1. Recent experience from modern synchrotron light sources
S.M.Liuzzo

2. How to achieve low emittance low-emittance lattice first turns
Outline
How to achieve low emittance
low-emittance lattice
first turns
BPM-quad offsets
emittance measurement, natural vs apparent emittance
Normal and skew resonance driving terms correction (Response matrix fit)
How to keep low emittance
emittance feedback loop using resonances amplitude and phase
emittance feedforward when undulators gaps move (specific, may be usefull if wigglers are foreseen)
injection perturbation damping systems
Emittance during top-up
orbit stability FOFB
l Recent experience from modern synchrotron light sources l future Tau-Charm factory 4-7 Dec 2018 l S.M.Liuzzo

3. Reduce emittance for higher brilliance
B = Photons/(s mm2 mrad2 BandWidth )
Diffraction limit,
at ln=10nm is 10 pmrad
(lower ε does not increase B) n
Lattice + optics tuning
coupling tuning
Dipole-quadrupoles
Small bending angles
Low beam Energy
X-ray energy
Available space, €
Optics: Twiss and dispersion
Photon beam
Beam lifetime
Injection
l Recent experience from modern synchrotron light sources l future Tau-Charm factory 4-7 Dec 2018 l S.M.Liuzzo

4. current ESRF storage ring lattice: Double Bend Achromat
Already a “low-emittance lattice”
dipoles
quadrupoles
sextupoles
undulators
BM source
undulators
16 superperiods (mirrored cell above, 32 cells in total).
Achromatic condition broken for lower emittance (ex from 7 nmrad to 4 nmrad ).
l Recent experience from modern synchrotron light sources l future Tau-Charm factory 4-7 Dec 2018 l S.M.Liuzzo

5. Esrf-EBS Upgrade in 2020:Hybrid Multi Bend Achromat
Strong focusing (large K1)
Dx, 7 dipoles
2 Local dispersion bumps at –I,
large sext. for chromaticity correction with low sextupole fields (K2)
Ex = 0.135nm
dipoles
quadrupoles
sextupoles
BM source
undulators
undulators
Dipoles + quadrupole gradient
Dipoles longitudinal gradient
l Recent experience from modern synchrotron light sources l future Tau-Charm factory 4-7 Dec 2018 l S.M.Liuzzo

6. Main Lattice Parameters
ESRF-EBS
ESRF
Energy [GeV]
6.00
6.04
Tunes
75.21, 26.34
36.44, 13.39
Emittance x [pmrad]
135
4000
Emittance y (target) [pmrad] 5
Energy loss per turn [MeV]
2.6
4.9
RF voltage (acceptance) [MV]
6 (5.6%)
9 (4%)
Chromaticity
6, 4
4, 7
Circumference [m]
843.98
844.39
Energy spread [%]
0.095
0.106
Beam current [mA]
200
Lattice type
HMBA
DBA
Touschek lifetime [h]
~20
~80
S28
S28A
l Recent experience from modern synchrotron light sources l future Tau-Charm factory 4-7 Dec 2018 l S.M.Liuzzo

7. First Turns, FIRST TRoUBLES FOR LOW-EMITTANCE LATTICES
Beam store
Injection on axis (static bump) or off axis (fit injected beam oscillation) available. Start from injection off axis.
Power orbit steerers to achieve first turn (from simulations, beam survives about 3-4 cells without orbit steering, if magnets & alignment within tolerances).
Measure and correct tune (most relevant for off-axis injection)
Switch on RF, search for correct frequency and phase, store beam
Video: first-turn correction simulations for beam injected on axis. Large BPM offsets are included.
EBS simulated
l Recent experience from modern synchrotron light sources l future Tau-Charm factory 4-7 Dec 2018 l S.M.Liuzzo

8. Trajectory correction scheme for first turns
measured ESRF-SR (and booster)
Commissioning-like SR
Operation SR
Maximum possible current from injectors,
1/3 filling pattern,
3 Gun shots
Horizontal trajectory
Turn #1
Turn #2
100/224 BPMs
40/96 steerers
SVD for trajectory correction
(to reference off-axis injection trajectory)
Acceptable signal on more BPMs or smaller rms trajectory
iterate
l Recent experience from modern synchrotron light sources l future Tau-Charm factory 4-7 Dec 2018 l S.M.Liuzzo

9. First-turns trajectory correction progress on tbt BPMs
ESRF – SR measured
Beam stored
l Recent experience from modern synchrotron light sources l future Tau-Charm factory 4-7 Dec 2018 l S.M.Liuzzo

