Real-time measurement system of the ion temperature profile has been developed for the feedback (FB) control of the ion temperature gradient (grad-T_i) with the filter charge exchange recombination spectroscopy (CXRS) system in JT-60U. The rapid analytical scheme without non-linear least square fitting enables us to calculate the ion temperature with four spatial points every 10 ms using a real-time processor system. The FB control experiment of grad-T_i has been demonstrated in ELMy H-mode plasmas by use of the neutral beam injectors having different deposition profiles as actuators. Grad-T_i was controlled to the reference value in the ramp-down phase, however, it did not recovered in the ramp-up phase because the internal transport barrier or transport was affected by the ramp-down of grad-T_i, From the transient response analysis of grad-T_i, the increase in the central T_i using the additional heating was required to recover the deteriorated grad-T_i.

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The high flux source for the Pulsed High Density Experiment (PHDX) has been constructed, and field-reversed configuration (FRC) plasmas are being produced. To diagnose FRC plasma temperatures three kinds of diagnostic systems have been set up on PHDX; λ = 632.8 nm He-Ne laser interferometer system at the midplane for total temperature T_total, 16 channel spectrometer for ion temperature T_i and soft x-ray (SXR) measurement system for electron temperature T_e viewed along z-axis, respectively. The SXR measurement system consists of five sets of collimators and AXUV100 photodiodes with directly deposited filters which have different bandpass regions. As a result of preliminary temperature diagnostics, the following plasma parameters are estimated during a relatively quiescent phase of FRCs; T_total ∼ 50 eV, T_i ∼ 50 eV and T_e ∼ 25 eV. This result does not agree with the equilibrium relation of T_total ≈ T_i + T_e, and it must be caused by plasma condition and our assumptions in the spectral analysis.

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A spectroscopy system was installed on the diagnostic neutral beam injector in LHD. The H_α lines spectrum emitted by full, half and one-third energy component are clearly observed, and the proton ratio and the beam divergence were estimated by the line intensity and the line width, respectively. The proton ratio of 85∼90 % is achieved in high arc power discharge. The beam divergence of them shows their minimum with the same perveance. It was experimentally confirmed that the spectroscopy system is useful for the monitor of the proton ratio and the divergence of the beam.

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The object of the present paper is an infrared video bolometer with a bolometer foil consisting of two layers: the first layer is constructed of radiation absorbing blocks and the second layer is a thermal isolating base. The absorbing blocks made of a material with a high photon attenuation coefficient (gold) were spatially separated from each other while the base should be made of a material having high tensile strength and low thermal conductance (stainless steel). Such a foil has been manufactured in St. Petersburg and calibrated in NIFS using a vacuum test chamber and a laser beam as an incident power source. A finite element method (FEM) code was applied to simulate the thermal response of the foil. Simulation results are in good agreement with the experimental calibration data. The temperature response of the double layer foil is a factor of two higher than that of a single foil IR video bolometer using the same absorber material and thickness.

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Three emission lines of neutral helium, i.e., the λ 667.8 nm (2¹P-3¹D), λ 728.1 nm (2¹P-3¹S), and λ 706.5 nm (2³P-3³S) lines, are observed with an array of parallel lines-of-sight which covers an entire poloidal cross section of the plasma in the Large Helical Device (LHD). Their emission locations and intensities are determined from the Zeeman profiles. The electron temperature and density are evaluated from intensity ratios among the observed emission lines at each emission location and the poloidal distribution of ionization flux or its equivalent quantity, inward neutral particle flux, is derived with the help of collisional-radiative model calculations. A relatively strong neutral flux is observed at the inboard-side X-point and this result implies a high particle recycling in the inboardside divertor region. The result is consistent with the ion flux distribution onto the helically located divertor plates measured with Langmuir probes.

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The optical design of Impurity Influx Monitor (divertor) was carried out for new ITER design and ray-tracing analysis shows that the spatial resolution of ITER requirement (50 mm) will be achieved by these optical systems designed here. The mechanical design of front end optics also carried out based on the optical design and results of port integration. In the upper port, front end optics can be installed inside the pipe of inner diameter of φ300 mm. In the equatorial port, all the optical component are placed to avoid the interaction with other diagnostic equipments. Heat analysis was carried out for the optimization the cooling method of mirrors, mirror holders and mounting modules to reduce the temperature rise caused by the nuclear heating. It indicates that mirrors can be cooled by the thermal conduction using mirror holders made of a copper alloy and making many cooling channels on the mounting module. Finally, the effect of the thermal deformation to the optical properties is estimated by using the optical design code.

