The microbunching instability is an ubiquitous problem in storage rings at high current density. However, the involved fast time-scales hampered the possibility to make direct real-time recordings of theses structures. When the structures occur at a cm scale, recent works at UVSOR*, revealed that direct recording of the CSR electric field with ultra-high speed electronics (17 ps) provides extremely precious informations on the microbunching dynamics. However, when CSR occurs at THz frequencies (and is thus out of reach of electronics), the problem remained largely open. Here we present a new opto-electronic strategy that enabled to record series of successive electric field pulses shapes with picosecond resolution (including carrier and envelope), every 12 ns, over a total duration of several milliseconds. We also present the first experimental results obtained with this method at Synchrotron SOLEIL, above the microbunching instability threshold, and we present direct tests of Vlasov-Fokker-Planck and macroparticle models. The method can be applied to the detection of ps electric fields in other situations where high repetition rate is also an issue.

Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany