An ultracold electron source as an injector for a compact SASE-FEL

Ultracold electron sources based on near-threshold photoionization of laser-cooled atomic gases can produce ultrashort electron pulses with a brightness potentially exceeding conventional pulsed electron sources. They are presently being developed for single shot ultrafast electron diffraction, where a bunch charge of 100 fC is sufficient. For application as an injector for x-ray free electron lasers (FEL) a larger bunch charge is generally required. Here we present preliminary calculations of an ultracold electron source operating at bunch charges up to 1 pC. We discuss the relevant bunch degradation processes that occur when the charge is increased. Using general particle tracer tracking simulations we show that bunches can be produced of sufficient quality for driving a 1 Å self amplified spontaneous emission free electron laser (SASE-FEL) at 1.3 GeV electron energy. In addition we speculate on the possibility of using the ultracold source for driving a 15 MeV SASE-FEL in Compton backscatter configuration into the quantum FEL regime. (paper)