Progress on the MuCool and MICE Coupling Coils*Progress on the MuCool and MICE Coupling Coils*L. Wanga, X. K Liua, F. Y. Xua, A. B. Chena, H. Pana, H. Wua, X. L. Guoa, S. X Zhenga,

D. Summersb, M. A. Greenc D. Lic, S.P Virostekc, and M. S. Zismanc

aInstitute of Cryogenics and Superconductivity Technology, HIT, Harbin 1500001, China; bUniversity of Mississippi, University MS 38667, USA; cLawrence Berkeley National Lab Berkeley, CA 94720, USA

Abstract— The superconducting coupling solenoid for MuCool and MICE will have an inside radius of 750 mm, and a coil length of 285 mm. The coupling magnet will have a self-inductance of 592 H. When operated at its maximum design current of 210 A (the highest momentum operation of MICE), the magnet stored energy will be about 13 MJ. These magnets will be kept cold using two pulse tube coolers that deliver 1.5 W at 4.2 K and 55 W at 60 K. This report describes the progress on the MuCOOL and MICE coupling magnet design and engineering. Fabrication plans for the coupling coil are discussed.

Introduction

Revised Coupling Magnet Design

Parameter Flip Non-flip

Coil Length (mm) 285

Coil Inner Radius (mm) 750

Coil Thickness (mm) 102.5

Number of Layers 96

No. Turns per Layer 166

Magnet Self Inductance (H)* 591.8

Magnet J (A mmŠ2)* 114.6 108.1

Magnet Current (A)* 210.1 198.2

Magnet Stored Energy (MJ)* 13.1 11.6

Peak Induction in Coil (T)* ~7.4 ~7.0

Coil Temperature Margin (K)* ~0.8 ~1.1

Coupling Magnet Design Parameters

* This work is supported by funds of the cryogenic and technology innovation project underthe “985-2” plan of the Harbin Institute of Technology. This work is also supported by theUS National Science Foundation through NSF-MRI-0722656 and by the Office of Science,United States Department of Energy under DOE contract DE-AC02-05CH11231.

The ICST Coupling Magnet Test Coil Program

Concluding Comments

Small Test Coil, Insulated Coil, and Small Coil Cryostat at ICST

Winding Welding and Assembling the Large Test Coil at ICST

Large Coil Cryostat Vacuum Vessel and Insulated Cold Mass Assembly

3D View of the CouplingMagnet Assembly

3D View of the Coil, shield andCryostat with a Cross-section

Coolers

Lead and Cooler Neck

Cold Mass Cold Mass Support Tube

Coil Banding

S/C Coil

Cooling Tube

70 K Shield

3D View of the Magnet Vacuum Vessel

Double Band Cold Mass Support

4 K Bracket

300 to 70 K Band

Thermal Intercept

300 K Bearing & Rod

70 to 4 K Band

The changes made to the vacuum vesseldesign will reduce both the stress anddeflection in the vacuum vessel. The newcold-mass support is a double bandsupport similar to t hat used in thespectrometer magnets. The double bandsystem has lower stresses in th e orientedfiberglass bands and the metallic parts ofthe cold mass support system.

Updated ICST Magnet Design

B E R K E L E Y L A B

The coupling coil is a single 285 mm long solenoid wound on a 6061-T6 aluminum mandrel. The inner coil radius is 750 mm and its thickness is 102.5 mm at room temperature. A standard MRI magnet conductor with a critical current of ~760 A at 5 T and 4.2 K is used. Insulated conductor dimensions are 1.0 1.65 mm. With this conductor, the magnet operating margin at maximum current will be ~0.8 K when the peak field on the coil is 7.4 T while operating at 4.2 K. Basic parameters of the coupling magnet are listed in the table below.

The design of the coil itself remains unchanged, but the cold mass now has a thicker cover plate. The thicker plate improves heat transfer to the coil and provides a good platform for mounting the cold mass supports with far lower stresses compared with the earlier design.

The Muon Ionization Cooling Experiment (MICE) will be a demonstration of muon cooling in a configuration that could be used for a Neutrino Factory. Step 6 of MICE (its final configuration) consists of: 1) two spectrometer solenoids used for measuring muon emittance, particle-by-particle, before and after passage through the cooling cell; 2) three absorber focus coil (AFC) modules where ionization cooling takes place in liquid-hydrogen absorbers within the magnetic field of the surrounding focus coils; and 3) two RF coupling coil (RFCC) modules where the energy lost in the absorbers is restored by RF cavities while maintaining a focusing field with a large-diameter coupling coil.

In each RFCC module, the superconducting coupling coil solenoid surrounds a 1.4-m diameter vacuum chamber that houses four individually powered normal conducting 201.25-MHz RF cavities. Each cavity iris is closed with a 42-cm diameter, 0.38 mm thick beryllium window, through which the muon beam passes. The coupling coil can provide an on-axis field of up to 2.6 T to keep the beam focused within the 42-cm aperture of the RF cavities.

MuCool is a related component R&D program where a 201.25 MHz MICE RF cavity prototype can be tested under magnetic field conditions similar to those that will be encountered in MICE. To do so, we are fabricating a third, stand-alone coupling coil that will operate in the MuCool Test Area at Fermilab. The MuCool RF cavity is nearly identical to those of MICE, but is designed to operate in air, i.e., without the surrounding vacuum vessel used in MICE. The designs of the MuCool coupling coil and its cryostat are identical to those of the MICE magnets.

This paper discusses recent improvements to the coupling coil design, progress on test coils fabricated at ICST, and fabrication plans for the MICE and MuCool magnets.

The large test coil was installed in its cryostat, the Linde refrigeration system was debugged, and the coil was cooled down in May 2009. Unfortunately, the refrigeration system as configured was unable to provide enough mass flow to properly cool its load. The matter is presently under study, with the goal of reconfiguring the system to deliver sufficient cooling to the load as soon as possible.. After the large coil test, a small test coil will be used to provide a 4 T field for testing the quench protection diodes in both parallel and normal field orientations. In the meantime, preparatory R&D is under way at a vendor in Beijing. It is expected that a fabrication contract between HIT and the vendor will soon be in place to fabricate the three required magnets under HIT supervision, in consultation with LBNL.