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

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

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

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

Closed 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 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

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

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

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

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

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

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

Static Orbit Correction 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 0.1 % 0.2 mrad 100 µm 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 30 µm 0.1 % 0.2 mrad 50 µm Joint Accelerator Workshop Rutherford Appleton Laboratory 28th -29th April 2004

Static Orbit Correction – No Girders Closed Orbit in Straights Corrector Strengths Uncorrected Maximum RMS Horizontal Vertical 15.5 mm 7.2 mm 4.5 mm 1.7 mm Corrected 0.35 mm 0.17 mm 0.06 mm 0.04 mm Plane Max Correction RMS Correction Horizontal Vertical 0.26 mrad 0.06 mrad 0.05 mrad Joint Accelerator Workshop Rutherford Appleton Laboratory 28th -29th April 2004

Static Orbit Correction – With Girders Closed Orbit in Straights Corrector Strengths Uncorrected Maximum RMS Horizontal Vertical 10.1 mm 2.9 mm 2.3 mm 0.7 mm Corrected 0.20 mm 0.19 mm 0.05 mm 0.06 mm Plane Max Correction RMS Correction Horizontal Vertical 0.14 mrad 0.03 mrad Joint Accelerator Workshop Rutherford Appleton Laboratory 28th -29th April 2004

Static 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 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

Dynamic Orbit Correction Orbit corrections applied to minimise the effects and damp the oscillations Specification that residual beam motion < 10% beam dimensions at source points 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 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 Sextupole 0.22 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 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 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 - 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

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