121021517
A honeycomb sandwich structure vacuum jacket for cryogenic targets
Abstract Cryogenic targets (H 2 , D 2 and 4 He) have been built for use in the study of photonuclear reactions with a π sr spectrometer, TAGX, at the 1.3 GeV Tokyo electron synchrotron. A new type of vacuum jacket, fabricated from plastic honeycomb core and Mylar skins, has been used in the target system for more than 5000 hours. The average radiation thickness and the average density of this jacket are measured to be 3.3 × 10 −3 X 0 and 0.15 g/cm 3 , respectively.
119848927
A new type of liquid-3He target system using small mechanical refrigerators
Abstract A new type of liquid- 3 He target has been developed for photoabsorption experiments at intermediate energies. Using the cooling power of liquid 4 He at reduced vapour pressure, 3 He gas is liquefied into a cylindrical target cell of 180 ml and is maintained at 2.0 K during the experiment. Evaporated 4 He gas is evacuated by a rotary pump and returned into the 4 He bath in the cryostat, where two small mechanical refrigerators with cooling capacities of 3 W at 4.3 K and 10 W at 20 K are operated for the purpose of 4 He recondensation. A maintenance-free operation of more than 1000 hours has become possible by adopting the 4 He circulation system.
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.
123710203
Precise measurement of Ag KLM and KLN Auger spectra
Abstract Ag KLM and KLN Auger spectra have been measured with a momentum resolution of 0.02%. With this resolution, most of the lines in these transitions are well separated and the complex spectral structure is revealed. Energies and intensities of these lines are precisely determined and compared with the results of the theoretical calculations.
3231612
Neutral-pion photoproduction on the deuteron.
Large-angle cross sections for ..gamma..d..--> pi../sup 0/d are systematically measured in a photon energy range between 500 and 1000 MeV. A good fit is obtained by use of a Glauber model calculation which includes the dibaryon resonances /sup 3/F/sub 3/(2.26) and /sup 1/G/sub 4/(2.51), but the fit has an unusual nature in the role of resonance and nonresonance contributions.
123100999
Differential cross sections of neutral pion photoproduction from hydrogen in the energy region from 390 MeV to 975 MeV
The differential cross sections of the reaction γp→π0p have been measured at photon energies between 390 MeV and 975 MeV with an energy step of 20 or 25 MeV. The angular region covers 11 angles between 15° and 130° in the c.m.s. A combination of a magnetic spectrometer and photon detector was used for the measurement in the angular region from 50° to 130°. At forward angles of 15°, 35° and 50°, π0 mesons were detected using a π0 detector consisting of a pair of photon detectors. The data obtained with two different detection systems overlap at the angle of 50° and coincide with each other within the experimental error. The results are compared with those of phenomenological partial-wave analyses.
56414452
The vacuum system of KEKB
Abstract For the KEK B-factory, two rings with a circumference of 3016 m , mainly made of copper, were constructed. A gap between the flanges is filled using Helicoflex as a vacuum seal. The contact force of an RF finger in a bellows is assured by using a spring finger. Pumping slots are backed by crossing bars to prevent the penetration of beam-induced fields. To obtain a pressure of 10 −9 Torr with the beam when the photo-desorption coefficient reaches 10 −6 , the design of pump layout is aimed to realize 100 l s −1 m −1 . NEG strips are used as the main pump. Chemical polishing is applied to clean the extruded surface of a copper chamber. Almost all chambers were baked before installation. Only ion pumps were baked in situ. The photo-desorption coefficient at the start of commissioning was slightly higher than expected, but a decrease of the coefficient is as expected on the whole. At high currents, some bellows were found to be warmed by the TE mode of beam induced fields. The effect of the electron cloud became evident, especially in the LER. Direct damage by the beam is seen at the surface of the movable mask.
7967891
Beam-beam effect observed in the KEKB
This report summarizes observed phenomena related to the beam-beam effects in the KEKB collider. A general performance of the beam-beam effect is described. An em- phasis is put on the reduction of the specific luminosity with shorter bunch spacing. ible with the present maximum beam current. The scrub- bing effect of the chamber wall also possibly contributed to suppress the blowup. The present beam current limitation comes from a heating problem in the IR region. Another feature of the KEKB is that working points are very close to the half integer resonance particularly in the horizontal direction as is seen in the table. These horizon- tal tunes make the horizontal emittance large and the hori- zonal beta functions small to a large extent. This large emit- tance compensates the large bunch currents and contributes to stabilize the beams against the beam-beam effect. As is seen in the table, both of the horizontal and vertical tunes of the both rings are located above the half integer resonance, while the vertical tunes are above the integer resonance in the design. In the early days of the KEKB, the vertical tunes were above the integer resonance. In February 2001, the vertical tunes moved to above the half integer based on results of new beam-beam simulations. This change of the tunes brought some increase of the luminosity.
2544869
Thermal equilibria of accretion disks
We show that most of hot, optically thin accretion disk models which ignore advective cooling are not self-consistent. We have found new types of optically thin disk solutions where cooling is dominated by radial advection of heat. These new solutions are thermally and viscously stable.
523124
Development of a 56 mm aperture superconducting dipole model magnet for LHC
A 56 mm single aperture superconducting dipole model magnet, which is one of the frameworks of the LHC collaboration between KEK and CERN, has been developed. A central field of 8.65 T is provided at a load line ratio of 90% with a 5 block coil wound with NbTi superconducting cables. The magnet has a straight section of 0.8 m and a total length of 1.2 m. The distinctive features of the magnet are a magnetically symmetrical configuration being applicable to the twin aperture magnet and mechanical consideration sharing the magnetic forces with a high manganese steel collar and a horizontally split iron yoke. The magnet showed almost no training at 4.4 K. The first quench current at 1.8 K was 91% of the short sample I/sub c/ and the magnet reached a central magnetic field of 8.8 T. Finally it could be excited with the current of more than 99% of the short sample limit which corresponds to a central field of 9.63 T.
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