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Deflecting Cavities for Light Sources
Ali Nassiri
Advanced Photon Source
Argonne National Laboratory
ICFA Beam Dynamics Min-Workshop on Deflecting/Crabbing Cavity Applications in Accelerators
April 23 – 25, 2008, SINAP, Shanghai, China
2A. Nassiri Crab Cavities for Light Sources April 23, 2008 - Shanghai
Outline
Scientific Case Scheme Expected Performance and Tolerances Transient Schemes Technology Options Conclusions
3A. Nassiri Crab Cavities for Light Sources April 23, 2008 - Shanghai
Scientific Case
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Time Scales: Physical, Chemical, and Biological Changes
10-3 10-8 10-1110-9 10-10 10-12 10-13 10-14 10-15
Nano
Pico FemtoMilli
Radicals
Spectr.
and
Reactions
IVR and Reaction Products
Transition States and Reaction Intermediates
Atomic Resolution
Single Molecule Motion
Femto-chemistry
Radiative Decay Rotational Motion Vibrational Motion Fundamental
Internal Conversion & Intersystem Crossing Vibrational Relaxation
Collisions in Liquids
Physical
Predissociation Reactions
Harpoon Reactions
Norrish Reactions
Dissociation Reactions
Chemical
Proton Transfer
Abstraction, Exchange & Elimination
Diels-Adler
Charge Recomb.
Protein Motion Photosynthesis Biological
106
Period of Moon
PS Source
X-ray Techniques
Storage Ring Sources X-ray FELs
Sec.
5A. Nassiri Crab Cavities for Light Sources April 23, 2008 - Shanghai
A New Era of Ultrafast X-ray Sources
LCLS: 120Hz
SPPS 10Hz
Photo courtesy: D. Reis, UM
APS Concept
6A. Nassiri Crab Cavities for Light Sources April 23, 2008 - Shanghai
Science Enabled by ps Sources
The field of time domain scientific experiments using hard x-rays from synchrotron radiation sources is gaining momentum.
The time range covered by ongoing and future experiments is from sub-picoseconds to thousands of seconds, which is 16 to 17 decades of spread.
The scientific disciplines that will benefit from these studies include:
– Atomic and molecular physics
– Biology and chemical science• Photochemistry in solution
– Condensed matter physics• Ultrafast solid state phase transition
– Engineering and environmental science
– Material and nuclear science
7A. Nassiri Crab Cavities for Light Sources April 23, 2008 - Shanghai
Existing and Future Sources Table-top Plasma Sources
– Short pulse 300 fs - 10 ps– Divergent radiation - low flux– Low rep-rate (10 Hz -1kHz)– Not tunable (target dependent)
Storage Rings– ~100-ps duration pulse– Spontaneous x-ray radiation– High average brightness at high repetition rate
Laser Slicing (ALS, SLS, BESSY)– Short pulse 100-300 fs– Rep-rate kHz– Low flux 105 ph/s @ 0.1% BW– Not effective at high-energy sources
Linacs (LCLS/XFEL)– Short pulse 100 fs– Fully coherent– Extremely high brilliance – Low rep-rate (100 Hz)– Limited tunability
8A. Nassiri Crab Cavities for Light Sources April 23, 2008 - Shanghai
Time-resolved Experiments Today
Pump-probe
– Pump : laser pulses (100 fs – 10 ns), s flash lamps
– Probe: 100-ps x-ray or longer pulse train Data collection
– Slow variable: crystal angular setting
– Fast variable: pump-probe delay time, t• For each crystal orientation collect:
– No laser, t1, t2, t3….Laue frames
Repetition rate depends on:
– Sample (lifetime of intermediates)
– Heat dissipation (laser-induced heating)• 1 – 3 Hz typical
40 – 60 images per data set 2-30 angular increment with undulator sources (few % bandwidth)
X-ray pulse
ns laser pulse
9A. Nassiri Crab Cavities for Light Sources April 23, 2008 - Shanghai
Time-resolved Macromolecular Crystallography
Pulse duration: structural changes to be probed sub-ps – min
– 100 ps available at synchrotron sources
– Longer pulse trains suitable for slow reactions
– Sub-100ps desirable to probe very fast structural changes:• Short-lived intermediates• Fast protein relaxation• Rapid ligand migration
Desired X-ray flux greater than 1010 photons/pulse for single image acquisition Single-pulse acquisition will allow study of fast, irreversible processes X-ray energy: few% bandwidth at 12-15 keV
– Softer X-rays increase radiation damage
– Harder X-rays diffract less strongly and are detected less efficiently
10A. Nassiri Crab Cavities for Light Sources April 23, 2008 - Shanghai
Scheme
11A. Nassiri Crab Cavities for Light Sources April 23, 2008 - Shanghai
Deflecting cavity introduces angle-time correlation into the electron bunch, “crabbing” the beam. Bx kicks head and tail of the bunch in opposite directions in the vertical plane.