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Fast cameras are powerful tool to visualize the edge turbulence in peripheral plasmas. Under Bi-directional collaborations recently in Heliotron J and GAMMA10 filamentary structures along the magnetic field line were firstly observed with GPI (gas puff imaging) by fast camera. In both machines the filamentary structures had similar stripe pattern in the images and simultaneous measurements of the ion saturation current by electrostatic probes show that the filamentary structures were relatively higher electron density/temperature regions in peripheral plasmas. It is not sufficient to conclude both filamentary structures are the same, however, these phenomena were thought to be related to the energy confinement. Thus the physics mechanism should be solved in the near future.

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Details of two-dimensional imaging performed in the central-cell of the GAMMA 10 tandem mirror by using high-speed camera are described. At the GAMMA 10 central-cell midplane, a high-speed camera (MEMRECAM fx-K4, NAC Inc.) was mounted and the shape and the motion of plasmas were precisely investigated. In the standard ion cyclotron range of frequency (ICRF) heated plasmas, gas puffing of hydrogen with short pulse (3-5 ms) close to the central-cell midplane was carried out to illuminate the periphery plasma and the time evolution of visible light emitted from the gas was captured. The Hα line-emission was localized close to the port of gas puffer. In the pellet injection experiments, 2-D images of the ablation light induced by hydrogen ice-pellet injection were successfully captured at the GAMMA 10 central-cell. Analysis of 2-D images clarified that the electron cyclotron heating applied in the central-cell (c-ECH) has a significant influence on the edge plasma turbulence and the ablation of hydrogen ice-pellet.

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In the GAMMA 10 tandem mirror, the pellet injection system is installed near the mid-plane of the central cell to improve plasma parameters and to study the pellet-plasma interactions in an open system. In recent experiments, hydrogen pellets are injected with ECRH at the plug/barrier and central cells. Consequently, increases in electron densities and H_α line emission with three peaks are observed. The radial profiles of H_α line emission at the peak time have a peak in the peripheral region of the injection side. These results show that the pellet cracks into three small pieces somewhere of the injection path. In this discharge, the pellet of the third peak penetrates deeper than the pellet of first peak, although the third pellet smaller than the first pellet. This phenomenon is occurred by the decrease of the ion temperature caused by the first and second pellet.

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Electric field profiles play an important role in the improvement of plasma confinement. It is essential to develop techniques to measure the electric field profiles in each region of a fusion device. We have developed a technique to measure the electric field profiles in cylindrical plasmas by measuring the Doppler shift of the CII spectrum. Recently, we have developed a collisional-radiative model for the lower charge state of oxygen ions. The oxygen emissions are stronger than those of carbon in GAMMA 10. In order to achieve a higher resolution for the electric field measurements, the technique for measuring the electric field profiles was improved by using the measurements of the oxygen spectra and the calculation of the newly developed collisional-radiative model. The electric field profile was successfully obtained under the condition of a weak electric field.

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Characteristics of spontaneous transition to a high confinement mode (H-mode) have been studied in a helical-axis heliotron device, Heliotron J. The radiation profile measured with a silicon photodiode array shows that a interesting change in the profile occurs at the plasma edge region in the transition phase, forming a strong gradient near the last closed flux surface (LCFS). Relating to the transition, characteristics of bursty density and particle-flux fluctuations current in the scrape off layer (SOL) have been investigated. The probability distribution function for the fluctuations has a tail structure in the L-mode phase, while the tail is suppressed and its direction is reversed after the transition, which may be related to the suppression of edge-plasma turbulence.

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Spectroscopic data on high-Z materials for impurity diagnostics are important due to its possible use as a plasma facing component in the next generation fusion device. For this purpose molybdenum and tungsten are injected by an impurity pellet injector into the large helical device (LHD) plasmas. Emissions from such highly ionized elements mostly fall in extreme ultraviolet (EUV) and soft X-ray ranges. The EUV spectra in a range of 20-500 Å are recorded using a flat-field EUV spectrometer. The observed emissions are identified with the help of its temporal evolution and detailed analysis is done with electron temperature profiles. At high central electron temperature (∼2.2 keV) molybdenum appears as an Al-, Mg- and Na-like ionization stages. Typical examples of identified transitions are Mo XXXI 190.46 Å (3 s^{2 1}S-3s3p ³P) and Mo XXXII 176.63 Å (3s ²S-3p ²P). For tungsten, on the other hand, three well-separated bands appear in wavelength range of 24-80 Å. The transitions around 33 Å have been tentatively identified with the help of calculated values. Most of the isolated lines on the top of pseudo-continuum bands around 50 and 60 Å are identified, and the wavelengths are compared with previous experimental studies and also with calculated values.

