Quench Protection of a Nb$_3$Sn Superconducting Magnet System for a 45-GHz ECR Ion Source

Abstract

Abstract-Lawrence Berkeley National Laboratory (LBNL) in collaboration with the Institute of Modern Physics (IMP) has developed a Nb3Sn-based superconducting magnet system for a fourth-generation Electron Cyclotron Resonance (ECR) source, with a goal of achieving the magnetic field required for operating at the microwave frequency of 45 GHz. The magnet system is composed of one sextupole magnet inside three solenoids of different sizes manufactured from Nb3Sn round wire. Given the high stored energy density and relatively low wire copper fraction, the coils are not self-protected in the case of a quench. The study of the transient following a quench is carried out by means of the LEDET (Lumped-Element Dynamic Electro-Thermal) program, which includes a detailed simulation of the inter-filament coupling losses developing in the wire. Non-linear effects occurring in the magnet, such as coupling loss and differential inductance reduction, have a significant impact on protecting these magnets. The resulting baseline quench protection strategy based on four independent energy extraction systems protecting the four magnets meets the quench protection requirements. Furthermore, in order to enhance the redundancy of the quench protection system and reduce the peak voltages to ground, the implementation of a CLIQ (Coupling-Loss Induced Quench) system is considered.

Fast time-varying current triggering flux jumps of multi-filamentary Nb3Sn wire exposed to oblique magnetic field

“…As shown in figure 1(a), we consider the thermomagnetic instabilities in a superconducting magnet system consisting of six racetrack coils and three solenoid coils [50][51][52][53]. Unlike the single solenoid coil investigated before [45,46], the magnetic field profile generated by the excitation currents is much more complex in the system investigated here.…”

Superconducting ECR ion source: From 24-28 GHz SECRAL to 45 GHz fourth generation ECR

“…The relevant key technologies need to be prototyped which are being conducted at IMP and XSMT company in Xi'an, China, including coil fabrication, quench protection system, system assembly, and so on. Up to now, sextupole coil fabrication with wire, quench protection, 31 and precise assembly are the most challenging issues to be addressed. A prototype of the FECR magnet consisting of two solenoids and 1/2-length sextupole will be first fabricated and tested in order to verify the designed mechanical structure and accumulate some engineering experiences.…”