A 90 Ghz Photoinjector

Photocathode rf guns depend on mode locked laser systems to produce an electron beam at a given phase of the rf. In general, the laser pulse is less than σz = 10° of rf phase in length and the required stability is on the order of ∆φ = 1°. At 90 GHz (W-band), these requirements correspond to σz = 333 fsec and ∆φ = 33 fsec. Laser system with pulse lengths in the fsec regime are commercially available, the timing stability is a major concern. We propose a multi-cell W-band photoinjector that does not require a mode locked laser system. Thereby eliminating the stability requirements at W-band. The laser pulse is allowed to be many rf periods long. In principle, the photoinjector can now be considered as a thermionic rf gun. Instead of using an alpha magnet to compress the electron bunch, which would have a detrimental effect on the transverse phase space quality due to longitudinal phase space mixing, we propose to use long pulse laser system and a pair of undulators to produce a low emittance, high current, ultra-short electron bunch for beam dynamics experiments in the 90 GHz regime.