The Primary Target Facility for a Neutrino Factory Based on Muon Beams


Neutrino beams from the decay of muons in a storage ring offer the prospect of very high flux, well-understood spectra, and equal numbers of electron and muon neutrinos, as desirable for detailed exploration of neutrino oscillations via long baseline detectors [1]. Such beams require large numbers of muons, and hence a high performance target station at which a 1-4 MW proton beam of 16-24 GeV impinges on a compact target, all inside a high field solenoid channel to capture as much of the phase volume of soft pions as possible. A first concept was based on a carbon target, as reported in 2000 the Neutrino Factory Study-I [2]. A higher performance option based on a free mercury jet has been studied in 2001 as part of the Neutrino Factory Feasibility Study-II [3, 4]. An overview of a mercury jet target facility is presented here, including requirements, design concept and summaries of simulated performance. Further details are presented in related papers at this conference. 1 THE TARGET FACILITY A muon collider [18] or a neutrino factory based on a muon storage ring [1, 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, as illustrated in Fig. 1. For proton energies above 10 GeV, the pion yield per unit of proton beam energy is larger for a high-Z target [5]. For proton beam energies in the MW range, beam heating would melt/boil a stationary high-Z target, so a moving target must be used. A mercury jet target is the main option considered here, although several alternatives remain under active study [6, 7]. For greater detail, consult Chap. 3 of [3]. See also [8]. The low-energy pions are produced with relatively large ∗ Figure 1: Comparison of pion yield measured in BNL E910 with a MARS calculation. angles to the proton beam, and efficient capture into a decay and phase rotation channel [9] is obtained by surrounding the target with a 20-T solenoid magnet, whose field tapers down to 1.25 T over several meters, as sketched in Fig. 2. Pion yield is maximized with a mercury target in the form a 1-cm-diameter cylinder, tilted by about 100 mrad with respect to the magnetic axis. To permit the proton beam to interact with the target over 2 interaction lengths, the proton beam is tilted by 33 mrad with respect to the mercury jet axis. See also Fig. 3. A mercury pool inside the capture solenoid intercepts the mercury jet and the unscattered proton beam, as shown in Fig. 4. The mercury pool, surrounding tungsten carbide/water shielding, and the resistive insert of the 20-T capture magnet [10] are isolated from upstream and downstream beamline elements by a pair of double-walled Be windows. This entire unit can be replaced by remote manipulation should failure occur. The absorbed radiation dose on components near the target is quite large [5], as illustrated in Fig. 5, such that in a 4 Mw proton beam, their 0-7803-7191-7/01/$10.00 ©2001 IEEE. 1583 Proceedings of the 2001 Particle Accelerator Conference, Chicago

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@inproceedings{Hassenein2001ThePT, title={The Primary Target Facility for a Neutrino Factory Based on Muon Beams}, author={Ashraf M Hassenein and Roman Samulyak and Nicholas Simos and I. Stumer}, year={2001} }