Fabrication, Testing and Modeling of the MICE Superconducting Spectrometer Solenoids

FABRICATION, TESTING AND MODELING OF THE MICE SUPERCONDUCTING SPECTROMETER SOLENOIDS * S.P. Virostek, M.A. Green, F. Trillaud and M.S. Zisman Lawrence Berkeley National Laboratory, Berkeley CA 94720, USA Abstract The Muon Ionization Cooling Experiment (MICE), an international collaboration sited at Rutherford Appleton Laboratory in the UK, will demonstrate ionization cooling in a section of realistic cooling channel using a muon beam. A five-coil superconducting spectrometer solenoid magnet will provide a 4 tesla uniform field region at each end of the cooling channel. Scintillating fiber trackers within the 400 mm diameter magnet bore tubes measure the emittance of the beam as it enters and exits the cooling channel. Each of the identical 3-meter long magnets incorporates a three-coil spectrometer magnet section and a two-coil section to match the solenoid uniform field into the other magnets of the MICE cooling channel. The cold mass, radiation shield and leads are currently kept cold by means of three two-stage cryocoolers and one single-stage cryocooler. Liquid helium within the cold mass is maintained by means of a re-condensation technique. After incorporating several design changes to improve the magnet cooling and reliability, the fabrication and acceptance testing of the spectrometer solenoids have proceeded. The key features of the spectrometer solenoid magnets, the development of a thermal model, the results of the recently completed tests, and the current status of the project are presented. assembly is provided in Fig. 2. Match Coil 1 and Match Coil 2 operate as a focusing doublet to match the beam in the spectrometer solenoid with the beam in the adjacent AFC modules. The spectrometer solenoid portion of the module consists of End Coil 1, the Center Coil, and End Coil 2, which generate a 4 Tesla uniform field (ΔB/B < 3×10 -3 ) over a 1-meter long and 0.3 meter diameter volume. The tracker detectors, which are made up of five planes of scintillating fibers, are located in the bore of these three coils and are used to measure the emittance of the muons as they enter and exit the cooling channel. Additional details of the spectrometer solenoid design and operating parameters were presented previously [4,5]. INTRODUCTION The Muon Ionization Cooling Experiment (MICE) will consist of a cooling channel [1] which is made up of three absorber focus-coil (AFC) modules [2], each containing a liquid hydrogen absorber and two focusing coils, along with two RF and coupling-coil (RFCC) modules [3], each of which contain four 201 MHz accelerating RF cavities centered on a superconducting solenoid. Located at either end of the cooling channel are the spectrometer solenoid modules (Fig. 1). Figure 2: Spectrometer solenoid cold mass assembly. MAGNET THERMAL MODELING A 3D finite element model of the first stage cooling for the MICE spectrometer solenoid has been recently developed. The model has been used to perform a parametric study of the magnet cooling system under load. The model was been written using Cast3M software [6] that is based on an object-oriented language, Gibiane, which has been specifically developed for finite element analysis. The solver uses the concept of Lagrangian multipliers to enforce the first law of thermodynamics. A number of assumptions have been made in the analysis as follows: - steady state conditions - idealized geometry (perfect thermal connections) - temperature dependent material properties - linear interpolation of the cryocooler thermal performance map - approximation of the superinsulation cooling as an equivalent heat transfer coefficient Figure 1: MICE cooling channel 3D CAD image. The absorbers perform muon ionization cooling to reduce the beam emittance while the RF cavities re- accelerate the beam. Each spectrometer solenoid consists of five superconducting coils wound on a common 2923 mm long aluminum mandrel. A CAD image of the coil * This work was supported by the Office of Science, U.S. Department of Energy under DOE contract number DE-AC02-05CH11231.