Micro-bunching diagnostics for inverse Cherenkov acceleration by coherent transition radiation

Here, we propose an effective method to detect micro-bunching effects (10 fs bunch length), produced by the inverse Cherenkov acceleration (ICA) interaction, by using the coherent transition radiation (CTR) spectrum. The pre-bunching of initially energy modulated electron beam passing through a hydrogen gas cell is studied via a Monte Carlo simulation code (STI), as well as in a space-charge dominated region by a multi-particle time domain tracking code (PARMELA). The results show that even in a strong space-charge dominated region the pre-bunching effect is still very pronounced. The ''erosion'' of bunching due to the space-charge defocusing ''washes out'' the final bunching peak only by about 10% (FWHM). The longitudinal distribution of a micro-bunched beam is Fourier analyzed to find the dominant harmonics contributing to the CTR. The CTR spectrum is calculated analytically for the ICA situation. A schematic of the experimental set up is also proposed. (orig.)