Characterization of changes in the crystal structure for radiated positron source materials

• Tim Lengler (Helmholtz-Zentrum Hereon)

The production of secondary beams at future positron sources for the Continuous Electron Beam Accelerator Facility (CEBAF), the International Linear Collider (ILC) or the Future Circular Collider (FCC), features unprecedented mechanical and thermal stresses which may compromise sustainable and reliable operation. Candidate materials must possess high melting temperature together with excellent thermal conductivity and radiation hardness. This presentation reports about the investigation of radiation hardness properties of different materials, performed at the injector of the MAMI (Mainzer Mikrotron) facility and characterized at the HEMS (High Energy Materials Science) beamline operated by the Helmholtz-Zentrum Hereon at the PETRA III synchrotron facility.

Conceptual design of the capture magnet

• Jay Benesch (JLab)

Initial studies of capture cavities for the CW polarized positron source Ce$^+$BAF

• Shaoheng Wang (Jefferson Lab)

Preliminary calculations for a two photon exchange experiment with electrons in Hall B at JLab

• August Friebolin (George Washington University)

Two photon exchange is one possible explanation for the disparity in the proton form factor ratio when comparing results from Rosenbluth scattering and polarization transfer experiments. To measure the effect of two photon exchange alone we intend to compare the different scattering asymmetries for electrons and positrons scattering off a polarized proton target. The asymmetry difference in these two measurements results from the sign of their charge alone, which is related solely to two photon exchange. Using a Monte Carlo simulation to account for the CLAS detector acceptance, beam shift due to the target holding field, and factoring in uncertainties from target dilution and detector resolution we found that meaningful data can be obtained from a couple weeks of beamtime.