1. Low emittance rings for light sources ICFA Higgs Factory Workshop, FNAL, 16 November 2012 R. Bartolini Diamond Light Source and John Adams Institute for Accelerator Science University of Oxford

2. Overview of third generation light sources users requirements operating low emittance rings design strategies performance achieved Diffraction limited storage ring light sources Conclusions Outline ICFA Higgs Factory Workshop, FNAL, 16 November 2012

3. Broad Spectrum: which covers from microwaves to hard X-rays High Flux: high intensity photon beam High Brilliance (Spectral Brightness): highly collimated photon beam generated by a small divergence and small size source (partial coherence) Polarisation: both linear and circular (with IDs) Pulsed Time Structure: pulsed length down to tens of picoseconds High Stability: submicron source stability Flux = Photons / ( s  BW) Synchrotron radiation sources properties Brilliance = Photons / ( s  mm 2  mrad 2  BW ) ICFA Higgs Factory Workshop, FNAL, 16 November 2012

4. 1992ESRF, France (EU) 6 GeV ALS, US 1.5-1.9 GeV 1993TLS, Taiwan1.5 GeV 1994ELETTRA, Italy2.4 GeV PLS, Korea 2 GeV MAX II, Sweden1.5 GeV 1996APS, US7 GeV LNLS, Brazil1.35 GeV 1997Spring-8, Japan8 GeV 1998BESSY II, Germany1.9 GeV 2000ANKA, Germany2.5 GeV SLS, Switzerland2.4 GeV 2004SPEAR3, US 3 GeV CLS, Canada2.9 GeV 2006:SOLEIL, France2.8 GeV DIAMOND, UK 3 GeV ASP, Australia3 GeV MAX III, Sweden700 MeV Indus-II, India2.5 GeV 2008SSRF, China 3.4 GeV 2009PETRA-III, Germany6 GeV 2011ALBA, Spain3 GeV 3 rd generation storage ring light sources ESRF ALBA

5. > 2012NSLS-II, US 3 GeV MAX-IV, Sweden1.5-3 GeV SOLARIS, Poland1.5 GeV SESAME, Jordan 2.5 GeV TPS, Taiwan 3 GeV CANDLE, Armenia3 GeV PEP-X, USA4.5 GeV Spring8-II, Japan6 GeV BAPS, China5 GeV ESRF II, France 6 GeV 3 rd generation storage ring light sources under construction or planned NLSL-II Max-IV ICFA Higgs Factory Workshop, FNAL, 16 November 2012

6. 3 rd generation storage ring light sources operating under construction The electron beam energy and insertion devices properties define the photon energy reach of the machine. ICFA Higgs Factory Workshop, FNAL, 16 November 2012

7. Brilliance with IDs (medium energy light sources) Medium energy storage rings with in-vacuum undulators operated at low gaps (e.g. 5-7 mm) can reach 10 keV with a brilliance of 10 20 ph/s/0.1%BW/mm 2 /mrad 2 ICFA Higgs Factory Workshop, FNAL, 16 November 2012 Flux (and brightness) increases with higher current Brightness and trans. coherence Increase with lower lower emittance Wavelength reach increases with beam energy

8. Emittance in 3 rd generation light sources Transverse coherence requires small emittance Diffraction limit at 0.1 nm requires 8 pm operating under construction This is the geometric emittance SLS wertical normalised emittance is ~5 nm

9. Low emittance lattices Lattice design has to provide low emittance and adequate space in straight sections to accommodate long Insertion Devices Zero dispersion in the straight section was used especially in early machines limit the effect of IDs on energy spread and emittance avoid increasing the beam size due to energy spread allow straight section with zero dispersion to place RF and injection decouple chromatic and harmonic sextupoles DBA and TBA lattices provide low emittance with large ratio between Minimise  and D and be close to a waist in the dipole Flexibility for optic control for apertures (injection and lifetime)

10. DBA used at: ESRF, ELETTRA, APS, SPring8, Bessy-II, Diamond, SOLEIL, SPEAR3... TBA used at ALS, SLS, PLS, TLS … Lattices: DBA and TBA APS ALS Double Bend Achromat (DBA) Triple Bend Achromat (TBA)

