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A high-power coaxial pulse tube cryocooler, originally developed in KEK and technology-transferred to Iwatani Industrial Gases Corp (IIGC), has been installed in a large liquid xenon calorimeter to evaluate liquid nitrogen-free (LN2-free) operation of the rare μ-particle decay experiment (MEG). Features of this pulse tube cryocooler include the cold-end heat exchanger, designed with sufficient surface area to ensure high-power cooling, and a cylindrical regenerator placed inside the pulse tube giving compact design and ease of fabrication. This production-level cryocooler provides a cooling power of ∼200 W at 165 K, using a 6 kW Gifford-McMahon (GM)-type compressor. The paper describes the detailed configuration of the cryocooler, and the results of the continuous LN2-free operation of the large prototype liquid xenon calorimeter, which ran for more than 40 days without problems. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

As a large-scale plasma experimental device is planned and designed, the importance of investigations on irradiation effect of 14 MeV neutron increases and an experimental database is desired to be piled up. Recently, intense streaming of fast neutron from ports are reported and degradation of superconducting magnet performance is anticipated. To investigate the pure neutron effect on superconducting magnet materials, a cryogenic target system was newly developed and installed at Fusion Neutronics Source in Japan Atomic Energy Research Institute. Although production rate of 14 MeV neutron is not large, only 14 MeV neutron can be supplied to irradiation test without gamma ray. Copper wires, superconducting wires, glass fiber reinforced composites are irradiated and the irradiation effects are characterized. At the same time, sensors for measuring temperature and magnetic field are irradiated and their performance was investigated after irradiation. This paper presents outline of the cryogenic target system and some irradiation test results. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Design activity of International Thermonuclear Experimental Reactor clarifies intense neutron streaming from ports for neutral beam injectors. Energy spectrum of the streaming is very wide and 14 MeV neutron and gamma ray are the typical radiations. Large amount of glass fiber reinforced plastics will be used in a superconducting magnet system as an electric insulation material and a support structure, for such organic material is easy to manufacture, and light and cheap. In this report, effects of 14 MeV neutron and gamma ray irradiation on interlaminar shear strength and fracture mode are investigated using G-10CR small specimen of which configuration was proposed as a standard for evaluation of the interlaminar shear strength. A short beam test under three point bending was conducted at room temperature and 77 K. Neutron fluence of 3.91 × 1019 n/m2 was irradiated and the specimens did not show clear degradation of the strength. On the other hand, gamma ray irradiation of 1 MGy made the specimen weaker and 10 MGy caused delamination. Most of the specimens showed both of interlaminar cracking and bending fracture, but some specimens were fractured with irregular shear occurred on the planes connecting loading point and supporting points. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

A new spectrometer has been developed, including a pencil-beam 14-MeV neutron source and a telescope system with two SSDs of ΔE and E, in order to measure double differential charged-particle emission cross sections (DDXs). The spectrometer can supply quite good performance, i.e., low minimum measurable energy of below 2 MeV for alpha particles and a very high S/N ratio over 10. Highly accurate charged-particle emission DDX data can thus be expected to be measured by this spectrometer. From the test measurement for aluminum, the validity was confirmed by comparing the angular differential cross section (ADX) and the total charged-particle emission cross section with other data. Also, the measurement for beryllium has been carried out. From the result of the measurement, the acceptable agreement with the evaluation was confirmed in the energy spectrum. The precise branching ratio of the breakup nuclear reaction of beryllium is now being analyzed from the obtained DDX data. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

The current status of nuclear data evaluations for fusion technologies is reviewed. Well-qualified data are available for neutronics and activation calculations of fusion power reactors and the next-step device ITER, the International Thermonuclear Experimental Reactor. Major challenges for the further development of fusion nuclear data arise from the needs of the long-term fusion programme. In particular, co-variance data are required for uncertainty assessments of nuclear responses. Further, the nuclear data libraries need to be extended to higher energies above 20 MeV to enable neutronics and activation calculations of IFMIF, the International Fusion Material Irradiation Facility. A significant experimental effort is required in this field to provide a reliable and sound database for the evaluation of cross-section data in the higher energy range. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

