NIFS-Repository (National Institute for Fusion Science)
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Validation of the distribution of stripping loss neutrals in the accelerator of the negative ion source
Get PDF0000-0001-9781-231XThe difference of the stripping loss between hydrogen and deuterium is examined using two approaches. The first is the measurement of the optical beam emission. The wavelength of beam emission spectrum reflects the energy distribution of beam particles by the Doppler effect. The low-energy stripping peak is observed in the energy band corresponding to the extraction voltage, and also a moderate shoulder is distributed in the lower energy region. Secondly, the spatial and the energy distribution in the accelerator is estimated by the attenuation calculation using the vacuum pressure distribution in the accelerator. Stripping neutrals are concentrated in the low energy region, and a peak is formed at 9 keV in the energy distribution due to stripping neutrals inside the extraction grid aperture. The total stripping loss inside the accelerator is 16% for hydrogen and 24% for deuterium. The calculated Doppler-shifted spectra for hydrogen and deuterium clearly show the peak with the moderate shoulder on the redshift side, which is consistent with the measured results.journal articl
High-efficiency, continuous-wave Fe:ZnSe mid-IR laser end pumped by an Er:YAP laser
Get PDF0000-0001-6930-0843Fe:ZnSe lasers operating in the mid-IR spectral region have gained widespread attention due to their numerous potential applications. This study presents a high-efficiency, continuous-wave Fe:ZnSe laser end pumped by an Er:YAP laser at 2920 nm. The Er:YAP laser was home-constructed and generated an output power of 3.6 W and an average slope efficiency of 36.6% with a good beam quality (M2 ≤ 2). The Fe:ZnSe laser produced a maximum output power of 1 W at 4.06 µm for 2.1 W of absorbed pump power, corresponding to an average slope efficiency of 48%. Theoretical modeling of the continuous-wave Fe:ZnSe laser is presented to determine the prospects for further power scaling.journal articl
Trajectory Shift in Propagation of Electron Cyclotron Waves Due to Berry Curvature in Magnetized Plasma
Get PDF0000-0002-2983-5920The polarization-dependent Hall effect of light was investigated in full-wave simulations for propagation of electron cyclotron waves in magnetized plasma as an anisotropic medium. The transverse shift of the wave packet, which is comparable to the wavelength in the vacuum, was observed in propagation of extraordinary (X) waves under a static magnetic field. This transverse shift is produced by the Berry curvature for the X wave strongly enhanced at the right-hand cutoff. The direction of the transverse shift is perpendicular not only to the gradient of the refractive index but also to the static magnetic field.journal articl
Analysis of the Motional Stark Effect (MSE) diagnostic to measure the rotational transform and current profile in the Large Helical Device
Get PDF0000-0002-5759-0967The analysis method of the Motional Stark Effect (MSE) diagnostic to measure the rotational transform and current profiles in the Large Helical Device has been improved. This was done by using the Variational Moments Equilibrium Code to calculate an equilibrium database for various pressure profiles and current profiles. This method looks for the radial profile of the rotational transform in the equilibrium database that gives the best fit to the polarization angle profiles measured with the MSE diagnostic. This analysis improves the measurements of rotational transform, especially near the magnetic axis, where the sensitivity of the polarization angle measurements becomes low and the uncertainty due to error in the estimation of the Pfirsch–Schlüter current becomes large. The radial profiles of the rotational transform and current profiles for Electron Cyclotron Current Drive and Neutral Beam Current Drive are obtained in the new analysis method with a sufficiently high accuracy to discuss the discrepancy of the current density profiles between the measurements and the calculations.journal articl
Effects of electron cyclotron heating on the toroidal flow in LHD plasmas
Get PDF0000-0002-2197-1506The toroidal force related to electron cyclotron heating (ECH) is investigated in large helical device (LHD) plasmas. When we apply the ECH to the plasma kept by neutral beam injection (NBI) heating, the radial profile of the toroidal flow velocity changes drastically in LHD. ECH-generated supra-thermal electrons can apply forces on the plasma through radial electron current and collisions. We investigate the perturbed electron distribution due to ECH by using the GNET code, which can solve the 5D drift kinetic equation. We also evaluate the electromagnetic force due to radial current and the collisional force driven by ECH. As a result, we find a comparable force driven by ECH to that by NBI heating. The direction of the force is the counter (co) direction radially inside (outside) from the ECH heating location, and these directions correspond with that of experiment results. Finally, we evaluate toroidal flows in ECH and NBI heated plasma solving the radial diffusion equation and compare them with that of experimental observations. We reproduce the co-rotating toroidal flow quantitatively in the balanced-NBI+ECH heated case, but we see a difference in the toroidal flow profiles in the co-NBI+ECH heated case.journal articl
Thermal change of microstructure and mechanical properties of dispersion strengthened tungsten
Get PDF0000-0001-9016-2318Using a mechanical alloying-hot isostatic pressing method, new dispersion strengthened tungsten (DS-W) alloys containing TiO2 particles on grain boundaries have been developed for improvement of plasma facing materials for divertor components of fusion reactors. In this study, effects of the dispersion strengthening on the thermal change of microstructure and the thermal conductivity at high temperature were investigated. Within contrast to pure tungsten, the DS-W did not show significant microstructural change or a drastic decrease of the bending strength after annealing at high temperature.journal articl
Measurements of self-field and voltage for the REBCO stacked tapes assembled in rigid structure (STARS) conductor at 77 K
Get PDFThe measurements of self-fields and voltages for the stacked tapes assembled in rigid structure (STARS) conductor were carried out when the conductor immersed in liquid nitrogen was energized. In the measurements, a 3 m straight line shaped STARS conductor, which is composed of 45 REBCO tapes (15 tapes × 3 rows) embedded in a copper stabilizer, was used as a conductor sample. The measurement results indicate that the ramp rate at the conductor excitation and the one-time thermal cycle of the conductor do not affect the self-fields but the voltages.
