M. Minakawa

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.

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.

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 Indirect-Cooling Radiation-Resistant Magnets

In a high-intensity proton beam facility, beam line elements downstream of a production target are exposed to a huge amount of radiation and heat. Beam pipes are closer to the beam than the magnet poles and more difficult to cool sufficiently without tritium production. Therefore, the magnets are placed in a large vacuum chamber, instead of using vacuum pipes located within the pole gaps. We have adopted indirect-cooling mineral-insulation-cable (MIC) coils for these magnets. They have a great advantage that the mechanical strength and the insulation performance can be significantly improved by avoiding the use of ceramic insulation pipes, because electric circuits are completely separated from water passages. We have made coils using 1000-A-class solid-conductor MICs and stainless-steel pipes, and tested magnet operation in vacuum. By improving the structure of end parts of MICs and increasing their emissivity, we have successfully fed the current of DC 1000 A to the solid-conductor MIC coils in vacuum.

The Beam-Handling Magnet System for the J-PARC Neutrino Beam Line

The facility of the long baseline neutrino oscillation experiment using the J-PARCs 50 GeV-0.75 MW proton beam is now under way. The primary proton beam line consists of three sections, i.e. the first preparation (PP) section with normal conducting magnets, the second arc (ARC) section with superconducting magnets and the third final focus (FF) section with normal conducting magnets. In the PP section, we have to clean the primary proton beam extracted from the 50 GeV-PS and transport halo-less pure beam only to the ARC section. In the FF section the magnets have to be placed very close to the pion production target and horns. Therefore the normal conducting magnets have to work in the very high radioactive environment. The R&D works on the radiation resistant magnets for handling a high-intensity proton beam have already been continued at KEK as reported in . Another important point regarding high-intensity beam handling is to realize easy maintenance of the beam line. Any magnet experiencing trouble can be easily removed from beam line and repaired remotely. For this purpose, we developed new tools for the magnet maintenance. These are automatic sling apparatus, quick alignment and installation guide, and the quick disconnect devices of cooling water and electric power. In this paper, we will report the beam line maintenance scheme developed for the neutrino beam line, as well as the design of normal conducting magnet sections

Development of residual gas ionization profile monitor for high intensity proton beams

Nondestructive beam profile monitor utilizing ionizations of residual gas has been developed for continuous monitoring of 3/spl times/10/sup 14/ protons at Japan Proton Accelerator Research Complex (J-PARC). Knock-on electrons produced in the ionizations of residual gas vacuumed to 1 Pa are collected with a uniform electric field applied between electrodes. Applying a uniform electric field parallel to the electric field is essential to reduce diffusion of electrons crossing over magnetic flux. A prototype monitor has been constructed and installed in EP2-C beam line at KEK 12 GeV proton synchrotron (12 GeV-PS). The profiles measured with the present monitor agree with the ones measured with the existing destructive profile monitor. The present monitor shows sufficient performances as a candidate of the profile monitor at J-PARC. In the present article, the working principle of the present monitor, the results of test experiments, and further developments are described in detail.

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.

Magnet Operation in Vacuum for High Radiation Environment Near Production Target

In a high-intensity proton beam facility, beam line elements downstream of a production target are exposed to a huge amount of radiation and heat. A water-cooled beam collimator must be located between the target and the magnets, and the iron yokes of the magnets also have to be cooled by water. Moreover, beam pipes are closer to the beam than the magnet poles and more difficult to cool sufficiently without tritium production. Therefore, the magnets are placed in a large vacuum chamber, instead of using vacuum pipes located within the pole gaps. In order to reduce the residual radiation dose during maintenance, the chamber lid and feedthroughs are 4 meter above the beam line, and radiation-shielding blocks are also stacked in the chamber. We have tested magnet operation in vacuum using a dipole magnet with mineral-insulation-cable (MIC) coils and a nickel-coated yoke. A magnet with 2500-A-class hollow-conductor MIC coils has worked successfully with the current of DC 3000 A. The stability of operation in vacuum was confirmed by measuring the temperature with thermocouples and the magnetic field with a NMR probe. We have also succeeded in operating a 1000-A-class solid-conductor MIC coil in vacuum

The K1.8BR spectrometer system at J-PARC

A new spectrometer system was designed and constructed at the secondary beam line K1.8BR in the hadron hall of J-PARC to investigate

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

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