MOPLT106. MICE: The International Muon Ionisation Cooling Experiment. 201 MHz RF. Liquid Hydrogen Absorbers. Abstract
MICE: The International Muon
Ionisation Cooling Experiment
201 MHz RF
Liquid Hydrogen Absorbers
The provision of intense stored muon beams would allow the properties of neutrinos to be measured precisely and provide a route to multi-TeV lepton-anti-lepton collisions. The short muon-lifetime makes it impossible to employ traditional cooling techniques while maintaining the muon-beam intensity. Ionisation cooling, a process in which the muon beam is passed through a series of liquid hydrogen absorbers followed by accelerating RF-cavities, is the proposed cooling technique. The international Muon Ionisation Cooling Experiment (MICE) collaboration proposes to perform an engineering demonstration of ionisation cooling. The MICE cooling channel, the instrumentation and the implementation at the Rutherford Appleton Laboratory is described together with the predicted performance of the channel and the measurements that will be made.
Hydrogen was chosen as the most suitable absorber material because of its large ionization energy-loss rate (‘cooling’) and small probability of multiple scattering (‘heating’).
The first prototype MICE absorber module has been built at KEK and is waiting to be shipped to Fermilab where it will be tested at 20K later this year.
The baseline MICE channel operates with muons at an average momentum 200 MeV/c and b = 42 cm at the centre of the absorber. Eight 201-MHz RF cavities, in two 4-cavity assemblies, are needed in the cooling section. The MICE cavities will produce an accelerating gradient of 8 MV/m. By selecting muons passing through the cooling channel ‘on crest’ the desired cooling effect will be produced. The RF power will be provided by four 2 MW amplifiers, each amplifier serving two cavities. The cavity shape chosen is based on a slightly re-entrant rounded profile with a large beam aperture and a small nose cone. To achieve high shunt impedance, the beam aperture is terminated electromagnetically using thin beryllium foils.
Three TOF stations equipped with fast scintillators are foreseen. The first two, upstream of the cooling section and separated by about 3 m, will provide the basic trigger for the experiment in coincidence with the ISIS clock. These have precise timing (around 70 ps) and will provide muon identification as well as the muon timing (relative to the RF phase) necessary for the measurement of the input longitudinal emittance. The coincidence with a third station of similar nature, downstream of the second measuring station, will select particles traversing the entire cooling section.
The two tracking detectors will each consist of five sets of scintillating-fibre planes per spectrometer, deployed in three stereo views, with the fibres individually read out using cryogenic visible-light photon counters (VLPCs). A prototype detector using this technology, and to the MICE design has been built and operated at Fermilab.
Additional detectors will provide redundant particle identification to eliminate from the sample any residual pions in the incoming beam or muons that decay within the apparatus. These detectors include time-of-flight scintillation counters, Cherenkov detectors and a calorimeter. While these are standard ingredients for particle-physics experiments, an emittance measurement with 0.1% precision has never been performed and will require careful design of diagnostics and attention to system integration and calibration.