Volker Schlott

Commissioning of the Swiss Light Source

The Swiss Light Source (SLS) at the Paul Scherrer Institute (PSI) consists of a turn key 100 MeV linac, a novel type of booster synchrotron and a 12-TBA storage ring providing 5 nm-rad natural emittance at 2.4 GeV, The SLS project was approved by Swiss Government in Sept. 1997. By June 1999 the building was finished. Linac and booster commissioning concluded by April, resp. Sept. 2000. First beam in the ring was stored Dec. 15, 2000. By June 2001 storage ring commissioning entered the final phase: The design current of 400 mA was reached, an excellent agreement of lattice functions with design calculations was achieved and first undulator spectra were measured. Commissioning of booster and storage ring included commissioning of the innovative subsystems like the digital BPM system, the digital power supplies, the high stability injection system and the CORBA based beam dynamics software.

A scheme for a shot-to-shot, femtosecond-resolved pulse length and arrival time measurement of free electron laser x-ray pulses that overcomes the time jitter problem between the FEL and the laser

The recent entry of X-ray free electron lasers (FELs) to all fields of physics has created an enormous need, both from scientists and operators, for better characterization of the beam created by these facilities. Of particular interest is the measurement of the arrival time of the FEL pulse relative to a laser pump, for pump-probe experiments, and the measurement of the FEL pulse length. This article describes a scheme that corrects one of the major sources of uncertainty in these types of measurements, namely the jitter in the arrival time of the FEL relative to an experimental laser beam. The setup presented here uses a combination of THz streak cameras and a spectral encoding setup to reduce the effect of an FELs jitter, leaving the pulse length as the only variable that can affect the accuracy of the pulse length and arrival time measurement. A discussion of underlying principles is also provided.

Commissioning of the SLS digital BPM system

During the commissioning of the Swiss Light Source (SLS) first operational experience has been gathered with the newly developed digital beam position monitor (DBPM) system. The DBPM performance could be characterized in all available operation modes, which are: single turn, turn-by-turn, closed orbit and tune. All modes can be selected independently for each sector of the booster and storage ring through the EPICS-based SLS control system by simple re-programming of the digital processing chain. Laboratory measurements as well as measurements on the SLS accelerators will be presented, offering insights in the operational experience and the performance of the DBPM system. In addition, a monitoring system (POMS) for the transverse mechanical positions of each BPM block in reference to the adjacent quadrupole magnets has been installed and commissioned. First results will be presented, showing a horizontal and vertical movement of the BPM blocks as a function of beam current (heat load on the vacuum chamber) in the SLS storage ring.

Single-shot electron bunch length measurements using a spatial electro-optical autocorrelation interferometer

A spatial, electro-optical autocorrelation (EOA) interferometer using the vertically polarized lobes of coherent transition radiation (CTR) has been developed as a single-shot electron bunch length monitor at an optical beam port downstream the 100 MeV preinjector LINAC of the Swiss Light Source. This EOA monitor combines the advantages of step-scan interferometers (high temporal resolution) [D. Mihalcea et al., Phys. Rev. ST Accel. Beams 9, 082801 (2006) and T. Takahashi and K. Takami, Infrared Phys. Technol. 51, 363 (2008)] and terahertz-gating technologies [U. Schmidhammer et al., Appl. Phys. B: Lasers Opt. 94, 95 (2009) and B. Steffen et al., Phys. Rev. ST Accel. Beams 12, 032802 (2009)] (fast response), providing the possibility to tune the accelerator with an online bunch length diagnostics. While a proof of principle of the spatial interferometer was achieved by step-scan measurements with far-infrared detectors, the single-shot capability of the monitor has been demonstrated by electro-optical correlation of the spatial CTR interference pattern with fairly long (500 ps) neodymium-doped yttrium aluminum garnet (Nd:YAG) laser pulses in a ZnTe crystal. In single-shot operation, variations of the bunch length between 1.5 and 4 ps due to different phase settings of the LINAC bunching cavities have been measured with subpicosecond time resolution.

Correction of Insertion Device Induced Orbit Distortions at the SLS

Corrections of insertion device (ID) induced orbit distortions at the SLS are performed by means of feed forward schemes down to the micron level at the corresponding photon beam position monitors (XBPMs). The remaining orbit fluctuations are suppressed by XBPM feedbacks which are an integral part of the fast orbit feedback system. As a result, sub-μm RMS stability at the XBPMs is achieved while the ID settings are varied.

Fast Orbit Feedback and Beam Stability at the Swiss Light Source

A global, fast orbit feedback (FOFB) based on the digital beam position monitor (DBPM) system has been in user operation at the Swiss Light Source (SLS) since November 2003. The SVD‐based correction scheme acts at a sampling rate of 4 kHz using position information from all 72 DBPM stations and applying corrections with all 72 horizontal and 72 vertical corrector magnets. As a result, the FOFB successfully damps orbit distortions, which are mainly caused by ground and girder vibrations as well as the 3‐Hz booster crosstalk. It also allows fast and independent ID gap changes, which are completely transparent to all SLS users. With top‐up as a regular operation mode at SLS, global beam stability on a μm‐level has been achieved from days to milliseconds.

Design and Commissioning of the Bunch Arrival-Time Monitor for SwissFEL

The Bunch Arrival-Time Monitor for SwissFEL (BAM) is based on the concept which was successfully tested at the SwissFEL Test Facility (SITF). During the gap between the SITF decommissioning and the start of SwissFEL, all key components underwent design improvement. In this paper, we report on some of these new developments and on the commissioning progress.