Secondary Particle Production and Capture for Muon Accelerator Applications S.J. Brooks, RAL, Oxfordshire, UK Abstract Intense pulsed muon beams are required for projects such as the Neutrino Factory and Muon Collider. It is currently proposed to produce these from a high-Z target using a multi- megawatt proton driver. This paper examines the effect of proton energy on the yield and distribution of particles produced from tantalum and mercury, with further analysis using a tracking code to determine how these distributions will behave downstream, including a breakdown of loss mechanisms. Example ‘muon front end’ lattices are used from the UK Neutrino Factory design. H − Ion Source LEBT (Low Energy Beam Transport) RFQ (Radio Frequency Quadrupole) Beam Chopper 180MeV DTL (Drift Tube Linac) Stripping Foil (H - to H + /protons) Achromat for removing beam halo Two Stacked Proton Synchrotrons (boosters) 1.2GeV 39m mean radius Both operating at 50Hz Two Stacked Proton Synchrotrons (full energy) 6GeV 78m mean radius Each operating at 25Hz, alternating for 50Hz total Proton bunches compressed to 1ns duration at extraction Mean power 5MW Muon Cooling Ring FFAG I (2-8GeV) FFAG II (8-20GeV) FFAG III (20-50GeV) R109 Near Detector Muon Decay Ring (muons decay to neutrinos) To Far Detector 2 To Far Detector 1 Muon Linac to 2GeV (uses solenoids) Schematic of the current UK neutrino factory design (under study). Our design includes several unique features such as a solid, rapidly-moving target, and split extraction of pulses from the main proton synchrotron to alleviate thermal shocks in the target. This proton machine could be realised for instance via staged upgrades of ISIS at RAL. The area of interest in this poster and paper is the “front end” highlighted in blue. Pulsed power 16TW Target enclosed in 20Tesla superconducting solenoid (produces pions from protons) Proton Beam Dump Solenoidal Decay Channel (in which pions decay to muons) RF Phase Rotation Transforms longitudinal phase space as shown in the diagram (right). Transmission of positive muons to the end of the phase rotator for various target materials. The main results in this paper derive the optimum proton driver energy for a target of tantalum, mercury or copper, 1cm in radius with lengths given by the table below. Targets are simulated using MARS15 then the resulting particles are tracked through the UKNF decay channel and phase rotator using the code Muon1. This is done for each energy and material, and the muons leaving the channel with the desired energy of 180±23 MeV are counted in units of muons per “proton.GeV” on target, which is actually proportional to the muon yield rate for a fixed power. The pion distribution does not change radically enough with proton energy to affect the optimal lattice. Comprehensive optimisations of all parameters of the decay channel and phase rotator were conducted on a distributed computing network. Two independent runs, one starting with secondary particles from a 2.2GeV proton beam and the other from a 10GeV beam, each produced an “optimal” lattice after several months. The table above shows their yields and what happens when they are run on each others’ beams: in fact, the lattices are almost identical, as shown by the parameter graphs below, so not “specialised” for pions coming from one energy of beam. Relative performance of a channel for capturing negative particles. By changing the phases of the RF systems by 180° negative particles will be treated analogously to positive ones in the optimised channel. The graph below shows the difference in performance between the two. Primary energy (heat) deposition in rod. Proton beams deposit heat directly in the target as well as by the particle reabsorption mechanism shown in red (top figure). The graph above shows how much power out of a 5MW beam would be converted directly into heat in the target. This is one of the driving factors of the solid target design so it is fortunate that this optimum of minimum heating (8GeV) coincides with the optimum of muon capture in the phase rotator. Analysis of how beam loss mechanisms change as proton energy varies. For higher primary beam momentum, even the more forward-directed secondary particles can have a transverse momentum sufficient to be outside the channel’s acceptance. Here we see the higher energies experiencing losses further down the decay pipe from smaller-angled particles. The current phase rotator captures one muon sign, with the other falling between RF buckets. The effect on the opposite sign can be seen in the blue particles in the longitudinal phase space diagram above. This means that when all the muons are counted, as seen in the diagram below, only a few of the negative muons are in the correct energy band, but the target always produces both signs anyway so there is no way of getting rid of these. Proportion of muons leaving the channel in the correct energy band. This seems to be functionally independent of the proton energy, so although losses may redistribute in the early-mid decay channel, by this stage they are simply proportional to yield as proton energy varies, thus the phase rotator decouples from the proton energy issue.