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Effects of the resonance modification by electron cyclotron current drive on the linear and nonlinear dynamics of energetic particle driven magnetohydrodynamics modes in Heliotron J
Get PDFORCID 0000-0001-7332-037XThis study investigates the effects of electron cyclotron current drive (ECCD) on the linear and nonlinear dynamics of energetic-particle (EP)-driven magnetohydrodynamics (MHD) instability (mode) in Heliotron J (HJ), using MEGA, a nonlinear hybrid EP-MHD simulation code. The effects of ECCD are included through the modification of the equilibrium magnetic field. Five MHD equilibria with plasma currents (Ip) of −2.00, −1.00, 0.00, 0.50, and 1.00 kA are considered, where negative and positive Ip represent counter and co-ECCD, respectively. To account for the EP finite charge-exchange loss observed in HJ, a bump-on-tail velocity distribution is assumed for EP. The study finds that the stabilization trends in terms of the linear growth rate (γω−1A ) are qualitatively similar to the FAR3D linear simulation and experimental results. In addition to the enhancements of the local magnetic shear and continuum damping by ECCD as proposed in previous studies, the study suggests that changes in the linear EP and shear Alfvén wave resonance are another important factor, especially for the n/m = 1/2 mode.
The study shows that in the currentless equilibrium, the high-velocity toroidicity-induced resonance between the n/m = 1/2 mode and the co-passing EP (L = −1) has the highest EPjournal articl
Effects of bootstrap current on magnetic configuration in Chinese first quasi-axisymmetric stellarator
Get PDFhttps://orcid.org/0000-0002-0424-645XNeoclassical properties in quasi-axisymmetric (QA) stellarators are analogous to these in tokamaks. Consequently, a substantial bootstrap current could significantly modify the MHD equilibrium properties of a QA stellarator, which is an important characteristic in this type of stellarator. This paper is dedicated to systemically investigate the effects of bootstrap current on the magnetic configuration in Chinese first quasi-axisymmetric stellarator (CFQS). For the first
time, self-consistent bootstrap currents in free-boundary equilibria are calculated with an accurate Fokker–Planck neoclassical numerical mode in CFQS. Several important results are achieved: (a) as the bootstrap current grows with increasing volume-averaged normalized pressure β, magnetic shear develops in the bulk plasma and meanwhile, a deep magnetic well is robustly sustained, which leads to improved stabilization of interchange modes up to β ∼ 2.0%. (b) In the analysis of global ideal MHD instability, as the bootstrap current rises to 39 kA (β ∼ 1.3%), external kink modes become destabilized and the unstable mode with m/n = 2/1 is dominant. (c) From β = 0 to 1.5%, the bootstrap current hardly changes the QA property and a low neoclassical transport is maintained. However, as β is enhanced beyond 2.0%, the substantial bootstrap current gives rise to an increase of non-QA magnetic field components, which weakens the neoclassical transport properties. (d) An increase of the negative magnetic shear at the core region by the bootstrap currents has a favorable effect on the properties of J (second adiabatic invariant). The maximum-J region can be extended by raising bootstrap
currents.journal articl
New Q and V-band ECE radiometer for low magnetic field operation on LHD
Get PDF0000-0001-5473-2109To meet the demand for information on electron temperature fluctuations in low magnetic field experiments in the Large Helical Device (LHD), a new ECE radiometer covering the Q and V bands has been installed. Combination mirrors are installed in the vacuum vessel to focus the beam and efficiently propagate the radiated electron cyclotron waves. Notch filters are used to eliminate stray light from the gyrotron, and a 32-channel heterodyne radiometer is constructed using a filter bank system. As a result, oscillations of electron temperature and both electromagnetic and electrostatic fluctuations were successfully observed.journal articl
Study of the intermittent plasma structure around the divertor simulation experimental module in GAMMA 10/PDX
Get PDF0000-0002-8025-008XWe have investigated the generation region of intermittent plasma structures, which could be due to the blob-like cross field transport around the divertor simulation experimental module (D-module) in the tandem mirror device GAMMA 10/PDX. A positive skewness of the ion saturation current was clearly seen when the electrode of the movable probe was located at the radial edge and just in front of the entrance limiter of the D-module. Fourier analysis and conditional averaging clarified that positive spikes intermittently appeared in the same region. This is the first indication that the phenomenon producing the high-density isolated plasma structures occurred in the upstream of the D-module. A negative skewness was also found, and large amplitude fluctuation was detected between regions showing positive and negative skewness. Furthermore, this and light emission fluctuations become stronger during the transient state from attached to detached state on the V-shaped target.journal articl
Non-ideal MHD growth of current interchange tearing modes at plasma edge and response to externally-imposed flow
