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.
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Recent progress of KEKB
We summarize the machine operation of KEKB during past one year focusing on progress for this period.
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Experiences at the KEK B-factory vacuum system
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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
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.
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GENERATION OF HIGH-ENERGY ELECTRON BEAM BY LASER-PLASMA ACCELERATOR
An energy gain of the monoenergetic component of electrons γ were successfully increased to 25 MeV by decreasing an electron density ne to 4 × 1019cm-3 and increasing a laser power PL to 4 TW. An empirical scaling law of the energy gain of γ ∝ PL/ne was derived from the experiment. A forward scattering spectrum of the laser pulse showed anti-Stokes satellite peaks up to third-order harmonics around a second harmonic light and a Stokes satellite peak around a laser wavelength, which indicated that a wakefield was excited in a self-modulation laser wakefield regime. A density modulation of wakefield was estimated at 60 ± 10 % from intensity ratios of satellite peaks. The empirical scaling law well agrees with results obtained at other institutes by using higher laser power of 10 ~ 30 TW.
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Coherent bremsstrahlung from the internal target of the 1.3 GeV electron synchrotron
Abstract A Si single crystal has been mounted on the conventional internal target holder of the 1.3 GeV electron synchrotron at the Institute for Nuclear Study, Tokyo. The energy spectrum measured with the pair spectrometer has a clear enhancement due to the coherent bremsstrahlung process. The linear polarization of the photon beam thus obtained is estimated to be 27% and 10% at the photon energy of 200 and 540 MeV, respectively.
118498018
An Attempt to Describe Frequency Correlations among kHz QPOs and HBOs by Two-Armed Nearly Vertical Oscillations
We examine whether the two-armed ($m=2$) vertical p-mode oscillations trapped in the innermost region of magnetized accretion disks with finite disk thickness can describe kHz QPOs and HBOs in LMXBs. First, we derive the frequency-frequency correlation of the two basic oscillations (both are fundamental modes in the vertical direction, but one is the fundamental and the other the first overtone in the radial direction), and compare it with the observed frequency correlation of twin kHz QPOs. Results show that the calculated frequency correlation can well describe observed correlation with reasonable values of parameters. Second, we examine whether the observed frequency correlation between kHz QPOs and HBO can be described by regarding HBO as the first overtone oscillation in the vertical direction (and the fundamental in the radial direction). The results suggest that i) innermost parts of disks on the horizontal branch are strongly diminished in their vertical thickness (presumably by hot coronae) and ii) the branch is roughly a sequence of variations of magnetic fields or disk temperature.
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.
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Correlated Frequency-Changes of Trapped Vertical p-mode Oscillations and kHz QPOs
AbstractWe have examined the frequencies of trapped two-armed (m = 2) nearly verticaloscillations (vertical p-mode) in vertically isothermal disks with toroidal magneticﬁelds. The magnetic ﬁelds are stratiﬁed so that the Alfv´en speed, c A , is constant inthe vertical direction. We have particularly focused our attention on how frequenciesof the fundamental mode (n r = 0) and ﬁrst overtone (n r = 1) in the radial directionchange with correlation, when theratioc 2A /cs changes, c s beingthe isothermal acousticspeed. The results show that in the case where the oscillations are fundamentalmode (n=1) in the vertical direction, the correlated frequency changes of the above-mentioned oscillations seem towell describe, withstandard values ofthe mass andspinof the central sources, the frequency correlation of kHz QPOs observed in neutron-starX-ray binaries.Key words:accretion, accrection disks — quasi-periodic oscillations — verticalp-mode oscillations — waves — X-rays; stars1. IntroductionMany authors now think that the kilo-hertz quasi-periodic oscillations (kHz QPOs) ob-served in low-mass X-ray binaries (LMXBs) are some kinds of disk oscillations in a strong gravi-tational ﬁeld. Understanding their origin is of importance, since it will become a promising toolto evaluate the mass and spin of the central sources as well as the disk structure surrounding thesources. Many models of kHz QPOs related to disk oscillations and waves have been proposed.None of them, however, can suﬃciently well describe the observed frequency correlation of thetwin kHz QPOs (Lin et al. 2010).As one of possible models of kHz QPOs, for example, we proposed a disk-oscillationmodel in deformed disks (Kato and Fukue 2006), based on the fact that in deformed disks aset of oscillations with positive and negative wave energies are excited resonantly (Kato 2004,1
121185850
New lead glasses for Cherenkov counters
Abstract Attempts have been made to improve the characteristics of glasses suitable for Cherenkov counters of the total-absorption type. Many kinds of new lead glasses were prepared and examined in the transmittance, radiation lengths, and methods of manufacturing. Several kinds of glass blocks having the dimension of 65 × 65 × 235 mm 3 were manufactured successfully. The transmittance of one of the new glasses is higher than the usual lead glass of F-2 ∗ . It was also found that the discoloration of the new glasses is smaller than the usual lead glasses upon irradiation of 60 Co γ rays of 10 4 to 10 7 Roentgens. The Cherenkov counters of the total-absorption type with the new glasses, together with the ones with usual lead glasses of F-2, SF-2, SF-5, and SF-6, were tested by using electron beams with energies from 300–1000 MeV. It was found that the energy resolution of the first ones is better by a few percents than that of the latter in the whole energy region.