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. LatticeDBA 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 Diamond Light Source 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 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

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 <~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

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 < 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

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 (σy’=2.6 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