Observation of distorted Maxwell-Boltzmann distribution of epithermal ions in LHD

A distorted Maxwell-Boltzmann distribution of epithermal ions is observed associated with the collapse of energetic ions triggered by the tongue shaped deformation. The tongue shaped deformation is characterized by the plasma displacement localized in the toroidal, poloidal, and radial directions at the non-rational magnetic flux surface in toroidal plasma. Moment analysis of the ion velocity distribution measured with charge exchange spectroscopy is studied in order to investigate the impact of tongue event on ion distribution. A clear non-zero skewness (3rd moment) and kurtosis (4th moment –3) of ion velocity distribution in the epithermal region (within three times of thermal velocity) is observed after the tongue event. This observation indicates the clear evidence of the distortion of ion velocity distribution from Maxwell-Boltzmann distribution. This distortion from Maxwell-Boltzmann distribution is observed in one-third of plasma minor radius region near the plasma edge and disappears in the ion-ion collision time scale

Electron temperature profile collapse induced by double-odd-parity MHD mode in the Large Helical Device

In this paper, we report new results of a beam switching experiment aiming at a reversed magnetic shear profile formation for the study of an MHD-mode-induced profile collapse event. A transient MHD mode, whose oscillation frequency chirps down, is observed. The electron temperature profile collapse is induced by the mode activity, leading to the flattening of the central electron temperature profile. The radial mode structure is the double-oddparity at the beginning, but it transits to the even-parity in its final stage. The central electron temperature profile recovers after the radial mode structure changes to the even-parity, even though the mode itself does not disappear

Response of plasma toroidal flow to the transition between nested and stochastic magnetic field in LHD

Response of the plasma toroidal flow to the forward and backward transition between the nested and the stochastic magnetic field is studied using the charge exchange spectroscopy in the large helical device (LHD). Abrupt damping of toroidal flow associated with a transition from nested magnetic flux surface to a stochastic magnetic field is observed when the magnetic shear at the rational surface decreases to 0.5 after the exchange of the neutral beam injection (NBI) direction from co- to counter-direction in LHD. The stochastization of magnetic field occurs only in a narrow range of magnetic shear near 0.5 and spontaneousback-transition from stochastic to nested magnetic field (healing) is observed in the steady-state phase of magnetic shear. When the NBI direction is changed from counter- to co-direction, the healing of magnetic field occurs associated with the increase of magnetic shear

Distorted magnetic island formation during slowing down to mode locking in helical plasmas

We report the first observation of the formation of a magnetic island before the occurrence of mode locking in helical plasma. New analysis and observation techniques applied to the ECE signal and poloidal flow in LHD experiments yield the following results. (i) A magnetic island structure is present, rotating at the end of the rotating phase. (ii) The rotation speed of the island is not uniform in space and time. The rotation of the island changes significantly at the end of the rotating phase, and the deformation increases until the mode is locked

W-band millimeter-wave back-scattering system for high wave number turbulence measurements in LHD

A 90 GHz W-band millimeter-wave back-scattering system is designed and installed for measuring electron scale turbulence (kρs ∼ 40). Ametal lens relay antenna is used for in-vessel beam focusing, and a beam diameter of less than 40mm is achieved in the plasma core region.This antenna can be steered at an angle of 159○ ± 6○, which almost covers the plasma radius. The estimated size of the scattering volume is ∼105mm at the edge and 135mm at the core, respectively. A 60m corrugated waveguide is used to achieve a low transmission loss of ∼8 dB. A heterodyne detection system for millimeter-wave circuits with probing power modulation can distinguish the scattered signal frombackground noise

Isotope effect in transient electron thermal transport property and its impact on the electron internal transport barrier formation in LHD

In this study, we perform a comprehensive comparison of the transport hysteresis width in deuterium (D) plasmas, hydrogen (H) plasmas, and D-H mixed plasmas. The core focused modulation electron cyclotron resonance heating (MECH) is applied as the heat source perturbation, and the heat flux is evaluated using the energy conservation equation with the measured electron temperature response and the ECH deposition profile calculated by the ray-tracing scheme. Systematic density scan in plasmas with different ion mass reveals that there is no significant isotope effect in their hysteresis width. It is found that plasmas with heavier isotope mass can easily form the electron internal transport barrier. As the hysteresis width is insensitive to the isotope mass, the classical part of the diffusivity is considered to be responsible for the isotope effect in the transport barrier formation

Effects of HLA-DRB1 alleles on susceptibility and clinical manifestations in Japanese patients with adult onset Still’s disease

BackgroundHLA-DRB1 alleles are major determinants of genetic predisposition to rheumatic diseases. We assessed whether DRB1 alleles are associated with susceptibility to particular clinical features of adult onset Still’s disease (AOSD) in a Japanese population by determining the DRB1 allele distributions.MethodsDRB1 genotyping of 96 patients with AOSD and 1,026 healthy controls was performed. Genomic DNA samples from the AOSD patients were also genotyped for MEFV exons 1, 2, 3, and 10 by direct sequencing.ResultsIn Japanese patients with AOSD, we observed a predisposing association of DRB1*15:01 (p = 8.60 × 10−6, corrected p (Pc) = 0.0002, odds ratio (OR) = 3.04, 95% confidence interval (95% CI) = 1.91–4.84) and DR5 serological group (p = 0.0006, OR = 2.39, 95% CI = 1.49–3.83) and a protective association of DRB1*09:01 (p = 0.0004, Pc = 0.0110, OR = 0.34, 95% CI = 0.18–0.66) with AOSD, and amino acid residues 86 and 98 of the DRβ chain were protectively associated with AOSD. MEFV variants were identified in 49 patients with AOSD (56.3%). The predisposing effect of DR5 was confirmed only in patients with AOSD who had MEFV variants and not in those without MEFV variants. Additionally, DR5 in patients with AOSD are associated with macrophage activation syndrome (MAS) and steroid pulse therapy.ConclusionThe DRB1*15:01 and DR5 are both associated with AOSD susceptibility in Japanese subjects. A protective association between the DRB1*09:01 allele and AOSD was also observed in these patients. Our data also highlight the effects of DRB1 alleles in susceptibility to AOSD

Effects of core stochastization on particle and momentum transport

The effects of the stochastic magnetic field in a plasma center produced by electron cyclotron current drive (ECCD) on transport have been revealed. Because the electron temperature profile is flat in the core region, in the case of counter-directed ECCD (ctr-ECCD) against the toroidal magnetic field, the magnetic field is stochastic in the core region with rotational transform ᵼ ∼ 1/3. The particle diffusion coefficient of the ctr-ECCD plasma is approximately 20 times as large as that of the plasma without the stochastic magnetic field produced by co-directed ECCD (co-ECCD) at the maximum. Furthermore, in the stochastic magnetic field with ctr-ECCD, counter-directed intrinsic rotation is observed in the plasma with balanced NBI discharge