High flux polarized gamma rays production: first measurements with a four-mirror cavity at the ATF

TL;DR

This paper reports the first measurements of high flux polarized gamma rays produced via inverse Compton scattering using a four-mirror Fabry-Perot cavity at the ATF, demonstrating a flux of 4 million gamma rays per second.

Contribution

It introduces a novel optical system with a four-mirror cavity for efficient polarized gamma ray production at the ATF, including experimental setup and preliminary results.

Findings

Achieved a gamma ray flux of approximately 4×10^6 gamma/sec.

Produced gamma rays with an average energy of about 24 MeV.

Implemented an ultra-stable non-planar cavity geometry and digital feedback system.

Abstract

The next generation of e+/e- colliders will require a very intense flux of gamma rays to allow high current polarized positrons to be produced. This can be achieved by converting polarized high energy photons in polarized pairs into a target. In that context, an optical system consisting of a laser and a four-mirror passive Fabry-Perot cavity has recently been installed at the Accelerator Test Facility (ATF) at KEK to produce a high flux of polarized gamma rays by inverse Compton scattering. In this contribution, we describe the experimental system and present preliminary results. An ultra-stable four-mirror non planar geometry has been implemented to ensure the polarization of the gamma rays produced. A fiber amplifier is used to inject about 10W in the high finesse cavity with a gain of 1000. A digital feedback system is used to keep the cavity at the length required for the optimal power enhancement. Preliminary measurements show that a flux of about $4\times10^6 \gamma$/s with an average energy of about 24 MeV was generated. Several upgrades currently in progress are also described.