Get PDF0000-0001-5668-6900Current interchange tearing modes (CITMs) have been proposed to explain an intermittent eruption of electric current toward a divertor at an edge region of a tokamak device. Extended magnetohydrodynamic (MHD) simulations combined with the Scrape-Off-Layer diffusion model, which has been developed by the authors [Miura et al., Phys. Plasmas 24, 092111 (2017)], are carried out in order to study the growth of a CITM under influences of two-fluid and gyro-viscous effects, or non-ideal MHD effects. Numerical simulations both with and without an externally imposed azimuthal flow show that the growth of a CITM is observed for a relatively small flow velocity, and that a CITM can be a candidate mechanism for the intermittent eruption of the current in a tokamak, whether the growth is under influences of non-ideal MHD effects or not. The growth can be suppressed when an externally imposed azimuthal flow is sufficiently large to cause a finite radial displacement because such a displacement prevents a transition from an interchange to a tearing mode that is the key process of a CITM. Furthermore, it is also found that a stripe pattern similar to so-called streamers is formed in the course of the CITM growth. The basic nature of this streamer-like structure is also presented.journal articl
Sensitivity of Gaussian energy broadening function of MCNP pulse height spectra on CLYC7 scintillation detector
Get PDFThe Cs2LiYCl6:Ce crystal (CLYC) is an inorganic scintillator which has been developed for the γ-ray and neutron measurement with the high detection efficiency, high resolution, and no need unfolding technique. To enhance the measurement of the fast neutron, the CLYC with 7Li-enrichment (CLYC7) scintillator is developed. In this work, the response of the CLYC7 detector to γ-ray is obtained using 137Cs γ-ray calibration source and calculated using Monte Carlo N-Particle transport code (MCNP). A comparison of measured and calculated γ-rays spectra is complicated by the fact that physical radiation detectors have finite energy resolution. In this study, we treated detector energy resolution effect by Gaussian energy broadening (GEB) in MCNP pulse height spectra calculation. We observe the parameters in the GEB function which provides simulation spectrum matches the experiment spectrum, especially on the photopeak region. The detail sensitivity of GEB function on CLYC7 scintillation detector is presented in this work.journal articl
Active Control of Alfvén Eigenmodes by Externally Applied 3D Magnetic Perturbations
Get PDF0000-0002-3237-5195The suppression and excitation of Alfvén eigenmodes have been experimentally obtained, for the first time, by means of externally applied 3D perturbative fields with different spatial spectra in a tokamak plasma. The applied perturbation causes an internal fast-ion redistribution that modifies the phase-space gradients responsible for driving the modes, determining, ultimately their existence. Hybrid kinetic-magnetohydrodynamic simulations reveal an edge resonant transport layer activated by the 3D perturbative field as the responsible mechanism for the fast-ion redistribution. The results presented here may help to control fast-ion driven Alfvénic instabilities in future burning plasmas with a significant fusion born alpha particle population.journal articl
Phase-space tomography in magnetically confined plasmas
Get PDF0000-0001-5669-1937In this paper, a tomography approach aiming at reconstructing a phase-space structure is proposed. For the phase-space resolved diagnostic system, a signal must be decomposed in real-space, velocity-space, and time; therefore, it is challenging to obtain a sufficiently high signal intensity in a single detector bin. To overcome this difficulty, three different sets of data having different integration directions in real-space, velocity-space, and time are simultaneously used, and a reconstruction of the original structure in the phase-space is attempted by a tomographic manner. The proposed method is demonstrated using a synthetic dataset in the actual diagnostic setup in the Large Helical Device. Time evolution of a phase-space perturbation induced by the Landau damping, which is caused by energetic particle-driven magnetohydrodynamic bursts, is successfully reconstructed by this method. Robustness against realistic diagnostic noise is also presented.journal articl
ブロンズ法Nb3Sn線材における内部補強による機械特性の改善 ―固溶強化機構による内部マトリックス補強―
Get PDF0000-0002-5112-3065We approached the internal matrix reinforcements using the Cu-Sn-Zn and Cu-Sn-In ternary bronze alloy matrices. After Nb3Sn phase synthesis, these ternary bronze alloy matrices were transformed into（Cu, Zn）or（Cu, In）solid solutions having much higher mechanical strength. Jc degradation due to the transverse compressive stress on the internal matrix reinforced Nb3Sn multifilamentary wire was evaluated. No Jc degradation was observed at approximately 100 and 150 MPa, which values were much higher than the conventional bronze processed Nb3Sn wire. We found that the internal matrix reinforcement was effective for suppressing Jc degradation due to transverse compressive stress.journal articl
Change in Critical Surface of Nb3Sn Wire by Neutron Irradiation
Get PDFNeutron irradiation on Nb3Sn wire changes its superconducting properties. It is well known that the critical current increases by the irradiation once and then decreases by further irradiation. In this paper, the effective upper critical magnetic field and the critical temperature of the irradiated Nb3Sn wire were investigated, and the mechanism that causes such changes were discussed qualitatively by focusing on the role of the irradiation defects together with the normal metallurgical flaws. In addition, a critical surface was taken up and the general tendency of the change in the surface was discussed.journal articl