International Muon Ionization Cooling Experiment

The International Muon Ionization Cooling Experiment (or MICE) is a high energy physics experiment designed to observe ionization cooling of muons.[1] This is a process whereby the emittance of a beam is reduced in order to reduce the beam size, so that more muons can be accelerated in smaller aperture accelerators and with fewer focussing magnets. This might enable the construction of high intensity muon accelerators, for example for use as a Neutrino Factory or Muon Collider.

MICE will reduce 6D emittance over a single 5.5 m cooling cell and measure that reduction. The MICE design is based on a scheme outlined in Feasibility Study II.[2] Pions will be produced from a target in the ISIS neutron source and transported along a beamline where most will decay to muons before entering MICE. MICE will measure cooling performance over a range of beam momenta between about 150 and 250 MeV/c, for various absorber materials and magnetic field configurations.

Beamline

The MICE muon beamline provides a low intensity muon beam for MICE. Pions will be transported from a target dipping into the fringe of the ISIS proton beam, through a pion decay channel, into a muon transport line and then into MICE. For efficient use of muons it is desirable to have a reasonably good match between the transport beamline and the cooling channel, with selection performed in analysis. Also, the beamline must suppress non-muon events from entering the cooling channel. A beam rate of a few hundred muons per second is expected.

Cooling channel

The final MICE magnetic lattice is made up of 18 superconducting coils. Three solenoid coils provide a constant field for each of the two MICE tracking detectors and matching coils match the beam from the spectrometers into, and out of, the cooling channel. Each of the three absorbers sits between two focus coils. These focus the muon beam in the absorbers to provide optimal cooling. At the centre of each RFCC module, a single coupling coil creates the second harmonic term in the field that improves the range of momenta that the cooling channel can accept.

The MICE linacs consist of four normal-conducting copper cavities approximately 430 mm in length and 610 mm in radius. The RF cavities operate at 201.25 MHz with a peak field of 8 MV/m. The full muon energy will be replaced for muons that pass through the rf cavities on-crest. As there is no time distribution in the incoming beam, muons at all phases will be sampled.

The cavities must have a large aperture in order to avoid significant scraping from the high emittance beam. Hence, 0.38 mm thick beryllium windows are used to electromagnetically seal the cavities to avoid a high shunt impedance. These are nearly invisible to the muon beam. The windows have been designed to prevent electromagnetic heating from buckling the windows.

The baseline MICE absorber consists of a 21-litre, 350 mm long liquid hydrogen vessel sealed with a pair of curved, cylindrically symmetric aluminium windows at each end and cooled using cryocoolers. The absorber is removable, so that different materials may be used. For example, solid absorbers constructed from materials such as lithium hydride may replace the liquid hydrogen absorbers.

Detectors

Muons pass through the cooling channel one by one. The muons' phase space coordinates will be measured by time of flight scintillators and scintillating fibre tracking detectors upstream and downstream of the cooling channel. Muons will be distinguished from other particles in the beam using a combination of the spectrometers and the so-called Particle Identification (PID) detectors, three time of flight scintillators, a Cerenkov detector and an electron-muon calorimeter.

Status

As of 2010, MICE is in the final stages of construction at Rutherford Appleton Laboratory in the UK. The muon beamline is in place and commissioning has begun. During the rest of 2010 further instrumentation will be installed and commissioned. Starting in 2011 and until 2014, measurements with progressively more powerful muon cooling devices will aim at effecting the first experimental demonstration of ionization cooling itself. Also during this phase they are using grid resources provided by GridPP to model and simulate the behaviour of the beam in the machine.[3]

Compare to: MUCOOL

References

  1. ↑ MICE [RETRIEVED: 2012-01-07]
  2. ↑ The BNL Advanced Accelerator Group (ed.) S. Ozaki, R. Palmer, M. Zisman, and J. Gallardo, Feasibility Study-II of a Muon-Based Neutrino Source, BNL-52623, (2001) [RETRIEVED: 2007-11-16]
  3. ↑ GridPP - UK Computing for particle physics - gridpp.ac.uk [RETRIEVED: 2011-12-09]

External links