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A hybrid matrix array detector is developed for ultra-fast plasma imaging applications with the use of XUV Si photodiodes (SPD diodes) manufactured according to Ioffe Institute original technology. A basic 16 × 16 hybrid module is comprised of eight stacked sub-modules with 2 × 16 linear SPD diode arrays combined with a circuit board with a 32-channel preamplifier and four 8-channel fast multiplexers. Array front size is 31 × 31 mm² with ∼25 % sensitive area. The module has a “zero-edge” design providing an option of stacking into the larger arrays, if necessary. The data acquisition system (DAS) consists of eight 4-channel synchronous 12-bit ADC modules with 40 MS/s upper sampling rate, thus providing less than 1 μs minimum time for the complete read-out of the array. Each channel has a 64 MB on-board memory limiting the duration of the acquired period to 0.8 sec at the maximum sampling rate. A common TCP/IP Ethernet protocol is used for the data transmission into the main PC operating as a DAS control console, data preview and storage computer.

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Radiation brightness and impurity behaviors have been studied for reheat mode discharges in the Compact Helical System (CHS) by three different types of impurity diagnostics. Total radiation power measured by a pyroelectric detector significantly reduces after entering the reheat mode, whereas the line-averaged radiation brightness measured by an absolute extreme ultraviolet (AXUV) photodiode array increases especially for a center viewing chord due to the impurity accumulation in the plasma core. One possible reason for this opposite behavior between the two bolometric detectors is the reduced sensitivity of the AXUV photodiode for lower energy photons in vacuum ultraviolet (VUV) region. This speculation is supported by temporal evolutions of VUV spectra measured by a grazing incidence spectrometer. These results demonstrate that the comparison of three impurity diagnostics would be beneficial to the determination of the major impurity radiators and a comprehensive understanding of impurity behaviors in the reheat mode discharges.

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A soft X-ray (SXR) imaging system (consisting of a microchannel plate, a phosphor plate and an image intensifier CCD camera) has been installed in the STE-2 RFP (R/a = 0.4 m/0.1 m) to obtain high-resolution two-dimensional (2-D) SXR images to see if 3-D magnetic structures can be deduced from the 2-D SXR image. The SXR images obtained in standard RFP plasmas have been compared with those in RFP plasmas with different MHD properties. We have identified characteristic structures in the 2-D SXR images depending upon the MHD properties with the present system. Optimization of the image data processing such as noise filtering from the data or tone correction of brightness distribution is also discussed.

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A soft X ray (SXR) imaging system for diagnosing magnetic islands of a reversed field pinch (RFP) plasma is proposed. The SXR imaging system utilizes a microchannel plate (MCP) to record a higher-resolution distribution of two-dimensional (2D) luminosity on a phosphor plate. In order to identify the structure of the magnetic island from the obtained SXR image, we have calculated the 2D image expected from RFP plasmas. It is found that the 2D image reflects the change in the radiation intensity caused by the magnetic island. Also, the magnetic island can be distinguished clearly when the radiation power emitted from the magnetic island is more than about 20 % of that on the magnetic axis of RFP. Regarding with the view angle α of the SXR imaging system, the magnetic island due to a tearing mode on the m = 1/n = 8 rational surface can be detected as far as α > π/10.

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Mode structures during MHD events in the TST-2 spherical tokamak are revealed by means of singular value decomposition. Soft X-ray and magnetic coil signals show growths of modes with toroidal mode numbers n = 1 and 2. Slow evolution of the soft X-ray profile indicates beginning of localized crash. Occurrence of these events is correlated with the spatial gradient of the soft X-ray profile, suggesting that these events are driven by the pressure gradient. Increases in impurity ion temperatures (CIII and OV) are observed. These are positively correlated with the increment of the plasma current during these events.

