Orbit Control For Diamond Light Source Ian Martin Joint Accelerator Workshop Rutherford Appleton...

Orbit Control For Diamond Light SourceOrbit Control For Diamond Light Source

Ian Martin

Joint Accelerator Workshop

Rutherford Appleton Laboratory 28th -29th April 2004

Talk OutlineTalk Outline

• Introduction to Diamond

• Orbit control methods

• Orbit control for Diamond

– Hardware (BPMs/corrector magnets)– Static orbit correction scheme– Dynamic orbit correction scheme



Diamond Light SourceDiamond 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



Diamond Light SourceDiamond Light Source

Lattice DBAEnergy 3 GeVLength 561.6 mSymmetry6 FoldStructure 24 cellTune Point

27.2/12.3Emittance 2.7nm.radStraights ~5m/~8m



Closed Orbit CorrectionClosed Orbit Correction

• Errors in the magnet alignments and field strengths mean closed orbit doesn’t 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.



Closed Orbit CorrectionClosed Orbit Correction

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

jijii

j

j

i RRR

RRR

RRR

Y

Y

Y

2

1

21

22221

11211

2

1

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

YR 1

)cos()sin(2

,,,,

correctorjbpmi

correctorjbpmiijR



Inverting the Response MatrixInverting 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)

ionDecompositValueSingular• 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:

22 RY



Inverting the Response MatrixInverting the Response Matrix

T

N

V

w

w

UR

00

00

001

T

N

U

w

wVR

100

00

0011

1



Beam Position MonitorsBeam 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



Correctors in SextupolesCorrectors 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



Fast Corrector MagnetsFast 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



Static Orbit Correction 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

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

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

Courtesy Jacobs Gibb



Static Orbit CorrectionStatic 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

Error Type – With Girders RMS Size

Girder Transverse Displacement

Girder Longitudinal Displacement

Element Transverse Displacement

Element Longitudinal Displacement

Dipole Field Error

Dipole / Quad Roll Error

BPM Transverse Displacement

100 µm

100 µm

30 µm

30 µm

0.1 %

0.2 mrad

50 µm

Error Type – No Girders RMS Size

Dipole Transverse Displacement

Dipole Longitudinal Displacement

Dipole Field Error

Dipole / Quad Roll Error

Quad / Sext Transverse Displacement

BPM Transverse Displacement

50 µm

50 µm

0.1 %

0.2 mrad

100 µm

50 µm



Static Orbit Correction – No GirdersStatic Orbit Correction – No Girders

• Closed Orbit in Straights

• Corrector Strengths

Plane Max Correction RMS Correction

Horizontal

Vertical

0.26 mrad

0.26 mrad

0.06 mrad

0.05 mrad

Uncorrected Maximum RMS

Horizontal

Vertical

15.5 mm

7.2 mm

4.5 mm

1.7 mm

Corrected Maximum RMS

Horizontal

Vertical

0.35 mm

0.17 mm

0.06 mm

0.04 mm



Static Orbit Correction – With GirdersStatic Orbit Correction – With Girders

• Closed Orbit in Straights

• Corrector Strengths

Plane Max Correction RMS Correction

Horizontal

Vertical

0.14 mrad

0.14 mrad

0.03 mrad

0.03 mrad

Uncorrected Maximum RMS

Horizontal

Vertical

10.1 mm

2.9 mm

2.3 mm

0.7 mm

Corrected Maximum RMS

Horizontal

Vertical

0.20 mm

0.19 mm

0.05 mm

0.06 mm



Static Orbit Correction - SummaryStatic Orbit Correction - Summary

• Can reduce rms closed orbit distortions from ~1-5mm to <~50µm in straights

• 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



Dynamic Orbit CorrectionDynamic Orbit Correction

• Vibrations caused by:– Ground vibrations– Water flow in cooling pipes– Power supplies

• Beam motion on short timescales mainly due to motion of quadrupoles.

• 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



Dynamic Orbit CorrectionDynamic Orbit Correction

• Orbit corrections applied to minimise the effects and damp the oscillations

• Specification that residual beam motion < 10% beam dimensions at source points

zrmsZ 1.0)( zrmsZ 1.0)(

• Vibrations modelled as random, Gaussian-distributed uncorrelated translations on all quadrupoles, sextupoles and BPMs

• Can use correctors in sextupoles or dedicated fast correctors



Dynamic Correction - ID Source PointsDynamic 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

Corrector Xrms (µm)

X’rms (µrad)

Yrms (µm)

Y’rms (µrad)

Fast 0.23 0.05 0.23 0.05

Sextupole 0.23 0.05 0.22 0.05

ID Source Point

σX

(µm)σX’

(µrad)σY

(µm)σY’

(µrad)

Beam Size 123 24.2 6.4 4.2



Dynamic Correction - Dipole Source PointsDynamic 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 (σy’=2.6 µrad)

Corrector Xrms (µm)

X’rms (µrad)

Yrms (µm)

Y’rms (µrad)

Fast 0.23 0.10 0.22 0.09

Sextupole 0.29 0.26 0.26 0.23

Bending Magnet

σX

(µm)σX’

(µrad)σY

(µm)σY’

(µrad)

Beam Size 36.8 87.2 24.5 2.6



Dynamic Orbit Correction - SummaryDynamic 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



AcknowledgementsAcknowledgements

• 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



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