Undulator-Based Production of Polarized Positrons, A Proposal for the 50-GeV Beam in the FFTB

G Alexander ,John R Turner ,V Gharibyan ,Yu Efremenko ,A Mikhailichenko ,V Bharadwaj ,S M Spanier ,M Olson ,K P Schüler ,T Behnke ,Gudrid Moortgat‐Pick ,D Onoprienko ,R Iverson ,Perry Anthony ,J E Clendenin ,F.j Decker ,T Handler ,S Berridge ,T Hirose ,T Omori ,H Kolanoski ,J.c Sheppard ,R Carr ,C Lü ,M V Purohit ,Z M Szalata ,Klaus Flöttmann ,K.t Mcdonald ,D Walz ,Y Batygin ,K Mönig ,W Bugg ,G R Bower ,T Löhse ,Yu Kamyshkov ,Masafumi Fukuda ,A W Weidemann ,R Pitthan ,A Stahl ,N Meyners ,N Pavel ,R Michaels ,E Chudakov ,L Rinolfi ,T Fieguth ,J G Weisend

doi:10.2172/825067

Abstract

The full exploitation of the physics potential of future linear colliders such as the JLC, NLC, and TESLA will require the development of polarized positron beams. In the proposed scheme of Balakin and Mikhailichenko [1] a helical undulator is employed to generate photons of several MeV with circular polarization which are then converted in a relatively thin target to generate longitudinally polarized positrons. This experiment, E-166, proposes to test this scheme to determine whether such a technique can produce polarized positron beams of sufficient quality for use in future linear colliders. The experiment will install a meter-long, short-period, pulsed helical undulator in the Final Focus Test Beam (FFTB) at SLAC. A low-emittance 50-GeV electron beam passing through this undulator will generate circularly polarized photons with energies up to 10 MeV. These polarized photons are then converted to polarized positrons via pair production in thin targets. Titanium and tungsten targets, which are both candidates for use in linear colliders, will be tested. The experiment will measure the flux and polarization of the undulator photons, and the spectrum and polarization of the positrons produced in the conversion target, and compare the measurement results to simulations. Thus the proposed experiment directly tests for the first time the validity of the simulation programs used for the physics of polarized pair production in finite matter, in particular the effects of multiple scattering on polarization. Successful comparison of the experimental results to the simulations will lead to greater confidence in the proposed designs of polarized positrons sources for the next generation of linear colliders. This experiment requests six-weeks of time in the FFTB beam line: three weeks for installation and setup and three weeks of beam for data taking. A 50-GeV beam with about twice the SLC emittance at a repetition rate of 30 Hz is required.

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