10. quadrupole offset measurement
Once first turn is established and some beam is accumulated:
measure quadrupole offsets and/or BPM offsets to minimize closed orbit
ESRF-SR measurement
l Recent experience from modern synchrotron light sources l future Tau-Charm factory 4-7 Dec 2018 l S.M.Liuzzo

11. Bpm offset setting to center beam in quadrupoles
ESRF-SR measurement
Optimal Offset (d)
(0,0) For BPM C17-6
H : -30 um
V : 310 um
Initial guess (a)
For each BPM-quadrupole couple:
Beam bump at BPM
At each bump amplitude measure oscillation induced by gradient change.
Set bump that minimize oscillation amplitude
Set BPM reading as ZERO.
Remove bump
Correct orbit
Initial oscillation amplitudes
Closest to quad center (c bis)
Effect of closest quadrupole gradient change on orbit
Zero crossing value (c)
3 points fine scan (b)
l Recent experience from modern synchrotron light sources l future Tau-Charm factory 4-7 Dec 2018 l S.M.Liuzzo

12. Optics and coupling correction
ESRF – SR measured
Response matrix measurement
Precise orbit control (full)
Optics and coupling tuning (partial)
AC or DC steerers measurement
1) Create lattice error model fitting ‘measured’ RM (partial, 16/96 cor.)
ORMerr = [ ORM/K ] * Kfit
2) Lattice errors model using: present correctors and fitted quadrupole errors
3) Compute Resonance Driving Terms and correct normal and skew quadrupole RDT and dispersion
Dhx ~ 28mm -> 3 mm
Dhy ~ 10mm -> 3 mm
Db/bx 50% -> 4%
Db/by 50% -> 3%
Vertical emittance 4-10pm
(depending on gap settings)
 ORM/K can be obtained analytically
To be published, arXiv: v2
A. Franchi et al.
l Recent experience from modern synchrotron light sources l future Tau-Charm factory 4-7 Dec 2018 l S.M.Liuzzo

13. Optics and coupling correction: applications view
This is not LOCO (Linear Optics from Closed Orbit), it is the ESRF tool for RM fit.
LOCO (J. Safranek, NIMA, 388, 27 (1997)) is at present the most used optics and coupling correction tool.
l Recent experience from modern synchrotron light sources l future Tau-Charm factory 4-7 Dec 2018 l S.M.Liuzzo

14. Need to measure emittance at several locations
equilibrium emittance
measurable emittance
In presence of coupling:
Emittance should be measured at several locations along the lattice.
l Recent experience from modern synchrotron light sources l future Tau-Charm factory 4-7 Dec 2018 l S.M.Liuzzo

15. Measured vertical emittances
Vertical emittance measured and simulated form the fitted error model
expected after correction
measured
l Recent experience from modern synchrotron light sources l future Tau-Charm factory 4-7 Dec 2018 l S.M.Liuzzo

16. Top-Up operation, FOFB, gaps movements
Top-up operation requires injection every 20 minutes. Beam must be available to users also during injection.
During delivery magnet vibrations and gap movements induce fluctuations of the closed orbit. The Fast Orbit Feedback powers 96 AC steerers to keep horizontal and vertical orbit stability at less then 1 mm from the reference orbit.
Hor. beam position
Top-up
time
ID gaps change. Immediately corrected, globally invisible. Red > 1um orbit change.
beam
Effective beam size 1s
0.1s
Beam stability
l Recent experience from modern synchrotron light sources l future Tau-Charm factory 4-7 Dec 2018 l S.M.Liuzzo

17. Undulators gaps impact on vertical emittance
Undulators gaps are moved by users during operation. The impact on vertical emittance is usually small (but visible), apart from some exceptional cases where skew quadrupole correctors are powered to counteract the effect of the gap movement following measured look- up tables.
l Recent experience from modern synchrotron light sources l future Tau-Charm factory 4-7 Dec 2018 l S.M.Liuzzo

18. TRIM coupling Resonances to adjust emittance
Vary skew quadrupole strenghts to continuosly minimize resonance stopbands via their
amplitude and phase :
AQx+Qy=103, FQx+Qy=103
AQx-Qy=49, FQx-Qy=49
Then tune empirically (or automatically) for optimum amplitude and phase.
3Qy=82
Qx+2Qy=131
Qx-2Qy=22
2Qx+Qy=180
2Qx-Qy=125
3Qx=228, 2Qx=152
3Qx=229
2Qy=54
2Qy=55
Qx-Qy=49
Qx+Qy=104
l Recent experience from modern synchrotron light sources l future Tau-Charm factory 4-7 Dec 2018 l S.M.Liuzzo

