Probabilistic n/γ discrimination with robustness against outliers for use in neutron profile monitors.

A method to stochastically discriminate neutron and γ-ray signals measured with a stilbene organic scintillator is proposed. Each pulse signal was stochastically categorized into two groups: neutron and γ-ray. In previous work, the Expectation Maximization (EM) algorithm was used with the assumption that the measured data followed a Gaussian mixture distribution.

Novel analysis technique for measuring edge density fluctuation profiles with reflectometry in the Large Helical Device.

A new method for measuring density fluctuation profiles near the edge of plasmas in the Large Helical Device (LHD) has been developed utilizing reflectometry combined with pellet-induced fast density scans. Reflectometer cutoff location was calculated by proportionally scaling the cutoff location calculated with fast far infrared laser interferometer (FIR) density profiles to match the slower time resolution results of the ray-tracing code LHD-GAUSS. Plasma velocity profile peaks generated with this reflectometer mapping were checked against velocity measurements made with charge exchange spectroscopy (CXS) and were found to agree within experimental uncertainty once diagnostic differences were accounted for.

In situ analysis of reaction kinetics of reduction promotion of NiMnO under microwave H-field irradiation.

Reaction kinetics during microwave H-field heating and electric furnace heating were investigated to verify the effect of rapid heating and the non-thermal microwave effect. This work is focused on the ferromagnetic material NiMnO, and the reduction reaction under rapid heating is investigated using an in situ analysis device. The results showed that the activation energy varied with the heating rate under microwave H-field irradiation, and it was the same as that in an electric furnace when the heating rate was the same.

Conceptual design of imaging bolometer for use of computed tomography in JT-60SA.

An InfraRed imaging Video Bolometer (IRVB) system in JT-60SA has been designed for the two-dimensional (2D) Computed Tomography (CT) analysis of radiation. To achieve complete viewing of the whole poloidal cross section for plasmas having a low aspect ratio, a new IRVB concept, which has two sets of pin-hole camera systems viewing two different directions, has been introduced. Fields of view of the IRVB have been successfully designed by moving apertures to be sufficient for CT use without installation in tangential ports.

DEVELOPMENT OF ISOTOPICALLY ENRICHED BORON-DOPED ALUMINA DOSIMETER FOR THERMAL NEUTRONS.

A novel optically stimulated luminescence (OSL) detector containing isotopically enriched boron was developed for thermal neutron dosimetry. Alumina containing isotopically enriched boron (Al2O3:B) was synthesised by the sol-gel method. The Al2O3:B was annealed up to ~1800 K.

Isotope Effects on Trapped-Electron-Mode Driven Turbulence and Zonal Flows in Helical and Tokamak Plasmas.

Impacts of isotope ion mass on trapped-electron-mode (TEM)-driven turbulence and zonal flows in magnetically confined fusion plasmas are investigated. Gyrokinetic simulations of TEM-driven turbulence in three-dimensional magnetic configuration of helical plasmas with hydrogen isotope ions and real-mass kinetic electrons are realized for the first time, and the linear and the nonlinear nature of the isotope and collisional effects on the turbulent transport and zonal-flow generation are clarified. It is newly found that combined effects of the collisional TEM stabilization by the isotope ions and the associated increase in the impacts of the steady zonal flows at the near-marginal linear stability lead to the significant transport reduction with the opposite ion mass dependence in comparison to the conventional gyro-Bohm scaling.

Development of 2-D horn-antenna millimeter-wave imaging device (HMID) for the plasma diagnostics.

The two-dimensional (2-D) Horn-antenna Millimeter-wave Imaging Device (HMID) has been developed for the O-mode Microwave Imaging Reflectometry (O-MIR) in the Large Helical Device (LHD). The detectable frequency range of the HMID is 23-33 GHz, which corresponds to the cutoff electron density of 0.8-1.

How turbulence fronts induce plasma spin-up.

