the observation area is 6.5 m away from the neutralizer. The numerical simulation needs to be carried out for the design study because the requirement of the divergence angle is severe for the development of the high-brightness ion gun. The simulation results show the beam loss of 50 % caused by the clash to the electrode such as the cathode and the neutralizer. Moreover, the beam transport efficiency from the neutralizer to the observation area is low due to the broadening of the divergence angle. The total beam efficiency is about 5 %. Extracted beam profile affects the beam focusing and the efficiency. The peaked profile achieves better efficiency than the hollow one. As a result, beam current of 1 mA is obtained at the observation area by the simulation for the prototype ion gun.

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A test stand of a fast neutral helium beam device has been developed for proof of principle experiments to produce a candidate beam of alpha particle diagnostics method for ITER. A fast He⁰ beam will be produced and its qualities will be diagnosed on the test stand. In addition, it is also important to produce an intense and stable He^- beam from a negative ion source in the test stand because a fast He⁰ beam have to be produced from an accelerated He^- beam. In this article, the method of the fast He⁰ beam production, and the experimental results on the einzel lens effect for He⁺ beam transport in the negative ion source are shown. Several experiments on the test stand, which are necessary to clarify the availability of the alpha particle diagnostics method, are described.

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We have carried out absolute calibrations of the LHD YAG Thomson scattering system by using Raman scattering and Rayleigh scattering in order to verify the applicability of Rayleigh calibration in the LHD Thomson scattering, and make a comparative study of Raman and Rayleigh calibrations. In the LHD Thomson scattering device, Rayleigh calibration is expected to give more reliable calibration factors. For the Rayleigh calibration, additional Rayleigh channel was installed into 20 polychromators. The other 124 polychromators without Rayleigh channel were calibrated by only Raman scattering. In the Raman calibration, pure gaseous nitrogen was introduced into the LHD vacuum vessel whereas the Rayleigh calibration was made by using air as target gas. The calibration factors obtained from the Raman and Rayleigh calibrations show good agreements. Uncertainties in the calibration factors obtained from the Raman and Rayleigh calibrations are discussed.

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Recently we modified the Thomson scattering diagnostic (TS) installed on LHD so that DC levels (V_DC) of all avalanche photodiodes (APD) used for detecting scattered light can be registered every 1 ms, which enabling us to make validity check on TS data taken under very intense plasma radiation. In the line of this task, we first examined how the pulse-performance of an APD degrades as the intensity of continuous light (J_DC) incident to the APD increases. We found two effects are involved in deteriorating the pulse-performance of the APD: (1) the responsivity of the APD to a pulsed light drops as J_DC increases, causing a systematic errors on the deduced electron temperature (T_e) and density (_ne); (2) the frequency response of the APD and the following circuit drops as J_DC increases, which deforms the pulse shape. The bias voltage applied to the APD (V_b) has large influence on these behaviors, showing the best overall performance for a high J_DC around V_b ∼ 0.5V_r, where V_r is the recommended voltage giving responsivity of 675 kV/W at 1060 nm. Considering these effects together, we set a conservative validity criterion for the pulse APD performance in term of the V_DC: V_DC < 0.5 V. The V_b = 0.5 V_r setup gives much reliable T_e-profiles without a collapse in T_e-profile for a much wider range of plasma radiation intensity. With this criterion, we check the validity of T_e- and n_e-profiles of two example data.

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A new two-dimensional Thomson scattering measurement (2-D TS) system has been developed using multiple reflections and time-of-flight (TOF) of laser light. Its new ideas of our 2-D TS system are (1) to reflect YAG laser light for multiple times to cover the whole r - z plane of the ST (Spherical Tokamak) plasma, and (2) to reduce the number of polychromators and detectors using the time delay of the scattered light along the laser beam. We measured for the first time, Rayleigh scattering light signals with 50 ns time difference from two measurement points using a single detector, demonstrating the basic principle of the 2-D Thomson scattering system.

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For measurement of electron density fluctuations (up to 1 MHz), an HCN laser scattering measurement system with a super rotating grating was developed on CHS. When we measured electron density fluctuations with kr = 5.4 cm^-1 in a plasma edge region at the outer side of torus, fluctuation spectra which have harmonic components up to the fifth were observed. The fundamental frequency was less than about 60 kHz, which changed during the discharge. The change in frequency correlated best with the plasma stored energy divided by the line averaged density. An edge transport barrier (ETB), which can improve particle transport in the edge region, has been observed in CHS and the measured fluctuation amplitude also decreases. The fluctuations decreased in about 5 ms, and the decrease of the fluctuations preceded by 3 ms to the drop of Hα emission signal.