19. Emittance feedback using coupling difference resonance Qx-Qy = N
AQx-Qy=23, FQx-Qy=23
Every hour at the 35th minute:
0) check if above threshold
Set some amplitude (if 0.0)
Look for optimum phase
Look for optimum amplitude
Qx-Qy=23
Step 1
Step 2
Step 3
Vert. Emittance above 10pm
Gap movement
Vertical emittance [nm]
(average)
ESRF-SR Operation
@hh.35 Automatic tuning of Qx-Qy = 23
Amplitude and phase.
l Recent experience from modern synchrotron light sources l future Tau-Charm factory 4-7 Dec 2018 l S.M.Liuzzo

20. Stored beam is perturbed during Injection into the Storage ring
~19mm
sextupoles
PERTURBATIONS:
Septa: fringe fields, depends on field strength and distance to the stored beam dominated by S1/2. Un-shielded current leads
Kickers: bump non-closure, 4 identical kickers pulse shape (timing, pulse shape,…)
Sextupoles inside the bump: non closure, envelop oscillations
Vertical perturbations also observed: Coupling, misaligned elements, shims,...
Must allow continuous beam lines data acquisition over injection in Top-Up
every 20 minutes
l Recent experience from modern synchrotron light sources l future Tau-Charm factory 4-7 Dec 2018 l S.M.Liuzzo
S.White

21. Injection perturbation damping
Injection bump not closed during rise-fall.
S.White, B.Roche
l Recent experience from modern synchrotron light sources l future Tau-Charm factory 4-7 Dec 2018 l S.M.Liuzzo

22. Kicker passive compensation
Idea: add copper shims inside the kickers ferrite gap to generate a non-linear field
Shape this field with the shims dimension in order to cancel the sextupole field: reduction of both beta-beat and orbit distortions
Creates vertical field gradient: alignment is now critical
Presently
installed
Ideal conditions and 18mm bump amplitude, simulations indicate a factor 3 improvement
l Recent experience from modern synchrotron light sources l future Tau-Charm factory 4-7 Dec 2018 l S.M.Liuzzo
S.White

23. injection efficiency / Lifetime
Figure: normalized lifetime evolution during optimization, vs tested correctors sets
Injection efficiency and lifetime require online optimization. Many knobs are available, though their setting can be time consuming.
Automated optimizers and resonance correction knobs will be available, as today.
Injection efficiency
Single-turn injection efficiency measurement optimized with injection elements
Lifetime:
Lifetime or BLD measurement optimized with 12 sextupoles
* X. Huang, J. Corbett, J. Safranek, J. Wu, "An algorithm for online optimization of accelerators", Nucl. Instr. Meth., A vol. 726,pp , 2013.
Figure: injected beam current evolution during for 2 RCDS* optimizations
l Recent experience from modern synchrotron light sources l future Tau-Charm factory 4-7 Dec 2018 l S.M.Liuzzo

24. New sextupole setting for the 16 bunch mode
Lifetime of one week of operations with the old sextupole setting and with the new sextupole setting, in 16 bunch mode
l Recent experience from modern synchrotron light sources l future Tau-Charm factory 4-7 Dec 2018 l S.M.Liuzzo

25. How to achieve low emittance
summary
How to achieve low emittance
low emittance lattice :with strong quadrupole and week dipoles
first turns :more difficult with tight tolerances
BPM-quad offsets :critical to minimize closed orbit distortion
emittance measurement: (S!), measurable emittance(s) not equal to natural emittance
normal and skew quadrupole resonance driving terms correction: Response matrix fit for low beta-beating and coupling
How to keep low emittance
emittance feedback loop using resonances amplitude and phase: operation, every h.35
emittance feedforward when undulators gaps move: look-up tables and empiric tuning
injection perturbation damping systems: several systems to dump perturbations
Emittance during top-up : several systems to damp perturbations
orbit stability FOFB: ID gaps changes do not affect other experiments nor themselves.
l Recent experience from modern synchrotron light sources l future Tau-Charm factory 4-7 Dec 2018 l S.M.Liuzzo

26. backup
l Recent experience from modern synchrotron light sources l future Tau-Charm factory 4-7 Dec 2018 l S.M.Liuzzo

