Y. Yamanoi

Large horn magnets at the KEK neutrino beam line. II

For pt.I see Yamanoi et al., Proc. on Magnet Technology, p.711 (1997) We report on the status of the latest operation of the horn magnets. Our two types of large horn magnets were installed in the neutrino beam line at the KEK-12 GeV Proton Synchrotron (KEK-PS) and have been operated since March 1999. These two focusing magnets were designed to be excited at pulsed-high currents of up to 250 kA. One of the special characters of our horn magnet is a built-in pion-production target at the most upstream part of the inner conductor. This configuration enable us to increase the neutrino flux as high as possible with low-energy primary protons from the KEK-PS. Our horns have a coaxial-shape structure with a large diameter, i.e. a large volume of the magnetic field, in order to collect as many pions as possible. We estimate that the neutrino flux is enhanced by a factor of 14 by using this horn system. Both horns have been excited over 10/sup 6/ times at pulsed currents of 175 kA-250 kA. Some beginning problems were found in the peripheral apparatus of the horn magnets, and the built-in production target was found have a fatal mechanical damage. In the spring run, the performance of our horn magnet system was almost sufficient as a pion focusing device for a long-baseline neutrino oscillation experiment.

Subthreshold antiproton production in pA, dA and αA reactions

Abstract An enormous enhancement of antiproton production in deuteron- and α-induced reactions has been observed in the subthreshold energy region between 2 and 5 GeV/nucleon. Antiprotons produced at 5.1° with a momentum range of between 1.0 and 2.5 GeV/ c were measured by a beam-line spectrometer and identified by the time-of-flight method. The production cross sections in the deuteron- and α-induced reactions at an incident energy of 3.5 GeV/nucleon were 2 and 3 orders of magnitude larger than those in proton-induced reaction at the same energy. The enhancement in light-ion reactions could not be explained by the internal motion in the projectile and target nuclei. The target-mass dependence (C, Al, Cu and Pb) of the cross sections has also been studied. Further, the cross sections of π and K productions were measured.

Precision positioning of SuperKamiokande with GPS for a long-baseline neutrino oscillation experiment

Abstract A positioning of the neutrino detector SuperKamiokande (SK) was made for a long-baseline neutrino oscillation experiment planned at KEK. For positioning, Global Positioning System (GPS) was employed. It has been demonstrated that GPS is of practical use for measuring the positions of SK and KEK, being 250 km distance from each other, to a better resolution. The geodetic coordinates at the SK center were obtained to be Lat. 36°25′32.5862″ N., Long. 137°18′37.1241″ E., H. 371.839 m in the global ellipsoidal coordinate system, WGS-84. The obtained coordinates are based on the coordinates given at a triangulation point at the KEK site. The present work will be fed back for constructing the neutrino beam line.

Application of Bragg-curve counters to a target multifragmentation measurement

Abstract We have constructed Bragg-curve counters (BCCs) to detect the intermediate-mass fragments (IMFs) emitted during target multifragmentation induced by 12-GeV primary protons on Au, Ag targets. An energy resolution of ∼1.0% and an atomic-number resolution of 2.0% have been achieved. Long-term stability of the output pulse-heights, which was necessary for actual IMF measurements, was realized by employing a continuous gas-flow system with a constant pressure.

Optical design of beam lines at the KEK-PS new experimental hall

Abstract A new counter experimental hall [K.H. Tanaka et al., IEEE Trans. Magn. 28 (1992) 697] was designed and constructed at the KEK 12-GeV Proton Synchrotron (KEK-PS). The extracted proton beam from the KEK-PS is introduced to the new hall through the newly-prepared primary beam line, EP1, and hits two production targets in cascade. The upstream target provides secondary particles to the low momentum ( 0.4–0.6 GeV c ) separated beam line, K5, and the downstream target is connected to the medium momentum (0.6–2.0 GeV/c) separated beam line, K6. Several new ideas were employed in the beam optical designs of EP1, K5 and K6 in order to increase the number and the purity of the short-lived secondary particles, such as kaons and pions, under the limited energy and intensity of the primary protons provided by the KEK-PS. These new ideas are described in this paper as well as the first commissioning results.