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Electron temperature and density measurements of low temperature Helium plasmas are performed in the divertor/edge plasma simulator MAP-II, by means of Laser Thomson Scattering (using a ND:YAG Laser, a double monochromator and an ICCD detector) and optical emission spectroscopy (using a spectrometer and a CCD detector). The recent upgrades of our LTS system (reduction of the level of stray light and reduction of the band width of the notch filter) allowed the measurement of temperatures as low as 0.1 eV and the investigation of Electron Ion Recombination (EIR) processes in He plasma. Spatial profiles of electron temperature and density along the plasma column have been taken moving the plasma recombination front across the measurement point by controlling the gas pressure from 80 to about 145 mTorr. A comparison between LTS results and spectroscopic analysis based on a He I CR model including radiation trapping is shown in order to confirm the consistency of the diagnostics. CR model results, obtained fitting the excited state populations with principal quantum number n = 3,4, are consistent with those from LTS. The discrepancies are found to be attributable to the mixing of the ionization and recombination regimes over the line of sight of the optics.

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A collective Thomson scattering (CTS) diagnostic using carbon dioxide (CO₂) laser is being developed to establish a diagnostic method of confined α-particles in burning plasmas. To realize the CTS diagnostic, a transversely excited atmospheric CO₂ laser has been developed. To obtain single-mode output, which is needed for the CTS diagnostic, seed laser is injected to the cavity with an unstable resonator. Using this technique, output energy of 17 J at a repetition rate of 15 Hz has been achieved. This result gives a prospect for the CTS diagnostic on International Thermonuclear Experimental Reactor (ITER). Proof-of-principle test of the CTS diagnostic is being performed with the new laser system on JT-60U. A method to improve spatial and spectral resolutions, which is subject to be resolved for the CO₂ laser CTS, is proposed using a resonance at the lower hybrid frequency. Calculation results show that the scattering power increases more than a factor of 10, and spatial and spectral resolution improve about 30% if the scattered wave vector is nearly perpendicular to the magnetic field.

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In order to optimize the viewing chord arrangement of the poloidal polarimeter in International Thermonuclear Experimental Reactor (ITER), we studied the sensitivity between the toroidal current profile and the viewing chord position. The current profile is scanned around the ITER operation scenario which is estimated as one of burning plasma operations. The sensitive viewing chords to distinguish changes of the central toroidal current density, the finite beta effect and the magnetic shear, are shown. The physical mechanisms of those sensitivities are also shown.

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A short wavelength laser whose wavelength is about 50 μm is preferable for a polarimeter and an interferometer in large fusion devises. This paper reports the development of a polarimeter with a photoelastic modulator (PEM) for a CH₃OD laser (wavelengths of 57.2 and 47.6 μm). The PEM with a high-resistive silicon as a photoelastic element has been newly developed. The transmissivity of the high-resistive silicon is high in a far infrared region. The polarimeter with the Si PEM has been tested and the polarization angle is successfully measured. Noise sources (a multi-reflection of the laser beam in the photoelastic element, a measurement error of amplitude of a detector output and an estimation error of the retardation) of the measured angle are also discussed.

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Powerful 48- and 57-μm CH₃OD lasers pumped by a 9R(8) CO₂ laser have been developed to establish a new two-color FIR laser interferometer system for high density and large volume plasma diagnostics. To design the collimated beams for the interferometer, the beam profiles and the divergence angles have been measured for the 48- and 57-μm CH₃OD lasers oscillated simultaneously. Water vapor absorptions for the laser wavelengths have been measured at 22 °C C to realize an efficient transmission line. Optical constants and transmittance and reflectance of crystal quartz, silicon, CVD-diamond, polyethylene sheet, Mylar film, TPX plate, metal mesh and wire grid have been measured to design the optical components (observation windows and beam splitters) in the 48- and 57-μm laser interferometer system.

