1. Design, status and roadmap of next generation low emittance ring
R. Bartolini
Diamond Light Source
and
John Adams Institute, University of Oxford
Thanks to B. Hettel and M. Borland
ESLS XXII Workshop
Grenoble, 25 November 2014

2. Outline Overview of machine upgrade programmes (2010 vs 2014)
Short survey of new ring desing
Challenges in design and technology of ultra low emittance rings
Matching users requests and conclusions
ESLS XXII Workshop
Grenoble, 25 November 2014

3. New rings and upgrades R&D programmes (2014)
MAX-IV 330 pm 3 GeV 7BA
Spring-8 II 70 pm (48) 6 GeV 6BA
PEP-X 5 pm 6 GeV 7BA
APS 100 pm (25) 7 GeV 7BA
USR 3 pm 9 GeV 7BA
SIRIUS 280 nm 3 GeV TBA
ESRF II 140 pm (28) 6 GeV 7BA-hybrid
Diamond II pm (20-10) 3 GeV (270 pm DDBA pm 5BA)
ALS 100 pm (20) 2 GeV 9BA
BAPS 50 pm 5 GeV 10BA
SOLEIL pm (10) 2.7 GeV DB-split
SLS 250 pm (20) 2.4 GeV Longitudinal gradient bend
ELETTRA 250 pm (28) 2 GeV 6BA
ANKA pm (18) 2.5 GeV split-TME
CLS 800 pm (22) 2 GeV 7BA
SPEAR III 750 pm (13) 3 GeV DQBA
IPAC 11-12
USR Beijing 12
IPAC13-14
ESLS XXII Workshop
Grenoble, 25 November 2014

4. Upgrade programmes ~ 2010
Up until ~2010 upgrade of existing third generation light sources targeted
e.g .ESRF purple book
Lower vertical emittance (lower coupling)
Longer straight sections (longer IDs or canted Ids)
Higher current (from 200 mA to 300 mA)
Top Up for 16 and 4 bunches modes
New technology: CPMU, RF NC HOM free cavities, SS amplifiers, BPMs.
e.g. APS studies
ERL option
other intermediate upgrades options (not precluding the ERL option):
Longer straight sections (longer IDs, customized optics, canted Ids)
Higher current (from 100 mA to 200 mA)
Short pulses programme with crab cavities,
Increase BW of orbit feedback system to achieve sub-m stability up to 200 Hz
ESLS XXII Workshop
Grenoble, 25 November 2014

5. Why now ?
Science case is growing: NSLS-II, MAX-IV, APS, Spring-8, ESRF, …
science enabled by better photon properties
Growing confidence in “aggressive” low emittance lattice designs
from DBA to MBA
injection in smaller apertures (…eventually on axis)
Excellent control of the beam properties proven at many light sources
orbit, optics, stability, lifetime, losses, customised optics…
beam based tuning tools
Key enabling technologies appear to be mature
no showstoppers in magnets, vacuum, diagnostics, RF, …
ESLS XXII Workshop
Grenoble, 25 November 2014

6. Science case
A number of workshop have discussed the science case for ultra low emittance lattices
XDL 2011 Workshops for ERLs and DLSRs, Cornell, June 2011
Beijing USR Workshop, Huairou, October 2012
DLSR Workshop, SPring-8, December 2012
DOE BESAC Subcommittee on Future Light Sources, July 2013
SLAC DLSR Workshop, SLAC, December 2013
DLSR Workshop, Argonne, November 2014
A dedicated issue in Journal of Synchrotron Radiation is in publication
High brilliance and transversely coherent x-rays
Uniform phase wavefronts: coherent imaging, holography, speckle, etc.
Focusable to smallest spot size: nano-focus
High flux (~ photons/sec) in small spot: slits may not be required, etc.
Round beams: H-V symmetric optics, circular zone plates, flexibility in optics
ESLS XXII Workshop
Grenoble, 25 November 2014

7. MBA lattices (large rings favoured)
Lattice design
Growing confidence in “aggressive” low emittance lattice design
Lattice design evolution from DBA, TBA to 4BA,…MBA:
Lattice optimisation tools improved (linear and nonlinear dynamics)
Low emittance lattice require small angle bending
Minimise  and D and be close to a waist in the dipole
MBA lattices (large rings favoured)
ESLS XXII Workshop
Grenoble, 25 November 2014