The current center position in the conductor cross-section during the conductor excitation was analyzed from the measurement results of the self-fields. The current center position always maintains the same position in the middle of the cross-section during the excitation. The analysis indicates that the current distribution of the STARS conductor is stable during the excitation. In addition, two-dimensional magnetic field calculations were conducted using the various models for the cross-sectional configuration of the STARS conductor. As a result, the calculation results agree with the measurement results regarding the self-fields.journal articl
Evaluation AC Losses in Large-Scale Conductors Consisting of Stacked REBCO Tapes
Get PDF0000-0003-3100-6328In this work, stacked model conductors consisting of dozens of YBCO tapes were fabricated and experimentally investigated to determine whether the hysteresis and coupling losses affect each other. When an oblique magnetic field is applied to the tape, hysteresis and coupling losses are expected to be generated simultaneously. A uniform AC transverse magnetic field was applied to the sample in liquid nitrogen, and the AC losses were measured via the pickup coil method. The measurements were carried with the magnetic field applied at various angles with respect to the tape wide surface. The measured AC losses were separated into hysteresis and coupling losses. The measured hysteresis losses well agreed with the theoretical values for a square cross-section superconductor. This indicates that hysteresis losses can be considered in terms of the magnetic field component perpendicular to the flat face of the YBCO tape. The coupling time constant was found to be independent of the applied magnetic field angle. This shows that coupling losses can be considered in terms of the magnetic field component parallel to the tape's wide surface, and the permeability in the conductor can be assumed to be the vacuum permeability.journal articl
Development of the Molybdenum Millimeter Wave Target Tile for ECRH Antenna Alignment after the Evacuation in LHD
Get PDF0000-0002-4541-1757Alignment of the quasi-optical millimeter wave antenna for the electron cyclotron resonance heating (ECRH) can be required even after the evacuation of the vacuum vessel in fusion oriented plasma experimental devices. We developed a molybdenum millimeter wave target tile and installed it as one of the protection tiles of the vacuum vessel wall of the Large Helical Device (LHD) on the opposite side of the ECRH antennas. Inside the target tile, a sheathed thermocouple is mounted to measure the temperature increase during the millimeter wave injection toward this tile. In magnetic field configurations where neither the first nor the second electron cyclotron resonance (ECR) exists, the measured temperature increased sufficiently to be detected by the millimeter wave injection of approximately 100 kW for 0.1 s toward the target tile. Under the assumption that the distance between the target point that brings the largest temperature increase and the target point just above the thermocouple head gives the offset of the target point to be corrected, the offset of the antenna injection angle was confirmed with an accuracy of 0.4° with changing the target point shot by shot.journal articl
Accelerated/reduced growth of tungsten fuzz by deposition of metals
Get PDFFrom the helium (He) plasma irradiations to tungsten performed in the Magnum-PSI device, the effects of deposition of metals on the helium-plasma induced fiberform nanostructures (fuzz) are discussed. It was found that fuzz was not formed at the center of the plasma cylinder if there were significant metallic impurities from the source. Deposition of metallic impurities (mainly molybdenum and copper) counteracted the growth of fuzz. In addition to the effects of metals from the source, we installed a sputtering source near the sample to replicate the deposition environment in fusion devices. The thickness of fuzzy layer was ∼ 7 μm, which was about five times greater than that without deposition, at the He flux of 1.3 × 1026 m−2, suggesting that the growth rate of fuzz layer was significantly accelerated due to the deposition of tungsten.journal articl