Speaker
Dr
Igor Pogorelsky
(Brookhaven National Laboratory)
Description
This scheme employs Compton backscattering from a 4 GeV linac’s e--beam inside a CO2 laser amplifier cavity. The scheme relies on commercially available lasers and does not require positron stacking. The required number of positron per bunch is produced in every laser shot at 50 Hz repetition rate.
The essential features of this scheme are: using a mid-IR CO2 laser that provides 10 times more laser photons per Joule to compare with a solid-state laser, and the most energy-efficient back-scattering geometry. This allows attaining the gamma-ray production of 1 photon per electron, Ng/Ne-=1, as has been demonstrated in the experiment.The conversion efficiency of the polarized gamma photons into polarized positrons is expected to be about 2%. Therefore, every positron requires, as precursors, fifty gamma photons. With Ng/Ne-=1, and 5-10 nC/bunch delivered from the electron linac, correspondingly ten-five consecutive Compton IPs will be required to accumulate the gamma flux for the 1-nC positron bunch production. Intra-cavity positioning of the interaction point (IP) allows laser energy recycling to compensate for optical losses inside the cavity (assumed here 2-5% per round trip).
The linac’s electron beam is formatted into: trains of ~300 bunches at ~5-12 ns spacing and 50-150 Hz repetition rate. This matches the optimum regime for the energy extraction from the laser.
The 1-nC positron bunches, produced on a target by the Compton-scattered gamma-photons, will be injected into a dumping ring were reformatting into bunch separation required for ILC or CLIC will be achieved.
Simulations and experiments on laser pulse injection and train production inside the Compton cavity are in progress at BNL.
Author
Dr
Igor Pogorelsky
(Brookhaven National Laboratory)
Co-authors
Dr
Mikhail Polyanskiy
(BNL)
Dr
Vitaly Yakimenko
(BNL)
