arXiv subjects

T. Kawate

Publications and source records attributed to T. Kawate.

4 recordsLinked to original sources

arXiv2026

Evaluation of spatiotemporal tungsten density profiles using Unresolved Transition Arrays in the Large Helical Device

Tungsten spectroscopic studies have been conducted in the Large Helical Device with a pellet injection technique. Spatiotemporal profiles of tungsten density were evaluated using a space-resolved spectrometer, for plasmas with an electron temperature of below 1 keV and electron density of $10^{19}-10^{20}$ $m^{-3}$. Slice & Stack, a method for reconstructing emissivity, was applied to a line at 191.7 {\AA} , which is a part of the Unresolved Transition Array (UTA) spectrum at 90-250 {\AA}. Tungsten density was obtained using photon emission coefficients of $\mathrm{W}^{17+} - \mathrm{W}^{27+}$, evaluated from collisional-radiative model. The tungsten pellet injected from outside the plasma was first ablated in the edge plasma and subsequently diffused throughout the plasma. This behavior is typical of pellet injection experiments. Furthermore, after an event triggered by NBI breakdown, tungsten accumulated in the core plasma. The radiation power was estimated from the evaluated tungsten density profile and cooling factor dataset, and compared with bolometer measurement. This sequence of processes would be useful for validating atomic data of tungsten ions in low-to-intermediate charge states.

physics.plasm-ph↗

arXiv2017

UV/EUV High-Throughput Spectroscopic Telescope: A Next Generation Solar Physics Mission white paper

The origin of the activity in the solar corona is a long-standing problem in solar physics. Recent satellite observations, such as Hinode, Solar Dynamics Observatory (SDO), Interface Region Imaging Spectrograph (IRIS), show the detail characteristics of the solar atmosphere and try to reveal the energy transfer from the photosphere to the corona through the magnetic fields and its energy conversion by various processes. However, quantitative estimation of energy transfer along the magnetic field is not enough. There are mainly two reason why it is difficult to observe the energy transfer from photosphere to corona; 1) spatial resolution gap between photosphere (a few 0.1 arcsec) and corona (a few arcsec), 2) lack in temperature coverage. Furthermore, there is not enough observational knowledge of the physical parameters in the energy dissipation region. There are mainly three reason why it is difficult to observe in the vicinity of the energy dissipation region; 1) small spatial scale, 2) short time scale, 3) low emission. It is generally believed that the energy dissipation occurs in the very small scale and its duration is very short (10 second). Further, the density in the dissipation region might be very low. Therefore, the high spatial and temporal resolution UV/EUV spectroscopic observation with wide temperature coverage is crucial to estimate the energy transport from photosphere to corona quantitatively and diagnose the plasma dynamics in the vicinity of the energy dissipation region. Main Science Target for the telescope is quantitative estimation for the energy transfer from the photosphere to the corona, and clarification of the plasma dynamics in the vicinity of the energy dissipation region, where is the key region for coronal heating, solar wind acceleration, and/or solar flare, by the high spatial and temporal resolution UV/EUV spectroscopy.

astro-ph.SR↗

arXiv2016

Observations and simulations of the Na I D1 line profiles in an M-class solar flare

We study the temporal evolution of the Na I D1 line profiles in the M3.9 flare SOL2014-06-11T21:03 UT, using high spectral resolution observations obtained with the IBIS instrument on the Dunn Solar Telescope combined with radiative hydrodynamic simulations. Our results show a significant increase in line core and wing intensities during the flare. The analysis of the line profiles from the flare ribbons reveal that the Na I D1 line has a central reversal with excess emission in the blue wing (blue asymmetry). We combine RADYN and RH simulations to synthesise Na I D1 line profiles of the flaring atmosphere and find good agreement with the observations. Heating with a beam of electrons modifies the radiation field in the flaring atmosphere and excites electrons from the ground state $\mathrm{3s~^2S}$ to the first excited state $\mathrm{3p~^2P}$, which in turn modifies relative population of the two states. The change in temperature and the population density of the energy states make the sodium line profile revert from absorption into emission. Analysis of the simulated spectra also reveals that the Na I D1 flare profile asymmetries are produced by the velocity gradients generated %and opacity effects in the lower solar atmosphere.

astro-ph.SR↗

arXiv2009

Multi-Wavelength Observation of Electron Acceleration in the 2006 December 13 Flare

We present a multi-wavelength observation of a solar flare occurring on 2006 December 13 with Hinode, RHESSI, and the Nobeyama Radio Observatory, to study the electron acceleration site and mechanism. The Solar Optical Telescope (SOT) on board Hinode observed elongated flare ribbons, and RHESSI observed double-footpoint hard X-ray (HXR) sources appearing in part of the ribbons. A photospheric vector magnetogram obtained from SOT reveals that the HXR sources are located at the region where horizontal magnetic fields change the direction. The region is interpreted as the footpoint of magnetic separatrix. Microwave images taken with the Nobeyama Radioheliograph show a loop structure connecting the HXR sources. The brighter parts of the microwave intensity are located between the top and footpoints of the loop. We consider these observations as an evidence of the electron acceleration near the magnetic separatrix and injection parallel to the field line.

astro-ph.SR↗