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Photon Beam Position Monitors and Beam Stabili ty at the Swiss Light Source

Photon Beam Position Monitors and Beam Stabili ty at the Swiss Light Source. Elsa van Garderen March 12 th , 2008. What are the XBPMs?. principle: 4 blades of Tungsten read the tails of the photon beam. Beam position

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Photon Beam Position Monitors and Beam Stabili ty at the Swiss Light Source

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  1. Photon Beam Position Monitorsand Beam Stabilityat the Swiss Light Source Elsa van Garderen March 12th, 2008

  2. What are the XBPMs? • principle:4 blades of Tungsten read the tails of the photon beam. Beamposition • deduced by asymmetries. Design of K. Holldack (BESSY), produced by FMB (Berlin). Front end of ID beamlines (top view) (front view) Source point XBPM1 XBPM2 Beam profile xBPM2 XBPM1 Front end of Bending beamlines (top view) (frontview) SPM1 Source point SPM1 SPM2 SPM2 Beam profile

  3. VME signal processing (Hytec). Transition Module 8201 Analog signal Carrier board 8002 VxWorks EPICS LCAD: Low Current Asymmetry Detector triaxe cables; Bias voltage= -70 V; I/U converter ADC 8401 3.5 cm ID beamlines => XBPMs have motors

  4. XBPM launcher Slow XBPM feedback Fast Orbit feedback 30 min archiver data can be saved (for offline analysis)

  5. XBPM Feedback XBPM2 XBPM1 • Fast Orbit Feedback (100 Hz) corrects electron beam movements. Based on readings of DBPMs. • Problem:reference of DBPMs is not static. Fluctuations (μm level) due to: • Air temperature variation at location of DBPM electronics • Temperature changes in SLS tunnel due to beam loss • Solution:XBPM feedback (slow: 0.5 Hz) photon beam changes = angle variation of orbit at source point → changes the reference of DBPMs • Update: fast XBPM feedback (implies hardware upgrade). DBPM1 DBPM2 Photon beam Electron beam Source point M. Böge et al., User operation and upgrades of the fast orbit feedback at the SLS, proceedings PAC05, Knoxville, USA

  6. XBPM DBPM without XBPM feedback (X09LA) DBPM before ID x y DBPM after ID x y with XBPM feedback (X10SA) DBPM before ID DBPM after ID

  7. XBPMs and Feed forward Move gap • Feed forward (IDFF) corrects a priori distortions due to ID gap changes. (currently for in-vacuum undulators) • Acts on correctors upstream and downstream of the ID. → good efficiency to stabilise electron beam. → but internal ID steering effects cause displacement of photon beam. • Therefore, XBPMs are included in IDFF determination procedure (high level: Java): • IDFF tables implemented on low level EPICS based control system (10 Hz). Step 2 Step 1 Observe effect on photon beam position Observe effect on electron orbit Deduce correction kicks on electron orbit Apply correction

  8. XBPM aligned for gap = 8.5 mm and calibrated for each gap IDFF off: 150 μm excursion when gap closes from 8.5 to 5 mm IDFF on: excursion removed U19 gap size (mm) J. Chrin at al., A feedforward procedure to counteract orbit distortion and photon beam displacements from insertion device operation at the SLS, proceedings ICALPECS07, Knoxville, USA

  9. Conclusion • XBPMs at SLS: XBPMs feedback (slow) part of FOFB (bending+ in vacuum ID beamlines) XBPMs used to create feedforward tables (in-vacuum ID beamlines) • Future: XBPM feedback becomes fast feedback feedback and feedforward for all ID beamlines • XBPMs in the world: Developed at BESSY Recently bought for SOLEIL and DIAMOND Interest of ALS Deep involvement of SLS

  10. I would like to thank • PSI: • J. Krempaský for daily support • M. Böge for FOFB and XBPM feedback • J. Chrin for feed forward tables • Th. Schmidt for insertion devices issues • The beamline scientists of their comments • Q. Chen and R. Wullschläger for technical support • BESSY: • K. Holldack for useful discussions

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