Beam Diagnostics at Diamond Light Source

1. Beam Diagnosticsat Diamond Light Source Guenther Rehm Head of Diagnostics Group 1st DITANET school on Diagnostics 1 April 2009 1st DITANET school on Diagnostics

2. Outline • What is a Light Source? • Diagnostics Requirements for a Light Source • Diagnostics in the Injector • Diagnostics in the Storage Ring 1st DITANET school on Diagnostics

3. A Light Source? 1st DITANET school on Diagnostics

4. How Is Synchrotron Light Produced? Synchrotron Light (or Radiation) is electromagnetic radiation emitted when a high energy beam of charged particles (electrons) is deflected by a magnetic field a single bending magnet produces a wide fan of radiation multiple bends in an "undulator" or "wiggler" magnet give higher intensity and more directed radiation 1st DITANET school on Diagnostics

5. A Brief History of Synchrotron LightSources : • Discovery: 1947, General Electric 70 MeV synchrotron • First use for experiments: 1956, Cornell 300 MeV synchrotron • 1st generation: machines built for other purposes, mainly High Energy Physics • 2nd generation: purpose-built storage rings for production of synchrotron light • 3rd generation: higher brightness synchrotron light sources, using mainly ‘insertion devices’ (undulators and wigglers) as the X-ray sources • 4th generation: LINAC followed by ‘Free Electron Laser’, i.e. a series of undulators producing coherent synchrotron light of even higher peak brightness and shorter duration 1st DITANET school on Diagnostics

6. SR and the Electromagnetic Spectrum Electromagnetic waves 1st DITANET school on Diagnostics

7. Layout of a 3G Light Source A beam of electrons is accelerated in a LINAC, further accelerated in a booster synchrotron, then accumulated in a storage ring. The circulating electrons emit intense beams of synchrotron light that are sent along beamlines to the experimental stations. 1st DITANET school on Diagnostics

8. Layout of Diamond 100 MeV Linac 3 GeV Booster C = 158.4 m 3 GeV Storage Ring C = 562.6 m Experimental Hall and Beamlines technical plant peripheral labs. and offices office building 235 m future long beamlines 235 m 1st DITANET school on Diagnostics

9. Key Parameters of Diamond Electron Beam Energy 3 GeV Storage ring circumference 561.6 m Available space for Insertion Devices 4x8m, 18x5m Beam current 300 mA Emittance (hor., vert.) (nm rad) 2.7, 0.03 Minimum ID gap5 mm Electron beam sizes (hor., vert) (mm)123, 6 Electron beam divergences (hor., vert)24, 4 mrad Peak brightness*2*1020 Peak brightness* (1Å) 1019 * photons/s/mrad2/mm2/0.1%bw 1st DITANET school on Diagnostics

10. Diagnostics Requirements • Track charge trough Injector • Integrating Current Transformers, Faraday Cups and Wall Current Monitors • Stripline BPMs in transfer paths, buttons in booster • Screens / Cameras / Synchrotron Light Monitors • Keep stored beam stable • Fast Global Orbit Feedback: Monitor beam position and correct orbit 10000 per second to sub-um • Transverse Bunch by Bunch Feedback: Monitor bunch motion and correct after each turn to damp coupled bunch instabilities • Measure betatron tunes without visibly disturbing beam • Monitor beam size, calculate emittance, coupling and energy spread • Measure stored current and bunch by bunch charge 1st DITANET school on Diagnostics

11. 5 Faraday-C 7 ICT 2 DCCT 17 Screens 5 SLM 2 Pinholes 2 Tune Excite 204 BPMs 230 BLM 1st DITANET school on Diagnostics

12. Faraday Cups, WCMs, ICTs ICT and electronics ICT shield LINAC FC 1st DITANET school on Diagnostics LTB FC WCM for LINAC,LTB,BTS

13. The first bunches on WCM and ICT 1st DITANET school on Diagnostics

14. from LINAC from booster Bunch Charge and Train Structure WCMs in transfer paths Button in SR 1st DITANET school on Diagnostics

15. Booster Current on DCCT First measurement 1st DITANET school on Diagnostics Later with extraction after 100ms

16. Strip Line BPM Pickups in Transfer Paths 1st DITANET school on Diagnostics

17. Screens and Optics 1st DITANET school on Diagnostics

18. IEEE1394 Cameras Controls Network Event Network Diagnostics VME crate IEEE1394 PMC Camera Repeater Repeater PPC IOC2 Event Rx PPC IOC1 Camera 24 V PSU Trigger 1st DITANET school on Diagnostics

19. EDM Camera Display 1st DITANET school on Diagnostics

20. Precisely Triggered Acquisition kicked beam before main septum beam in booster during ramp edge of screen 1st DITANET school on Diagnostics

21. Image Analysis 2D fit 1D fits 1st DITANET school on Diagnostics

22. Orbit Stability Requirements in 3rd Generation Light Sources Beam stability should be better than 10% of the beam size For Diamond nominal optics (at short straight sections) 1st DITANET school on Diagnostics

