Coherent Smith-Purcell Radiation for use in electron beam diagnostics

Coherent Smith-Purcell Radiation (CSPR) is quite useful in the area of intense ultra-short pulse electron beams. This is because it offers the potential for non-destructive, real time measurements of high brightness pulses being developed for use in many next-generation electron beam accelerator projects, such as NLC, TESLA test facility, and various other plasma-based accelerator schemes. Both the non-destructive and real time aspects of using CSPR are significant to ultra-short pulse measurement. Preliminary calculations show that CSPR is capable of producing usable signals from realistic electron beam and electron beamline operating parameters that can be analyzed to provide pulse structure, energy, emittance, and timing information. At the same time, induced emittance growth is well below an amount that would seriously deteriorate beam quality for even ultra-high brightness beams. Timing measurements using CSPR is a critical area for development efforts, because of the lack of existing techniques for accurate single pulse sub-picosecond measurements. Injection accuracy for advanced accelerator techniques, as is the case for conventional RF structures, is dictated by getting the pulse into the accelerator at the correct phase. This implies absolute timing accuracies on the order of 10-20 femtoseconds, for a laser-accelerator system that pulses at much less than once per second. By producing CSPR at one or more locations along the beamline, interferometric techniques can then mix this radiation with a timing signal from the laser and beamline timing measurements, useful for fine tuning the transport system and laser beam delay lines, will become obtainable