IPAC2020 Abstracts » History » Revision 2
First Demonstration of Ionization Cooling by the Muon Ionization Cooling Experiment
Muon colliders have the potential to carry the search for new phenomena to energies well beyond the reach of the LHC in the same or smaller footprint. Muon beams may be created through the decay of pions produced in the interaction of a proton beam with a target. To produce a high-brightness beam from such a source requires that the beam be cooled. Ionization cooling is the novel technique by which it is proposed to cool the beam. The Muon Ionization Cooling Experiment collaboration has constructed a section of an ionization cooling cell and used it to provide the first demonstration of ionization cooling. Here the observation of ionization cooling is described. The cooling performance is studied for a variety of beam and magnetic field configurations. The cooling performance is related to the performance of a possible future muon collider facility.
Emittance reduction of muon beams provides an essential component in the design of a next-generation Neutrino Factory or Muon Collider. The demonstration of ionization cooling at the Muon Ionization Cooling Experiment (MICE) would contribute greatly in future discourse surrounding these facilities.
Due to angular momentum build-up considerations towards cooling channel performance, recent designs have featured ‘flip’ magnetic fields - opposite polarity in the upstream vs downstream solenoid fields. Measurements obtained from individual muon tracks passing through liquid-hydrogen and lithium-hydride absorbers under same-polarity solenoid fields are presented with corresponding transverse emittance change.
Muon Ionization Cooling Demonstration by Normalized Transverse Emittance Reduction in MICE 'Flip Mode
Low emittance muon beams are central to the development of facilities such as a Neutrino Factory or a Muon Collider. The international Muon Ionization Cooling Experiment (MICE) was designed to demonstrate and study the cooling of muon beams. Several million individual muon tracks have been recorded passing through a liquid hydrogen and a lithium hydride absorber. Beam sampling routines were employed to account for imperfections in beam matching at the entrance into the cooling channel and enable an improvement of the cooling performance. Measurements of the change in normalized transverse emittance in a flipped polarity magnetic field configuration are presented and the characteristics of the cooling effect are discussed.
Emittance Exchange in MICE
Highly brilliant muon beams for a muon collider can be made from the bombardment of protons against a target producing pions, which subsequently decay into muons. Such a muon beam occupies a large phase-space volume and must be cooled to achieve luminosities suitable for a collider. The Muon Ionization Cooling Experiment (MICE) has demonstrated transverse ionization cooling. A muon collider requires both longitudinal and transverse cooling. This can be achieved through a wedge-shaped absorber, where the longitudinal and transverse phase spaces are mixed during the ionization cooling process. The change in longitudinal and transverse phase space densities obtained from placing a polyethylene wedge into the MICE cooling channel are presented here.
Transmission effects for phase-space density calculations
As a consequence of Liouville's theorem, the phase-space volume (and the phase-space density) of an ensemble of particles remains constant, unless it experiences a dissipative force. This can be seen by a constant change in the ratio of the upstream to downstream densities of an ensemble of particles across the face of the beam when an absorber is present for that ensemble of particles. When no absorber is present, then there is no change between the upstream and downstream densities. This can be used to give an indication of the cooling or heating performance of a particular absorber.
For an actual beam, there may be transmission effects due to scattering or scraping of the beam as well as magnetic field imperfections resulting in beam loss. The beam loss is non-random changing the distribution of the remaining beam sample. Presented are the changes that must be applied to a phase-space density calculation to account for transmission losses and the subsequent change in measured beam distribution.