11. ASP APS Leaking dispersion in straight sections reduces the emittance ESRF 7 nm  3.8 nm APS7.5 nm  2.5 nm SPring84.8 nm  3.0 nm SPEAR318.0 nm  9.8 nm ALS (SB)10.5 nm  6.7 nm The emittance is reduced but the dispersion in the straight section increases the beam size Breaking the achromatic condition Need to make sure the effective emittance and ID effects are not made worse

12. New designs envisaged to achieve sub-nm emittance involve Damping Wigglers Petra-III: 1 nm NSLS-II: 0.5 nm MBA MAX-IV (7-BA): 0.33 nm Spring-8 (10-BA): 83 pm (2006) 10-BA had a DA –6.5 mm +9 mm reverted to a QBA (160 pm) now 6BA with 70 pm Low emittance lattices MAX-IV 10 DBA (old) Spring-8 upgrade

13. Performance of third generation light sources Linear optics correction Beta beating coupling Non-linear optics DA off-momentum dynamics Stability short term – orbit feedbacks long term – Top Up ICFA Higgs Factory Workshop, FNAL, 16 November 2012

14. FLS2010, SLAC, 02 March 2010 Linear optics modelling with LOCO Linear Optics from Closed Orbit response matrix – J. Safranek et al. Modified version of LOCO with constraints on gradient variations (see ICFA Newsl, Dec’07)  - beating reduced to 0.4% rms Quadrupole variation reduced to 2% Results compatible with mag. meas. Hor.  - beating Ver.  - beating LOCO has solved the problem of the correct implementation of the linear optics Quadrupole gradient variation

15. Measured emittances and reduced coupling With beta-beating < 1%  agreement on measured emittance and energy spread Emittance [2.78 - 2.74] (2.75) nm Energy spread [1.1e-3 - 1.0-e3] (1.0e-3) betatron coupling corrected to ~ 0 using skew-quadrupoles emittance coupling ~0.08% achieved → vertical emittance ~ 2.0 pm closest tune approach  0 Pinhole camera images before/after coupling correction C. Thomas, R. Bartolini et al. PRSTAB 13, 022805, (2010) 6  m rms vertical Diamond is currently running at reduced coupling 0.3% (8pm V) for users

16. SLS world record for smallest vertical emittance Courtesy L. Rivkin PSI and EPFL ICFA Higgs Factory Workshop, FNAL, 16 November 2012

17. Comparison machine/model and Lowest vertical emittance Model emittance Measured emittance  -beating (rms) Coupling* (  y /  x ) Vertical emittance ALS6.7 nm 0.5 %0.1%4-7 pm APS2.5 nm 1 %0.8%20 pm ASP10 nm 1 %0.01%1-2 pm CLS18 nm17-19 nm4.2%0.2%36 pm Diamond2.74 nm2.7-2.8 nm0.4 %0.08%2.0 pm ESRF4 nm 3-4%0.1%3.7 pm SLS5.6 nm5.4-7 nm4.5% H; 1.3% V0.02%0.9 pm SOLEIL3.73 nm3.70-3.75 nm0.3 %0.1%4 pm SPEAR39.8 nm < 1%0.05%5 pm SPring83.4 nm3.2-3.6 nm1.9% H; 1.5% V0.2%6.4 pm SSRF3.9 nm3.8-4.0 nm<1%0.13%5 pm * best achieved

18. FM measuredFM model Sextupole strengths variation less than 3% multipolar errors to dipoles, quadrupoles and sextupoles (up to b10/a9) correct magnetic lengths of magnetic elements fringe fields to dipoles and quadrupoles Substantial progress after correcting the frequency response of the Libera BPMs detuning with momentum model and measured Frequency map and detuning with momentum comparison machine vs model (I)

19. DA measuredDA model Synchrotron tune vs RF frequency Frequency map and detuning with momentum comparison machine vs model (II) The fit procedure based on the reconstruction of the measured FM and detunng with momentum describes well the dynamic aperture, the resonances excited and the dependence of the synchrotron tune vs RF frequency R. Bartolini et al. PRSTAB 14, 054003 (2011) ICFA Higgs Factory Workshop, FNAL, 16 November 2012

