Coherent synchrotron radiation detector for a non-invasive subpicosecond bunch length monitor

A Coherent Synchrotron Radiation (CSR) detector has been developed in a collaboration involving CEBAF and the University of Virginia (UVA) to monitor non-destructively the length of a sub-picosecond bunch with high sensitivity. The monitor employs a state of the art GaAs Schottky whisker diode developed at UVA, which is operated at room temperature at a wavelength of a few hundred microns. The detector is capable of detecting radiation power as low as ten nanowatts, depending on the operating wavelength. In this paper we describe the details of design specifications, parameter ranges, and features of the monitor and also report its performance and comparison between the measurement results and calculation. The measurement results are cross-compared with an independent bunch length measurement using a phase modulation and detection technique. Following a brief discussion of the need for such a monitor, the following topics are discussed: brief discussion on the theory of the device and the experimental arrangement, the properties of the Schottky diode detectors which are particularly convenient for our application, a summary of the measurement results, a summary of future plans and improvements to the monitor, and finally, a set of conclusions