Measurement of Sub-picosecond Bunch Length with the Interferometry from Double Diffraction Radiation Target*

Reliable and precise methods for non-invasive diagnostics of sub-picosecond electron bunches are required for new accelerator facilities (FEL, LWFA, et al.). Measurements of spectral characteristics of coherent radiation generated by such bunches using interferometer allow to determine a bunch length [1]. Here we present a compare experimental study between the measurement from the double diffraction radiation target interferometry and the measurement from the Michelson interferometer. INTRODUCTION Non-invasive methods of the sub-picosecond bunch length diagnostics are very important nowadays for such accelerator facilities as free electron lasers with typical bunch lengths of some hundreds of femtoseconds. One of the ways to measure the electron bunch length is based on coherent radiation that is generated at wavelengths comparable to, or longer than, the bunch length, when all electrons in the bunch irradiate more or less in phase. The intensity of coherent radiation is proportional to the square of the bunch population. The spectral distribution of the coherent radiation contains information about the electron bunch distribution. Coherent diffraction radiation (CDR) is suggested as the mechanisms for coherent radiation generation due to their non-invasive nature. DR appears when a charged particle moves rectilinearly in a vacuum in the vicinity of a medium. If the particle passes through a slit between two semi planes, it induces time-varying currents on both semi planes. These currents generate radiation. Two cones propagate in the direction of specular reflection producing an interference pattern. The interference pattern obtained by two diffraction radiation beams from two shifted plates (double DR target) may be used instead an interferometer [2]. Recently, the coherent DR interferometry scheme was established [3] on the femtosecond accelerator facility at SINAP [4, 5]. EXPERIMENTAL SETUP Our experimental equipments were consisted of a linear accelerator, a vacuum chamber with targets driven by motion-control system, a Michelson interferometer and a detector.