Single-shot spectral fingerprints for continuous observation of the microbunching instability at KARA

The micro-bunching instability occurring in an electron storage ring for short electron bunches leads to the emission of coherent synchrotron radiation (CSR) in the terahertz range. This collective instability can be studied by observing the resulting fluctuations in the emitted CSR power with fast THz detectors. The measurements presented in this contribution were conducted at the KIT electron storage ring KARA (KArlsruhe Research Accelerator) in a dedicated short-bunch operation mode. For the measurements of these instability-induced CSR power fluctuations, an on-chip THz spectrometer providing a spectral fingerprint was used. The mm-sized chip contains eight antennas that are sensitive in different frequency ranges from 50 GHz up to 700 GHz, each connected to a Schottky-diode detector element. The on-chip spectrometer was read-out with the new version of the KArlsruhe Pulse Taking and Ultrafast Readout Electronics system, KAPTURE-2, providing continuous bunch-by-bunch data.