The R&d Program for Targetry at a Neutrino Factory

The need for intense muon beams for muon colliders [1] and for neutrino factories based on muon storage rings [2, 3, 4] leads to a concept of 1-4 MW proton beams incident a moving target that is inside a 20-T solenoid magnet, with a mercury jet as a preferred example. Novel technical issues for such a system include disruption of the mercury jet by the proton beam and distortion of the jet on entering the solenoid, as well as more conventional issues of materials lifetime and handling of activated materials in an intense radiation environment. As part of the R&D program [5] of the Neutrino Factory and Muon Collider Collaboration, R&D effort related to targetry is being performed within the context of BNL E951 [6], first results of which are discussed here and in other contributions to this conference. 1 THE TARGETRY CONCEPT A muon collider [1] or a neutrino factory based on a muon storage ring [2, 3, 4] require intense beams of muons, which are obtained from the decay of pions produced in proton-nucleus collisions. To maximize the yield, pions of momentum near 300 MeV/c should be captured [7, 8]. For proton energies above 10 GeV, the pion yield per unit of proton beam energy is larger for a high-Z target [7]. For proton beam energies in the MW range, beam heating would melt or crack a stationary high-Z target [9], so a moving target must be used. A mercury jet target is the main focus of BNL E951 [6], although R&D is also being conducted on a carbon target option [2, 10, 11] as might be suitable for a low-energy proton source [12], and conceptual studies have been carried out for rotating-band targets [13, 14], a tantalum/water target [15], and a liquid-lithium target [16]. The low-energy pions are produced with relatively large angles to the proton beam, and efficient capture into a decay and phase rotation channel is obtained by surrounding the target with a 20-T solenoid magnet, whose field tapers down to 1.25 T over several meters [17, 18], as sketched in ∗[email protected] length (cm) 0 250 500 750 -100 -50 0 50 100