Investigation of Ramp-Rate Limitation on the Superconducting Magnet for the Grenoble 40-T Hybrid System

Abstract

The superconducting magnet for the Grenoble 40-T Hybrid system has been tested, up to its guaranteed value of 7 T, on its own and together with the resistive magnet. Although the superconducting magnet has been consistently operated at 7 T several times, it has shown ramp-rate limitations. In particular, when trying to ramp to field in less than 1 hour, premature quenches have been observed. Subsequent measurement of the voltages across the sections of the superconducting coil has revealed the presence of anomalous voltage spikes during ramp-up and ramp-down of the magnet. These spikes have been attributed to the presence of a shorted turn in the superconducting magnet. A theoretical model simulating the shorted turn has been developed and used to reproduce the observed magnet behavior. In particular, by analyzing the relative amplitude of the voltage spikes, we have determined the likely position of the short in the magnet and the amplitude of the current induced in the shorted turn during ramping. In this paper, both theoretical and experimental aspects of the analysis are presented. Finally, the plan of actions to fix the problem is reported.

Cryogenic Design of the 43 T LNCMI Grenoble Hybrid Magnet

“…The ECS is adapted from the former SC magnet [1], [8], [9], [10]. The ECS consists of 5 massive OFHC copper cylinders inserted in a specific shrink cylinder made of stainless steel.…”

The magnet program of the High Field Magnet Laboratory at NCAS

“…A conventional 45T hybrid is operational in Tallahassee [3], and indeed shows all the complications of hybrid magnets mentioned before. The magnet laboratory in Grenoble is still commissioning their hybrid magnet [7]. A SCCF hybrid magnet which would be part of the NCAS is taking advantage of the most modern developments and is expected not to suffer from the problems others experience with earlier technology.…”

A New Design for the Superconducting Outsert of the GHMFL 42+ T Hybrid Magnet Project

“…The present state-of-the-art hybrid magnet system has been built by the NHMFL in Tallahassee, Florida, and has produced the highest DC magnetic field of 45.2 T in a 32 mm warm bore diameter [1]. Unfortunately, the last hybrid coil project of GHMFL (now LNCMI-Grenoble) aiming to produce 40 T failed because of the defectiveness of the superconducting outsert coil [2]. To keep the scientific competiveness Manuscript and attractiveness of the GHMFL, its "Comité de Direction" has decided at the beginning of 2007 to rebuild the defective superconducting outsert coil instead of fully restarting a new project, mostly because of the shorter delivery time scale.…”