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Simple Pretreatment Method for Tritium Measurement in Environmental Water Samples using a Liquid Scintillation Counter
Get PDF0000-0002-0580-0328The aim of this study is to evaluate quantitatively the effectiveness of the ion exchange resins and activated carbon in tritium measurement. A standard water sample was adjusted to a tritium concentration of 5 Bq L−1. This sample was stirred with the cation exchange (PCH) and anion exchange (PAO) resins and activated carbon. After stirring the samples, the supernatant in each sample was filtered through 0.45 μm membrane filters. The electrical conductivity in an experimental condition, where the amounts of PCH, PAO, and activated carbon were 0.3 g, 0.3 g, and 0.6 g, respectively, was lower than that of the sample treated by the distillation method. The distillation method requires approximately 12 h to process; however, the same level of results was achieved in 5 min. The tritium concentration in each experiment was within the standard deviation. These results suggested that proposed batch method involving ion exchange resins and activated carbon had negligible effect on tritium measurement. The ion concentration and the total organic carbon for the samples were decreased in 5 min. These results demonstrate the effectiveness of the impurity removal from the sample water by ion exchange resins.journal articl
Particle Simulation of Controlling Particle and Heat Flux by Magnetic Field
Get PDF0000-0001-5600-5722An idea for shielding high energy ion and electron fluxes is proposed by applying external magnetic fields. In this work, we model a flowing plasma in a small region by utilizing one spatial dimension and three coordinates for velocities (1D3V) Particle-In-Cell (PIC) code. The plasma which consists of ion and electron is produced from the source region and absorbed at the conductor wall. The external magnetic field is modified by applying the change of the magnetic field in the direction perpendicular to the plasma flow. This magnetic field is localized and switched from strong negative values to strong positive values at several locations in the simulation region. We found that this localized reversed magnetic field traps the particles, and then reduces the particle and heat fluxes to the wall. Based on the modeling results, external localized-reversed magnetic fields can control the particle and heat fluxes to the wall. These results can be applied for shielding high energy ion and electron fluxes to the satellite or spacecraft in the space.journal articl
Optical Properties of Fiberform Nanostructured Tungsten in the Infrared Wavelength Range
Get PDF0000-0001-8616-6041Fiberform 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.journal articl
Isotope effects on transport in LHD
Get PDF0000-0002-1606-3204Isotope effects are one of the most important issues for predicting future reactor operations. Large helical device (LHD) is the presently working largest stellarator/helical device using super conducting helical coils. In LHD, deuterium experiments started in 2017. Extensive studies regarding isotope effects on transport have been carried out. In this paper, the results of isotope effect studies in LHD are reported. The systematic studies were performed adjusting operational parameters and nondimensional parameters. In L mode like normal confinement plasma, where internal and edge transport barriers are not formed, the scaling of global energy confinement time (τE) with operational parameters shows positive mass dependence (M0.27; where M is effective ion mass) in electron cyclotron heating plasma and no mass dependence (M0.0) in neutral beam injection heating plasma. The non-negative ion mass dependence is anti-gyro-Bohm scaling. The role of the turbulence in isotope effects was also found by turbulence measurements and gyrokinetic simulation. Better accessibility to electron and ion internal transport barrier (ITB) plasma is found in deuterium (D) plasma than in hydrogen (H). Gyro kinetic non-linear simulation shows reduced ion heat flux due to the larger generation of zonal flow in deuterium plasma. Peaked carbon density profile plays a prominent role in reducing ion energy transport in ITB plasma. This is evident only in plasma with deuterium ions. New findings on the mixing and non-mixing states of D and H particle transports are reported. In the mixing state, ion particle diffusivities are higher than electron particle diffusivities and D and H ion density profiles are almost identical. In the non-mixing state, ion particle diffusivity is much lower than electron diffusivity. Deuterium and hydrogen ion profiles are clearly different. Different turbulence structures were found in the mixing and non-mixing states suggesting different turbulence modes play a role.journal articl
Fast deuteron diagnostics using visible light spectra of 3He produced by deuteron–deuteron reaction in deuterium plasmas
Get PDF0000-0003-3198-042XThe fast deuteron (non-Maxwellian component) diagnostic method, which is based on the higher resolution optical spectroscopic measurement, has been developed as a powerful tool. Owing to a decrease in the D–H charge-exchange cross section, the diagnostic ability of conventional optical diagnostic methods should be improved for ∼MeV energy deuterons. Because the 3He–H charge-exchange cross section is much larger than that of D–H in the ∼MeV energy range, the visible light (VIS) spectrum of 3He produced by the dueteron–dueteron (DD) reaction may be a useful tool. Although the density of 3He is small because it is produced via the DD reaction, improvement of the emissivity of the VIS spectrum of 3He can be expected by using a high-energy beam. We evaluate the VIS spectrum of 3He for the cases when a fast deuteron tail is formed and not formed in the ITER-like beam injected deuterium plasma. Even when the beam energy is in the MeV energy range, a large change appears in the half width at half maximum of the VIS spectrum. The emissivity of the VIS spectrum of 3He and the emissivity of bremsstrahlung are compared, and the measurable VIS spectrum is obtained. It is shown that the VIS spectrum of 3He is a useful tool for the MeV beam deuteron tail diagnostics.journal articl
