Magnetic Field Measurement System in Superconducting Combined Function Magnets for the J-PARC Neutrino Beam Line

Magnetic field measurements have been performed for the first full-scale magnet system assembled with the cryostat for the J-PARC proton beam line of neutrino experiment. In the measurement system, the probe position with respect to magnet central axis is measured by a Helium Neon laser and a position sensitive detector, PSD, in order to obtain an exact dipole field strength. Errors associated with the PSD misalignment and influences on the PSD signals by the magnetic field were evaluated. The measured dipole components approached to the design values by compensating those with the probe position. The latest beam simulation indicated that the measured values of magnetic field were good enough for the primary proton beam transport.

I. Introduction

A Next generation long-baseline neutrino oscillation experiment is planned to study the fundamental nature of neutrinos [1], [2]. It will require the proton beam to be extracted from J-PARC, a 50 GeV, 0.75 MW proton accelerator jointly built by JAEA and KEK. The beam line which guides the proton beam to the production target of secondary particles consists of 28 superconducting combined function magnets [3], [4]. The magnets in the cryostat are cooled below 5 K by forced flow supercritical helium. The magnet system have been successfully developed and tested at KEK, and the quench and thermal performance of the magnet system are almost consistent with the design [5], [6].