Positron Source from X-rays Emitted by Plasma Betatron Motion

A new method for generating positrons has been proposed that uses betatron X-rays emitted by an electron beam in a high-K plasma wiggler. The plasma wiggler is an ion column produced by the head of the beam when the peak beam density exceeds the plasma density. The radial electric field of the beam blows out the plasma electrons transversely, creating an ion column. The focusing electric field of the ion column causes the beam electrons to execute betatron oscillations about the ion column axis. At the proper plasma density, this leads to synchrotron radiation in the 1-50 MeV range. These photons strike a thin (.5Xo), high-Z target and create electron-positron pairs. Experimental results from work conducted at the Stanford Linear Accelerator Center (SLAC), where a 28.5 GeV electron beam was used in a proof-of-principle demonstration of this scheme, were matched with a simulation model. This model was expanded to design a potential positron source, giving positron yields of 0.44 positrons/electron, a number that is close to the target goal of 1-2 positrons/electron for future positron sources.