8. Multiple bend achromats
DBA
7BA
Simplified explanation
– Emittance is driven by randomness of photon emission in presence of dispersive (energy-dependent) orbits – electron recoils randomly
– Breaking up dipoles and putting focusing (quadrupoles) between the parts allows reducing the amplitude of dispersive orbits – smaller electron recoils
ESLS XXII Workshop
Grenoble, 25 November 2014

9. Design challenges Linear optics
To reduce the amplitude of dispersive orbits, must bend more gently (small bending angles) and focus more frequently and more strongly
Finding good optics with existing layout constraints is non trivial
Focusing (quadrupole) elements have chromatic aberrations
Sextupole magnets added to correct these
Introduces higher order aberrations that must be corrected
Require magnets with small bore radia
Stronger focusing leads to difficult non-linear dynamics
Poor “momentum aperture”  reduced lifetime  frequent injection
Poor “dynamic aperture”  greater difficulty injecting
Some designs are considering on-axis injection
Collective instabilities are amplified with short bunches
ESLS XXII Workshop
Grenoble, 25 November 2014

10. Optimisation of beam dynamics
ESLS XXII Workshop
Grenoble, 25 November 2014

11. Lattice designs
MAX–IV (Sweden) is taking the first pioneering step with 7BA, under construction
3 GeV, 528 m, 0.25 nm
Sirius (Brazil) just started construction of 5BA with superbend
3 GeV, 518 m, 0.28 nm
L. Liu, LNLS.

12. Lattice designs ESRF (France) APS (US - preliminary) SPring-8 (Japan)
6 GeV, 844 m, 4 nm → 150 pm
Dispersion bumps for efficient sextupoles
Longitudinal gradient dipoles (D1, D2, D6, D7) to further reduce emittance
Combined dipole-quadrupoles D3-4-5
3-pole wiggler as hard X-ray source
now - ESRF DBA
future - ESRF 7BA
APS (US - preliminary)
7 → 6 GeV, 1104 m, 3.1 nm → ~65 pm
ESRF-style lattice, 3-pole wiggler
Swap-out injection
Superconducting undulators
SPring-8 (Japan)
8 → 6 GeV, 1436 m, 2.8 nm → <100 pm
lattice under development

13. Lattice designs ALS-U (US - LBNL) Other rings: SLS (Switzerland - PSI)
1.9 GeV, 200 m, 2 nm → 52x52 pm
9BA
Swap-out injection from accumulator ring
3-T PM superbend insertions
ALS-II swap-out/accumulator
Other rings:
SLS (Switzerland - PSI)
2.4 GeV, 288 m, 5 nm → 0.25 nm
Soleil (France)
2.75 GeV, 354 m, 3.9 nm → 0.5 nm
…..
ALS-U 24-mm ID chamber
ESLS XXII Workshop
Grenoble, 25 November 2014

14. A modified 4BA lattice for Diamond-II
Increase dispersion at chromatic sextupoles
Optimize magnets positions and length leaving more distance between dipoles (no coil clash)
removed sextupoles in the new straight
Longer mid-cell straight section from 3m to 3.4 m – longer is unmanageable
ESLS XXII Workshop
Grenoble, 25 November 2014

15. upgrade with Diamond-II (200pm): 300mA and 1%K
Brilliance plot using U27 – 72 periods 2 m long with Kmax = 2.02
Tuning curves computed with Spectra 8.0
ESLS XXII Workshop
Grenoble, 25 November 2014

16. Survey of low emittance lattices
ESLS XXII Workshop
Grenoble, 25 November 2014

17. Experimental control of the beam optics
Growing confidence in the experimental control of the electron optics
Proven correction strategies
beam based tuning techniques
(better instrumentation: diagnostics, power supplies, …)
e.g. Diamond operates with a very good control of the beam optics
Optics deviation (beta-beating) redecue to 1% level
Emittance [ ] (2.75) nm
Energy spread [1.1e e3] (1.0e-3)
Emittance coupling ~0.08% achieved → vertical emittance ~ 2.0 pm (2009 WR)
6 mm rms vertical

18. Records for smallest vertical emittance (2011-2014)
SLS
0.9 pm
Courtesy L. Rivkin
PSI and EPFL
APS
0.35 pm
ESLS XXII Workshop
Grenoble, 25 November 2014

