1. Orbit Control For Diamond Light Source Ian Martin Joint Accelerator Workshop Rutherford Appleton Laboratory28 th -29 th 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 Laboratory28 th -29 th April 2004

3. Diamond Light Source Diamond is a 3 rd generation electron synchrotron Consists of: –100 MeV Linac –100 MeV to 3 GeV Booster synchrotron –3 GeV storage ring Joint Accelerator Workshop Rutherford Appleton Laboratory28 th -29 th April 2004

4. Diamond Light Source LatticeDBA Energy3 GeV Length561.6 m Symmetry6 Fold Structure24 cell Tune Point27.2/12.3 Emittance2.7nm.rad Straights~5m/~8m Joint Accelerator Workshop Rutherford Appleton Laboratory28 th -29 th April 2004

5. 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 Laboratory28 th -29 th 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 Laboratory28 th -29 th 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 Laboratory28 th -29 th April 2004

8. Inverting the Response Matrix Joint Accelerator Workshop Rutherford Appleton Laboratory28 th -29 th 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 Laboratory28 th -29 th 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 Laboratory28 th -29 th 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 Laboratory28 th -29 th 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 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 Laboratory28 th -29 th 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 Error Type – With GirdersRMS 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 Error Type – No GirdersRMS 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 50 µm Joint Accelerator Workshop Rutherford Appleton Laboratory28 th -29 th April 2004

14. Static Orbit Correction – No Girders Closed Orbit in Straights Corrector Strengths PlaneMax CorrectionRMS Correction Horizontal Vertical 0.26 mrad 0.06 mrad 0.05 mrad UncorrectedMaximumRMS Horizontal Vertical 15.5 mm 7.2 mm 4.5 mm 1.7 mm CorrectedMaximumRMS Horizontal Vertical 0.35 mm 0.17 mm 0.06 mm 0.04 mm Joint Accelerator Workshop Rutherford Appleton Laboratory28 th -29 th April 2004

15. Static Orbit Correction – With Girders Closed Orbit in Straights Corrector Strengths PlaneMax CorrectionRMS Correction Horizontal Vertical 0.14 mrad 0.03 mrad UncorrectedMaximumRMS Horizontal Vertical 10.1 mm 2.9 mm 2.3 mm 0.7 mm CorrectedMaximumRMS Horizontal Vertical 0.20 mm 0.19 mm 0.05 mm 0.06 mm Joint Accelerator Workshop Rutherford Appleton Laboratory28 th -29 th April 2004

16. 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 Laboratory28 th -29 th April 2004

17. Dynamic 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 Laboratory28 th -29 th April 2004

18. 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 Laboratory28 th -29 th 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 CorrectorX rms (µm) X’ rms (µrad) Y rms (µm) Y’ rms (µrad) Fast0.230.050.230.05 Sextupole0.230.050.220.05 ID Source Point σ X (µm) σ X ’ (µrad) σ Y (µm) σ Y ’ (µrad) Beam Size12324.26.44.2 Joint Accelerator Workshop Rutherford Appleton Laboratory28 th -29 th 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 ( σ y ’=2.6 µrad) CorrectorX rms (µm) X’ rms (µrad) Y rms (µm) Y’ rms (µrad) Fast0.230.100.220.09 Sextupole0.290.26 0.23 Bending Magnet σ X (µm) σ X ’ (µrad) σ Y (µm) σ Y ’ (µrad) Beam Size36.887.224.52.6 Joint Accelerator Workshop Rutherford Appleton Laboratory28 th -29 th 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 Laboratory28 th -29 th April 2004

22. Acknowledgements Close Orbit Work James Jones Diamond/ASTeC Accelerator Physics Groups Sue SmithHywel OwenDavid Holder Jenny VarleyNaomi WylesJames Jones Riccardo BartoliniBeni SinghIan Martin Joint Accelerator Workshop Rutherford Appleton Laboratory28 th -29 th April 2004