A calculation which describes the spin-up of toroidal plasmas by the radial propagation of turbulence fronts with broken parallel symmetry is presented. The associated flux of parallel momentum is calculated by using a two-scale direct-interaction approximation in the weak turbulence limit. We show that fluctuation momentum spreads faster than mean flow momentum.

Development of an active tritium sampler for discriminating chemical forms without the use of combustion gases in a fusion test facility.

A new type of active tritium sampler that can discriminate between chemical forms in a fusion test facility without the use of combustion gases was developed. The proposed tritium sampler was operated using water vapour instead of combustion gases. To test the operation and performance of the device when water vapour is used, we evaluated the catalytic oxidation properties, and the evaporation and collection of water vapour under actual sampling conditions.

Suppression of Trapped Energetic Ions Driven Resistive Interchange Modes with Electron Cyclotron Heating in a Helical Plasma.

The resistive interchange mode destabilized by the resonant interaction with the trapped energetic ions is fully suppressed when the injected power of electron cyclotron heating exceeds a certain threshold. It is shown for the first time that the complete stabilization of the energetic-particle-driven mode without relaxing the energetic particle (EP) pressure gradient is possible by reducing the radial width of the eigenmodes δ_{w}, especially when δ_{w} narrows to a small enough value relative to the finite orbit width of EP.

Space-resolved visible spectroscopy for two-dimensional measurement of hydrogen and impurity emission spectra and of plasma flow in the edge stochastic layer of LHD.

A space-resolved visible spectrometer system has been developed for two-dimensional (2D) distribution measurements of hydrogen and impurity emission spectra and of plasma flow in the edge stochastic layer of Large Helical Device (LHD). Astigmatism of the spectrometer has been suppressed by introducing additional toroidal and spherical mirrors. A good focal image at the exit slit is realized in a wide wavelength range (75 nm) as well as in a wide slit height direction (26 mm) with a 300 grooves/mm grating.

Weak size dependence of resuspended radiocesium adsorbed on soil particles collected after the Fukushima nuclear accident.

Most studies of the properties of airborne radionuclides emitted from the Fukushima Daiichi Nuclear Power Plant have focused on the relatively early stages of the accident, and little is known about the characteristics of radiocesium in the long-term. In this study, we analyzed activity size distributions of airborne radiocesium collected over 5 months in Tsukuba, Japan. Radiocesium in the accumulation mode size range (0.

Boosting laser-ion acceleration with multi-picosecond pulses.

Using one of the world most powerful laser facility, we demonstrate for the first time that high-contrast multi-picosecond pulses are advantageous for proton acceleration. By extending the pulse duration from 1.5 to 6 ps with fixed laser intensity of 10 W cm, the maximum proton energy is improved more than twice (from 13 to 33 MeV).

Data-driven sensitivity inference for Thomson scattering electron density measurement systems.

We developed a method to infer the calibration parameters of multichannel measurement systems, such as channel variations of sensitivity and noise amplitude, from experimental data. We regard such uncertainties of the calibration parameters as dependent noise. The statistical properties of the dependent noise and that of the latent functions were modeled and implemented in the Gaussian process kernel.

Measurement system for alpha and beta emitters with continuous air sampling under different exposure situations.

In the present study, a continuous radioactive aerosol measurement system (CRAMS) was developed for measurements of radioactive plume (e.g. I, Cs and Cs) under the emergency situation, and measurements of radon/thoron progeny under the existing situation.

Bench testing of a heterodyne CO laser dispersion interferometer for high temporal resolution plasma density measurements.

A heterodyne detection scheme is combined with a 10.59 μm CO laser dispersion interferometer for the first time to allow large bandwidth measurements in the 10-100 MHz range. The approach employed utilizes a 40 MHz acousto-optic cell operating on the frequency doubled CO beam which is obtained using a high 2nd harmonic conversion efficiency orientation patterned gallium arsenide crystal.

Up-down asymmetry measurement of tungsten distribution in large helical device using two extreme ultraviolet (EUV) spectrometers.