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Spatially resolved spectra have been measured with visible spectroscopy in Large Helical Device (LHD). Strong line emissions of H I, He I and C III have been observed at a limited area near the inboard-side X-point. Such a poloidally inhomogeneous radiation structure is drastically changed when the radius of the magnetic axis is shifted from R_ax = 3.6 m to 3.9 m: another strong emission emerges near the outboard-side X-point. In order to understand the physical mechanism the electron temperature and density are evaluated from intensity ratios of neutral hydrogen and helium lines at poloidal locations near both the X-points and at the bottom O-point edge. It is found that the changes of the electron temperature and density along the poloidal direction are too moderate to explain the inhomogeneity of line emissions for both the configurations. The present result suggests that the poloidal inhomogeneity of neutral emissions arises owing to the inhomogeneous neutral density distribution rather than the difference of the electron density or temperature.

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We obtained the local foil properties of the JT-60U imaging bolometer foil (a single graphite-coated gold foil with an effective area of 9 × 7 cm² and a nominal thickness of 2.5 μm) such as the thermal diffusivity, κ, and the product of the thermal conductivity, k, and the thickness, t_f , by calibrating some parts of the foil. Calibration of the foil was made in situ using a He-Ne laser (∼27 mW) as a known radiation source to heat the foil. The thermal images of the foil are provided by an infrared (IR) camera (microbolometer type). The parameters are determined by finite element modeling (FEM) of the foil temperature and comparing the solution to the experimental results. In this work we apply this calibration technique to investigate the spatial variation of the foil parameters. Significant variation in the local temperature rise of the foil due to local heating by the laser beam indicates a spatial variation of the foil parameters κ, k and t_f. This variation is possibly due to nonuniformity in carbon coating and/or the thickness of the foil.

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Plasma diagnostic data analysis often requires the original raw data as they are, in other words, at the same frame rate and resolution of the CCD camera sensor. As a non-interlace VGA camera typically generates over 70 MB/s video stream, usual frame grabber cards apply the lossy compression encoder, such as mpeg-1/-2 or mpeg-4, to drastically lessen the bit rate. In this study, a new approach, which makes it possible to acquire and store such the wideband video stream without any quality reduction, has been successfully achieved. Simultaneously, the real-time video streaming is even possible at the original frame rate. For minimising the exclusive access time in every data storing, it has adopted the directory structure to hold every frame files separately, instead of one long consecutive file. The popular ‘zip’ archive method improves the portability of data files, however, the JPEG-LS image compression is applied inside by replacing its intrinsic deflate/inflate algorithm that has less performances for image data.

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Computer simulation of burning plasmas as well as computational plasma modeling in image processing requires a number of accurate data, in addition to a relevant model framework. To this aim, it is very important to recognize, obtain and evaluate data relevant for such a simulation from the literature. This work focuses on the simultaneous search of relevant data across various online databases, extraction of cataloguing and numerical information, and automatic recognition of specific terminology in the text retrieved. The concept is illustrated on the particular terminology of Atomic and Molecular data relevant to edge plasma simulation. The IAEA search engine GENIE and the NIFS search engine Joint Search 2 are compared and discussed. Accurate modeling of the imaged object is considered to be the ultimate challenge in improving the resolution limits of plasma imaging.

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In the reversed Field Pinch Experiment RFX-mod a Gas Puffing Imaging Diagnostic (GPID) is used to investigate the turbulence of the edge plasma. The system consists of a gas puffing nozzle and 32 optical channels to measure the HeI (668 nm) line emission. The lines of sight are arranged into three fans intersecting each other in an area normal to the main magnetic field. The diagnostic system provides an analogue bandwidth of 2 MHz and all channels are simultaneously sampled at 10 MSamples/s for the whole discharge duration (350 ms). Different inversion techniques have been applied to the data in order to obtain a 2D tomographic reconstruction of the light emission pattern from the line integrals. Comparison shows that the most suitable method is based on 2D spatial Fourier expansion, applying the Singular Value Decomposition technique with regularisation. The high sampling time allows to obtain a 2D image every 100 ns. It is found that emission structures (“blobs”) emerge from the background turbulence; a characterisation is given by computing the energy of the Fourier modes.

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Fast camera systems for imaging tokamak plasmas are becoming increasingly popular. Edge fluctuations and plasma instabilities can be imaged in the visible and X-ray wavelengths using presently available cameras. While viewing the plasma tangentially, the lines of sight (LOS) pass through the plasma integrating the light through a number of flux surfaces. Here we report a reconstruction code for tomographic unfolding of the emissivity profile of the poloidal cross section from the tangential image, using pixel method. The poloidal cross section of the tokamak has been divided into pixels, each of which is a footprint of a subtorus. The emissivity of each of this subtorus (pixels) is assumed to be constant and uniform around the torus.

