Femtosecond laser clocked compact X-band high gradient photoinjector and accelerator for Compton scattering.

摘要

High brightness and low emittance electron beams have found application throughout a variety of scientific research. The ability to produce such beams in the MeV range has previously been restricted to National Laboratory size facilities. While these sources have been successful, the reduction in size could provide valuable access for further scientific endeavors. One such application is the production of monochromatic x-rays through Compton scattering with a high intensity laser pulse. These x-rays would be tunable from 10 keV to more than 100 keV. A compact source of synchrotron type radiation capable of installation in medical institutions would be desirable for further investigation. A combination of X-band microwave and vacuum technologies developed at the Stanford Linear Accelerator Center (SLAC) was assembled. The system uses a pair of X-band klystrons. The first provides the microwave drive power for a 5.5 cell RF gun capable of operating with an accelerating gradient of 200 MV/m. Following the RF gun is a 1.05 m linac capable of accelerating the electron bunches to over 60 MeV with an energy spread of less than 1%. Using a novel frequency selection scheme a Titantium:Sapphire femtosecond laser oscillator serves as both the master clock for the microwave components and optical seed for the following amplifiers. This insures the tabletop laser amplifiers are inherently synchronized to the RF sources. A regenerative amplifier provides the first boost in energy. Half of the output is used for producing UV light for photo injection of the RF gun. The other half is sent to a multi-pass amplifier capable of producing 100 mJ pulses compressed to 50 fs for the Compton scattering. This interaction laser is then focused inside the electron beam vacuum system. The final timing between the optical pulses and the electron beam is achieved with a physical delay line placed after the final amplifier compressor. Background Bremsstrahlung radiation due to interception of the electron beam limited initial detection of the Compton x-rays. The first evidence of Compton x-rays was demonstrated through a scan of the time delay between the electron bunch and the optical pulse at the point of collision.