119218322
A Resonantly-Excited Disk-Oscillation Model of High-Frequency QPOs of Microquasars
A possible model of twin high-frequency QPOs (HF QPOs) of microquasars is examined. The disk is assumed to have global magnetic fields and to be deformed with a two-armed pattern. In this deformed disk, set of a two-armed ($m=2$) vertical p-mode oscillation and an axisymmetric ($m=0$) g-mode oscillation are considered. They resonantly interact through the disk deformation when their frequencies are the same. This resonant interaction amplifies the set of the above oscillations in the case where these two oscillations have wave energies of opposite signs. These oscillations are assumed to be excited most efficiently in the case where the radial group velocities of these two waves vanish at the same place. The above set of oscillations is not unique, depending on the node number, $n$, of oscillations in the vertical direction. We consider that the basic two sets of oscillations correspond to the twin QPOs. The frequencies of these oscillations depend on disk parameters such as strength of magnetic fields. For observational mass ranges of GRS 1915+105, GRO J1655-40, XTE J1550-564, and H1743-322, spins of these sources are estimated. High spins of these sources can be described if the disks have weak poloidal magnetic fields as well as toroidal magnetic fields of moderate strength. In this model the 3 : 2 frequency ratio of high-frequency QPOs is not related to their excitation, but occurs by chance.
16806997
Spin of Stellar-Mass Black Holes Estimated by a Model of Quasi-Periodic Oscillations
We have proposed in previous papers that the high-frequency pair of quasi-periodic oscillations observed in black-hole binaries with a frequency ratio of 3 : 2 are inertial-acoustic oscillations (nearly horizontal oscillations with no node in the vertical direction) or g-mode oscillations, which are resonantly excited on warped relativistic disks. The resonance occurs through horizontal motions. In this model, the dimensionless spin parameter, a∗ ,o f the central sources can be estimated when their masses are known from other observations. This estimate is done for
118396687
Tidal Instability and Superhump by a Wave-Wave Resonant Model
On a disk deformed to a non-axisymmetric form, a set of oscillations can be excited by their resonant interaction through the disk deformation (Kato et al. 2011). This resonant instability process has been proposed to suggest a possible cause of the high-frequency quasi-periodic oscillations (HF QPOs) observed in black-hole lowmass X-ray binaries. In the present paper, we examine whether the above-mentioned wave-wave resonant process can describe the tidal instability and superhump in dwarf novae. The results show that the process seems to well describe the observations. If this process is really the cause of the tidal instability and superhump, a two-armed oscillation with high frequency roughly on the magnitude of three times the orbital frequency is present on disks, although its expected amplitude may be small.
19434452
Resonant excitation of disk oscillations in deformed disks. VII. Stability criterion in MHD systems
In a disk with an oscillatory deformation from an axisymmetric state with frequency ωD and azimuthal wavenumber mD, two normal mode oscillations with a set of frequency and azimuthal wavenumber being (ω1, m1) and (ω2, m2) are resonantly coupled to each other through the disk deformation when the resonant conditions (ω1 + ω2 + ωD = 0 and m1 + m2 + mD = 0) are satisfied. In the case of hydrodynamical disks, the resonance amplifies the set of the oscillations if (E1/ω1)(E2/ω2) > 0 (Kato 2013b, PASJ, 65, 75), where E1 and E2 are wave energies of the two oscillations with ω1 and ω2, respectively. In this paper we show that this instability criterion is still valid even when the oscillations are ideal MHD ones in magnetized disks, if the displacements associated with the oscillations vanish on the boundary of the system.
14220941
Frequency Correlations of QPOs Based on a Disk Oscillation Model in Warped Disks
In previous papers, we proposed a model that high-frequency quasi-periodic oscillations (QPOs) observed in black-hole and neutron-star X-ray binaries are disk oscillations (inertial-acoustic and/or g-mode oscillations) resonantly excited on warped disks. In this paper we examine whether time variations of the QPOs and their frequenc yc orrelations observed in neutron-star X-ray binaries can be accounted for by this disk-oscillation model. By assuming that a warp has a time-dependent precession, we can well describe the observed frequency correlations among kHz QPOs and low-frequency QPOs over a wide range of frequencies.
