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3rd International Workshop on Beam Orbit Stabilization - IWBS2004

Announcement First / Second Accommodation Registration Participants Program Overview Details Orals by Session Orals with Abstracts Download PDF (gs) Download for PDAs Presentation   Upload / Download Summary Support Information No. #1 / #2 / #3 Pictures Gallery #1 / #2 / #3 Upload / Download SLS & Sponsors WWW psi.ch Updated: 25.01.2005		USER EXPERIENCE In this session, two SLS beam-line scientists reported on the orbit stability requirements of experiments carried out at their beam-lines and compared them with the present performance of the SLS. The opening talk covered the surfaces/interfaces microscopy (SIM) beam-line operating an APPLE II double undulator (2$\times$UE56). The measurement of absorption spectra requires a frequent movement of ID gaps/phases, which should not effect other beam-lines. Since it is a difficult task to make these IDs transparent on a $\mu$m level through shimming and FFs for all thinkable modes of operation, the remaining orbit distortions are left to the FOFB to handle. On critical time scales (10 Hz - 1/3 h$^{-1}$) a horizontal/vertical orbit movement of 0.5/1 $\mu$m, leading to an intensity/energy variation of $\approx$0.1 % (no normalization) /$\approx$1 meV, can be tolerated for the measurement of circular polarization difference absorption spectra. With the SLS FOFB running the aforementioned requirements are fulfilled. The SOFB is clearly not sufficient. The protein crystallography beam-line (PXI) operating an in-vacuum undulator (U24, replaced by U19 in 2004) has always been imposing high stability requirements on the SLS since the beginning of user operation in 2001. Knowing the magnetic properties of U24 very well the PXI beam-line could deduce the electron beam energy and spread from the undulator spectrum. Since the field strength in a small-gap undulator strongly depends on the absolute vertical beam position within the ID, the vertical orbit should be confined to $<\pm$10/100 $\mu$m over a user-/SLS-run ($\approx$1 day/several weeks). In multiple wavelength anomalous dispersion (MAD) experiments, photon beam energy stability requirements ($\Delta$E/E$<$10$^{-5}$) translate directly into angular orbit stability $\Delta$y'$<\pm$1.5 $\mu$rad (Se K-edge at 12.66 keV, Si (111) mono). These requirements are fulfilled by the SLS running with SOFB provided the settings of other IDs are kept constant. The FOFB makes ID operation transparent but there are indications that the noise on the photon intensity (0.5-500 Hz) increases which needs further investigation. Future time resolved experiments may require orbit stabilization to frequencies $>$100 Hz.