PEPPo : Polarized Positron Production Phys. Rev. Lett. 116 214801 (2016) APS Focus Article Editor’s Suggestion For these data we had at 4 MeV yield of ~10-5 e+/e-

High Impact Potential – Based upon JLab expertise in polarized electron beams CEBAF - NP Jefferson Lab Positron Working Group (JLAB-PWG) formed in 2016 120 members (>90% are JLab Users) and 39 Institutions Letter of Intent “Physics Program with Positron Beams at CEBAF 12 GeV” to PAC46 (2018) “These measurements all have significant physics interest.” Jefferson Lab Accelerator Advisory Committee, November 2018 Two recommendations (R27 and R28) to assess conceptual design EIC - NP Enables new probe for flavor/amplitude separation Standard Model (2g/DVCS, neutral/charged current DIS) Beyond Standard Model (PVDIS, Right handed W boson, SUSY) LEPTON COLLIDERS - HEP New interest expressed at LCWS 2018 to consider PEPPo for conventional source at ILC New research topic on polarized positron production proposed to US-Japan HEP collaboration LOW ENERGY SCIENCE – BES/NSF Invited talk at International Conference of Positron Annihilation 2018 Community has interest to have new US facility providing intense polarized positron beams

PhD quality research that can be performed at the UITF Polarization Transfer Experiments Test single-converter thickness – complete an original PEPPo goal to benchmark polarization transfer on target thickness (affects EM shower and spin-filtering of low-E positrons) Test double-converter design – test original PEPPo design to separate gamma converter “beam dump” and generate positrons in a second “quiet” target (only photons go in). Develop Compton transmission polarimeter at UITF – measure longitudinal spin polarization of electrons or positrons readily, using CEBAF Mott as a basis for calibration Target and Yield Experiments Build our first positron collection beam line – learn how to optimize collection and manage beam power at target for useful cw re-acceleration (i.e. we don’t need to re-accelerate, but rather measure distributions transverse/longitudinal). Test high power targets (at low power!) – composed of moving or composite materials such as liquid lead bismuth targets already developed for JLab in SBIR-II. Physics Experiments Do Physics – Bowling Green State University to use polarized gamma and polarized positrons at MeV energies (unmoderated) to study magnetic nanostructures and bulk magnetic properties.

Beam Requirements at the UITF Parameter UITF e- Beam Comment Energy 1-10 MeV OK if dp/p is high Intensity 1-10 uA >10uA OK for “high-power” targets Rep Rate 750 MHz (or sub) 62.5 MHz useful for ToF Duty Factor Any CW preferred Spin Polarization Typical >80% Tests w/ low- or no-P OK Helicity Reversal Typical 30 Hz Faster clock for noise measurements We retained many useful components from PEPPo, and gained useful experience for next measurements.