(+) m.apollonio@physics.ox.ac.uk Poster session, EPAC08 Genoa – WEPP108

empty abs full absT (mm) e3N a b (cm) s_x,y (cm) P_before(GMeV/c) T (mm) e3N a b (cm) s_x,y (cm) P_before (MeV/c)

0 2.65 0.09 34.3 2.19 200 200 MeV/c 207MeV/c 0 2.70 0.09 34.30 2.19 207.007.5 6 0.23 78.02 3.3 210.81 7.5 6.15 0.46 84.96 3.45 217.7315.5 10.09 0.44 131.74 4.29 222.34 15.5 10.84 1.28 168.92 4.86 229.18

1.5 2.93 0.31 53.93 2.75 142.39 140 MeV/c 148.4 MeV/c 1.5 3.00 0.19 56.24 2.81 150.755 6.13 0.67 113.15 3.98 147.98 5 6.06 0.32 112.69 3.97 156.2210 10.81 1.22 200.71 5.3 155.96 10 10.60 0.60 197.78 5.26 164.04

0 3.18 0.06 40.84 2.39 240 240 MeV/c 245.2 MeV/c 0 3.25 0.09 41.85 2.42 245.207.5 6.18 0.14 79.61 3.34 250.44 7.5 6.24 0.19 80.58 3.36 255.6115.5 9.93 0.25 128.25 4.24 261.58 15.5 9.98 0.32 129.42 4.26 266.71

e3N (mm rad) 3 6 10P(MeV/c)140/148.4 1.5 5 10200/245.2 0 7.5 15.5240/245.2 0 7.5 15.5

eq. 1

A slab of material placed across the beam will not only inflate its emittance but will also change the optical functions: therefore special care must be taken to produce matched values inside the tracker.Following [2] the system of equations governing the change in emittance and Twiss parameters can be shown as in (eq. 1) with fig. 4 illustrating the naming convention for emittances and optical functions before and after the diffuser. The optical functions upstream the diffuser plate and the material thickness can be found by solving this system of equations: results are summarized in tab. 1.

Introduction

Tab. 1 Emittances and optics for two possible configuration of the MICE experiment (with and without hydrogen in the absorbers) as a function of the five chosen thicknesses for the lead plates. The three cases at 140, 200 and 240 MeV/c illustrate the coverage of the (,p) space as required.

The Muon Ionisation Cooling Experiment (MICE, fig. 1c) at RAL[1] will demonstrate ionization cooling in a variety of initial emittances and momenta (,p). Protons in the ISIS synchrotron hit a titanium target producing pions which are focussed with an F-D-F quadrupole triplet and steered by means of a dipole towards a 5T solenoid where they decay into muons. Hence a second dipole transports them towards the experimental apparatus by means of two other quadrupole F-D-F triplets. This system constitutes the MICE beam line (fig.1a).The transverse phase space emittance of the initial muon beam depends on the production mechanism and is estimated to be around 1.5 mm rad. In order to change this value to the desired ones (up to 10 mm rad) multiple scattering can be used in a controlled fashion, by

fig. 1a MICE beamline

fig. 1c MICE experiment

fig. 1b beamline/experiment interface: the MICE diffuser

An ideal diffuser should have a large radius to produce a uniform emittance inflation over the entire sample of muons. Due to mechanical constraints the maximum radius can be only 15 cm, further reduced to 13 cm by practical limitations in the insertion/extraction of the lead plates. In order to improve the uniformity of emittance inflation at higher amplitudes an external annulus (1 cm thick) is foreseen, which is relevant for higher emittances, being practically inactive for lower ones. Fig. 3 illustrates the effect of using a finite radius disc. It also shows how the external annulus helps reducing non-uniformities, especially at low momenta.

Radial Size

Thickness

[2] F.J.M. Farley, “Optimum Strategy for energy degraders and ionization cooling”, Nucl. Instr. And Meth. In Phys. Res. A, Vol. 540, Issues 2-3, 21 March 2005, Pages 235-244

fig. 3

Fig. 4: evolution of optical functions and emittance from the TOF1 position along the beamline to the spectrometer solenoid. This naming convention is the one used in (eq. 1).

