26(a): High Duty Cycle Inverse Free Electron Laser

Laser based advanced accelerators can achieve very high accelerating gradients, but their duty cycle is limited by the laser power availability and media recovery time. Inverse Free Electron Laser (IFEL) is a vacuum farfield laser accelerator scheme which does not rely on a medium (plasma) or a structure (metal or electric) and therefore is potentially capable of accelerating charged particles very efficiently and at very high duty cycles; however, it requires TWlaser power to reach GV/m gradients which still stands as the limiting factor for high average power applications. Technical approach In response to this opportunity, RadiaBeam is developing an active recirculated CO2 optical cavity to recover and recycle and reamplify the laser power after each IFEL interaction, enabling efficient laser driven acceleration of electron bunch trains at 20 MHz. Phase I Results: A conceptual design, initial engineering and thorough numerical simulations of the proposed intracavity IFEL has been carried out. A mock up optical cavity was assembled and tested to establish basic properties of the recirculated laser beam, and gain confidence in the ability to control the laser transverse profile and intensity over the duration of the pulse train. Phase II Plan: In Phase II, the subsystems will be fabricated and tested, and the full intracavity IFEL system will be integrated and commissioned at the Accelerator Test Facility at BNL. The goal of the project is the first ever demonstration of high gradient high energy gain laser acceleration of electron bunch trains at MHz frequencies. Commercial applications and other benefits: There are three commercialization thrusts: IFEL based Inverse Compton Scattering gamma ray source, IFEL based soft Xray FEL, and an IFEL decelerator light source (TESSA). The gamma ray source will target nuclear detection, safety and nuclear spectroscopy applications. IFEL driven FEL can offer a compact room size light source solution for universities and research laboratories; and TESSA will offer a high efficiency light source capability to multiple applications, including semiconductor industry. Key words Inverse Free Electron Laser, IFEL, CO2 laser, active optical cavity, gamma ray source, Inverse Compton Scattering, Free Electron Laser Summary for members of congress This project will develop an extremely bright, compact source of tunable gamma rays, which will uniquely enable detection of concealed nuclear materials at a stand off distances up to 1 km.