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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

Photon Beam Position Monitorsand Beam Stabilityat the Swiss Light Source

Elsa van Garderen

March 12th, 2008


What are the xbpms
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


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


XBPM launcher

Slow XBPM

feedback

Fast Orbit feedback

30 min archiver

data can be saved (for offline analysis)


Xbpm feedback
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


    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


    Xbpms and feed forward
    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


    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


    Conclusion
    Conclusion gap

    • 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


    I would like to thank
    I would like to thank gap

    • 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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