27. Number of turns vs error amplitude without correction
EBS simulated
On axis
Increasing the vertical displacement of quadrupoles introduces vertical orbit and coupling.
For an uncorrected lattice a beam injected on axis can perform 100 turns with 50 um vertical quadrupole offsets
A beam injected off axis, can perform only 10 turns for the same error rms.
With several error sources, without correction, only a partial turn (4-5 lattice cells)
Off axis
l Recent experience from modern synchrotron light sources l future Tau-Charm factory 4-7 Dec 2018 l S.M.Liuzzo

28. Strong focusing (large K1) Dx, βx~0 @ dipoles
Low emittance lattice
Strong focusing (large K1)
Dx, dipoles
large sext. for chromaticity correction with low sextupole fields (K2)
Ex order of nm or below
l Recent experience from modern synchrotron light sources l future Tau-Charm factory 4-7 Dec 2018 l S.M.Liuzzo

29. Impact of alignment errors
The above correction scheme is used for each simulated lattice.
The same figure generated for D.A., emittances, optics,… and several other error sources to determine tolerable lattice errors.
l Recent experience from modern synchrotron light sources l future Tau-Charm factory 4-7 Dec 2018 l S.M.Liuzzo

30. Tolerable random errors
Each error, on each magnet family, is studied individually looking at the dependence of DA, lifetime, emittances and all relevant parameters vs error amplitude.
Required: DX DY DS
DPSI DK mm
mrad
10^-4 DL
>100
1000
500 10
DQ, QF[68] 70 50
200 5
Q[DF][1-5]
100 85
SFD 35 OF
Sextupoles and high gradient quadrupoles are the most relevant limitations, nevertheless, these alignment specifications are currently achievable.
(DX=DY=60mm, 84 mm between two magnets).
l Recent experience from modern synchrotron light sources l future Tau-Charm factory 4-7 Dec 2018 l S.M.Liuzzo

31. Liftime and dynamic apertures vs error sources
10h
17h
DA=-10mm
Lifetime = 10h
l Recent experience from modern synchrotron light sources l future Tau-Charm factory 4-7 Dec 2018 l S.M.Liuzzo

32. Comparable tolerance table
DQ (combined function dipoles) behave as quadrupoles concerning errors. Evident the impact on vertical dispersion compared to the other quadrupoles (defocussing quadrupoles).
Quadrupoles have large impact on orbit and horizontal dispersion, also in this case, lifetime and DA are strongly affected. QF6 and QF8 are dominant.
Sextupoles have the largest impact on DA, they are also the strongest source of beta-beating and emittance as expected.
Octupoles influence is limited compared to quadrupole and sextupoles, nevertheless they do have an impact on DA. Their effect on lifetime is very small.
Rotations up to 100urad have impact on the various parameters but limited.
l Recent experience from modern synchrotron light sources l future Tau-Charm factory 4-7 Dec 2018 l S.M.Liuzzo

33. Injection efficiency and Lifetime
26/07/2013
Injection efficiency and Lifetime
Injection efficiency depends on the dynamic aperture. Touschek lifetime depends on the momentum aperture:
Stored beam
Kicked beam
septum
Injected beam
3sh=2.2 mm
Injection bump
On-energy dynamic aperture and momentum aperture depend on the linear and nonlinear lattice.
l KEK Accelerator Seminar l June 2016 l S.M.Liuzzo

34. Injection efficiency booster-SR
26/07/2013
Injection efficiency booster-SR
Injected beam distribution at the septum
S28A lattice
104 particles for 1000 turns, radiation, diffusion. Injection efficiency are average of 10 error seeds.
82+/-6%
93+/-4%
98+/-1%
The colors correspond to:
the actual booster beam (ex=120nm),
reduced emittance by injecting with the booster off-energy (ex=60nm),
round beam (ex=ey=30nm) obtained exciting the coupling resonance in the booster.
emittance swap in the Booster under study
Beam shaping in the injection transfer line using a Sextupole
The beta function at end of the transfer line are optimized for each beam
l KEK Accelerator Seminar l June 2016 l S.M.Liuzzo

35. Injector upgrade: Emittance reduction
The injection efficiency is a critical point for the new machine, so the following improvements are foreseen:
Reduction of the horizontal emittance:
Booster linear optics optimisation: εx: 120 to 95 nm On-going tests
Work off-energy by shifting the RF frequency: εx: 95 to 60 nm Tested
Couple H and V emittances via equal tunes: εx: 60 to 30 nm Tested
Beam shaping using a sextupole in the TL2 transfer line: X'
Stored beam
Injected beam X
Emittance shaping using a sextupole
Classical injection
Septum
The optics is ready
The sextupole is installed and connected since the March shut- down.
Tests will start in the upcoming months
1st MAC MEETING – April L. Farvacque