Two space-resolved extreme ultraviolet spectrometers working in wavelength ranges of 10-130 Å and 30-500 Å have been utilized to observe the full vertical profile of tungsten line emissions by simultaneously measuring upper- and lower-half plasmas of LHD, respectively. The radial profile of local emissivity is reconstructed from the measured vertical profile in the overlapped wavelength range of 30-130 Å and the up-down asymmetry is examined against the local emissivity profiles of WXXVIII in the unresolved transition array spectrum. The result shows a nearly symmetric profile, suggesting a good availability in the present diagnostic method for the impurity asymmetry study.

Beam emission spectroscopy with radially and poloidally elongated optical sightlines.

Beam emission spectroscopy is widely used as local density fluctuation measurement of fusion plasmas. We have installed a beam emission spectroscopy system in the large helical device (LHD) with radially and poloidally elongated optical configuration to enhance both signal-to-noise ratio and wavenumber sensitivity in radial and poloidal directions. The calculation considering the integral effect of the line of sight showed the radially and poloidally elongated sightlines have increased sensitivity compared with the square shaped bundle design of the same sampling area.

New type of wavelet-based spectral analysis by which modes with different toroidal mode number are separated.

A new type of wavelet-based analysis for the magnetic fluctuations by which toroidal mode number can be resolved is proposed. By using a wavelet, having a different phase toroidally, a spectrogram with a specific toroidal mode number can be obtained. When this analysis is applied to the measurement of the fluctuations observed in the large helical device, MHD activities having similar frequency in the laboratory frame can be separated from the difference of the toroidal mode number.

Faraday-cup-type lost fast ion detector on Heliotron J.

A Faraday-cup type lost-fast ion probe (FLIP) has been designed and installed in Heliotron J for the purpose of the studies of interaction between fast ions and MHD instabilities. The FLIP can measure the co-going fast ions whose energy is in the range of 1.7-42.

Upgraded millimeter-wave interferometer for measuring the electron density during the beam extraction in the negative ion source.

The upgraded millimeter-wave interferometer with the frequency of 70 GHz is installed on a large-scaled negative ion source. Measurable line-averaged electron density is from 2 × 10 to 3 × 10 m in front of the plasma grid. Several improvements such as the change to shorter wavelength probing with low noise, the installation of special ordered horn antenna, the signal modulation for a high accuracy digital phase detection, the insertion of insulator, and so on, are carried out for the measurement during the beam extraction by applying high voltage.

In situ calibration of the foil detector for an infrared imaging video bolometer using a carbon evaporation technique.

The InfraRed imaging Video Bolometer (IRVB) is a useful diagnostic for the multi-dimensional measurement of plasma radiation profiles. For the application of IRVB measurement to the neutron environment in fusion plasma devices such as the Large Helical Device (LHD), in situ calibration of the thermal characteristics of the foil detector is required. Laser irradiation tests of sample foils show that the reproducibility and uniformity of the carbon coating for the foil were improved using a vacuum evaporation method.

Upgrade of the tangentially viewing vacuum ultraviolet (VUV) telescope system for 2D fluctuation measurement in the large helical device.

A high-speed tangentially viewing vacuum ultraviolet (VUV) telescope system, using an inverse Schwarzschild-type optic system was developed to study fluctuations in the Large Helical Device (LHD). However, for the original system, the sampling rate was restricted to below 2000 Hz due to the low signal to noise (S/N) ratio in the experiment. In order to improve the S/N ratio, upgrade of the system was made.

High time resolved electron temperature measurements by using the multi-pass Thomson scattering system in GAMMA 10/PDX.

High time resolved electron temperature measurements are useful for fluctuation study. A multi-pass Thomson scattering (MPTS) system is proposed for the improvement of both increasing the TS signal intensity and time resolution. The MPTS system in GAMMA 10/PDX has been constructed for enhancing the Thomson scattered signals for the improvement of measurement accuracy.