Superconducting Dipole Magnet for Strangeness Physics Program at J-PARC

A large-acceptance superconducting dipole magnet is currently under construction for extensive strangeness nuclear physics programs at Japan Proton Accelerator Research Complex (J-PARC), Japan. The conduction-cooled superconducting magnet is composed of two circular coils with a radius of 500 mm, vertically 500 mm apart from each other. This Helmholtz-type magnet was designed to keep the field uniformity Br/By at the level of 1% over the inner region of 500 mm in diameter and 500 mm in height. Our main detector is a time projection chamber that uses parallel E and B fields. If there is a transverse component, drifting electrons would take helical paths due to the E⃗ × B⃗ effect. As a result, the field uniformity is crucial in the design of the magnet. The maximum field strength is 1.5 T. We report our design study and coil test results using a test cryochamber.

I. Introduction

Strangeness degree of freedom opens a new dimension to our evolving picture of nuclei and also to our understanding of quark confinement in hadrons. Hyperons are baryons involving -quark(s) and hypernuclei are nuclei with embedded hyperon(s). Extensive strangeness physics programs have started with the advent of high-intensity hadron beams at J-PARC, Japan. A new E42 experiment [1] aims at searching for a six-quark dihyperon state, called H-dibaryon, in reaction.