IAP/RAS, Nizhny Novgorod, Russia
Euclid Beamlabs LLC, Bolingbrook, USA
Euclid TechLabs, LLC, Solon, Ohio, USA
IAP/RAS, Nizhny Novgorod, Russia
The photoinjector of short electron bunches is a key element of investigations aimed on particle acceleration by pulses of the subpetawatt laser PEARL (10 J, 50-70 fs). The projected parameters of the photoinjector are an electron energy level of 5 MeV, a charge > 0.1 nC, a bunch length of about 3 mm, a transversal emittance no worse than 1 mm*mrad, and an energy spread no more than ~0.1%. The photoinjector is based on klystron KIU-111 at frequency 2.45 GHz, produced by company Toriy (output power ~ 5 MW, pulse length ~ 7 mcs, efficiency ~ 44%, power gain ~ 50 dB). It is proposed to use this klystron in order to feed the accelerating resonator of the classical design consisted of 1.5 cells in which the photocathode is inserted. On a base of third harmonics of a Ti:Sa laser, we plan to produce picosecond pulses of no less than 100 mcJ in energy. The photocathode is planned to be made of CVD diamond film which is not critical to vacuum degree and surface contamination, has high QE, a long lifetime, and is capable of being used with cheap, long wavelength optical lasers.
IAP/RAS, Nizhny Novgorod, Russia
Euclid TechLabs, LLC, Solon, Ohio, USA
UNN, Nizhny Novgorod, Russia
We propose an efficient XFEL consisting of sequential RF undulator sections using: 1) tapered flying RF undulators, 2) short pulse, high peak-power RF and 3) driving undulator sections by spent electron beam. In a flying RF undulator, an electron bunch propagates through a high-power, nanosecond, co-propagating RF pulse. Helical waveguide corrugation supports a space harmonic with a negative propagation constant, providing a large Doppler up-shift. The undulator tapering technique improves FEL efficiency by 1-2 orders of magnitude in comparison with other facilities by decreasing the undulator period so that particles are trapped in the combined field of the incident x-ray and undulator field. We develop a so-called non-resonant trapping regime not requiring phase locking for feeding RF sources. Simulations show that by decreasing the corrugation periodicity one can vary an equivalent undulator period by 15%. The spent electron beam can be used to produce wakefields that will drive the RF undulator sections for interaction with the following beam. We have already manufactured and tested the 30 GHz simplified version of the 50 cm long undulator section for cold measurements.