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Time-dependent plasma transport simulation for the study of edge impurity radiation dynamics with magnetic island in large helical device
Get PDFThe dynamics of impurity radiation distribution during detachment transition with edge magnetic island induced by the application of resonant magnetic perturbation (RMP) is studied numerically by solving time-dependent plasma fluid equations together with impurity and neutral transports in a 2D grid system. Computations provide the appearance of a macroscopic structure in the heat transfer along the island separatrix and outside the island. The resultant parallel temperature gradient generates the plasma flow and the density gradient according to the parallel momentum balance. The resulting plasma flow effectively transports impurity towards the X-point region. As a result, the impurity radiation is more intense near the X-point than in the vicinity of the O-point. This leads to the predominant cooling of the region around the X-point. These results are in agreement with experimental observation with RMP application in the large helical device (LHD). The time scale of the thermal condensation instability is found to be of the order of 10 ms.journal articl
MHD stability of JT-60SA operation scenarios driven by passing energetic particles for a hot Maxwellian model
Get PDF0000-0002-6114-0539We analyze the effects of the passing energetic particles on the resistive ballooning modes (RBM) and the energetic particle driven modes in JT-60SA plasma, which leads to the prediction of the stability in N-NBI heated plasma. The analysis is performed using the code FAR3d that solves the reduced MHD equations describing the linear evolution of the poloidal flux and the toroidal component of the vorticity in a full 3D system, coupled with equations of density and parallel velocity moments for the energetic particle (EP) species assuming an averaged Maxwellian EP distribution fitted to the slowing down distribution, including the effect of the acoustic modes. The simulations show the possible destabilization of a TAE with a frequency (f) of 115 kHz, a TAE with f = 98 kHz and a 6/4 or 7/4 BAE with f = 57 kHz in the ITER-like inductive scenario. If the energetic particle β increases, beta induced Alfven Eigenmodes (BAE), toroidal AEs (TAE) and elliptical AEs (EAE) are destabilized between the inner-middle plasma region, leading to the overlapping of AE of different toroidal families. If these instabilities coexist in the non-linear saturation phase the EP transport could be enhanced leading to a lower heating efficiency. For a hypothetical configuration based on the ITER-like inductive scenario but an center peaked EP profile, the EP β threshold increases and several BAEs are destabilized in the inner plasma region, indicating an improved AE stability with respect to the off-axis peaked EP profile. In addition, the analysis of a hypothetical JT-60SA scenario with a resonant q = 1 in the inner plasma region shows the destabilization of fishbones-like instabilities by the off-axis peaked EP profile. Also, the EPs have a stabilizing effect on the RBM, stronger as the population of EP with low energies (below 250 keV) increases at the plasma pedestal.journal articl
Collective Thomson scattering with 77, 154, and 300 GHz sources in LHD
Get PDF0000-0003-2410-7550Collective Thomson scattering (CTS) is one of attractive diagnostics for measuring locally and directly the fuel temperature and the velocity distribution of fast ions in fusion plasmas. A mega-watt class source of millimeter or sub-millimeter waves is required to detect a weak scattered radiation superimposed on background radiation owing to electron cyclotron emissions (ECEs) from plasmas. Based on electron cyclotron resonance heating (ECRH) system with the frequencies of 77 GHz and 154 GHz in the Large Helical Device (LHD), the CTS diagnostic system has been developed to measure bulk ion temperatures from a few keV to ∼10 keV and fast ions originated from 180 keV-neutral beam injection in the LHD. The measured CTS spectra and their time evolutions are analyzed with the electrostatic scattering theory. The bulk ion temperatures obtained from CTS spectra increase with the neutral beam injections and decrease with the heating terminated. The velocity map of simulated fast ions explains that the bumps on tail of measured CTS spectra are caused by the co- and counter- fast ions. A new prescription for anisotropic velocity distribution function is proposed. As for 154 GHz bands, the CTS spectrum broadenings for D and H plasmas are distinguished reasonably at the same temperature, and its ion temperatures are comparable to those of the charge exchange recombination spectroscopy. As reactor-relevant diagnostics, a 300 GHz gyrotron and a corresponding receiver system have been implemented in LHD to access high density plasmas with low background ECEs. The recent progress for CTS diagnostics and their spectrum analysis with the probe frequencies of 77 GHz, 154 GHz, and 300 GHz in the LHD experiments is described.journal articl