20. off momentum FM (SOLEIL) Simulations Measurements Agreement few % up to dp/p  4 % Courtesy L. Nadolski SOLEIL

21. Beam stability should be better than 10% of the beam size For Diamond nominal optics (at short straight sections) usually within a band 1-100 Hz IR beamlines might have tighter requirements Orbit stability requirements for 3GLS ICFA Higgs Factory Workshop, FNAL, 16 November 2012

22. Ground vibrations to beam vibrations: Diamond Amplification factor girders to beam: H 31 (theory 35); V 12 (theory 8); 1-100 Hz HorizontalVertical Long Straight Standard Straight Long Straight Standard Straight Position (μm) Target17.812.31.260.64 Measured3.95 (2.2%)2.53 (2.1%)0.70 (5.5%)0.37 (5.8%) Angle (μrad) Target1.652.420.220.42 measured0.38 (2.3%)0.53 (2.2%)0.14 (6.3%)0.26 (6.2%)

23. Significant reduction of the rms beam motion up to 100 Hz; Higher frequencies performance limited mainly by the correctors power supply bandwidth Global fast orbit feedback: Diamond 1-100 Hz Standard Straight H Standard Straight V Positio n (μm) Target12.30.64 No FOFB2.53 (2.1%)0.37 (5.8%) FOFB On0.86 (0.7%)0.15 (2.3%) Angle (μrad) Target2.420.42 No FOFB0.53 (2.2%)0.26 (6.2%) FOFB On0.16 (0.7%)0.09 (2.1%)

24. Top-Up operation consists in the continuous (very frequent) injection to keep the stored current constant – with beamline shutters open. Top-Up Operation Already in operation at APS, SLS, SPring8, TLS New machines such as Diamond, SOLEIL are also operating Top-Up Retrofitted in ALS, SPEAR3, ELETTRA, BESSY-II, ESRF (few bunches mode) Operating modes are machine specific (frequency of injection, # of shots, charge)  I/I  10 –3 Standard decay modeTop-Up mode

25. Higher average brightness Higher average current Constant flux on sample Improved stability Constant heat load Beam current dependence of BPMs Flexible operation Lifetime less important Smaller ID gaps Lower coupling Top-Up motivation BPMs block stability without Top-Up  10  m with Top-Up < 1  m Crucial for long term sub-  m stability ICFA Higgs Factory Workshop, FNAL, 16 November 2012

26. Top-Up at Diamond Longest period with no trip 147h – current stability < 1% ICFA Higgs Factory Workshop, FNAL, 16 November 2012

27. Kicker transient at diagnostic BPM: +/- 250 μm horizontal p.t.p +/- 75 μm vertical Septum produces no observable effect Gating signals supplied to beamlines No complaints so far from transient at injection, users seem happy, but IR (and others..) beamlines have yet to come. Injection transient during Top-Up ICFA Higgs Factory Workshop, FNAL, 16 November 2012

28. Modern trends Stability improvements over 1-1kHz IDs development (CPMU, Superconducting undulators) Higher current and collective effects Short pulses Tailored straight sections – broken symmetry Lower emittance for diffraction limited rings ICFA Higgs Factory Workshop, FNAL, 16 November 2012

29. Emittance in 3 rd GLS, DR and B-factories Transverse coherence requires small emittance Diffraction limit at 0.1 nm requires 8 pm ~ 2012

30. Max-IV 20-fold 7-BA achromat Courtesy S. Leemans Max-IV studies proved that a 7-BA (330 pm, and 260 pm with DW) can deliver suffcient DA and MA to operate with standard off-axis injection schemes Tools used FM – driving terms Additional octupoles were found to be effective

31. PEP-X 7 bend achromat cell Cell phase advances:  x =(2+1/8) x 360 0,  y =(1+1/8) x 360 0. Natural emittance = 29 pm-rad at 4.5 GeV 5 TME units Courtesy B. Hettel, Y. Cai ICFA Higgs Factory Workshop, FNAL, 16 November 2012

