Magnet quench during a training run

1. UPDATE ON THE MODIFICATION AND TESTING OF THE MICE SUPERCONDUCTING SPECTROMETER SOLENOIDS* S. Virostek, M. Green, N. Li, T. Niinikoski, H. Pan, S. Prestemon and M. Zisman Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA on behalf of the MICE Collaboration Abstract: The Muon Ionization Cooling Experiment (MICE) is an international effort sited at Rutherford Appleton Laboratory, which will demonstrate ionization cooling in a segment of a realistic cooling channel using a muon beam. A pair of identical, 3-m long spectrometer solenoids will provide a 4-tesla uniform field region at each end of the cooling channel. The emittance of the beam as it enters and exits the cooling channel will be measured within the 400 mm diameter magnet bores. The magnets incorporate a three-coil spectrometer magnet section and a two-coil section that matches the solenoid uniform field into the MICE cooling channel. The cold mass, radiation shield and leads are kept cold by means of a series of two-stage cryocoolers and one single-stage cryocooler. Previous testing of the magnets had revealed several operational issues related to heat leak and quench protection. A quench analysis using Vector Fields software and detailed heat leak calculations have been carried out in order to assess and improve the magnet design. Detailed analyses of the eddy currents, temperature distribution and stresses in a modified radiation shield design have been carried out as well. Details of the analyses and resulting magnet design modifications along with an update of the magnet assembly progress will be presented here. INTRODUCTION SHIELD ANALYSES COLD MASS COIL ASSEMBLY MICE consists of two spectrometer solenoids and a cooling channel. Muon ionization cooling occurs in three LH2 absorbers in the cooling channel, and the muons are reaccelerated by eight RF cavities. Scintillating fiber detectors in the solenoid bores measure the incoming and outgoing muonemittance. • Each magnet consists of five superconducting coils wound on a common 2923 mm long aluminum mandrel • Match Coils 1 and 2 operate as a focusing doublet to match the beam to the adjacent AFC modules • The spectrometer (End 1, Center, End 2 Coils) generate a 4Tuniform field over a 1m long, 0.3m dia. volume Several analyses were carried out to assess the integrity of the new 1100 aluminum radiation shield Spectrometer Solenoid #1 Eddy currents during quench MAGNET QUENCH ANALYSIS Stress during quench and shipping Magnet quench during a training run Steady state temperature distribution QUENCH RESISTOR COOLING 3D quench model of the spectrometer solenoid coils • The internal passive quench resistors were thermally damaged during previous testing • A larger than expected amount of energy was deposited in the resistors when one of the cold leads burned out at a 257 amp current • A scheme to cool the resistors conductively was developed and tested off line • An insulated copper clamp conducts the resistor heat to the coil winding mandrel SUMMARY • 3D analyses carried out using Opera-3D/QUENCH module • The 3D model provides detailed results for the quench process (quenchback, layer-to-layer voltages, etc.) • The analysis also considers the impact of a quench on critical components such as the LTS and HTS leads • A coil quench analysis has been completed, and the finalmagnet protection design developed • Thermal analyses have resulted indesign modifications to reduce the heat leak into the cold mass and increase thecryocooling power • Reassembly of the first of the two magnets is currently under way Current decay in coils during quench Field distribution in the MICE coils Cooling clamp test setup Paper ID: WEPO033 *This work was supported by the Office of Science, U.S. Department of Energy under DOE contract number DE-AC02-05CH11231.