Design Study of High Gradient Compact S-band TW Accelerating Structure for the ThomX LINAC Upgrade

ThomX is a Compton source project in the range of the hard X rays (45/90 keV). The machine is composed of a 50/70 MeV injector Linac and a storage ring where an electron bunch collides with a laser pulse accumulated in a Fabry-Perot resonator. The final goal is to provide an X-rays average flux of 10¹²-10¹³ ph/s. A demonstrator was funded and is being built on the Orsay university campus. The S-bandinjector Linac consists of 2.5 cell photocathodeRF gun and a TW accelerating section. During the commissioning phase, a standard LIL S-bandaccelerating section is able to achieve around 50 MeV corresponding to around 45 keV X-rays energy. Since the maximum targeted X-ray energy is 90 keV, the development of a new S-bandaccelerating section, intended to replace the LIL structure, will provide an electron beam energy of 70 MeV. This requires essentially the development of more reliable high gradient compact S bandaccelerating section. Such design is tailored for high gradient operation, low breakdown rates. We present here the RF design of the LINAC upgrade and the performances obtained in terms of beam dynamics.