(+) [email protected] Poster session, EPAC08 Genoa – WEPP108 em pty abs full abs T (m m) e3N a b (cm) s _x,y (cm ) P_before(G M eV/c) T (m m) e3N a b (cm) s _x,y (cm ) P_before (M eV/c) 0 2.65 0.09 34.3 2.19 200 200 M eV/c 207MeV/c 0 2.70 0.09 34.30 2.19 207.00 7.5 6 0.23 78.02 3.3 210.81 7.5 6.15 0.46 84.96 3.45 217.73 15.5 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 M eV/c 148.4 M eV/c 1.5 3.00 0.19 56.24 2.81 150.75 5 6.13 0.67 113.15 3.98 147.98 5 6.06 0.32 112.69 3.97 156.22 10 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 M eV/c 245.2 M eV/c 0 3.25 0.09 41.85 2.42 245.20 7.5 6.18 0.14 79.61 3.34 250.44 7.5 6.24 0.19 80.58 3.36 255.61 15.5 9.93 0.25 128.25 4.24 261.58 15.5 9.98 0.32 129.42 4.26 266.71 e3N (m m rad) 3 6 10 P(MeV/c) 140/148.4 1.5 5 10 200/245.2 0 7.5 15.5 240/245.2 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 1 3 b =1.4 mm rad x x’ fig. 4