Orbit Control For Diamond Light Source

1
Orbit Control For Diamond Light Source

• Ian Martin

Joint Accelerator Workshop Rutherford Appleton
Laboratory 28th -29th April 2004
2
Talk Outline

• Introduction to Diamond
• Orbit control methods
• Orbit control for Diamond
• Hardware (BPMs/corrector magnets)
• Static orbit correction scheme
• Dynamic orbit correction scheme

Joint Accelerator Workshop Rutherford Appleton
Laboratory 28th -29th April 2004
3
Diamond Light Source

• Diamond is a 3rd generation electron synchrotron
• Consists of
• 100 MeV Linac
• 100 MeV to 3 GeV Booster synchrotron
• 3 GeV storage ring

Joint Accelerator Workshop Rutherford Appleton
Laboratory 28th -29th April 2004
4
Diamond Light Source

• Lattice DBA
• Energy 3 GeV
• Length 561.6 m
• Symmetry 6 Fold
• Structure 24 cell
• Tune Point 27.2/12.3
• Emittance 2.7nm.rad
• Straights 5m/8m

Joint Accelerator Workshop Rutherford Appleton
Laboratory 28th -29th April 2004
5
Closed Orbit Correction

• Errors in the magnet alignments and field
  strengths mean closed orbit doesnt follow design
  orbit.
• Need to include corrector magnets in machine to
  combat the closed orbit distortions.
• BPM readings give beam position at certain points
  around the ring.
• Need to calculate what combination of corrector
  magnets would give opposite orbit to measured one.

Joint Accelerator Workshop Rutherford Appleton
Laboratory 28th -29th April 2004
6
Closed Orbit Correction

• Diamond will use GLOBAL orbit correction
• Create response matrix for correctors and BPMs

• Find corrector settings for given orbit by
  inverting response matrix and multiplying by
  vector of BPM readings

Joint Accelerator Workshop Rutherford Appleton
Laboratory 28th -29th April 2004
7
Inverting the Response Matrix

• Correction scheme could have different numbers of
  magnets and BPMs, so R could be a non-square
  matrix
• Matrix could be singular (or close to singular)

• SVD is analogous to eigenvalue decomposition,
  such that the matrix is decomposed into its
  orthonormal basis vectors and diagonal matrix
  containing the singular values
• It is a least squares minimisation

Joint Accelerator Workshop Rutherford Appleton
Laboratory 28th -29th April 2004
8
Inverting the Response Matrix
Joint Accelerator Workshop Rutherford Appleton
Laboratory 28th -29th April 2004
9
Beam Position Monitors

• 168 electron BPMs (7 per cell)
• Locations decided from phase advance, beta
  functions and engineering considerations
• Resolution 0.3µm in normal mode, 3µm in
  turn-by-turn mode
• 48 Primary BPMs
• mounted separately on stable pillars.
• Mechanically decoupled through bellows.

BPMs
Joint Accelerator Workshop Rutherford Appleton
Laboratory 28th -29th April 2004
10
Correctors in Sextupoles

• 168 combined function correctors housed in
  sextupoles (7 per cell)
• 0.8 mrad deflection at 1 Hz
• 13 µrad at 100 Hz
• Correctors can be used to correct both static and
  dynamic closed orbit errors

Correctors
Joint Accelerator Workshop Rutherford Appleton
Laboratory 28th -29th April 2004
11
Fast Corrector Magnets

• Single function magnets
• 96 in each plane (4 per straight)
• 0.3 mrad deflection at 50 Hz
• No intervening magnetic elements

Fast Correctors
Joint Accelerator Workshop Rutherford Appleton
Laboratory 28th -29th April 2004
12
Static Orbit Correction

• On long timescales, closed orbit distortions are
  caused by
• Magnet misalignments (mainly quadrupoles)
• Magnet roll errors (introduces coupling)
• Magnet field errors
• Ground motion
• Thermal effects

