DELTA, Dortmund, Germany
The upcoming upgrade of BESSY II, called BESSY-VSR*, involves the utilization of superconducting multicell RF-resonators with high accelerating gradients to provide short and long bunches in an electron storage ring simultaneously. Even under the assumption of strongest available damping of beam induced modes, the residual impedances of the cavities may cause collective multibunch instabilities at the frontier of stability available from current bunch-by-bunch feedback systems. At the DELTA electron storage ring, a phase modulation of the driving RF is used to suppress coupled-bunch instabilities and to increase the lifetime. The time dependent frequency variation in the order of the synchrotron frequency gives rise to additional damping of the bunch oscillators by decoherence and Landau damping. The behaviour and the additional damping of the bunch oscillators is investigated by the existing bunch-by-bunch feedback system e.g. the increase of the overall damping might support the capability of feedback systems under extreme operating conditions of BESSY-VSR.
* G. Wüstefeld et al., Proc. of IPAC'11, San Sebastián, THPC014
DELTA, Dortmund, Germany
KIT, Karlsruhe, Germany
DESY Zeuthen, Zeuthen, Germany
Coherent ultrashort THz pulses induced by a laser-electron interaction are routinely produced and observed at DELTA, a 1.5-GeV synchrotron light source operated by the TU Dortmund University. The turn-by-turn evolution of the radiation spectrum is known to shift to the sub-THz regime after the initial laser-electron interaction. Recently, an ultrafast YBCO-based THz detector has been permanently installed and a Schottky diode has been tested at the THz beamline. Measurements with these detectors showing the temporal evolution of the coherent signals after several revolutions are presented. Furthermore, the concept of a recently designed Fourier-transform spectrometer optimized for the sub-THz region is shown.
DESY, Hamburg, Germany
Uni HH, Hamburg, Germany
DELTA, Dortmund, Germany
DELTA, Dortmund, Germany
A laser-based method to generate ultrashort pulses of synchrotron radiation in electron storage rings is coherent harmonic generation (CHG) using two undulators to produce coherent radiation at harmonics of the initial laser wavelength by microbunching. The bunching factor and thus the pulse intensity, however, decreases exponentially with increasing harmonic order. Echo-enabled harmonic generation (EEHG), proposed in 2009 as FEL seeding scheme*, can be used to produce short synchrotron radiation pulses at higher harmonics, but requires three undulators in a straight section. In this paper, a less space-consuming method based on seeding with intensity-modulated laser pulses is introduced, which also has the potential of significant bunching factors at high harmonics.
* G. Stupakov, PRL 102 (2009), 074801.
DELTA, Dortmund, Germany
DESY Zeuthen, Zeuthen, Germany
At DELTA, a 1.5-GeV synchrotron light source operated by the TU Dortmund University, a source for coherent and ultrashort vacuum-ultraviolet (VUV) and terahertz (THz) pulses is now in operation. The VUV source is based on a laser-induced energy modulation and coherent harmonic generation (CHG). A subsequently developing dip in the longitudinal electron distribution gives rise to coherent THz radiation. Recent results regarding the optimization of the laser-electron interaction and characterization of the CHG pulses are presented.