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Tomography techniques using the two measurement arrays were investigated. To evaluate test reconstruction methods with three combinations of calculation grid and observation view lines, a model distribution was reconstructed. The two-dimensional distribution generated on a calculation grid arranged parallel to the actual apparatus view lines was in better agreement with the model distribution than the distribution generated on a square grid. This parallel grid was applied to the reconstruction of the deuterium Balmer-series lines in the JT-60U detached divertor plasmas.

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Rotational instability with toroidal mode number n = 2 has been known as a destructive instability which limits the configuration lifetime in a field-reversed configuration plasma. In recent experiments using tomographic technique, the spatial distribution of plasma radiation (bremsstrahlung) was measured with a newly developed multi-purpose optical diagnostic system. Global deformation of the cross-sectional structure of a FRC and its time evolution were investigated by a computed tomography (CT) reconstruction technique (ART method) [T. Asai et al., Physics of Plasmas 13, 072508]. These results indicate that the FRC plasma has an internal deformation, which has different phase from the deformation of separatrix surface. These two different toroidal deformations are difficult to be observed by spatially integrated methods, for example, magnetic probes, end-on camera and so on. In this work, detailed features of this internal behavior have been investigated by a newly improved tomographic reconstruction method.

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Penumbral imaging is a powerful imaging technique for radiations with long mean-free path. Since the reconstruction is based on deconvolution, the technique is sensitive to noise contained in penumbral images. Uniformly redundant penumbral array (URPA) technique can improve the SN ratio of penumbral images. In URPA, the penumbral apertures are arranged in m-sequence. In the reconstruction process from the coded data, penumbral image is obtained by correlation to decoding operator. The reconstructed image can be obtained by use of the Wiener filter. In this article, the three-dimensional reconstruction of the URPA and its tomographic resolution are stated.

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An improved tomographic algorithm in the scheme of Tikhonov-Phillips regularisation method, has been employed for multi-pixel bolometric measurements in order to get as much information as possible while keeping the assumptions to a minimum. The effects of finite detector size have been taken into account with a full three dimensional treatment of the detector geometry. The application of tomographic imaging was implemented to a two-array AXUVD (Absolute eXtreme UltraViolet photodiode) camera on the Large Helical Device (LHD) and a two-dimensional infrared imaging bolometric (IRVB) pinhole camera on JT-60U. Pertinent examples of the results are presented both to illustrate the analysis techniques and to demonstrate the wealth of physics which can be studied.

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An imaging spectrometry of plasmas using a tunable Lyot filter for the visible range (400-720 nm) is proposed. The typical passband and transmittance of the filter in the present study are 7 nm FWHM and 12 % at 550 nm. An optical system has been developed for a MAP-II divertor/edge plasma simulator. The line contamination was defined as the contributions of the adjacent lines in the passband of the filter and of the lines in the leak-band which were observed at longer than 548 nm at a specific wavelength setting below 455 nm. We found that it is desirable to use a low-pass or band-pass filter to cut leak-bands, and that the He I lines of 447, 471, 492, 501 and 587 nm can be used for pure He plasma. Based on the CR model, the parameter range where these line ratios were applicable in our discharge condition of 12 mTorr was evaluated for the electron temperature of T_e < 20 eV and the electron density of 10¹¹ < n_e < 10¹⁴ cm^-3.

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In the central-cell of the GAMMA 10 tandem mirror, a medium-speed camera (CCD camera, 400 frames per second, 216× 640 pixel) has been installed for the observation of plasma behavior. This camera system is designed for monitoring the plasma position and movement in the whole discharge duration. The captured two-dimensional (2-D) images are automatically displayed just after the plasma shot and stored sequentially shot by shot. This system has been established as a helpful tool for optimizing the plasma production and heating systems by measuring the plasma behavior in several experimental conditions. The camera system shows that the intensity of the visible light emission on the central-cell limiter accompanied by central electron cyclotron heating (C-ECH) correlate with the wall conditioning and immersion length of a movable limiter (iris limiter) in the central cell.

