Ultra low vertical emittance at SLS through systematic and random optimization

A new vertical emittance record of 0.9±0.4pmrad was established in the storage ring of the Swiss Light Source (SLS) at 2.4 GeV by the application of a sequence of methods: Magnet girders were remotely vertically realigned in order to suppress the dipolar fields that produce the spurious dispersion in the vertical plane. A systematic optimization was then performed by measuring and correcting the betatron coupling and the vertical dispersion by means of 36 skew quadrupole correctors. The correction is performed until a limit is reached from the orbit response matrix (ORM) measurement errors and residual model deficiencies. At this point, the method of random optimization (RO), a multi-variable optimization procedure, was invoked. In the present experiment, the vertical beam size is the target function while the skew quadrupole currents act as the correction variables. The methodology of RO and the systematic correction scheme are described.