Development of radiation-resistant magnet coils for high-intensity beam lines

In connection with the Japanese Hadron Facility (JHF) project, the development of new types of radiation-resistant magnet coils has been continued at KEK. One major program is the design and production of a mineral insulation cable (MIC) with a larger maximum current. We have already developed a 2000A-class MIC having a square-cross-section hollow conductor. A sample magnet coil was fabricated with this MIC. Tests of its stability and reliability are under progress. We are now planning to develop a 3000A-class MIC. The other program is R/D work on a completely inorganic wrapping insulation material which can be used like the usual type glass-fiber tape pre-impregnated with epoxy-resin. After tests of the mechanical strength and electric insulation of many combinations of tapes and bonds, we found a pure (99%>) alumina-fiber tape pre-impregnated with inorganic cement that is suitable for a magnet coil insulator after thermal curing. >

Development of radiation-resistant magnets for the JHF project

In connection with the Japan Hadron Facility (JHF) Project, R&D work on the radiation-resistant magnets has continued at KEK. JHF is the next-generation high-intensity accelerator project of Japan and aims to provide 1 MW 3 GeV/50 GeV proton beams for various fields of science.

Energy spectra and angular distribution of intermediate mass fragments emitted in AuAg(p,X) reactions with Ep = 12 GeV (The first result of the KEK-12GeV-PS experiment; E288)

Abstract The latest results of the first nuclear multifragmentation experiment, E288 [1], at the KEK 12 GeV Proton Synchrotron (KEK-PS) are presented. The energy spectra of intermediate mass fragments (IMFs) were measured inclusively from 30° to 150° with 20° step in the lab. system. Coincidence measurements with one extra IMF emitted toward 90° direction in the opposite hemisphere were performed at the same time. Characteristic sideward flow of IMFs toward 70° direction was found with the usual isotropic component. This isotropic component was trongly suppressed in the coincidence measurement. These facts may indicate the formation of unusually shaped nuclear matter such as an expanding toroid.

Indirectly Cooled Radiation-Resistant Magnets for Hadron Target Station at J-PARC

The target station in the hadron experimental facility at J-PARC consists of a production target and a huge vacuum chamber in which several secondary-beam-line magnets can work. This vacuum chamber system aims to remove the vacuum beam pipe from the magnet gap, because the cooling of the beam pipe is the most serious problem in the high intensity beam facility. We have developed indirectly cooled radiation-resistant magnets for the hadron target station. Their coils are made of solid-conductor type mineral-insulation cables and stainless-steel water pipes. They have the great advantages that electric circuits can be completely independent of water pass. The mechanical strength and the insulation performance of the coil are significantly improved also because the insulation water pipes can be avoided from the water pass. A C-type sector dipole and a figure-8-type quadrupole magnet have been fabricated by using indirectly cooled radiation-resistant magnet technology, and installed in the vacuum chamber. We have succeeded to operate them in vacuum stably with the current of DC 1000 A by improving the end structure of the MIC coils and increasing their emissivity. These magnets have been used for the real beam operation without any serious problems.

Development of radiation resistant magnets for JHF/J-PARC project

A series of the R&D works on the radiation resistant magnets for the Japan Hadron Facility (JHF) project has been continued at the High Energy Accelerator Research Organization (KEK). The JHF is a high-energy part of the Japanese high intensity Particle Accelerator Research Complex (J-PARC), which is Japanese next-generation high-intensity accelerator project. The main JHF accelerator is the 50 GeV proton synchrotron and will provide high intensity 15/spl mu/A proton beam for various nuclear and particle physics experiments. This time, the actual sized completely-inorganic radiation-resistant quadrupole magnet, designed for the 50 GeV proton beam transportation, was manufactured successfully by using mineral insulation magnet cable (MIC). The assembling procedure and the test results are presented in this issue.