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.
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.
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.
17631509
Quasi-Periodic Oscillations Resonantly Induced on Spin-Induced Deformed-Disks of Neutron Stars
We consider the situation where a spin-induced wavy perturbation is present on disks of neutron-star low-mass X-ray binaries. By non-linearly coupling with the perturbation, some modes of disk oscillations resonantly interact with the disks. We examine the resonant conditions under the assumption that the disks are vertically isothermal. The results show that when the spin frequency has some particular values, resonant coupling occurs at some radii. The modes and frequencies of these resonant oscillations are summarized. Some of these resonant oscillations seem to explain the frequencies of the observed kHz QPOs in objects of which the spin frequency is known.
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
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.
122772838
Test results of a single aperture 10 tesla dipole model magnet for the Large Hadron Collider
A single aperture dipole magnet has been developed with a design magnetic field of 10 tesla by using Nb-Ti/Cu conductor to be operated at 1.8 K in pressurized super fluid helium, The magnet features double shell coil design by using high keystone Rutherford cable and compact non-magnetic steel collars to be adaptable in split/symmetric coil/collar design for twin aperture dipoles. A design central magnetic field of 10 tesla has been successfully achieved in excitation at 1.95 K in pressurized superfluid helium. Test results of the magnet with a summary of the design and fabrication are presented.
100337653
VARIOUS RINSING EFFECTS TO MITIGATE CONTAMINANTS BROUGHT BY BCP ON NIOBIUM SRF CAVITY SURFACE
Various rinsing processes have been widely used after the surface treatment for niobium cavities. After the chemical treatment of the cavities some residues from the etching acids are left on the surface. To examine rinsing effects in detail, we carried out BCP experiment followed by post-polishing methods on a series of niobium samples at KEK. As a result of the BCP process [1,2] some contaminants like fluorine, carbon, etc. have been detected at the surfaces which may be the prominent cause of limiting the performance of SRF cavities. To remove these contaminants, various rinsing processes such as ultra pure water rinse, ultrasonic pure water rinse, alcoholic rinse, detergent rinse, high pressure water rinse (HPR) have been used after the BCP. In this article, we report the effect of HPR with different high pressures on the contaminants. The surface of the samples treated with HPR was analyzed using X-ray photo-electron spectroscopy.
121317828
MEASUREMENT OF POLARIZATION IN K$sup +$p ELASTIC SCATTERING AT 1.37, 1.45, 1.71, AND 1.89 GeV/c AND PHASE-SHIFT ANALYSIS.
123873319
Experimental observations of the ion-related coupled bunch instability in a bunch train in TRISTAN AR
An experiment was carried out in TRISTAN AR for the search of the fast beam-ion instability (FBII). A train of 100 bunches with 2 ns spacing was stored with the help of the transverse bunch feedback system. The nitrogen gas was intentionally leaked into the inside of the vacuum duct to enhance the ion effect. The oscillation patterns were recorded by the beam position monitor system which is capable of storing the transverse position of every bunch up to 1600 turns. The spectra of the bunch oscillations were also measured by a spectrum analyzer. This paper describes the results of the experiment and also discusses the possible explanation of them in terms of the FBII.
54716814
Performance of KEKB with crab cavities
20 years after they were initially proposed, in February 2007 crab cavities are for the first time installed in an operating collider, KEKB. The commissioning of KEKB with crab cavities is reported, and the performance of the collider is compared with the performance without crab cavities and with the beam-beam simulation. Operational experience of the crab cavities with beams is described.