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The ultra-short bunch is the key for producing strong terahertz coherent synchrotron radiation (CSR) and some other applications. A study is being conducted at MIT-Bates South Hall Ring to get 1 mm or shorter electron bunch length. A set of low momentum compaction lattice configurations have been designed. In first beam experiment in 2004, two of these configurations were successfully commissioned in which the momentum compaction was reduced by two orders of magnitude. About 1 mm rms bunch length was measured with a streak camera. It has been demonstrated that this storage ring machine has a great degree of flexibility and potential as an ideal test bed for various advanced beam physics studies.

We investigate the terahertz coherent synchrotron radiation (CSR) potential of the South Hall Ring (SHR) at MIT-Bates Linear Accelerator Center. The SHR is equipped with a unique single cavity, 2.856 GHz RF system. The high RF frequency is advantageous for producing short bunch length and for having higher bunch current threshold to generate stable CSR. Combining with other techniques such as external pulse stacking cavity, femtosecond laser slicing, the potential for generating ultra-stable, high power, broadband terahertz CSR is very attractive. Beam dynamics issues related to short bunch length operation, such as multi-bunch instability (perhaps associated with the high frequency RF system), are considered. The SHR is ideal for experimental exploration of such issues, which could affect bunch length, bunch intensity and beam stability. Results of initial tests of low momentum compaction lattices and bunch length measurements are presented and compared to expectations.