Improved performance of electron cyclotron resonance heating by perpendicular injection in the Large Helical Device
Get PDF0000-0002-2983-5920A real-time interlock system for power injection in electron cyclotron resonance heating
(ECRH) was developed to be applied to Large Helical Device (LHD) plasma. This system
enabled perpendicular injection, thus improving the performance of ECRH more than has ever
been achieved before in LHD. Perpendicular propagation of the electron cyclotron wave at
77 GHz became more insensitive to the effect of refraction in comparison to the conventional
oblique propagation. The achieved central electron temperature in the case of perpendicular
injection was approximately 2 keV higher than that in the case of standard oblique injection
for a central electron density of 1 × 1019 m−3 by 1 MW injection.With such improved
performance of ECRH, high-density ECRH plasma of 8 × 1019 m−3 was successfully
sustained after the injection of multiple hydrogen ice pellets for the first time in LHD.journal articl
Fast-ion D alpha diagnostic with 3D-supporting FIDASIM in the Large Helical Device
Get PDF0000-0003-2985-060XFor understanding the physics of energetic particles, the deuterium experimental campaigns
started in Large Helical Device (LHD) from March 2017. To investigate the behavior of
energetic particles, a Fast-ion D Alpha (FIDA) diagnostic was installed on the LHD. In the
FIDA diagnostic, the Doppler-shifted D alpha light from fast-neutrals are utilized as signals of
energetic particles, where these fast-neutrals are produced by the charge exchange process
between fast-ions in the plasma and actively injected neutrals by neutral beam (NB). The
advantages of the FIDA diagnostic are the velocity and the spatially resolved measurement of
fast-ions at the crossing point between its line of sight (LOS) and the incident line of NB. The
most recent FIDASIM is enhanced to simulate signals produced in three-dimensional magnetic
configurations. The new version of FIDASIM uses the fast-ion distribution function produced
by GNET as input to simulate FIDA signals at LHD. In order to validate the new version of the
code, measurements of radial profiles of fast-ions using the FIDA diagnostic are performed in
magnetohydrodynamic (MHD)-quiescent plasmas. The measured spectra are in good agreement
with the theoretical prediction by 3D-supporting FIDASIM at the center of the plasma
(R = 3.5 m~3.7 m, reff/a99 = −0.28~0.05) on the LHD when the line averaged electron density
is ne_avg < 1.23 × 1019 m−3. On the other hand, the measured spectra are in disagreement with
the theoretical prediction by 3D-supporting FIDASIM at even the center of the plasma when the
line averaged electron density is ne_avg ≥ 1.23 × 1019 m−3.journal articl
Enhancement of an E parallel B type neutral particle analyzer with high time resolution in the Large Helical Device
Get PDFIn order to study fast ion confinement and transport mechanisms both in quiescent plasmas and in the presence of magneto-hydrodynamic (MHD) activity, an electric field parallel to the magnetic field type neutral particle analyzer (E||B-NPA) was installed using Micro-Channel Plates (MCPs) in the Large Helical Device (LHD). The E||B-NPA is an established diagnostic used to measure the energy distribution of charge exchange neutral particles escaping from plasmas corresponding to hydrogen, deuterium, and tritium, respectively. The LHD deuterium experimental campaign started in 2017. To obtain more details of MHD behavior, we improved on time resolution performance of the E||B-NPA using a high-speed Pre-Amplifier and Discriminator (PAD) and Latching Scaler Module (LSM). For the last LHD experimental campaign, the E||B-NPA was installed on nearly the equatorial plane of the vacuum chamber to measure the passing energetic particles generated by tangentially injected neutral beams. As the results of the E||B-NPA commissioning, it is confirmed that the E||B-NPA successfully detected the energetic particles and obtained the energy distributions corresponding to hydrogen. Also, the effect of the neutron to E||B-NPA is estimated using the other neutron diagnostics during the experiments.journal articl
