AN SRF PHOTOCATHODE GUN FOR MEV ULTRAFAST ELECTRON MICROSCOPY

In order to achieve sharp, high resolution real-time imaging, electron beams in a MeV UEM (ultrafast electron microscope) beamline need to minimize instabilities and energy spread during generation and acceleration. The stability of the normal conducting photocathode gun which is currently used to produce short electron bunches has been one of main elements limiting the further improvement of beam instability. The Superconducting RF (SRF) photocathode gun is a promising candidate to produce highly stable electrons for UEM/UED applications. It operates in an ultrahigh Q, CW mode, and dissipates a few watts of RF power, which make it possible to achieve a 10s ppm level of beam stability by using modern RF control techniques. Following the Phase II work plan, we have accomplished the engineering design of the conduction-cooled SRF cavity in all possible practical aspects. We have measured the QE of Nb and Nb3Sn. We have fabricated the cryostat and Nb cavity, and completed infrastructure work to install the Cryocooler. The cryocooler and the cryostat were integrated. Both the cool-down test (to 4K) and the magnetic shielding (10^11 e-/s) MeV UED/UEM facility at BNL. Similarly to Phase II, this Phase IIA project will be a joint effort, and the close collaboration remains strong between BNL and Euclid. The development of MeV-range ultrafast electron diffraction/microscopy (UED and UEM) has been identified as an enabling instrumentation in numbers of published DoE reports, which may lead to breakthroughs in fundamental science and applied technologies. The electron source we are proposing will significantly improve performance of the current MeV UEM.