1. Status of Design of Muon Beamline for the Muon Ionisation Cooling Experiment (MICE)
K. Tilley, ISIS, Rutherford Appleton Laboratory, UK
Introduction
Pion Injection & Decay Section
Emittance Preparation & Matching
A Neutrino Factory based on a muon storage ring, is the ultimate tool for studying neutrino oscillations. Ionisation cooling forms one of the key stages in the complex, whereby the large emittances of the muon beam, produced from pion decay, can be reduced to fit within the acceptances of the downstream accelerators. Such a technique has never been demonstrated in practise, and an international collaboration has designed the Muon Ionisation Cooling Experiment (MICE) to demonstrate this technique.
MICE is proposed to be installed as a secondary beamline on the intense pulsed proton synchrotron at the ISIS facility, at Rutherford Appleton Laboratory (RAL). This poster describes the work undertaken in designing the muon beamline, which must supply the experiment with the required properties in emittance and momenta.
The first two sections of the beamline are designed for pion momenta of 350Mev/c with 2.5% momentum spread.
Beam is captured by a quadrupole triplet, and then focussed through a large aperture dipole, bending through 60°. A pion transmission efficiency of ~ 65% is obtained.
The decay section uses a 5m, 5Tpeak field, superconducting solenoid, re-used from the former μE4 beamline at PSI. The full-width pion beam profile for the first 2 sections is shown below-
The transport line supplies a normalised rms emittance ~ 1π mm rad vertically, and ~1.5π mm rad horizontally, at the momentum of interest. To reach up to 6π mm rad, multiple scattering will be used in a lead disk just before the experiment, to boost the angular spread of the beam.
For a thin scatterer, the effect on the geometric emittance ε and Twiss parameters (α,β) can be approximated by:-
where is the rms scattering angle.
Beamline Function & Description
It is also important to match the beam into MICE, of which the first element is a 4Tesla solenoid. The beam profile should be constant & this can be achieved with:-
The muon beamline must supply a muon beam with particular characteristics for MICE:-
A maximum momentum of 300MeV/c is required, together with wide momentum spreads.
Normalised rms transverse emitances from ~ 2.5π mm rad to at least 6.0π mm rad and possibly beyond.
High rates must be supplied for good statistics
High purity beams (<10% basic contamination) required.
The two conditions of emittance tuning and matching are achieved simultaneously as shown below:-
Muon Extraction
This section consists of a large aperture dipole, and two sets of large aperture quadrupole triplets. Vacuum chambers are omitted, in view of the higher transmissions derived.
The current configuration is designed for a muon beam with a central momentum of 250Mev/c. A 30° bend allows a large muon momentum spread to be achieved. These two properties combine to allow a momentum-transverse amplitude correlation expected in a Neutrino Factory to be constructed by offline particle selection:
The proposed solution is based on a conventional pion-muon decay channel, with the capability for emittance tuning & matching. The 5 main sections are labelled below:-
Performance & Plans
p = (ref) + 30(A.v.p) +
6.5 (MICE LH2)+13.5 (Pb) =
250MeV/c
The above scheme has been applied at 250Mev/c and for 6π mm rad. The scheme is presently driven by the smaller vertical emittance. Some results are shown below:-
The muon beam profile is shown below. This shows the equal emittance core at 250MeV/c which reach the lead scatterer.The final beam focus is discussed later.
The codes TRANSPORT and DECAY TURTLE have been used to design the beamline optics, supplemented by G4beamline, a simulation package based on version 4 of CERN’s GEANT package.
Target
A lead thickness of 0.8cm was used, giving a final central momentum of 236.5Mev/c. The momentum spread is large.
The titanium target is 1mm thick and 10mm long, is dipped 2-5mm into the halo of the ISIS proton beam at 800MeV. This provides pions with at least 350MeV/c which will decay to the required muon momenta. Studies with LAHET, GEANT4 and MARS have been undertaken to estimate particle production.
Current assessments with G4beamline and target modelling indicates 200 useful muons/ms, with a pion contamination approaching 0.1%. Modelling and simulation work will continue and with suitable funding, beam is anticipated at the end of the proposed ISIS 2005/06 long shutdown.