Abstract
At KARA, the KArlsruhe Research Accelerator of the KIT synchrotron, the so called short bunch operation mode allows the reduction of the bunch length down to a few picoseconds. The micro- bunching instability resulting from the high degree of longitudinal compression leads to fluctuations in the emitted THz radiation, referred to as bursting. For extremely compressed bunches at KARA, bursting occurs not only in one but in two different bunch-current ranges that are separated by a stable region. This work presents measurements of the bursting behavior in both regimes. Good agreement is found between data and numerical solutions of the Vlasov-Fokker-Planck equation.
Highlights
The Karlsruhe Research Accelerator (KARA) is the storage ring of the accelerator test facility and synchrotron light source of the Karlsruhe Institute of Technology (KIT) in Germany
The measurements will be compared to a model which considers the Coherent synchrotron radiation (CSR) wakefields generated by an electron moving on a purely circular orbit of radius R in between two parallel plates separated by a distance of 2h
The short-bunch-length bursting observed at KARA for certain machine settings corresponds to the behavior observed in the results of the Vlasov-Fokker-Planck solver calculations first published by Bane, Cai, and Stupakov [3]
Summary
As soon as the bunch becomes longitudinally unstable, the temporal variation of the particle distribution in the longitudinal phase space leads to a time-dependent modulation of the emitted CSR This longitudinal instability is driven by CSR self-interaction (described by the CSR impedance) and is referred to as microbunching [1], due to the formation of substructures on the longitudinal bunch profile. Indications can be seen in measurements at Diamond (see [7], Fig. 6), though it was not discussed further This additional region of instability was already predicted by simulations in Ref. This instability is referred to as short-bunchlength bursting (SBB) In this contribution, we discuss measurements of the SBB instability at KARA and compare them to existing theoretical predictions and numerical simulations. V, these simulation results are compared to the experimental ones, and some first ideas and possibilities are discussed in order to explain the small discrepancies and improve the already good agreement between the experiment and theory
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