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.
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.
123854343
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.
122032423
Experiences at the KEK B-factory vacuum system
8862999
Recent progress of KEKB
We summarize the machine operation of KEKB during past one year focusing on progress for this period.
89614487
High energy electron acceleration by stochastic acceleration mechanism
A stochastic acceleration mechanism which explains the high energy electron acceleration by intense laser pulses is analyzed by Fokker‐Planck approach. The Fokker‐Planck equation describing is derived from the equation of motion of electrons interacting with filamented laser field. The time evolution of electron distribution function, energy distribution, effective temperature are obtained for initially rest plasma. The acceleration of 10 MeV electron beam is examined and shown to be effective.
15347243
NONLINEAR RESONANCE IN THE ACCRETION DISK OF A MILLISECOND PULSAR
Two simultaneous frequencies of quasi-periodic millisecond modulation of the X-ray flux (twin kilohertz quasiperiodic oscillations) have recently been detected in an accreting 2.5 ms X-ray pulsar. Their difference, equal to about of the neutron star spin rate, clearly indicates that resonant oscillations of the accretion disk have been 1 2 observed. Similar nonlinear resonances may be spontaneously excited in the accretion disk in the absence of a pulsar, e.g., in black holes. We identify modes of disk oscillations whose frequencies are in agreement with the two observed ones when the rotating neutron star is modeled with realistic equations of state. Subject headings: stars: neutron — X-rays: general On-line material: color figures
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.
120413457
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.
125039861
A superconducting spectrometer for the study of hypernuclei via (π, K+) reactions
SummaryA superconducting kaon spectrometer (INS-SKS) is under construction at Institute for Nuclear Study, University of Tokyo. The spectrometer, with 1/1000 momentum resolution and 100 msr acceptance, has been designed for intensive study of hypernuclei via (π, K+) reactions. It is to be installed in a new experimental hall of the KEK 12 GeV proton synchrotron and is scheduled to be ready for experiments by the end of 1990.RiassuntoUno spettrometro superconduttore a kaoni (INS-SKS) è in fase di costruzione all’Institute for Nuclear Physics dell’Università di Tokyo. Lo spettrometro, con una risoluzione di impulso di 1/1000 e accettanza 100 msr, è stato progettato per uno studio intensivo degli ipernuclei attraverso reazioni (π, K+). Dovrà essere installato in una nuova sala sperimentale del sincrotrone a protoni a 12 GeV del KEK e l’inizio degli esperimenti è previsto per la fine del 1990.РеэюмеВ институте ядерной фиэики при Токийском университете конструируется сверхпроводяший каонный спектрометр (INS-SKS). Спроектирован спектрометр с импульсным раэрещением 1/1000 и акцептансом 100 mcp для исследования гиперядер посредством (π, K+) реакций. Спектрометр смонтирован в новом зкспериментальном эале протонного синхротрона 12 ГзB в KEK. Начало зкспериментов планируется на конец 1990 г.
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.