Proposed Coherent Diffraction Radiation Measurements of Bunch Length at Asta

The feasibility of using the autocorrelation of coherent diffraction radiation (CDR) as a non-intercepting diagnostics technique for bunch length and indirectly rf phase measurements is evaluated and proposed for the Advanced Superconducting Test Accelerator (ASTA) facility under construction at Fermilab. Previous experiments on an rf thermionic cathode gun beam at 50 MeV provide a proof-of-principle reference for the ASTA injector. The ASTA injector is based on an L-band rf photocathode (PC) gun with UV pulse drive laser, two Lband superconducting accelerator structures, a chicane bunch compressor, and an electron spectrometer. The injector energy of 40-50 MeV is expected. The 3-MHz micropulse repetition rate with micropulse charges up to to 3.2 nC and 1-ps bunch lengths should generate sufficient CDR signal for standard pyroelectric detectors to be used. The CDR signals will also be evaluated as a bunch compression signal for beam-based feedback for rf phase. The technique would also be applicable at high energy in straight transport lines after the cryomodules.