Abstract:
The Inverse Compton Scattering (ICS) X-ray source of ELSA accelerator at CEA-DAM, presents an efficient approach for generating X-rays with a compact linac. The source consists of a 30 MeV, 15 ps rms, up to 3 nC electron beam; and a table-top Nd:YAG laser. X-rays are produced in the
10-80 keV range, higher X-ray energies achieved with frequency doubling of the laser. The yield is increased by a factor of 8 thanks to an optical mirror system developed at CEA, folding the laser beam path and accumulating successive laser pulses. We present a new version of the device, with improvement of mechanical constraints management, adjunction of motorized mirrors, and a new imaging system. A Chirped Pulse Amplification (CPA) system was also designed, enabling higher amplification levels without exceeding laser damage threshold. The uniqueness of this CPA system lies in its use of a short wavelength bandwidth, ±250 pm after Self-Phase Modulation (SPM) broadening, and a line density of 1850 lines/mm for the gratings of the compressor. The pulse is stretched with a chirped fiber Bragg grating (CFBG) before amplification in Nd:YAG amplifiers, and compressed by a double pass grating compressor. Recently, a 1.3 GHz decelerating cavity was installed to achieve linear chirp before compression, and an upgrade of the 1.3 GHz accelerating cavity, modulator and klystron systems is upcoming (in the next 5 years). These efforts strongly contribute to the optimisation of our Inverse Compton Source. In order to maximise the yield of the ICS source, it is also necessary to optimize the charge and Twiss parameters of the electron bunches. Simulations are used to find the best working point. A difficulty arise: the electron bunches are compressed in two alpha magnets. In such a system, electron trajectories are curved with a short radius (~10cm), using field maps and appropriate PIC code seems necessary.