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A new type of fluorescent screen with a gridded energy analyzer is proposed. This new method clearly has an advantage of clarifying both space distribution of number density and particle energy simultaneously. The fluorescent screen has three potential grids in front of it. Using the set of grids, the particle energy is analyzed. The preliminary data show that the potential grids have successfully analyzed the energy of the injected electrons. The fluorescent screen seems to emit visible light even after the number of electrons is somewhat reduced by the potential grids.

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We investigated whether the activity in MT/V5 is influenced by a face contour and/or features such as the mouth using magnetoencephalography (MEG). We compared two conditions as visual motion stimuli using apparent motion as follows; (1) CDL: A schematic face consisting of a face Contour, two Dots & a horizontal Line and (2) D: Two Dots only. Subjects described a simple movement of dots for D, but eye movement for CDL, though movement modalities were the same through both conditions. We used a single equivalent current dipole (ECD) model between 145-220 ms after stimulus onset and estimated the location, dipole moment (strength) and peak latency. There were no significant differences in the peak latency of the estimated dipoles between each condition, but the activity was significantly stronger for CDL than for D (p < 0.01) in the right and left hemispheres. These results indicated that there is specific information processing for eye movements in the occipitotemporal area, the human MT/V5 homologue, and this activity was significantly influenced by whether movements appeared with the face contour and/or features, in other words, whether the eyes moved or not, even if the movement itself was the same.

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This report shows the progress achieved in simulations of thermal and non-thermal effects which may appear for high power ECRH in the W7-X stellarator (under construction in Greifswald, Germany). Simulations are carried out with the new ray tracing code TRAVIS which was developed for electron cyclotron studies in arbitrary 3D magnetic configurations, with emphasis on heating, current drive and ECE diagnostic.

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Several codes have been developed to analyze plasma physics. However, most of them are developed to run on supercomputers. Therefore, users who typically use personal computers (PCs) find it difficult to use these codes. In order to facilitate the widespread use of these codes, a user-friendly interface is required. The authors propose Web interfaces for these codes. To demonstrate the usefulness of this approach, the authors developed Web interfaces for two analysis codes. One of them is for FIT developed by Murakami. This code is used to analyze the NBI heat deposition, etc. Because it requires electron density profiles, electron temperatures, and ion temperatures as polynomial expressions, those unfamiliar with the experiments find it difficult to use this code, especially visitors from other institutes. The second one is for visualizing the lines of force in the LHD (large helical device) developed by Watanabe. This code is used to analyze the interference caused by the lines of force resulting from the various structures installed in the vacuum vessel of the LHD. This code runs on PCs; however, it requires that the necessary parameters be edited manually. Using these Web interfaces, users can execute these codes interactively.

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The preliminary results of impurity transport studies in the Large Helical Device (LHD) by means of a newly developed the Stellarator Impurity Transport code SIT STRAHL [1] are reported. The attenuation of the emission lines from the ionized Ti ions, launched in the plasma edge by means of the TESPEL injector has been numerically simulated and compared with experiment. In the case of low plasma density discharges with positive radial electric field the outward directed neoclassical drift determines a low confinement time of the Ti impurity ions. The SX-ray emission signal can be reproduced fairly well, indicating the neoclassical nature of Ti ions behavior. In the case of high density regimes with a negative value of the electric field the increase of the confinement time seems not to be able to be explained only by neoclassical transport. The importance of radial electric field on impurity behavior is analyzed and impurity accumulation within the externally induced island is simulated.

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The new Stellarator Impurity Transport (SIT) code is an extended version of STRAHL code [1], which can be used for non-axisymmertic magnetic configurations to evaluate impurity behavior in the frame of the stellarator-specific neoclassical transport, which is strongly dependent on magnetic topology and the radial electric field. The code solves the system of 1D continuity equations (averaged over the magnetic flux surfaces) for impurity ions of each charge state, coupled due to the ionization and recombination. It calculates the time and space evolution of density and emission of impurity ions coming from the wall or deposited within the plasma during the pellet ablation. An analytical description of the neoclassical transport coefficient for the background plasmas was generalized to impurity ions of arbitrary mass and charge state and used in the code as a neoclassical transport model for impurities. Calculations of the electric field and transport coefficients are included within the time dependent iterative loop. Various models of anomalous drift velocities and diffusion coefficients were incorporated. The code can be used as an interpretative and predictive tool for simulation of impurity behavior in arbitrary non-axisymmetric configurations.

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