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In the Large Helical Device (LHD), several 20-channel Soft X-ray (SX) detector arrays are used to observe the radial structures of SX fluctuations related to MHD instabilities. Recently, 20-channel absolute extreme ultraviolet (AXUV) detector arrays have also been installed inside the vacuum vessel in the vertically and horizontally elongated sections of LHD to monitor MHD fluctuations of AXUV emissions emitted from edge plasma region. These AXUV detector arrays have often detected edge MHD fluctuations localized in low temperature and density edge region so that the SX detector arrays cannot be detected. In LHD, these SX and AXUV detector array systems are successfully employed in order to investigate radial structure and temporal behaviors of edge MHD modes.

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A new imaging high resolution x-ray crystal spectrometer (XCS) has been developed to measure continuous profiles of ion temperature and rotation velocity in fusion plasmas. Following proof-of-principle tests on the Alcator C-Mod tokamak and the NSTX spherical tokamak, and successful testing of a new silicon, pixilated detector with 1 MHz count rate capability per pixel, an imaging XCS is being designed to measure full profiles of T_i and v_φ on C-Mod. The imaging XCS design has also been adopted for ITER. Ion-temperature uncertainty and minimum measurable rotation velocity are calculated for the C-Mod spectrometer. The affects of x-ray and nuclear-radiation background on the measurement uncertainties are calculated to predict performance on ITER.

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A wide band and compact X-ray spectrometer has been developed using a Johan-type crystal and a back-illuminated CCD detector for charge state distribution measurement of highly ionized iron in LHD. In order to observe all charge states of iron ions a curved crystal of LiF(220) with a curvature of 430 mm was selected for the spectrometer. A wide energy range of 6.4-7.0 keV could be observed with use of CCD detector in a size of 26.6 × 6.7 mm² . An energy resolution of the spectrometer was 10 eV at full width at half maximum (FWHM). Time-developed Fe Kα spectra were thus measured with a time interval of 10 ms in the full binning mode of the CCD. The charge states from Fe ions of FeXXI to FeXXV were clearly observed, but FeXXVI has not been observed. In the next step, then, the charge state distribution measurement is focused on the measurement of FeXXI-XXV and a quartz(2023) curved crystal is selected to measure the energy range of 6.40-6.75 keV. The expected energy resolution is 4 eV at 6.7 keV for the quartz crystal, which is enough for further analysis of the iron charge state distribution.

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Radial profiles of impurity transport coefficients of argon have been successfully obtained in Large Helical Device, using an assembly equipped with conventional semiconductor detectors and soft x-ray pulse-height analyzers. Several fixed argon discharges have enabled the radial scanning of the assembly to measure the radial profiles of argon-K_α lines. The present experimental results indicate that the impurity transport study becomes possible with the soft x-ray pulse-height analyzers.

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A novel x-ray tube with a line filament has been developed for the in-situ calibration of the x-ray crystal spectrometer (XCS) in the KSTAR machine. The characteristics of the x-ray tube are investigated from the x-ray images obtained by using a pinhole and a CCD detector. It is found that the image has the width of about 0.1 mm, which is much improved as compared with the previous experimental results. In addition, there is a uniform region around the center of the image within its full length of 13.5 mm. This work may lead to the development of a novel x-ray tube with a line focus, which is required for the calibration of the XCS. Experimental results from the investigation of the x-ray tube are presented and the technical issues in a design of the in-situ calibration system using the x-ray tube for the KSTAR XCS are discussed.

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A new technique to measure the current profile in plasmas with asymmetric distribution function such as lower hybrid current drive (LHCD) by using hard X-ray (HXR) energy spectrum measurement along the top and bottom identical line of sights (ILOS) is proposed and is applied to the full and partially LHCD plasmas on the TRIAM-1M tokamak at the first time in the world. The pitch angles were measured at R - R₀ = ±2.5 cm, where R, R₀ mean the major radii of the ILOS and the magnetic axis, respectively. The measured pitch angle of the magnetic field inverted at the magnetic axis estimated magnetic measurement in partially LHCD plasmas. This indicates that the difference of the measured pitch angles is caused by the plasma current in the plasma and this new method is available in detecting the current profile in tokamaks. In full LHCD plasma, no difference between the HXR signals along the top and bottom ILOS appear. This indicates that the current density around the magnetic axis was reduced compared with that in partially LHCD plasmas. This observation is no contradiction with power deposition of LHCD.

