Download - Orbit Control For Diamond Light Source
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
Joint Accelerator Workshop
Rutherford Appleton Laboratory 28th -29th April 2004
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
Joint Accelerator Workshop
Rutherford Appleton Laboratory 28th -29th April 2004
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
Joint Accelerator Workshop
Rutherford Appleton Laboratory 28th -29th April 2004
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.
Joint Accelerator Workshop
Rutherford Appleton Laboratory 28th -29th April 2004
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
Joint Accelerator Workshop
Rutherford Appleton Laboratory 28th -29th April 2004
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
Joint Accelerator Workshop
Rutherford Appleton Laboratory 28th -29th April 2004
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
Joint Accelerator Workshop
Rutherford Appleton Laboratory 28th -29th April 2004
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
Joint Accelerator Workshop
Rutherford Appleton Laboratory 28th -29th April 2004
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
Joint Accelerator Workshop
Rutherford Appleton Laboratory 28th -29th April 2004
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
Joint Accelerator Workshop
Rutherford Appleton Laboratory 28th -29th April 2004
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
Joint Accelerator Workshop
Rutherford Appleton Laboratory 28th -29th April 2004
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
Joint Accelerator Workshop
Rutherford Appleton Laboratory 28th -29th April 2004
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
Joint Accelerator Workshop
Rutherford Appleton Laboratory 28th -29th April 2004
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
Joint Accelerator Workshop
Rutherford Appleton Laboratory 28th -29th April 2004
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
Joint Accelerator Workshop
Rutherford Appleton Laboratory 28th -29th April 2004
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
Joint Accelerator Workshop
Rutherford Appleton Laboratory 28th -29th April 2004
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
Joint Accelerator Workshop
Rutherford Appleton Laboratory 28th -29th April 2004
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
Joint Accelerator Workshop
Rutherford Appleton Laboratory 28th -29th April 2004
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
Joint Accelerator Workshop
Rutherford Appleton Laboratory 28th -29th April 2004
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
Joint Accelerator Workshop
Rutherford Appleton Laboratory 28th -29th April 2004
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
Joint Accelerator Workshop
Rutherford Appleton Laboratory 28th -29th April 2004