DIFFUSER

1. MICE The Muon Ionisation Cooling Experiment (MICE), under construction at the ISIS synchrotron at Rutherford Appleton Laboratory seeks to provide both a first measurement and the systematic study of ionisation cooling for use in a future neutrino factory or muon collider. The experiment is built in three stages, historically called Step I, Step IV(that incorporates STEP II and III) and Step V. In Step I, completed in 2013, the commissioning of the beamline and of the particle identification detectors was performed. In Step IV, scheduled to start data-taking in 2015, a first study of muon ionisation cooling will be performed. The Step IV setup includes an absorber sandwiched between two identical spectrometer solenoids instrumented with scintillating fibres tracker planes for precise position and momentum measurements. The absorber reduces the beam momentum in both longitudinal and transverse direction. Overall transverse emittance is reduced until equilibrium is reached between the cooling effect of ionization and the heating effects of multiple scattering. One of the aims of STEPIV is to measure the equilibrium emittance for different materials and experimentally test the ionization cooling theory predictions under a variety of conditions (different emittances, particle momenta and optics parameters). “Sustainable” cooling will be demonstrated in Step V, where the longitudinal momentum is restored by acceleration in RF cavities, resulting in a net reduction of emittance. The aim is to measure 10% emittance change within the cooling cell with a relative precision of about 1% using single particle measurements. See poster by Victoria Blackmore on the Physics of STEP IV. (completed) SPECTROMETER SOLENOIDS DIFFUSER The diffuser adds a controlled amount of material prior to the first superconducting solenoid to increase the emittance at the entrance of the cooling cell. Four separate irises of brass and tungsten of different thicknesses can introduce up to 3X0 of material. The diffuser has been built, tested and is ready to be delivered to RAL. The two superconducting solenoids provide 4T magnetic field uniform to better than 1% over a 1m long, 40cm diameter tracking volume. They also provide regions of matching the beam to the absorber magnet system. Both solenoids have met their acceptance criteria and have been successfully trained 102% of their operating current. They have also been field-mapped and delivered to RAL, where they were both fitted with a fibre tracker module. The status of the construction of MICE STEP IVStefania Ricciardi on behalf of the MICE Collaboration STEPIV cooling channel FIBRE TRACKER A scintillator fibre tracker module is composed of 5 stations, each formed by three doublet layers of 350micron fibres attached to a circular frame at 120 degrees to each other. The tracking volume is 110cm long and 30cm in diameter. Light is converted into charge via VLPCs maintained at a temperature of 9K in nearby cryostats. The scintillating fibre tracker and readout have been tested with cosmic rays and in a test beam at RAL. The two modules have been fitted with a LED calibration system and Hall probes and are installed in the SSs. ABSORBERS The liquid H2absorber has a volume of 20.7 litres. The vessel was built at KEK and has been delivered and tested at RAL. A number of solid absorbers can also be tested within the MICE cooling channel. The key solid absorber is a 65mm thick LiH disk. The support structure includes spacers for mounting disks made of other materials. PARTIAL RETURN YOKE The partial return yoke will surround the cooling channel. It has been designed to reduce the stray magnetic field in the MICE Hall and ISIS control rooms to <5 G Its procurement is underway: 95% of the parts for the support structure have arrived at RAL. ABSORBER FOCUS COIL The AFC provides strong focusing in the absorber region. It contains a pair of superconducting coils that can operate in “solenoid” or in “flip” mode. The AFC has been trained to reach “full current” in solenoid mode but just reached nominal current in flip mode. It is estimated that stable operation will be possible at 11-15% de-rated current. The reduced flip-mode current is still sufficient to support the Step IV programme. STEP V MICE STEP V contains, in addition to the STEP IV components, an additional AFC and a Radio-Frequency-Coupling-Coil module (RFCC). The second AFC has been built, but returned to vendor for diagnosis and repair of a cold-leak. It is now repaired and returned to RAL. The second LH2 absorber vessel has been prepared for shipment to RAL from Osaka. The RFCC contains four normal conducting 201.25 MHz RF cavities with a guiding magnetic field provided by a large diameter coupling coil (CC) solenoid. The 2.5T superconducting CC magnets located around the RF cavity assemblies are the largest magnets in the MICE cooling channel and provide an additional longitudinal magnetic field to confine the beam between the absorbers. All RF cavities have been fabricated and the first one is being tested at Fermilab. The first CC has also been fabricated and tested. During the first cold mass test the heat load was too high, so numerous improvements were made to mitigate the issue. After that the CC met the acceptance criteria. The coupling coil magnets and cryostats are designed by a collaboration between LBNL and HIT, China. The completed cryostat was shipped to FNAL. Cooling circuits and shield design details are well underway. A second coil winding is in process at Qi-Huan Corp (CHINA). Following the DOE review of MAP the MICE Collaboration is evaluating the option of an expedited completion of Step V with RF cavities and no CC, demonstrating ionization cooling with reacceleration by 2017.