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In Large Helical Device (LHD), it is possible to perform the simulation experiment of the α particle heating by using the ion cyclotron resonance heating (ICH) because high-energy particle generated by ICH is well confined in the plasma. The neutral particles (mainly hydrogen), which are generated by the charge exchange between the high-energy ion and the background neutrals, can be observed by using them. However a few neutral helium particles can be observed since fully ionized helium like α particle can emit only by double charge exchange process. Therefore we also introduce the pellet charge exchange system (PCX). The diagnostic pellet is injected to the plasma in order to obtain the charge exchange neutral particle, which is produced by the charge exchange reaction between the ablated pellet cloud and high-energetic particle. The helium distribution measurement in helium plasma is also demonstrated.

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A new multi-channel diagnostic for fast particles has been developed and successfully tested on the Large Helical Device (LHD) during 2005-2006 experimental campaign. The number of simultaneously used channels was significantly improved from 2 to 20 channels and additional improvements for noise reduction have been made. Same time location of the diagnostic has been changed that allowed one to make measurements in a much wider range of pitch angles from perpendicular to tangential (90-160 degrees). All these improvements allow one to make time, energy, and angle-resolved measurements of charge exchange neutral particles in a single plasma discharge and to check the presence of fast particles loss-cones from LHD plasma in different heating regimes. This new diagnostic can be a very helpful and powerful tool in studying of fast particle distribution in such a complex helical plasma geometry like the one of LHD. Example data from plasma discharges are presented.

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A numerical method is described that can be used to estimate the source of neutral particles within a helical plasma column as a function of the magnetic surface. The method is applicable to the data analysis of passive line-integral diagnostics of escaping neutrals. The magnetic surface structure taken from magnetohydrodynamic equilibrium calculations defines the kernel of the integral equation. A regularized solution is obtained over a discrete grid by minimizing the appropriate objective functional. The corresponding linear system is solved in terms of least squares using QR algorithm. The application is discussed to one particular charge-exchange diagnostic on the Large Helical Device and the model profile reconstruction examples are presented.

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On the basis of kinetic description, the analytical formula is derived as an evaluation formula of the energy spectra of fast ion produced by neutral beam injection (NBI) heating. The effects of particle loss due to the loss cone are newly considered in the kinetic equation. The distribution function is derived by integrating the kinetic transport equation as possible as analytical methods. Thus it will be able to reduce a computational time for the systematic analysis of the energy spectra of fast ion. The validity of the derived solution is appraised by comparing with the energy spectra experimentally measured by natural diamond detector (NDD) in the Large Helical Device (LHD). Good agreements in their behavior are obtained.

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Fast-ion-diagnostics have played an important role in investigating issues related to fast ion orbits and fast-ion-driven MHD instabilities in CHS experiments. The fast-ion diagnostics employed in CHS are reviewed and experimentally obtained knowledge is summarized.

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Mirror devices, having open-ended regions, provide intrinsic important advantages in terms of the control of radial-potential or E_r shear profiles on the basis of axial particle loss control for ambipolar potential formation. From the viewpoint of the mechanism investigation of radially localized transport-barrier formation, an idea of off-axis-resonant electron-cyclotron heating (ECH) is proposed and applied in the tandem mirror GAMMA 10, by the use of the aforementioned intrinsic advantage of mirror devices. The off-axis ECH produces a cylindrical layer with energetic electrons and facilitates the formation for a localized bumped ambipolar potential with a strong shear of radial electric fields E_r. Remarkable effects of dE_r/dr on the suppression of turbulent fluctuations with plasma confinement improvement are found by the use of signals of end-loss currents flowing from the central cell as well as the central-cell soft x ray. In association with the reduction of the fluctuations due to strong E_r shear formation, increases in ion and electron temperatures are found.

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The γ-ray emission rate by ⁶Li(d,p)⁷ Li^*, ⁷Li^* → ⁷Li+γ reaction when 50∼250 keV proton beam is injected into ⁶Li containing deuterium plasmas (n_e ∼10¹⁹ m^-3 and T_e = 1∼10 keV) is evaluated by simultaneously solving the Boltzmann-Fokker-Planck (BFP) equations for deuteron and proton. A possible experiment to verify the BFP simulations, e.g. knock-on tail effect on T(d,n)⁴ He reaction rate coefficient and/or plasma diagnostics which utilize the tail formation in ion distribution function, is proposed.

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Measurements of the densities of the molecular and atomic ions (n_H⁺, n_H2⁺, n_H3⁺) were carried out in hydrogen recombination plasma in the linear divertor plasma simulator, TPD-SheetIV. The molecular and atomic ion currents were detected using an omegatron mass analyzer. The ground-state vibrational temperature of hydrogen molecules T_vib is obtained by measurement with VUV emission spectroscopy. Taking into account of T_vib, a zero-dimensional model using the relevant rate balance equations was found to predict the observed dominant ion.

