1. Overview of optics corrections at Diamond and plans for Diamond-II
R. Bartolini
Diamond Light Source
and
John Adams Institute for Accelerator Science
University of Oxford
USR Workshop, Beijing,
31 October 2012

2. Outline Review of optics correction techniques at Diamond LOCO
turn-by-turn data analysis
old techniques
experimental results
Initial studies for an ultra low emittance lattice for Diamond-II
MBA with M =
and modified 4BA
Thanks to T. Pulampong, R. Walker, J. Kay and N. Hammond
USR Workshop, Beijing,
31 October 2012

3. Optics Correction ORM based – LOCO J. Safranek
very successful for linear optics (beta-beating and coupling)
Turn by turn data post processing
linear optics
LOCO outperform the analysis with tbt data
Nonlinear optics
FMA (now used everywhere!)
driving terms (diamond, ESRF, SOLEIL, …)
Old techniques
Closest tune approach
Quads variation for beta functions measurements
USR Workshop, Beijing,
30 October 2012

4. Linear optics modelling with LOCO Linear Optics from Closed Orbit response matrix – J. Safranek et al.
Hor.  - beating
Ver.  - beating
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.
Quadrupole gradient variation
FLS2010, SLAC, 02 March 2010
LOCO has solved the problem of the correct implementation of the linear optics

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

6. Comparison machine/model and Lowest vertical emittance
Model emittance
Measured emittance
-beating (rms)
Coupling*
(y/ x)
Vertical emittance
ALS
6.7 nm
0.5 %
0.1%
4-7 pm
APS
2.5 nm
1 %
0.8%
20 pm
ASP
10 nm
0.01%
1-2 pm
CLS
18 nm
17-19 nm
4.2%
0.2%
36 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
0.02%
0.9 pm
SOLEIL
3.73 nm nm
0.3 %
4 pm
SPEAR3
9.8 nm
< 1%
0.05%
5 pm
SPring8
3.4 nm nm
1.9% H; 1.5% V
6.4 pm
SSRF
3.9 nm nm
<1%
0.13%
* best achieved

7. Frequency map and detuning with momentum
comparison machine vs model (II)
detuning with momentum model and measured
FM measured
FM 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
FM and detuning used as a fit
DA is a result 7

8. Spectral line (-1,1) from tracking data observed at all BPMs
Spectral line (-1, 1) in V associated with the sextupole resonance (-1,2)
Comparison spectral line (-1,1) from tracking data and measured (-1,1) observed at all BPMs
Spectral line (-1,1) from tracking data observed at all BPMs
model
model; measured
BPM number
BPM number
USR Workshop, Beijing,
31 October 2012 8

9. Frequency map and detuning with momentum
comparison machine vs model (III)
Synchrotron tune vs RF frequency
DA measured
DA model
FM and detuning used as a fit; borders limited by the knowledge of the enginnering apertures
DA is a result
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, (2011)
USR Workshop, Beijing,
31 October 2012 9

10. Brilliance upgrade at Diamond
Brilliance improvement
reduce coupling 1%  0.3%
300 mA  500 mA
reducing diamond emittance with present hardware
2.7 nm  2.1 nm lattice test – ongoing: issues with SCWs
An ultra low emittance lattice for Diamond-II
5BA
7BA,
and modified 4BA
USR Workshop, Beijing,
31 October 2012

11. Emittance in 3rd GLS, DR and colliders
~ 2012 ?
Transverse coherence requires small emittance
Diffraction limit at 0.1 nm requires 8 pm

12. upgrade with Diamond-II (200pm): 300mA and 1%K
Assuming the operation with a 200pm lattice
Brilliance plot using U27 – 72 periods 2 m long with Kmax = mm gap
Tuning curves computed with Spectra 8.0
USR Workshop, Beijing,
31 October 2012

13. Low emittance design for a Diamond-II upgrade (WIP)
Wishlist for the upgrade of an existsting medium size mahcine
emittance lower than 200 pm in baseline
(a factor at least 10 better than now)
minimal changes to the machines
Leave the straight section as they are !
reuse grider and/or magnets if possible
beamline remains where they are (no offset or angle)
Avoid long interruptions.
Find options that can be phased...
Realistic engineering constraints (next…)
USR Workshop, Beijing,
31 October 2012

14. Engineering constraints on lattice design
Magnet and geometric constraints
quadruple gradient (100T/m) MAX IV has 40.4 T/m
quadrupoles in dipoles (30 T/m) MAX IV has 8.68 T/m
sextupoles (7000 T/m2) MAX IV has 2*2216 T/m2
space between magnets (hard edge) 10 cm MAX IV has 2.5 cm
Apertures = 20 mm diameter in arcs MAX IV inner diam. 22 mm
USR Workshop, Beijing,
31 October 2012