In order to produce the lower emittance electron beam, the higher field gradient must be used for the gun. From this point of view, we try to develop both of a polarized DC-gun and RF-gun. In case of a 200 keV polarized DC-gun at Nagoya University, the accelerating gradient at the photocathode surface was designed to be 3 MV/m, and the dark current emitted from the SUS electrodes was suppressed below 1 nA. To increase the gradient, we tested the property of pure Titanium as a new electrode material. The tested electrode showed small dark current (∼1 nA) even at field gradient of 88 MV/m, which is as twice as higher than that of SUS electrode. Concerning the feasibility of a polarized RF-gun, it seems difficult for the NEA surface to survive in high field gradient of 100 MV/m. Therefore, we proposed a new type of polarized electron source using two-photon excitation method, for which it is not necessary to use the NEA surface to extract electrons into vacuum. For this method, the polarization higher than 90 % was already demonstrated by the photoluminescence measurement using the bulk GaAs crystal. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

200 keV polarized electron source with load-lock system has been constructed to produce a beam with high peak current and low emittance that are required by a future linear collider. GaAs photocathode was cleaned by atomic hydrogen and dark currents between the electrodes of the gun that degrade an NEA (Negative Electron Affinity) surface of photocathode could be reduced to less than 1 nA at 200 kV. Recent data on photocathode preparation and dark current measurement are reported in this paper. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

Our collaboration group has been conducting the R&D works on the polarized electron source for Japan Linear Collider. The experimental results to produce the high-intensity multi-bunch beam from the superlattice photocathodes are summarized in this report. [ABSTRACT FROM AUTHOR]

We have tested two kinds of spin-polarized electron photocathodes, the GaAs-GaAsP strained layer superlattice and the GaAs-AlGaAs superlattice with distributed Bragg reflector. The experimental results of these photocathodes are briefly reported. [ABSTRACT FROM AUTHOR]

Several samples of GaAs/GaAsP superlattice were fabricated using a method of the Metalorganic Chemical Vapor Deposition (MOCVD) growth for the purpose of investigating various properties as a photocathode of spin-polarized electron sources. The MOCVD growth is easy to control in comparison with the Molecular Beam Epitaxial (MBE) growth in the fabrication procedure of the GaAs/GaAsP superlattices. We used Tertiarybutylarsine (TBAs) and Tertiarybutylphophine (TBP) as V-group sources to make the samples. It is for this reason that the toxicity of TBAs and TBP is lower than that of arsine (AsH[sub 3]) and phosphine (PH[sub 3]) which are commonly used, and the pyrolysis temperature for TBAs and TBP is lower than that for AsH[sub 3] and PH[sub 3]. A large spin-polarization exceeding 90% was observed using the sample made in this method. We also obtained large quantum efficiencies of approximately 0.4% in the wavelength range from 760nm to 780nm. [ABSTRACT FROM AUTHOR]

The field emission dark currents from stainless steel and copper electrodes were measured under DC high field gradient condition. The stainless steel electrode was made from special material called Clean-Z and was polished by electro-chemical buffing. The electrodes achieved 34MV/m with the dark current of 90pA at the gap separation of 1 mm. The copper electrodes were treated by four different types of surface cleaning procedures. The best results were obtained by using the electrode rinsed with ultra-pure water after diamond turning. A field gradient of 47MV/m was achieved with dark current at the level of 1nA, and the microscopic field enhancement factor was estimated to be a very low value of 56. The dark current from this electrode was dependent only on the field gradient at the cathode and not affected by the total voltage applied to the gap. This fact suggests that the surface fabricated by diamond turning method with ultra-pure water rinsing creates few secondary ions by the electron bombardment. [ABSTRACT FROM AUTHOR]

A 200 keV polarized electron gun system with a load lock mechanism has been developed to produce the high-intensity and low-emittance beam required by Japan Linear Collider. The construction of this system has been completed and the performance tests are in progress. Up to now, DC high voltage of 150 kV could be successfully applied to the accelerating electrodes with an extremely low dark current of < 0.1 nA. [ABSTRACT FROM AUTHOR]

Our collaboration group have continued to develop the polarized DC-gun system for future electron-positron linear colliders. In parallel, the feasibility study to develop the polarized RF-gun is planned. As the first step, the test of Cs[sub 2]Te photocathode was performed. [ABSTRACT FROM AUTHOR]

We are constructing a new polarized electron source for Japan Linear Collider. It is designed to operate the gun at 200kV. The "load-lock" mechanism is employed to avoid the dark current due to the Cs accumulation on the electrodes and to exchange the activated NEA photocathode quickly. We have developed superlattice photocathode which has advantages of high spin polarization, high quantum efficiency and high resistance against surface charge limit phenomenon. However, it seems difficult to clean the surface of such a thin layer photocathode by the normal etching procedure without destruction of its delicate structure if it has no As caplayer. Atomic hydrogen is expected to clean the surface of superlattice effectively. We have introduced these techniques to the new source design. [ABSTRACT FROM AUTHOR]