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In order to monitor the diverted plasma flux distribution for various field configurations in Heliotron J, a new edge-plasma monitor system was installed. During a single discharge, a high-speed video camera (250-500 fps) records a stack of two-dimensional images of visible light emission (mainly from recycling neutrals) near a movable carbon target, which is inserted to the peripheral region of the core plasma. A spontaneous shift of the brightest spot of the light emission along the target was clearly observed. This shift is qualitatively consistent with a poloidal shift of the diverted plasma position which was observed in the diverted plasma flux measurement with a Langmuir probe-array near the wall at a different toroidal position. These findings indicate the global shift of the edge plasma position during a discharge. The most plausible mechanism for the observed shift is the change of the edge field topology caused by a non-inductive plasma current of a few kA.

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The gas composition ratio inthe divertor region of a fusion reactor must be measured in order to evaluate its atomic-molecular processes precisely. In this research we propose a method to measure the gas composition ratio of He, H and H₂ of the H-He mixture plasmas in divertor simulator MAP-II by using passive spectroscopy of the Balmer series of hydrogen atoms, the Fulcher-α band of hydrogen molecules and the He I emissions.

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The method of measuring heat flow Q as a function of the sheath potential V is investigated in order to improve the time response of the thermal probe method. We found that the time constant τ for reaching a steady state in thermal phenomena was 123 ± 18 s. The result of τ indicated that the applicable method for measuring the Q-V characteristic was biasing the thermal probe in a stepwise manner, and this was verified experimentally. Although there existed a V-dependent offset of the Q-V curve deduced from the temperature gradients against that calculated from the ion current, a procedure to deduce the ion temperature T_i is developed. The experimental error in T_i was too large, and was caused by the error in Q. Thus we have to improve the accuracy of the Q measurement.

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A neutron spectrometer system based on TOF (time of flight) measurement has been studied for determination of fuel density ratio in ITER. The effective collimator diameter was examined against both the saturation of the first detector and measurement efficiency as a spectrometer to achieve the sufficient statistics with required time resolution. Relation between collimator diameter and lower limit measurement efficiency was obtained. Measurement efficiency for every design of TOF spectrometer was calculated with MCNP. Those results indicate that two or three collimators of different size are needed to attain statistics errors within 10 %. An experiment to test the TOF spectrometer and to evaluate the system efficiency was conducted using accelerator neutron source. The result shows that both DD and DT neutrons are measured separately and simultaneously with a fast discrimination electronics system. The fast discrimination improves the counting capability by one order of magnitude.

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The proton emission from the plasma focus device with the H₂ filling was analyzed. The ion beam characteristics, particle pinhole image and pinch plasma image were obtained with an aluminum filtered pinhole camera with CR-39 film and x-ray pinhole camera with Be filter respectively. Ring-shaped of ion bunches were observed and also on the pinched plasma column same shape was attributed.

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Several ceramic detectors were made by use of the insulation layer formed on two types of substrate, i.e. aluminum and silicon. Each detector was irradiated with alpha-rays from an Am-241 source and the electric charge induced in the detector was measured in the temperature range from room temperature up to 450 K. The alpha-ray detection signals were well observed with an oscilloscope at the properly high bias-voltage only for very short time from several seconds to several tens of seconds before the start of the sweeping insulation breakdown. Though this type of the simple detector made of a thin ceramic layer can be hardly used for the energy analysis, it might be effectively applicable to the measurement of the flux of alpha-particles at high temperature.

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Transverse ion loss in the thermal barrier region of the GAMMA10 tandem mirror is investigated with the mapping equations of ion drift orbits. The effects of a non-axisymmetric electrostatic potential in the thermal barrier are taken into account. The local stability of orbits and its diffusion are calculated numerically and these are compared with the results of A.B. Rechester and R.B. White [1]. It is found that there are two kinds of the transverse ion transport. One is chaotic ion orbits due to unstable ion drift, which cause cross-field ion diffusion. Another is the enhanced effects of ion radial step sizes on the transverse diffusion, because banana-like ion drift orbits appear due to the non-axisymmetric electrostatic potential formation.

