Low-α Operation of BESSY II and Future Plans for an Alternating Bunch Length Scheme BESSYVSR

Significant progress has been made in the last few years in short-bunch operation of third-generation synchrotron light sources, achieved by “lowα” optics for storage rings [1 Abo-Bakr, M. 2002. Phys. Rev. Lett., 88: 254801[Crossref], [PubMed] , [Google Scholar]–4 Müller, A.-S. Short-pulse operation of storage ring light sources. Proceedings of IPAC2013. Shanghai, China. (in press) [Google Scholar]]. The term α is a machine optics parameter describing the particle orbit length L as a function of the particle momentum p, L = L0(1 + α(p − p0)/p0), with respect to the nominal values indicated by the index “0”. The “zero current” bunch length σ is then proportional to . Included here is the rf-voltage temporal gradient, V′ = dV/dt, which additionally influences the bunch length and will be required further. Thus, lowering α leads to a reduced bunch length all around the ring and radiation of the short bunches is supplied to all beamlines. These short bunches produce short X-ray pulses of equal length suitable for time-resolved measurements. Simultaneously, the short electron pulses emit intense, coherent THz radiation.