Hiromi Hirabayashi

Radiation damage of BGO crystals due to low energy γ rays, high energy protons and fast neutrons

Abstract Results are presented on the effects of radiation on BGO crystals. It is shown that BGO has more than two orders of magnitude higher resistance against low energy γ rays than SF5 lead glass. Darkening of the crystal is hardly visible even after an irradiation of 3.6 × 10 6 R. The darkening faded by more than one half after several days and it has almost completely disappeared after much longer periods. The tolerable rate of synchrotron radiation on BGO calorimeters is 100 R/h in a conservative estimate if the degradation in transmittance is required to be less than 1 % over a depth of 20 radiation lengths. In BGO calorimeters, the degradation of scintillation efficiency is less important than that of the transmittance, 99.999% pure crystals have a two orders of magnitude better resistance than 99.99% pure ones. Sample darkening caused by 12 GeV protons or fast neutrons is an order of magnitude more severe than that by low energy γ rays. Moreover, the recovery is not complete even after a period of more than 100 days. Some data on sample activation are also presented.

Feasibility of Hydrogen Cooled Superconducting Magnets

It looks feasible to realize hydrogen cooled superconducting magnets with High Tc Superconductors (HTS) and newly discovered magnesium di-boride (MgB2). As is well known, liquid and slush hydrogen between 15~20 K, could be not only an excellent refrigerant for HTS and MgB2, but also a clean energy transporter without exhaust of carbon di-oxide. HTS cooled by liquid hydrogen at 22 K can carry as large as several times current at 77 K cooled by liquid nitrogen. These are reasons why liquid hydrogen is preferable for SMES refrigerant to liquid nitrogen. One of such possibilities, an emergent power supply composed with SMES, Liquid Hydrogen Storage, Fuel Cell and Lithium Battery is designed and proposed. As a practical example, the conceptual design of 200 MW, 10 hour emergency power supply is described

AC loss measurements of Rutherford type superconducting cables under mechanical stresses

Experimental apparatus for measurements of AC losses in Rutherford type cable conductors has been constructed. A number of compacted cable samples have been measured. Hysteresis loss, loss from coupling within strands and loss from interstrand coupling are distinguished from each other. The results show that even for cables without soldering and coating, the AC losses may be quite different from each other due to interstrand coupling loss. As the curing temperature increases, interstrand coupling loss tends to increase. For some cables, interstrand coupling loss increases nearly geometrically with the increase of curing temperature. Most of the samples did not show dependence of loss on mechanical pressure.<<ETX>>

Design of SMES System With Liquid Hydrogen for Emergency Purpose

The emergency power supply system, which is composed of a SMES system cooled by liquid hydrogen and a fuel cell (FC), is proposed as a backup for supplying electricity to hospitals, high-rise office buildings, and intelligent equipment. The capacity of the system is 2 MW for 10 hours. At a power failure, the SMES immediately functions to supply electric power at start-up for 60 seconds, and then after the FC generates electricity for 10 hours. Since the system is designed to be driven with liquid hydrogen and oxygen, it can be installed to any isolated spaces like spaceships, tunnels, and so on. The development scenario, that an 1-kW prototype, an 100-kW module as a basic unit and then a practical system will be developed step by step, is proposed. The system can be rather flexible for load requirements by adjusting the composition of the basic modules.

Liquid Hydrogen Cooled Superconducting Magnet and Energy Storage

The earth faces environmental problems such as temperature increase and energy crisis. One of the solutions for the problems may be to put hydrogen energy to practical use. Superconducting devices for power applications are promising technologies for saving energy. By convergence of high temperature superconductors (HTS) or MgB2 and liquid hydrogen, advanced energy systems can be introduced to power applications. We have proposed an emergency power supply system in combination with an HTS or MgB2 magnet (SMES) cooled with liquid hydrogen and fuel cells for hospitals, intelligent buildings, advanced factories like semiconductor industry, and so on. The superconducting magnet has merits of fast time response and high input/output electric power. On the other hand, the liquid hydrogen can store energy with high density and the fuel cell can supply electricity with high efficiency. The combination of these devices produces synergistic effects for environmentally friendly and energy saving measures. The development schedule and design for the prototype of the emergency power supply system are described.

Low-energy separated beam K3 at KEK

The design and the performance of the K3 beam at the KEK 12 GeV Proton Synchrotron are reported. The beam line provides separated kaons up to a maximum momentum of 0.8 GeV/c and separated antiprotons up to 1.1 GeV/c. The beam can be operated in two different modes: a high-intensity mode, K3-S, and a high-momentum-resolution mode, K3-L. The solid-angle momentum acceptance and the beam length of K3-S are 48.4 msr Δ PP and 14.45 m, respectively, and those of K3-L are 13.3 msr%ΔPP and 16.3 m. Measured optical parameters of K3-S agreed with the designed values. Measured intensity of K+ per 1012 protons and the π+μ+e+K ratio were 1.96 × 104 and 4.2 at 500 MeV/c, 3.12 × 104 and 3.0 at 540 MeV/c, and 5.18 × 104 and 2.6 at 600 MeV/c.

Measurement of a Cross Section for the 27Al(p, 3pn)24Na Reaction at 12 GeV

The cross section for the 27 Al(p, 3pn) 24 Na reaction was measured at 12 GeV in order to establish the calibration method of intensity monitors of the 12 GeV primary proton beam at KEK. The measured cross section of 8.1±0.9 mb is consistent with other measurements performed in energy regions close to 12 GeV.

Measurement of Propagation Velocities of the Normal Zone in a 1 mφ×1 m Superconducting Solenoid Magnet

Propagation velocities of the normal zone in a 1 m×1 m superconducting solenoid magnet were unambiguously measured as a function of the magnet excitation current by inducing quenches with a heater. The magnet was built to study the feasibility of constructing thin, large solenoid magnets and it has a single layer aluminum-stabilized NbTi/Cu superconductor of 269 turns. The ratio of Al:NbTi:Cu of the conductor is 24:1:1. The design current of the conductor is 4.5 kA at 1.5 Tesla. Measured velocities are 30, 65, and 90 m/s in the direction of the conductor at 2020, 3030, and 3540 A, respectively. Thermal distributions inside the coil after quenches were quite uniform and no local overheating was observed.

Development of Large Keystone Angle Cable for Dipole Magnet with Ideal Arch Structure

Compacted strand cables of NbTi with large keystone angle have been developed for applications to superconducting dipole magnets of big hadron collider accelerators. The trial-fabricated cables have the keystone angle of 1.6 to 3.0 degrees and the packing factor of 90 to 95 %. Strands of 0.808 mm in diameter with the filament diameters of 4.8 and 6 μm were used. The fabrication of those cables has not met with serious problems. The degradation measurements of the critical current have been performed and the degradation less than 3 % is observed up to the angle of 3.0 degrees for the cables with the packing factor of 90 %.

A NbTi Superconducting Dipole Magnet Installed in a Pressurized Helium II Cooling Bath

A double-bath pressurized helium II cryostat for an accelerator NbTi test dipole was constructed. Heat leakage into the cryostat was 5 W at 1.8 K. The dipole was excited in the cryostat. After several quenchings in pressurized helium II, the dipole achieved a highest central field of 6.75 T with an excitation current of 6.6 kA.