Fig. 3: emittance bias due to a finite size radius of the degrader plate. On the vertical axis the ratio of the measured emittance for a plate of radius Rdiff and the one determined with a plate of very large radius.

placing a layer of material, like a lead disc of defined thickness, at the proper location (fig. 1b).This element constitutes the diffuser, and the choice of its thickness is ruled by three basic requirements:• inflate the initial emittance to some desired value, • cover most of the amplitudes accessible by the tracking devices (and not cut off by the actual cooling channel),• be flexible enough to work for all the configurations of the (,p) matrix.The best position for the diffuser is inside the bore of the first spectrometer solenoid (fig. 1b) which poses several mechanical challenges.

the MICE Diffuser System(1)

M.Apollonio+, J.Cobb, M.Dawson, T.Handford, P. Lau, W.Lau, J.Tacon, M.Tacon, S.Yang

[1] the Scienc and Technology Facility Council Rutherford Appleton Laboratory, Didcot OX11 0QX (UK)

tab. 1

13 b

=1.4 mm

rad

x

x’fig. 4

the MICE Diffuser System(2)

(+) m.apollonio@physics.ox.ac.uk Poster session, EPAC08 Genoa – WEPP108

M.Apollonio+, J.Cobb, M.Dawson, T.Handford, P. Lau, W.Lau, J.Tacon, M.Tacon, S.Yang

Construction

The system consists of a revolving carousel with six fingers hosting five lead discs of different thickness and an empty disc (fig. 1). After the controlled rotation of the fingers the selected disc is being unloaded from the carousel, loaded onto a catcher and transported into the solenoid bore at the selected location. Fig. 3a and 3b illustrate

Fig. 3a-b: main movements for the diffuser system disc insertion sequence: (A) rotation of the main carousel, aligning the selected disc. (B) lock rotation, releasing the disc to the catcher. (C) rotation of the main cylinder causing the linear motion of the catcher towards the final location inside the solenoid bore. The extraction sequence is simply the opposite.

Fig 2: the three air motors (A-B-C) used to drive the system and the locking piston (P) used to ensure the alignment of the carousel with the beam axis. Gear boxes are coupled to the motors in order to provide the proper rpm ratio.

To ensure the accurate positioning of the carousel (A) and the alignment of the disc prior to locking/unlocking (B), a system of optical encoders will be used which guarantee a precision of less than 0.2 degrees. The insertion/extraction of the catcher is controlled by means of end course micro switches.

Control

The movements of the diffuser system will be issued by an FPGA programmed to perform the predefined tasks as defined in the MICE diffuser control sequence (fig. 4). Command selection could be made by either a program running on a remote PC located in the MICE control room (via optical link) or locally by buttons mounted on the electronics crate front panel. The status of the diffuser will be sent back to the remote PC and the electronics crate front panel using a legend and LED indicators. The FPGA will control the solenoid valves (fig. 5) used to direct the air flow towards the motors, receiving feedback from encoders and micro switches.

A BC

Fig. 4: scheme of the electronic control system.

P

Fig. 1: integration of the diffuser mechanism with the MICE spectrometer. The cross section reveals the tracker stations and the superconducting coils of the spectrometer solenoid.

A

B

C

Conclusions

The Diffuser System is presently being assembled for mechanical checks in the Oxford Mechanical Workshop (fig. 6). Contemporarily the control electronics is being developed and tested. Control and mechanics will be merged and tested in Oxford prior to their delivery to Rutherford Lab upon the arrival of the spectrometer solenoid where the device is to be mounted.

Fig. 6: (a) the diffuser system being mounted on the test stand in the Oxford Mechanical Workshop. (b) inset showing the packed volume with gears and motors. (c) detail of the disc insertion area.

Fig. 5: (a) the air system crate front panel. (b) air system back plane with the air purifying system, gas inlets and the solenoid valves used to direct the air flows used to drive the motors.

controllogic

solenoiddrivers

air valvesolenoids

sensors

air supplyselect valve

F/O link

electronics cratefront panel

switches

MUX

network

COM

FPGA

OXFORD PHYSICS prototyping board

select

limit switches, pressure switchesand encoders

motor control

default is local control

REMOTE PC(located in MICE CR)

the three basic movements characterizing the system. All the sequence of selection and deployment of the chosen disc is remotely controllable via three air motors (fig. 2), chosen for their compliance with the high magnetic fields (some Tesla) of the region, preventing the use of normal electric motors.

fig. 3b

fig. 3a

fig. 1

fig. 2

fig. 5b

fig. 5

fig. 6a

fig. 6bfig. 6c

fig. 5a