Proposal for a Study of Ionization Cooling


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DRAFT Proposal for a Study of Ionization Cooling of a Low-Energy Muon Beam by LH2 and LiH Absorbers C.-X. Wang Argonne National Laboratory, Argonne, IL 60439 D.B. Cline, Y. Fukui, K. Lee, Y. Pischalnikov University of California Los Angeles, Los Angeles, CA 90095 K.-J. Kim, M.J. Oreglia University of Chicago, Chicago, IL 60637 G.G. Hanson Indiana University, Bloomington, IN 47405 C. Lu, K.T. McDonald, E.J. Prebys Princeton University, Princeton, NJ 08544 T.R. Edgecock, R. Bennett Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, UK OX11 0QX (July 5, 2000) Abstract As a step in a larger program of muon cooling R&D, we propose to study ionization cooling of 170-MeV/c muons in LH2 and LiH absorbers inside a 2-2.5 T solenoid magnet but without rf acceleration (“minicooling”). The required flux of muons is small, such that only one muon is in the apparatus at a time; the desired muon bunch will be reconstructed offline via software. This study will validate the analytic and numerical calculations of ionization cooling via measurements of multiple scattering and straggling, will demonstrate transverse cooling of a muon bunch including the predicted coupling of transverse emittance to angular momentum when inside a solenoid channel, and will use diagnostics suitable for further cooling studies. The proposed demonstration of transverse cooling via the single-particle method is a natural extension of TRIUMF E875 that is making a precision measurement of muon multiple scattering in low-Z absorbers. 1 1 Introduction As has been noted since the earliest discussions of storage rings, “cooling” of the beam emittance is the key to a practical device [1]. In the case of muon storage rings, the cooling must be accomplished in a time of order 1 μs to avoid loss of the beam by muon decay. This excludes such relatively slow methods as stochastic cooling, electron cooling and radiative cooling. When charged particles pass through matter they lose energy to the medium via excitation and ionization of atomic electrons. This technique of ionization cooling [1, 2] is uniquely applicable to muon beams because the interaction of the muons with the atomic nuclei is negligible. Ionization cooling is critical to the success of both muon colliders [3] where a reduction of 6-dimensional phase volume by a factor of 106 is desired, and to neutrino factories based on muon storage rings [4, 5, 6] where a reduction factor of 10-100 is desired. However, ionization cooling of muons has not yet been demonstrated in the laboratory.1 The present proposal is to study the basic principles of ionization cooling of muons by low-Z absorbers, including the effect of a solenoid magnetic field which couples transverse emittance to canonical angular momentum. We first review the principles of ionization cooling in sec. 1.2, and then place the present proposal in a larger context of studies of ionization cooling in sec. 1.2. Etc..... 1.1 Analytic Expressions for Ionization Cooling If there were no fluctuations in the interaction of muons with atoms, perfect cooling could be achieved simply by removing all of the muons’ initial ...

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