19. Comparison machine/model and Lowest vertical emittance (back in 2011)
Model emittance
Measured emittance
-beating (rms)
Coupling*
(y/ x)
Vertical emittance
ALS
6.7 nm
0.5 %
0.1%
4-7 pm
ASP
10 nm
1 %
0.01%
1-2 pm
Diamond
2.74 nm nm
0.4 %
0.08%
2.0 pm
ESRF
4 nm 1%
3.7 pm
SLS
5.6 nm
5.4-7 nm
4.5% H; 1.3% V
0.04%
SOLEIL
3.73 nm nm
0.3 %
4 pm
SPEAR3
9.8 nm
< 1%
0.05%
5 pm
SSRF
3.9 nm nm
<1%
0.13%
* best achieved 2011
Since these early studies
SLS reached 0.9 pm V emittance
Diamond is providing 8 pm V emittance in users’ operation
ESRF is providing 8 pm V (and lower) emittance in users’ operation

20. heater tape for in-situ NEG bake-out Sirius
Enabling technology
Compact magnet and vacuum technology
Precision magnet pole machining for small aperture magnets, combined function magnets, tolerance for magnet crosstalk (e.g. MAX-Lab)
NEG-coated vacuum chambers enable small apertures to enable high magnet gradients
Pioneered at CERN, used extensively at Soleil, and adopted for MAX-IV and Sirius MBA lattices
MAX-IV
Courtesy S. Leemans
SPring-8
concept
K. Soutome
heater tape for in-situ NEG bake-out Sirius
Diamond, 11 July 2014

21. Enabling technology
Other advances in accelerator and light source technology:
Fast kickers (KEK ATF)
Fast kickers for on-axis injection
Higher order resonances detected by turn-turn BPMs (A. Franchi)
Sub-micron e- BPMs with micron resolution single pass capability: non-linear lattice tuning
Accelerator and beam line component mechanical positioning and stabilizing systems
SPring-8 concept based on NSLS-II vibrating wire method - K. Soutome
“In-situ” and beam-based magnet measurement and alignment methods
Mode-damped RF cavities (fundamental and harmonic)
Highly stable solid state RF power sources
High performance IDs (superconducting,
Delta, RF, etc.)
SC undulator development at LBNL (S. Prestemon et al.), APS (E. Gluskin et al.) and elsewhere
Delta undulator prototype - A. Temnykh
Advances in X-ray optics and detectors
start-to-end beam line system simulations, SC detectors, cryo-cooled mirrors, etc.

22. Conclusions Many 3GLS operates since 2000’s with nominal parameters
few nm H emittance mA
8pm V emittance
However:
2010 Petra-III was commissioned  1 nm H emittance
SLS and ASP ~1 pm V emittance (best achieved)
2012 ESRF et al. operate with 8pm V emittance
2013 ALS upgraded to a 2 nm H emittance lattice
2014 NSLS-II started operation  0.5 nm H emittance
2014 Petra III has tested a 160 pm lattice at 3GeV
2016 MAX IV 300 pm H emittance lattice
2019 ESRF II 140 pm H emittance lattice
ESLS XXII Workshop
Grenoble, 25 November 2014

23. Conclusions
Man 3GLS are investigating a full ring upgrade (Diamond–II, SLS-II, SOLEIL, …)
Various MBA options are under analysis.
Some of the designs have still lots of flexibility in the technical choices
Need input from PBSs and Users
what emittance?
are round beams needed?
alternate high beta – low beta ?
operating modes (e.g. low alpha, …)?
… open for any exotic ideas?
AP should explore tailoring the design to their specific beamlines
ESLS XXII Workshop
Grenoble, 25 November 2014

24. Low emittance ring community
The development of ultra low emittance rings is now seriously tackled by a large community, including damping rings and HEP colliders meeting regularly in workshop discussing general or dedicated topics (beam dynamics, collective effects, technology for low emittance rings
ICFA Low Emittance Rings Workshops (LowERing)
XDL 2011 Workshops for ERLs and DLSRs, Cornell, June 2011
Beijing USR Workshop, Huairou, October 2012
DLSR Workshop, SPring-8, December 2012
Low Emittance Ring Workshop, Oxford, July 2013
SLAC DLSR Workshop, SLAC, December 2013
Workshop on Low Emittance Rings Technology (ALERT 2014), Valencia, 2014
Low Emittance Rings Workshop (LER2014), Frascati, September 2014
DLSR Workshop, Argonne, November 2014
ESLS XXII Workshop
Grenoble, 25 November 2014