118539083
Simultaneous resonant excitation of low-frequency eccentric wave and tilt wave on tidally deformed disks
Simultaneous excitation of low-frequency eccentric precessing mode (one-armed p-mode) and tilt mode on tidally deformed disks is considered. If the orbit of the secondary star is eccentric and its orbital plane is misaligned with the disk plane of the primary, the above-mentioned two low-frequency oscillation modes are simultaneously excited on the primary disk, the former having prograte precession and the latter having retrograde precession. This excitation of disk oscillations is due to a wave–wave resonant excitation process considered by Kato (2013, PASJ, 65, 75). If parameter values relevant to Be/X-ray binary systems are adopted, the periods of these excited oscillations are around 10 times the orbital period of the secondary, which may be comparable with the timescale of giant outbursts observed in Be/X-ray systems.
137990200
Novel field emission scanner for surface study of niobium SRF cavity
Field emission strongly depends on Nb surface properties which are determined by its surface treatment and handling. Novel field emission scanner (FES) developed allows us to measure a distribution of the field emitting sites over a sample surface at a given field strength along with its SEM observation and energy dispersive x-ray analysis. A compact FES head driven by precise 3D stepping motors can be located in a space between the SEM object lens and a sample to be observed. For this reason, the scanner head is not required to be retracted for SEM-EDX observation. This design enabled us to have unique features of in-situ mapping of field emitters with a resolution of 250 nm together with SEM and EDX observation with an imaging resolution of 1.5 nm, vibration-free scanning, quite easy position matching between FES images and SEM images and easy cooperation of the two equipments. Preliminary result of the electropolished Nb surface with a plenty of segregated sulfate particles showed basic performance of this FES. It tuned out that the existence of insulating sulfate grown at Nb surface in electropolishing process would cause blasting of sulfate to deteriorate cavity performance.
523124
Development of a 56 mm aperture superconducting dipole model magnet for LHC
A 56 mm single aperture superconducting dipole model magnet, which is one of the frameworks of the LHC collaboration between KEK and CERN, has been developed. A central field of 8.65 T is provided at a load line ratio of 90% with a 5 block coil wound with NbTi superconducting cables. The magnet has a straight section of 0.8 m and a total length of 1.2 m. The distinctive features of the magnet are a magnetically symmetrical configuration being applicable to the twin aperture magnet and mechanical consideration sharing the magnetic forces with a high manganese steel collar and a horizontally split iron yoke. The magnet showed almost no training at 4.4 K. The first quench current at 1.8 K was 91% of the short sample I/sub c/ and the magnet reached a central magnetic field of 8.8 T. Finally it could be excited with the current of more than 99% of the short sample limit which corresponds to a central field of 9.63 T.
18044790
KEKB performance
The history of the KEKB commissioning is characterized by struggles with three obstacles, namely the electron-cloud instability, the beam-beam blowup and beam current limitations from many reasons. A rapid improvement in the luminosity in this year (2001) has been made by progress in each of these three problems. This report summarizes this year's progress of the KEKB accelerator, since the history of prior days is covered by other reports.
24439340
Direct electron acceleration by stochastic laser fields in the presence of self-generated magnetic fields.
A simple direct acceleration model is proposed, taking into account the stochastic phase disturbance of the coherent driving laser fields. A relativistic single particle simulation shows that plasma electrons are efficiently accelerated far above the ponderomotive energy. The energy and momentum distributions of the accelerated electrons are derived to examine the effects of the self-generated magnetic field on the characteristics of the electron beams. In addition to the beam collimation effect, the magnetic field is found to further enhance the electron acceleration, resulting in the generation of ultrahigh energy electrons.
121673805
Polarimeter System for High-Energy Protons Using Carbon Plate and Liquid Hydrogen
In order to measure recoil proton polarization for the reaction γ+p→π°+p in a wide energy range, a polarimeter system has been constructed using carbon plate and liquid hydrogen as the scatterer. It consists of multi-wire proportional chambers, wire spark chambers, scintillation counter hodoscopes, and scatterers. Carbon plates for lower energy protons and liquid hydrogen for higher-energy protons were used as scatterers. The liquid-hydrogen polarimeter has worked reliably in continuous operation for a long time. The performance of the system in the experiment is described.