Transcript The MICE Muon Beamline Optimisation and Emittance Generation

The MICE Muon Beamline Optimisation
and Emittance Generation
M. Apollonio, M. A. Rayner
Diffuser
(not drawn,
inflates the
emittance)
In the Muon Ionisation Cooling Experiment (MICE) at RAL muons are produced and transported in
a dedicated beamline connecting the production point (target) to the diffuser, a mechanism inside
the first spectrometer solenoid designed to inflate the initial normalized emittance up to 10 mm
rad in a controlled fashion. In order to match the incoming muons to the downstream experiment,
covering all the possible values of the emittance-momentum matrix, an optimisation procedure
has been devised which is based upon a genetic algorithm coupled to the tracking code
G4Beamline. Details of beamline tuning and initial measurements are discussed.
Upstream
spectrometer
Hydrogen
absorbers
RF cavities
TOF1
TOF2
Solenoidal focussing
magnets
(c)
(a)
Fig. 1
Q2
p
Q1
(b)
Downstream
spectrometer
Top View of the MICE Beamline
For the purpose of optimisation the muon beamline can be thought as split in an
upstream and downstream section.In the former pions produced in the Titanium target
are transported up to a 5T superconducting 5m long solenoid. Muons from pion decays
captured by the Decay Solenoid are carried through the downstream section towards the
MICE diffuser
Q3
Upstream Beamline (inside the
ISIS vault): (a) target, (b) 1st
quadrupole triplet, (c) dipole-1
Fig. 2
Fig. 3
m
GVA1
a) Upstream
beamline optimisation
Q4
Q5
Q6
TOF1
Q7
Q8
Q9
TOF0
A first aspect of the beamline optimisation consists in maximizing the number of p transported from the target
production point to the decay solenoid by acting on the first quadrupole triplet. Measurements of particle rate in
a downstream scintillator counter (GVA1) allowed to establish the best working point, as illustrated in Fig. (3).
Charged particle rate in GVA1 counter
when varying the currents of the first
triplet quadrupoles by the same factor
Cooling
channel
a,
b
e
1
2
Fig 4
t
Diffuser
b) Downstream beamline optimisation
Fig. 5
After fixing the upstream optics we need to set up the downstream section in order to match the beam with the MICE cooling channel.
The goal is to produce a definite optics for every momentum and emittance as required by the MICE program. This defines the so called
(e,P) matrix (Fig. (5)). Values for the Twiss parameters on the diffuser upstream end have been calculated in [1]. In order to tune the
beamline to these parameters the currents of the last 6 quadrupoles are changed. For every set Q4-9 a G4Beamline simulation
transports a beam of 20000 muons from the solenoid to the diffuser and this is repeated until the Twiss parameters match the target
values. An example of optimization as a function of the number of iterations is shown in Fig. (6)
c) Demonstrating the
emittance-momentum matrix
[1] M. Apollonio, “Emittance Generation in
MICE”, PAC09, Vancouver (CA)
Fig 6
MICE is equipped with three Time of Flight stations (TOF0,1,2) meant to
discriminate m from p and increase beam purity. Each station is constituted by
two segmented scintillating planes allowing the reconstruction of space points in
the transverse plane at a definite z-depth along the beamline. This capability
together with the high time resolution (50 ps) has been used for a first
characterization of the beam.
(e,P) matrix with the optics required to match
MICE lattice for all the cases foreseen in the In December 2009 the (6,140) and the (6,200) elements of the (e,P)
MICE program.
matrix were investigated. A comparison between the reconstructed data
for the (6,200) element and a G4MICE simulation is shown in Fig. (7).
Fig 7 After particle identification using the time of flight distribution,
momentum may be measured with a resolution of a few MeV/c. A
calculation of the transfer matrix between the two detectors may then
be used to deduce the initial and final PZ from the 1.5 cm resolution
horizontal and vertical position measurements made by each TOF. Finally,
a bias of a few MeV/c is removed by iteratively integrating each muon’s
path through the Q7-8-9 triplet between TOF0 and TOF1 (Fig. 8-9). The
method allows to find the muon phase space at both TOF stations.
Results are summarized in tables 1-2.
phase spaces from simulations (above) and
data (below) for the (6,200) matrix case.
Conclusions
Tab 1
Tab 2
Reconstructed momenta and
normalized emittances at TOF1
Emittances and Twiss parameters
extrapolations to the diffuser
faces.
A TOF station
Fig 8
Genetic algorithm optimisation to
determine the (6-240) optics
Fig 9
Iterative procedure in
momentum
reconstruction
Path modeling in the space
between TOF0,1 as used in the
momentum
reconstruction
procedure
The optimisation of the MICE muon beamline and the measurement of its beam parameters are part of the commissioning procedure of the
line itself. A first emittance matrix has been produced and a preliminary set of measurements performed for two of its configurations. Results
show that the emittance of the beam is close to the design value. Extrapolated figures for the Twiss parameters to the diffuser interface look
encouraging. We plan to resume and complete this process with an imminent campaign (June-August) before the ISIS long technical stop.
[email protected] , [email protected]
IPAC 2010 - Kyoto