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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

slide3

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

slide4

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

slide6

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

slide8

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
  • 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
    • 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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