The generation of brilliant, stable, and broadband coherent synchrotron radiation (CSR) in electron storage rings depends strongly on ring rf system properties such as frequency and gap voltage. We have observed intense coherent radiation at frequencies approaching the THz regime produced by the MIT-Bates South Hall Ring, which employs a high-frequency $S$-band rf system. The measured CSR spectral intensity enhancement with 2 mA stored current was up to 10 000 times above background for wave numbers near $3{\mathrm{cm}}^{-1}$. The measurements also uncovered strong beam instabilities that must be suppressed if such a very high rf frequency electron storage ring is to become a viable coherent THz source.

• Received 19 October 2005

DOI:https://doi.org/10.1103/PhysRevLett.96.064801