Modeling of the resonant magnetic perturbation effect on detachment in the Large Helical Device
Get PDF0000-0002-9536-9841An approach to describe the plasma parameter variation with the effective minor radius across the edge region in the heliotron Large Helical Device (LHD) in configurations without and with a resonant magnetic perturbation (RMP) is elaborated, by averaging fluid equations for transport of particles, momentum and heat over the flux surfaces. Numerical solutions of one-dimensional, time-dependent equations derived and analytical estimates performed allow us to interpret the LHD experiments on the density limit. Calculations reproduce qualitatively the principal difference between situations without and in the presence of RMP: in the former case a thermal collapse of the discharge occurs immediately after the plasma detachment from the divertor target plates at a radiation level of 0.4–0.5; in the latter the radiating layer is localized at the plasma edge even if the power radiated exceeds 90% of the input power. A prominent role for such a behavior of plasma particle flows along magnetic field lines perturbed by RMP, leading to a positive radial gradient of the plasma density inside the magnetic island, is demonstrated.journal articl
Current Distribution Optimization by Using Genetic-Algorithm Based On-Off Method: Application to Pellet Injection System
Get PDFThe current distribution in the electromagnet is optimized by using the genetic-algorithm based on-off method so as to maximize the acceleration performance of the Superconducting Linear Acceleration (SLA) system. In the SLA system, a pellet container is accelerated by the interaction between a shielding current density and an applied magnetic field. By using the equivalent-circuit model, the distribution of the shielding current density is approximated as a set of the multiple current loops. In contrast, the current distribution in the electromagnet is represented by means of the on-off method. As the method for optimizing the current distribution in the electromagnet, two types of genetic algorithms are adopted. The results of computations show that the pellet velocity for the optimized current distribution is 1.3 times as fast as that for the homogeneous current distribution.journal articl
Hydrogen Isotope (H2 and D2) Sorption Study of CHA-Type Zeolites
Get PDF0000-0001-8883-4373Using either single H2 and D2 or H2-D2 mixed gases, the sorption abilities of CHA (chabazite)-type zeolites ion-exchanged with K, Na, or Ca were studied at 77, 201, and 250 K. The LTA (Linde Type A) (3A) and FAU (faujasite)-type zeolites were also examined for comparison. The pore diameters in these materials were found to decrease on the order of FAU > Ca-CHA > [K-CHA, Na-CHA, and LTA(3A)]. The quantities of D2 adsorbed on these zeolites were larger than the amounts of H2. At higher temperatures, the CHA-type zeolites having smaller pores exhibited superior D2/H2 selectivity compared with the LTA(3A) and FAU, suggesting that hydrogen isotope separation using zeolites is affected by pore size.journal articl
Interactive Exploration of the In-Situ Visualization of a Magnetohydrodynamic Simulation
Get PDF0000-0003-0433-668XWe propose a new visualization method for large-scale computer simulations called “4D Street View”. This method uses omnidirectional in-situ visualization cameras to record a simulation from multiple viewpoints. The omnidirectional video dataset produced by the simulation is then analyzed interactively. In this paper, we apply the method to a magnetohydrodynamics turbulence simulation with 64 viewpoints to prove that it is possible to achieve interactive in-situ visualization for supercomputer simulations. Three types of in-situ visualization by omnidirectional cameras (with 4π steradian solid angle) from each viewpoint are applied. At the end of the simulation, a video dataset with 192 omnidirectional video files is produced. We demonstrate that we can change the viewing position, angle, and applied visualization method interactively using a specially designed application program.journal articl