Design and optimization of an advanced time-of-flight neutron spectrometer for deuterium plasmas of the large helical device
Get PDF0000-0001-9815-5083A time-of-flight neutron spectrometer based on the Time-Of-Flight Enhanced Diagnostic (TOFED) concept has been designed and is under development for the Large Helical Device (LHD). It will be the first advanced neutron spectrometer to measure the 2.45 MeV D–D neutrons (DDNs) from helical/stellarator plasmas. The main mission of the new TOFED is to study the supra-thermal deuterons generated from the auxiliary heating systems in helical plasmas by measuring the time-of-flight spectra of DDN. It will also measure the triton burnup neutrons (TBNs) from the d+t reactions, unlike the original TOFED in the EAST tokamak. Its capability of diagnosing the TBN ratios is evaluated in this work. This new TOFED is expected to be installed in the basement under the LHD hall and shares the collimator with one channel of the vertical neutron camera to define its line of sight. The distance from its primary scintillators to the equatorial plane of LHD plasmas is about 15.5 m. Based on Monte Carlo simulation by a GEANT4 model, the resolution of the DDN energy spectra is 6.6%. When projected onto the neutron rates that are typically obtained in LHD deuterium plasmas (an order of 1015 n/s with neutral beam injection), we expect to obtain the DDN and TBN counting rates of about 2.5 · 105 counts/s and 250 counts/s, respectively. This will allow us to analyze the DDN time-of-flight spectra on time scales of 0.1 s and diagnose the TBN emission rates in several seconds with one instrument, for the first time in helical/stellarator plasmas.journal articl
Consideration of signal to noise ratio for an imaging bolometer for ITER
Get PDF0000-0002-4446-4603An infrared imaging video bolometer (IRVB) is proposed for ITER having a tangential view of the entire ITER cross section. For the initial estimate of the signal level, a 840 m3 plasma is assumed to uniformly radiate 67.3 MW. A more detailed estimate of the signal strength is provided by synthetic images based on radiation data from SOLPS and SANCO models for the edge and core plasma, respectively. The Pt foil used as the radiation absorber would have the dimensions of 7 × 9 cm2 and a thickness of 16 μm that will stop 95% of the radiated power. Two different InSb based IR cameras having a sensitivity of 15 mK are considered for measuring the temperature rise of the foil due to the radiation. The first has 1280 × 1024 pixel2 and a frame rate of 105 fps. The second has 640 × 512 pixel2 and a frame rate of 1000 fps. The resulting IRVBs have 40 × 30 pixel2, 10 ms time resolution, and a signal to noise ratio (SNR) of 17 and 20 × 15 pixel2, 3 ms time resolution, and a SNR of 35, respectively. The synthetic image data give SNRs of 30 and 59, respectively.journal articl
Effects of ion polarization and finite-β on heat transport in slab electron-temperature-gradient driven turbulence
Get PDFORCID 0000-0001-9338-0740Effects of kinetic ions and electromagnetic fluctuations on slab electron-temperature-gradient (ETG) driven turbulence are investigated by means of gyrokinetic simulations covering scales from electron gyroradius to ion gyroradius and electron skin depth. Linear growth rates of electrostatic ETG modes are enhanced by the ion polarization at ion gyroradius scale. Nonlinear simulations show that this low-poloidal-wavenumber instability induces ion-scale eddies which cause heat transport higher than that in the adiabatic ion model. In finite-β plasma, electromagnetic fluctuations stabilize the low-wavenumber modes, and suppress the turbulent heat transport. Additionally, electromagnetic effects also weaken zonal flow generation, which slightly enhances turbulent transport than that in the electrostatic adiabatic ion model.journal articl
Multi-Objective Optimization of Superconducting Linear Acceleration System for Pellet Injection by Using Finite Element Method
Get PDF0000-0001-9924-9241The enhancement of the acceleration performance of a superconducting linear acceleration (SLA) system to inject the pellet container has been investigated numerically. To this end, a numerical code used in the finite element method has been developed for analyzing the shielding current density in a high-temperature superconducting film. In addition, the on/off method and the normalized Gaussian network (NGnet) method have been implemented in the code for the shape optimization of an acceleration coil, and the non-dominated sorting genetic algorithms-II have been used as the optimization method. The results of the computations show that the speed of the pellet container for the current profile of the optimized coil is significantly faster than that for the homogeneous current profile of the coil. However, for the on/off method, the current profile is scattered, whereas the coil shape becomes hollow for the NGnet method. Consequently, the NGnet method is an effective tool for improving the acceleration performance of the SLA system and for obtaining a coil shape that is easy to design.journal articl
Study of an Air-Core High Temperature Superconducting Current Transformer for Large Current Supply
Get PDF0000-0003-1390-4263Large AC current supply is essential for measuring the current transport characteristics of superconducting wires, such as AC loss in helical coil conductors. Commercial current supplies are generally too large and heavy, and therefore, they are inconvenient to use with the superconducting wires. The authors have been studying a small and lightweight large current supply with a high temperature superconducting (HTS) current transformer. An air-core HTS current transformer is suitable for the miniaturization of AC supply because this transformer does not have an iron core and thus does not have large volume and heavy weight. In this paper, we report that the current supply with the air-core HTS current transformer can output large current with high frequency by using the resonance phenomenon. Furthermore, we provide a method for the detection of normal transitions in the transformer by measuring the current transformation ratio of its primary and secondary currents. This detection method is composed of a simple measurement system, and experimental results show the usefulness of this detection method for the air-core transformer.journal articl