15. 5BA – 140 pm

16. 5BA cell Optics matched and optimised with MOGA (quads vs emittance)
14 quads per cell
14 sextupoles
10 cm distance
Straight section length
slightly reduced
11 m  9.5 m
8.3 m  6.5 m
USR Workshop, Beijing,
31 October 2012

17. Gradient in bend < 15 T/m
Quads gradient < 55 T/m
Parameters
Total length
Natural emittance
Natural chromaticity : hor./ver.
Straight length : long/short
561.6 m
142.5 pm-rad
-152/-53
9.5 m/ 6.5
Chrom(0,0)
S7X:SEXT,L=0.1,K2=786.45
S7Y:SEXT,L=0.2,K2=

18. 5BA sextupoles compensation5π
5 pi horizontal phase advance each cell,
5 pi vertical phase advance every two cells
USR Workshop, Beijing,
31 October 2012

19. Some 5BA solutions from MOGA
2 mm DA
Optimisation just started
Large tuneshift with amplitude to be compensated
USR Workshop, Beijing,
31 October 2012

20. Issue with path length and alignment of straights
Keeping the same circumference (same RF and harmonic number) generates an offset in the position of the straight sections.
This will require offsetting the beamlines – 1 cm is deemed acceptable
USR Workshop, Beijing,
31 October 2012

21. M. Borland quoting B. Hettel “if you can inject off-axis you have not pushed your lattice hard enough” 7BA – 45 pm

22. 7BA - giving up more straight section length
14 quads per cell
8 Sextupoles per cell
10 cm distance
Straight section length
slightly reduced
11 m  8.0 m
8.3 m  5.0 m
V and H sextupoles in dispersion bump only
USR Workshop, Beijing,
31 October 2012

23. 7BA – 45 pm emittance Chromatic Sextupoles (0,0) Parameters
Total length
Natural emittance
Natural chromaticity : hor./ver.
Straight length : long/short
561.6 m
45.7 pm-rad
-348/-118.7
8.0 m/ 5.0 m
Gradient in bend < 30 T/m
Quads gradient <100 T/m
Chromatic Sextupoles (0,0)
S7X: SEXT,L=0.3,K2=248.9
S7Y: SEXT,L=0.3,K2=-325.6

24. doubling the number of beamlines while still pushing the emittance down Modified 4BA - 320 pm
4BA with an additional short straight section between the dipole pairs emittance not pushed as for a pure 4BA but can double the number of straight sections Length of additional straight sections forced to be at least 3 m while keeping the remaining 6.7 m and 9 m straight sections

25. Broken the 4 BA cell to leave 3 m space
Modified 4BA cell
Broken the 4 BA cell to leave 3 m space
12 quads per cell
10 Sextupoles per cell
10 cm distance
Straight section length
slightly reduced
11 m  9.7 m
8.3 m  6.7 m
USR Workshop, Beijing,
31 October 2012

26. Modfied 4BA – one superperiod
Ring circumference shrinks from to > loss 1 harmonic of RF
Parameters
Total length
Natural emittance
Natural chromaticity : hor./ver.
Straight length : long/short/middle
561.0 m
314.7pm-rad
-146.7/-85.6
9.7/6.7/3
Gradient in bend < 15 T/m
Quads gradient < 70 T/m

27. 4BA 561m footprint comparison with the existing ring
Δ: cm
Δ: 0.19 cm
Δ: 0.39 cm
Current Diamond
Modified 4BA

28. MOGA optimisation for DA just started
Revising also tune point
12 quadrupoles per cell
10 sextuples per cell
1 mm DA insufficient (WIP)
USR Workshop, Beijing,
31 October 2012

29. Conclusion and (some) open issues
Leaving straight sections as they are looks very complicated. No space: the straight section must be slightly shortened
5BA, 6BA, 7BA and a less aggressive design with more beamlines (4BA – modified) are under investigation
DA and lifetime studies crucial for all such designs
Alternative injection schemes are under study
Collective effects, Harmonic Cavity for bunch lengthening, round beams to be studied
phase out installation strategy to avoid long interruptions still to be found..
However the subject is now seriously tackled by a large community, many rings already solved (PEP-X at 10 pm) and solutions will likely appear
USR Workshop, Beijing,
31 October 2012

30. 3rd LOWERING workshop in Oxford 8-10 July 2013
USR Workshop, Beijing,
31 October 2012