458 research outputs found
Nonlinear simulation of resistive ballooning modes in the Large Helical Device
Nonlinear simulations of a magnetohydrodynamic (MHD) plasma in full three-dimensional geometry of the Large Helical Device (LHD) [O. Motojima et al., Phys. Plasmas 6, 1843 (1999)] are conducted. A series of simulations shows growth of resistive ballooning instability, for which the growth rate is seen to be proportional to the one-third power of the resistivity. Nonlinear saturation of the excited mode and its slow decay are observed. Distinct ridge/valley structures in the pressure are formed in the course of the nonlinear evolution. The compressibility and the viscous heating, as well as the thermal conduction, are shown to be crucial to suppress the pressure deformations. Indication of a pressure-driven relaxation phenomenon that leads to an equilibrium with broader pressure profile is observed
Dynamics of spherical tokamak plasma on the internal reconnection event
Nonlinear magnetohydrodynamic (MHD) simulations are executed to investigate the dynamical behavior of the relaxation phenomenon observed in spherical tokamak (ST) plasma that is known as the Internal Reconnection Event (IRE). The simulation results successfully reproduce several key features of IRE, and the physical mechanisms are revealed. A sudden collapse of the pressure profile takes place as a result of a nonlinear time development of a pressure-driven instability. A magnetic reconnection induced between the internal and the external magnetic field is found to play a crucial role in determining the nature of the overall process, namely, the rapid expulsion of the plasma heat energy due to the pressure imbalance along the reconnected field lines, and the large distortion in the overall shape. The resultant deformations in overall shape of the plasma are in good agreement with the experimental observations
Suzaku and XMM-Newton Observations of the Fornax cluster: Temperature and Metallicity Distribution
Suzaku observed a central region and five offset regions within 0.2 r180 in
the Fornax cluster, a nearby poor cluster, and XMM-Newton mapped the cluster
with 15 pointings out to 0.3 r180. The distributions of O, Mg, Si, S, and Fe in
the intracluster medium (ICM) were studied with Suzaku, and those of Fe and
temperature were studied with XMM. The temperature of the ICM gradually
decreases with radius from 1.3 keV at 0.04 r180 to 1 keV at 0.2-0.3 r180. If
the new solar abundances of Lodders et al. (2003) and a single-temperature
plasma model are adopted, O, Mg, Si, S, and Fe show similar abundances: 0.4-0.6
solar within 0.02-0.2 r180. This Fe abundance is similar to those at 0.1-0.2
r180 in rich clusters and other groups of galaxies. At 0.2-0.3 r180, the Fe
abundance becomes 0.2-0.3 solar. A two-temperature plasma model yields ICM
abundances that are higher by a factor of 1.2-1.5, but gives similar abundance
ratios among O, Mg, Si, S, and Fe. The northern region has a lower ICM
temperature and higher brightness and Fe abundance, whereas the southern region
has a higher ICM temperature and lower brightness and Fe abundance. These
results indicate that the cD galaxy may have traveled from the north because of
recent dynamical evolution. The cumulative oxygen- and iron-mass-to-light
ratios within 0.3 r180 are more than an order of magnitude lower than those of
rich clusters and some relaxed groups of galaxies. Past dynamical evolution
might have hindered the strong concentration of hot gas in the Fornax cluster's
central region. Scatter in the IMLR and similarity in the element abundances in
the ICM of groups and clusters of galaxies indicate early metal synthesis.Comment: 15 pages, 13 figures, accepted for publication in PAS
Metallicity of the Fossil Group NGC 1550 Observed with Suzaku
We studied the temperature and metal abundance distributions of the
intra-cluster medium (ICM) in a group of galaxies NGC 1550 observed with
Suzaku. The NGC 1550 is classified as a fossil group, which have few bright
member galaxies except for the central galaxy. Thus, such a type of galaxy is
important to investigate how the metals are enriched to the ICM. With the
Suzaku XIS instruments, we directly measured not only Si, S, and Fe lines but
also O and Mg lines and obtained those abundances to an outer region of ~0.5
r_180 for the first time, and confirmed that the metals in the ICM of such a
fossil group are indeed extending to a large radius. We found steeper gradients
for Mg, Si, S, and Fe abundances, while O showed almost flat abundance
distribution. Abundance ratios of alpha-elements to Fe were similar to those of
the other groups and poor clusters. We calculated the number ratio of type II
to type Ia supernovae for the ICM enrichment to be 2.9 +- 0.5 within 0.1 r_180,
and the value was consistent with those for the other groups and poor clusters
observed with Suzaku. We also calculated metal mass-to-light ratios (MLRs) for
Fe, O and Mg with B-band and K-band luminosities of the member galaxies of NGC
1550. The derived MLRs were comparable to those of NGC 5044 group in the r<0.1
r_180 region, while those of NGC 1550 are slightly higher than those of NGC
5044 in the outer region.Comment: 11 pages, 7 figures, accepted for publication in PAS
X-ray Halo Around the Spiral Galaxy NGC 4631 Observed with Suzaku
Suzaku observation of the edge-on spiral galaxy NGC 4631 confirmed its X-ray
halo extending out to about 10 kpc from the galactic disk. The XIS spectra
yielded the temperature and metal abundance for the disk and the halo regions.
The observed abundance pattern for O, Ne, Mg, Si and Fe is consistent with the
metal yield from type II supernovae, with an O mass of about 1E6 Msun contained
in the halo. These features imply that metal-rich gas produced by type II
supernova is brought into the halo region very effectively, most likely through
a galactic wind. Temperature and metal abundance may be affected by charge
exchange and dust. An upper limit for the hard X-ray flux was obtained,
corresponding to a magnetic field higher than 0.5 uG.Comment: 8 pages, 11 figures, will be published in PAS
Study of the Intracluster and Intergalactic Medium in the Sculptor Supercluster with Suzaku
We studied the high temperature plasma in the direction of the Sculptor
supercluster at z=0.108 with Suzaku. Suzaku carried out four observations in
the supercluster: namely, A2811, A2811 offset, A2804, A2801 regions in 2005
Nov.--Dec., including the regions beyond the virial radii of these clusters.
The study needed precise background estimation because the measured intensity
of the redshifted lines, especially those from oxygen, were strongly affected
by the the Galactic emission. The spectra taken in the regions outside of the
virial radii of the member clusters were used as the background which included
both the Galactic and Cosmic X-ray Background (CXB) components. We also used
the background data which were taken near the Sculptor supercluster.
Temperature and metal abundance profiles were determined to the virial radii of
the member clusters, and then we searched for the oxygen line emission in the
region outside of the virial radii of the clusters. As a result, the
temperature of the clusters decreased toward the virial radii, and the spectral
fits for the filament region did not require extra component other than the
Galactic and CXB components. We constrained the intensities of O VII and O VIII
lines to be less than 8.1 and 5.1 photons cm^-2 s^-1 arcmin^-2, respectively,
as 2-sigma upper limits. The intensity of O VII indicates n_H < 1.6e-5 cm^-3
(Z/0.1 Z_solar)^-1/2 (L/25 Mpc)^-1/2, which corresponds to an over density,
delta < 60 (Z/0.1 Z_solar)^-1/2 (L/25 Mpc)^-1/2.Comment: 11 pages, 8 figures, accepted for publication in PAS
- …