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Neutral transport related to recycling phenomena on two limiters installed in the central-cell was studied in the GAMMA 10 tandem mirror plasmas. Dependence of iris limiter is investigated in terms of plasma diamagnetism and H_α-line intensity. It was found that a plasma diamagnetic signal was improved and H_α-line intensity near the iris limiter increased if the diameter of the iris limiter shrank to 340 mm. Fully 3-dimensional Monte-Carlo simulation (DEGAS) was executed with the recycling source on the limiters. The neutral sources on the limiters were consistently given so as to satisfy 2-dimensional (2-d) image obtained by a high-speed camera. The determined H_α-line intensity from DEGAS well explained the experimental result. The simulation result, in the 340 mm case, predicted the reduction in the peak value of H_α-line intensity on the central limiter and the enhancement on the iris limiter. It suggests that the reduction of the recycling on the central limiter makes it possible to lead the better plasma performance.

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The designs and analyses of the diagnostic port plug for installing diagnostics have been carried out from various aspects in order to advance the port plug concept to the realistic design. Manufacturing processes have been studied for the alternative structure using the rolling plates and ribs, in addition to the reference structure using forging material. Electromagnetic loads onto the upper port plug during a vertical displacement event have been evaluated. It has been shown that maximum moments are about half of the reference ones. The design integration of three diagnostics into one of the upper port plugs has been performed by considering required aspects such as diagnostic functions, neutron shielding, maintenance of diagnostic components and cooling channels.

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A nonneutral plasma confined on helical magnetic surfaces exhibits instability, although it is theoretically stable. In order to investigate the disruptive phenomenon in detail, electron particle flow into a probe tip is carefully measured inside the magnetic surfaces. Preliminary results indicate that the observed disruption is first to occur near the top of the plasma, and then, seems to propagate toward the center of the plasma.

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An advanced probe measurement system consisting of high-speed Langmuir probes with a preamplifier and a Copper shield was designed and installed in TU-Heliac. Potential and density fluctuations were measured in the hot-cathode biased plasma, and power spectra were calculated using the complex Fourier transform. There were low frequency fluctuations (f < 10 kHz), high frequency fluctuations (70 < f < 200 kHz) and sharp spectra applied for the plasma production (10 < f < 50 kHz). In the region above 200 kHz, the power decreased by a factor of 1/f² for the potential fluctuation and 1/f^2∼3 for the density fluctuation. The phase shift between potential and density fluctuations was almost 0 rad at ρ = 0.54. On the other hand, the phase shift was not 0 rad at ρ = 0.21, especially in the 100 ∼ 200 kHz region. The high frequency fluctuation at ρ = 0.21 grew on the time scale of 10^-5 s, which was obtained from the time dependent signals of the high frequency fluctuation.

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In the triple Langmuir probe (T-LP) method, the electron temperature (T_e) and density (n_e) can be simultaneously derived from potential measurements of electrode of T-LP and the ion saturation current (I_is) where no current flows in the electrodes for potential measurements. In the case of aiming at measuring high-frequency fluctuations, however, the smaller load resistance of electrode is required for high frequency response. Then the finite current can flow in the measurement circuits of the floating potential (V_f) and the plus-biased potential (V_p). When the current becomes comparable to I_is, the T_e derived from measured V_f and V_p without the current considerably deviates from an actual value. This would be significant for fairly low density plasma of the n_e <∼ 5 × 10¹⁷ m^-3 , and the correction of the finite current is necessary. A new relationship between T_e and potential signals (V_f and V_p) where the finite current in the electrodes for V_f and V_p measurements is taken into account was derived, and experimentally confirmed the validity in the experiments of the Compact Helical System.

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A hybrid directional probe method both “thermal and Langmuir probe” was applied for fast ion measurements in the compact helical system. In order to obtain absolute values of fast ion density and power density, a calibration of the probe was performed using neutral hydrogen beam and a mixture beam of hydrogen and proton, of which beam current and energy were controlled. The conversion factor from temperature increase of the probe head to local power density and secondary electron emission yield was obtained. The density of fast ions was obtained by directional thermal probe (DTP) method inside the last closed flux surface, and the density ratio was n_FastIon/n_BulkPlasma = 2.7 × 10^-3 at r/a = 0.9. The observation of the directional Langmuir probe (DLP) method is consistent with the DTP results.