Courtesy Jacobs Gibb
No sleeved piles Designed gap under all
slabs Piles at 4 m grid under Experimental
Hall Experimental Hall slab 600mm thick No joint
between Exp. Hall and Storage Ring

• Minimise by
• Good foundations for building
• Mounting magnets on girders
• Periodic magnet re-alignment

Joint Accelerator Workshop Rutherford Appleton
Laboratory 28th -29th April 2004
13
Static Orbit Correction

• Storage Ring modelled with and without girders
• No girders
• uncorrelated distribution of alignment errors
• With girders
• Element alignment errors correlated by girders
• Additional uncorrelated errors element to girder
• Realistic scenario

Joint Accelerator Workshop Rutherford Appleton
Laboratory 28th -29th April 2004
14
Static Orbit Correction No Girders

• Closed Orbit in Straights
• Corrector Strengths

Joint Accelerator Workshop Rutherford Appleton
Laboratory 28th -29th April 2004
15
Static Orbit Correction With Girders

• Closed Orbit in Straights
• Corrector Strengths

Joint Accelerator Workshop Rutherford Appleton
Laboratory 28th -29th April 2004
16
Static Orbit Correction - Summary

• Can reduce rms closed orbit distortions from
  1-5mm to
• Residual closed orbit errors dominated by BPM
  offsets
• Effects of correlating errors with girders
• Reduced closed orbit before correction
• Reduced residual closed orbit
• Corrector strength requirements halved

Joint Accelerator Workshop Rutherford Appleton
Laboratory 28th -29th April 2004
17
Dynamic Orbit Correction

• Dynamic orbit correction scheme is designed to
  keep the beam as stable as possible for users
• Slow time scales beam motion is seen as unwanted
  steering
• Fast time scales beam motion blurs photon beam
  and decreases brightness

• Vibrations caused by
• Ground vibrations
• Water flow in cooling pipes
• Power supplies
• Beam motion on short timescales mainly due to
  motion of quadrupoles.

Joint Accelerator Workshop Rutherford Appleton
Laboratory 28th -29th April 2004
18
Dynamic Orbit Correction

• Orbit corrections applied to minimise the effects
  and damp the oscillations
• Specification that residual beam motion beam dimensions at source points

• Vibrations modelled as random, Gaussian-distribute
  d uncorrelated translations on all quadrupoles,
  sextupoles and BPMs
• Can use correctors in sextupoles or dedicated
  fast correctors

Joint Accelerator Workshop Rutherford Appleton
Laboratory 28th -29th April 2004
19
Dynamic Correction - ID Source Points

• Find same residual orbit in straight sections,
  regardless of correctors used
• BPM errors dominate
• Vertical beam size of 6.4 µm is tightest
  tolerance

Joint Accelerator Workshop Rutherford Appleton
Laboratory 28th -29th April 2004
20
Dynamic Correction - Dipole Source Points

• Again find similar residual orbits at dipole
  source points for two schemes
• Vertical angle of electron beam places tightest
  restriction on correction scheme (sy2.6 µrad)

Joint Accelerator Workshop Rutherford Appleton
Laboratory 28th -29th April 2004
21
Dynamic Orbit Correction - Summary

• Dynamic correction scheme suppresses oscillations
  of electron beam to below 10 of the beam
  dimensions at the source points.
• Have degree of flexibility in which magnets to
  use for correction, and at frequency of
  operation.
• Can use dedicated fast correctors either locally
  on each straight or as part of global correction
  scheme

Joint Accelerator Workshop Rutherford Appleton
Laboratory 28th -29th April 2004
22
Acknowledgements

• Close Orbit Work
• James Jones
• Diamond/ASTeC Accelerator Physics Groups
• Sue Smith Hywel Owen David Holder
• Jenny Varley Naomi Wyles James Jones
• Riccardo Bartolini Beni Singh Ian Martin

Joint Accelerator Workshop Rutherford Appleton
Laboratory 28th -29th April 2004