A step closer to demonstrating muon ionization cooling

Mark Palmer

Mark Palmer, director of the Muon Accelerator Program, wrote this column.

This month, scientists of the Muon Accelerator Program celebrated the arrival of a U.S.-supplied magnet and six tons of RF hardware at the Muon Ionization Cooling Experiment (MICE), located at Rutherford Appleton Laboratory in the UK. The experiment’s goal is to demonstrate the feasibility of shrinking the size of a muon beam with a process called ionization cooling. Creating compact muon beams is a crucial step toward future muon accelerators and colliders.

In ionization cooling, muons are cooled by sending them through absorber materials made of light nuclei (such as hydrogen) and then are reaccelerated using RF cavities. This process can be repeated many times and reduces the transverse momentum of each muon relative to its longitudinal momentum.

In 2015, MICE scientists will begin key experiments that will characterize the interactions of muon beams with various absorbers. The muon trajectories will be carefully measured using scintillating fiber tracking detectors embedded in spectrometer solenoid magnets located at the beginning and end of the cooling beamline. A subsequent experimental configuration, expected to be in operation later in the decade, will employ a full “cooling cell” with suitable absorbers, focusing solenoid magnets and multiple RF cavities to characterize the evolution of the beam’s emittance as the beam travels through a whole sequence of devices.

In support of these R&D efforts, the DOE-funded U.S. Muon Accelerator Program is providing two spectrometer solenoid magnets and two coupling coil magnets, as well as RF and detector hardware for the experiment. The NSF has provided additional support for U.S. participation in the experiment.

Earlier this month, two important milestones were achieved with the arrival at RAL of the first U.S.-supplied spectrometer solenoid magnet along with a shipment of RF hardware funded through an NSF Major Research Instrumentation grant to Don Summers at the University of Mississippi. The construction of the spectrometer solenoid magnet took place at Wang NMR in Livermore, Calif., and was overseen by MAP participants at Lawrence Berkeley National Laboratory, with support from Fermilab and other collaboration members. Other U.S.-supplied components are in the process of being tested, and the MAP collaboration is anxiously awaiting the first data that will be taken in 2015.

The first MICE spectrometer solenoid magnet arrives at Rutherford Appleton Laboratory, Didcot, UK. Photo courtesy of Rutherford Appleton Laboratory