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With a skillful probing system, both large negative space potential φ_s and low electron current I_p of helical nonneutral plasmas have been measured. For the φ_s measurement, a differential circuit with a high-voltage probe is employed. In order to prevent the signal from delaying due to the large output impedance of the high-voltage probe, an operational amplifier is used to reduce the output impedance to ideally zero. For the I_p measurement, an instrumentation amplifier is employed to precisely cancel the common-mode noise. In addition, to alleviate the thermal noise due to the large feedback resistance in the circuit, a trick of T-network resistance is utilized instead of the single large resistance. Furthermore, to cancel the significant ground loop current, the reference potential of the circuit is grounded across a small resistance (100Ω).

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Characteristics of magnetic islands are investigated by magnetic diagnostics in the Large Helical Device (LHD). The structure of the magnetic island with m/n = 1/1 (where, m and n are poloidal and toroidal mode number, respectively) can be estimated from the perturbed magnetic field appearing when a magnetic island changes. To measure the toroidal profile of the perturbed magnetic field δb₁ originating from the plasma, a toroidal array of magnetic flux loops is set up in the LHD. The toroidal profile of δb₁ is then spatially Fourier decomposed to determine the amplitude of the n = 1 component, δb₁ⁿ⁼¹ and its phase, φ_n=1 which correspond the change of the island width and the toroidal position of the X-point of the island, respectively. Therefore, the information about the magnetic island structure can be obtained from δb₁ⁿ⁼¹ and φ_n=1. In case the island width becomes larger than the seed island, measurements show that δb₁ⁿ⁼¹ is non-zero and φ_n=1 is temporally constant. A non-zero δb₁ⁿ⁼¹ can also be observed when the island width becomes smaller than the seed island. In this case, the angle φ_n=1 shifts by about π[rad] compared with the increasing case and the δb₁ⁿ⁼¹ is limited to a certain value which corresponding to the magnetic field suppressing the seed island.

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Plasma shape reconstruction is important for plasma control of tokamak. Cauchy-Condition Surface (CCS) method is a numerical approach to reproduce plasma shape which has good precision in conventional tokamak. In order to apply it in the plasma shape reproduction of Compact PWI experimental Device (CPD) which is a new spherical tokamak in Kyushu University, the calculation precision of CCS method in CPD is analyzed in the paper.

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A sheet-shaped thermal lithium beam probe has been developed for two-dimensional density measurements in the edge region of the torus plasma. For the production of an intense and uniform beam, the optimization of the nozzle shape and slit width of the beam injector has been performed. Beam density profiles at the observing region in the plasma were estimated with numerical calculations using a Monte Carlo technique for several kinds of nozzles and combinations with slits. Experiments on the test stand were also carried out, and pretty good agreement was found between numerical and experimental results. Based on these examination and optimization for the nozzle and slits, we have constructed a sheet-shaped beam injector for the large helical device. In spite of the long distance (about 3 m) from the injector, it is estimated that the thickness of the sheet-shaped beam is ∼90 mm (full width at half maximum).

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The 3-D spatial structure - radial locality and poloidal/toroidal mode numbers - of the magnetohydrodynamic fluctuation called “edge harmonic oscillation (EHO)” in the compact helical system (CHS) was investigated using beam emission spectroscopy (BES) as the diagnostic method of the local density fluctuations and the magnetic probe array. We found two groups of harmonic oscillations in CHS, one with a frequency of 4.0 kHz and a harmonic located in the edge region of the normalized minor radius ρ = 0.95 near the rotational transform ι = 1 surface, and the other with a frequency of 3.5 kHz and a harmonic located in the core region ρ = 0.53 near the ι = 0.5 surface. The magnetic probe signals showed that the poloidal/toroidal mode numbers of the edge mode and the core mode were -1/1 and -2/1, respectively. They were consistent with the rotational transform of the magnetic field at the locations of those modes.

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In order to measure the potential in Large Helical Device (LHD), we have been developing a heavy ion beam probe (HIBP). For probing beam, gold beam is used, which is accelerated by a tandem accelerator up to the energy of 6 MeV. The experiments for calibration of beam orbit were done, and experimental results were compared with orbit calculations. The experimental results coincided fairly with the calculation results. After the calibration of the beam orbit, the potential in plasma was tried to measure with the HIBP. The experimental data showed positive potential in a neutral beam heating phase on the condition of n_e ∼ 5 × 10¹⁸ m^-3, and the increase of potential was observed when the additional electron cyclotron heating was applied to this plasma. The time constant for this increase was about a few tens ms, which was larger than a theoretical expectation. In the spatial position of sample volume, we might have an ambiguity in this experiment.

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