118371698
Electron Cloud Effects in the KEK‐PS and the KEK/JAERI Joint Project
An e‐p instability is potentially a serious problem for proton rings in JKJ, which forces us to study the e‐p instability in several high‐intensity proton rings. This work informs JKJ whether we have to take measures to cure the instability. A TiN coating on the chamber surface is one of remedies. Results of SEY measurements performed at KEK are discussed. The observation of electron cloud candidates at the KEK 12 GeV PS Main Ring is also presented.
121897579
Study of timing degradation and light attenuation in long plastic scintillation rods for time-of-flight counters in relativistic heavy ion experiments
Abstract We have studied the timing and light yield characteristics of long and thin scintillator samples of various sizes. Both the light yield and the time resolution degrade exponentially with respect to the distance from one end; the inverse slope parameters for the time resolutions are found to be twice those of the light yield. This is interpreted in terms of a photoelectron statistics picture, which can also explain the observed position dependence of time resolution for time-of-flight counters.
122032423
Experiences at the KEK B-factory vacuum system
86865953
Present Status of KEKB Vacuum System
The commissioning of KEKB (KEK B-factory) started in December 1998. The vacuum system has been working almost satisfactorily. The photon stimulated gas desorption coefficient of copper beam chamber is decreasing steadily and reached to about 2 - 4 × 10 -6
8862999
Recent progress of KEKB
We summarize the machine operation of KEKB during past one year focusing on progress for this period.
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.
120142226
Polarization of recoil neutrons from single-pion photoproduction off protons in the resonance region
Abstract The polarization of the recoil neutrons from the reaction γ p→ π + n was measured at a c.m. angle of 105° for incident photon energies between 675 and 1125 MeV. A scattered π + meson and a recoil neutron were detected in coincidence with a magnetic spectrometer and a neutron polarimeter system using liquid hydrogen. Results are compared with recent phenomenological analyses and the other existing data measured by the double polarization measurement technique.
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.
108290141
Thermal Instability of Advection-Dominated Disks against Local Perturbations
The thermal stability of advection-dominated accretion disks against local perturbations is re-examined in order to correct some errors in our previous paper. Thermal perturbations which are local in the radial direction are found to also be local in the vertical direction. Because of this, the using of vertically integrated quantities was irrelevant in analyzing the stability of local thermal perturbations when the disks are geometrically thick. Our new results, obtained by correcting the error, show that if the turbulence acts as a diffusion process in thermal energy transport, it strongly dampens the thermal perturbations. In these cases when the diffusion process is weak, however, perturbations grow due to a variation of the viscous heating associated with the perturbations. One such example of growth is in the case where radiation pressure greatly dominates the gas pressure.
121801533
New upper limit for the electron antineutrino mass from a third measurement at INS
A third measurement of the electron antineutrino mass by tritium beta decay at INS was carried out after making some improvements for enhancing the counting rate. Langmuir-Blodgett film beta -ray sources with a 5-times larger area (60*200 mm2) than those used in previous measurements were prepared, and a new position sensitive beta -detector with a 6-times larger sensitive area was developed. Using this modified equipment, about 150000 events, more than one order of magnitude higher numbers than in previous measurements, were accumulated in the last 100-eV region below the end-point energy.
17883234
A Vertical Resonance of g-Mode Oscillations in Warped Disks and QPOs in Low-Mass X-Ray Binaries
Resonant oscillations in warped disks are examined in order to explain high-frequency QPOs and horizontalbranch QPOs in low-mass X-ray binaries. Different from our previous work, addressed to the same subjects, we relax in this paper the assumption that the disks are isothermal in the vertical direction. That is, the pressure, density, and temperature are assumed to be distributed in the vertical direction with a polytropic relation, and the polytropic index changes as the disk state changes. By this generalization and by some subsidiaries we can qualitatively explain, within the framework of our resonance model, observed large frequency variations in neutron-star QPOs and little variations in black-hole QPOs. We consider vertical resonances of g-mode oscillations, since they are most appropriate to explain observations.