32. Reduced emittance with damping wigglers Emittance = 11 pm-rad at 4.5 GeV with parameters l w =5 cm, B w =1.5 T Courtesy Min-Huey Wang, B. Hettel, Y. Cai Average beta function at the wiggler section is 12.4 meter. Wiggler Field OptimizationWiggler Length Optimization ICFA Higgs Factory Workshop, FNAL, 16 November 2012

33. Cancellation of resonances All Geometrical 3 rd and 4 th Resonances Driven by Strong Sextupoles except 2Q x -2Q y Third OrderFourth Order ICFA Higgs Factory Workshop, FNAL, 16 November 2012 Courtesy B. Hettel, Y. Cai

34. Additional sextupoles for tuneshift and 2Q x -2Q y Without Harmonic SextupolesWith Harmonic Sextupoles Optimized with OPA (Accelerator Design Program from SLS PSI). Courtesy Min-Huey Wang, B. Hettel, Y. Cai ICFA Higgs Factory Workshop, FNAL, 16 November 2012

35.  USR – M. Borland A Tevatron-size USR based on a 7BA lattice Multi-bend achromats (  x ~ 1/N D 3 ) Courtesy M. Borland

36. A 5BA lattice for Diamond-II upgrade 14 quads per cell 14 sextupoles 10 cm distance between magnetic elements A 150pm lattice for a ~20-fold decrease in emittance Energy [GeV] Circumference [m] Tune: h/v Beam current [A] Coupling,% Emittance: x,y [pm·rad] Bunch length [mm] Energy spread (rms) Momentum compaction Damping time: x/y/s [ms] Natural chromaticity: x/y Energy loss per turn [MeV] RF voltage [MV] RF frequency[MHz] Length of ID straight [m]  @ ID centre (long, short): x/y [m] 3.0 561.6 55.32/26.62 300 10% 148.1 1.8 0.731×10 -3 0.000122 17.23/26.16/17.65 -152/-53 0.42964 2.5 500 4×9.5,18×6.5 8.76/5.62, 4.33/1.92 ICFA Higgs Factory Workshop, FNAL, 16 November 2012

37. Some 5BA solutions from MOGA 2 mm DA Optimisation just started Large tuneshift with amplitude to be compensated Spring8-II, and tUSR have similar DA It is likely that we have to learn to cope with these small DA New injection schemes need to be developed nonlinear pulsed kicker or swap out injection schemes are under investigation ICFA Higgs Factory Workshop, FNAL, 16 November 2012

38. Injection with one single pulsed magnet (I) Conventional injection with four kicker bump Requires a perfectly closed orbit bump to avoid perturbing stored beam Bump closure difficult in practise (residual oscillations 150um H – 100um V) New idea of pulsed multipole injection The stored beam is untouched (zero magnetic field at the centre) Can inject in significantly smaller dynamic apertures arc1arc24 ICFA Higgs Factory Workshop, FNAL, 16 November 2012

39. Injection with one single pulsed magnet (II) Multipole injection tested at Photon Factory (KEK) and BESSY-II Selected baseline for injection into MAX-IV BESSY-II test: single, non-linear injection kicker – not fully optimized: H < 60  V < 15  Inj. efficiency ~80 % up to 300 mA Effect on the stored beam in PF-AR

40. Conclusion and open issues Many light source operate with low emittance lattices. Vertical emittance in the 1-2 pm range are no longer uncommon. New projects aim at reaching diffraction limited rings in Horizontal plane as well. These are based on MBA lattices. DA and Touschek lifetime studies are crucial. Magnets and apertures design will be at the cutting edge of present R&D. Alternative injection schemes are under study Collective effects (IBS) will limit the stored current to 100-200 mA. They might be mitigated by Harmonic Cavity for bunch lengthening. Round beams could help and more R&D is needed. However the subject is now seriously tackled by a large community, some rings are already solved (e.g. PEP-X at 10 pm) and new solutions will likely appear for upcoming projects

41. 3 rd LOWERING workshop in Oxford 8-10 July 2013