23. Motivation and Challenges • Sources of beam motion: • Insertion devices not fully compensated, ID motion leads to orbit displacement • Ground vibrations amplified through girders • Magnet power supply drift • Vibrations from water cooling • Sources of errors in EBPM measurement: • Mechanical / electrical offsets • Noise • Beam current dependence • Pickup thermal motion Correct as fast as possible Minimise or remove from correction 1st DITANET school on Diagnostics

24. 7 BPMs each in 24 cells Primary BPM Standard BPM 1st DITANET school on Diagnostics

25. Button Pickup 1st DITANET school on Diagnostics

26. Primary BPM with reference pillar carbon fibre pillar with low temperature expansion coefficient bellows for mechanical isolation length gauges sense H/V position with 0.5um resolution 1st DITANET school on Diagnostics

27. Standard BPM near Quad 1st DITANET school on Diagnostics

28. Some BPMs move after beam loss 1st DITANET school on Diagnostics

29. Crossbar Switch A/D FPGA A/D A/D A/D Multiplexing in BPM Electronics • Crossbar switch routes all four inputs through all processing channels in parallel, but permutes routing • After digitisation, but before further filtering, the permutation is reversed • By averaging over 4 permutations, any differences/drifts between the channels will be removed (each input will have been routed through each channel during the averaging period) • By examining the changes in the outputs during permutation, the gains of the individual channels can be retrieved and then digitally equalised to reduce artefacts of switching 1st DITANET school on Diagnostics

30. Fast Orbit Feedback Controls Network Event Network PS VME crate Diagnostics VME crate PMC Rocket IO FB Processor PSU IF PSU IF Processor Processor Event Rx … PSU 1 PSU 14 14 Corrector PSUs eBPM eBPM eBPM eBPM eBPM eBPM eBPM Cell -n Cell +n Cell +m Cell -m 1st DITANET school on Diagnostics

31. FOFB Installation (one of 24 cells) Corrector power supplies Power supply VME crate Diagnostics rack 1st DITANET school on Diagnostics

32. FOFB Performance 60mA Suppression of beam motion 1st DITANET school on Diagnostics

33. Transverse Bunch-by-Bunch Feedback Control System 500 MHz RF clock History buffer 4 AD converters (slicing) Modulator and Amplifier RF Frontend 4-way Splitter D igital Signal D A Processing Converter FPGA based Feedback Processor Stripline Kicker Button Pickup 1st DITANET school on Diagnostics

34. Bunch-by-Bunch Feedback in Action • Beam artificially made unstable in both planes: • no feedback • → horizontally unstable • feedback in horiz. plane only • → vertically unstable • feedback in both planes • → stable in both planes 1st DITANET school on Diagnostics

35. Tune Measurement:Kick and Fourier Transform 1st DITANET school on Diagnostics

36. More Elegant Tune Measurement: Harmonic Excitation and Detection Exitation In phase cos Out of phase sin Beam Position Pickup 1st DITANET school on Diagnostics

37. 800 in phase signal 600 out of phase signal 400 200 0 -200 -400 0.2 0.205 0.21 0.215 0.22 0.225 0.23 tune 800 200 600 100 magnitude phase 400 0 200 -100 0 -200 0.2 0.2 0.205 0.205 0.21 0.21 0.215 0.215 0.22 0.22 0.225 0.225 0.23 0.23 tune Amplitude and Phase of Beam Response to Swept Sine Excitation 1st DITANET school on Diagnostics

38. Tune Measurement of Individual Bunches • Only one bunch is excited with swept sine wave • Tune depends on charge per bunch • Head-Tail mode leads to asymmetry of Synchrotron sidebands for larger charges 1st DITANET school on Diagnostics

39. X-ray Pinhole Cameras Magnification d1 d2 12.7m Source points 4.5m Pinholes Screens Optics Cameras 1st DITANET school on Diagnostics 9.6m 3.85m

40. Modified Beam Port Absorbers and Pinholes X/Z translation and rotation Aluminium/Steel explosion bonded flange as window 2 stacks of 4 slabs 5mm*1mm*30mm with shims as spacers 1st DITANET school on Diagnostics

41. Pinhole Screens and Optics 1024x768 camera 4.65um pixel focus and iris remote control 50mm macro lens magnification 1:1 mirror CdWO4 screen 1st DITANET school on Diagnostics

42. Pinhole Image Analysis Skew quads off Skew quads on 1st DITANET school on Diagnostics

43. Storage Ring DCCT Machine development Decaying beam Top-Up mode First accumulation of stored current at Diamond 1st DITANET school on Diagnostics Stored current and life time

44. Fill Pattern Measurement by Time Correlated Single Photon Counting 1st DITANET school on Diagnostics

45. Acknowledgements • Diagnostics: Alun Morgan, Cyrille Thomas, Chris Bloomer, Graham Cook • Controls: Michael Abbott, Isa Uzun,James Rowland, Mark Heron • Accelerator Physics: Ian Martin, Riccardo Bartolini • Engineering: Nigel Hammond, Ron Godwin, Darren Simmons 1st DITANET school on Diagnostics

46. Thank you for your attention! 1st DITANET school on Diagnostics