135949224
Residual gas analysis and electron cloud measurement of DLC and TiN coated chambers at KEKB LER
For future high-intensity positron or proton accelerators, beam instability caused by electron cloud is one of the most important problems. Some coatings on inner surface of beam chambers with materials having low secondary emission yields such as titanium nitride (TiN), nonevaporable getter and so on have represented good effects against the electron cloud instability. In this study, diamond like carbon (DLC) and TiN coated chambers, and a copper chamber without coating were installed to an arc section of KEKB LER to make comparisons of total pressure, residual gas components and electron cloud activity during the beam operation under the same condition. Residual gas observation for the DLC coating revealed much higher hydrogen gas desorption because a process gas including hydrogen was used for the film growth. No remarkable hydrocarbon gas desorption was found. On the other hand, a mass peak of amu = 14, that is N was prominent in the TiN coating. The electron cloud activity in the DLC coating was lower than the TiN coating and the copper chamber.
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.
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.
122032423
Experiences at the KEK B-factory vacuum system
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.
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.
119113589
Resonant Excitation of Disk Oscillations in Deformed Disks IV: A New Formulation Studying Stability
The possibility has been suggested that high-frequency quasi-periodic oscillations observed in low-mass X-ray binaries are resonantly excited disk oscillations in deformed (warped or eccentric) relativistic disks (Kato 2004). In this paper we examine this wave excitation process from a viewpoint somewhat different from that of previous studies. We study how amplitudes of a set of normal mode oscillations change secularly with time by their mutual couplings through disk deformation. As a first step, we consider the case where the number of oscillation modes contributing to the resonance coupling is two. The results show that two prograde oscillations interacting through disk deformation can grow if their wave energies have opposite signs.
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.
124431523
Strong-interaction form factor of proton in high-energy proton-proton elastic scattering
SummaryAn analysis of high-energy proton-proton elastic-scattering data is made in terms of one-particle exchange type amplitude. The results show that the proton form factor is constant at large momentum transfer. This may be interpreted as evidence for the existence of a pointlike core in the proton.RiassuntoSi esegue un'analisi dei dati dello scattering elastico protone-protone di alte energie in termini dell'ampiezza del tipo dello scambio di una particella. I risultati mostrano che il fattore di forma del protone è costante a grande trasferimento di impulso. Questo può essere interpretato come prova dell'esistenza di un nocciolo puntiforme nel protone.РезюмеВ терминах амплитуды с одно-частичным обменом проводится анализ данных по протон-протонному упругому рассеянию при высоких энергиях. Полученные результаты показывают, что протонный форм-фактор является постоянным при больших передаваемых импульсах. Это можно интерпретировать, как подтверждение существования точечной сердцевины в протоне.
119191781
Resonant Excitation of Disk Oscillations in Deformed Disks. VI. Stability Criterion Revisited
We re-examine the excitation of a set of disk oscillations in a deformed disk by a resonant process. We assume that the disk is deformed from an axisymmetric steady state by an oscillatory deformation with frequency !D and azimuthal wavenumber mD. Then, we consider two normal mode oscillations with a set of frequencies and the azimuthal wavenumber being (!1,m1) and (!2,m2) and satisfying the resonant conditions (!1 +!2 +!D = 0 and m1 +m2 +mD = 0). These oscillations are resonantly excited ifE1E2> 0, whereE1 andE2 are the wave energies of the above two oscillations, when the deformation is maintained by external forces, or has a large amplitude compared with the oscillations. This instability condition is rather general as long as the unperturbed density and pressure vanish on the surface of the system. The possibility of applications to superhumps and negative superhumps in the superoutburst state of dwarf novae are briefly discussed.