Electrons oscillate along the orbit. Bunch evolution through the lattice results in electrons and photons correlated with
vertical momentum along the bunch length. Second cavity at n phase cancels “kick”; rest of the storage ring unaffected.
A. Zholents, P. Heimann, M. Zolotorev, J. Byrd, NIM A 425, 385, (1999).
Crabbing Scheme
12A. Nassiri Crab Cavities for Light Sources April 23, 2008 - Shanghai
Expected Performance
and Tolerances
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Estimating X-ray Pulse Duration
X-ray pulse length can be estimated assuming Gaussian distributions1
Emittance growth matters because it increases the minimum achievable pulse duration.
Electron beamenergy
Deflectingrf voltage &frequency
Unchirped e-beamdivergence (typ.2-3 rad)
Divergence dueto undulator (typ.~5 rad)
For 4 MV, 2800 MHz (h=8) deflecting system, get ~0.6 ps
1M. Borland, Phys. Rev. ST Accel Beams 8, 074001 (2005).
22rad,ye,yrf
Vh
Eid
a
xray,t
14A. Nassiri Crab Cavities for Light Sources April 23, 2008 - Shanghai
Emittance Growth1,2
In the idealized concept, a second set of cavities exactly cancels the effect of the first set
– In reality, it doesn't work exactly and we have emittance growth Sources of growth in an ideal machine:
– Time-of-flight dispersion between cavities due to beam energy spread– Uncorrected chromaticity, if present (normally it is)– Coupling of vertical motion into horizontal plane by sextupoles– Quantum randomization of particle energy over many turns
Additional sources of growth in a real machine– Errors in magnet strengths between the cavities– Roll of magnetic elements about beam axis– Roll of cavities about beam axis– Orbit error in sextupoles– Errors in rf phase and voltage
Emittance growth is not just a worry for brightness.– It also limits how short an x-ray pulse can be achieved
1M. Borland, private communication, 2004.2M. Borland, Phys. Rev. ST Accel Beams 8, 074001 (2005).
15A. Nassiri Crab Cavities for Light Sources April 23, 2008 - Shanghai
Reducing Emittance Growth1,2,3,4
There are several methods of reducing emittance growth:– Don't power cavities past point of diminishing returns
– Manipulate sextupoles between cavities• Turning them off is not the best approach• Minimize emittance directly using particle tracking simulation• Tune sextupoles for zero chromaticity between cavities
– Choose vertical oscillation frequency (“tune”) to facilitate multi-turn cancellation of effects
– Increase separation of horizontal and vertical tunes
1M. Borland, private communication,2004.2M. Borland, Phys. Rev. ST Accel Beams 8, 074001 (2005).3V. Sajaev, private communication, 2005.4M. Borland and V. Sajaev, Proc. PAC 2005, 3886-3888, (2005), www.jacow.org.
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Comparison of Emittance Growth for Pulsed, CW
Starting vertical emittance is 13 pm (0.5% coupling) 10-k turn tracking results with parallel elegant1
“1 kHz” shows hybrid bunch emittance only “CW” is for 24-bunch mode, all bunches are affected
1Y. Wang, M. Borland, Proc. PAC07, 3444-3446,www.jacow.org, (2007).
17A. Nassiri Crab Cavities for Light Sources April 23, 2008 - Shanghai
Comparison of Emittance Growth
Starting vertical emittance is 20 pm (0.8% coupling)1
10-k turn tracking results with parallel version of elegant2
Hybrid-mode results are for intense bunch only
1L. Emery, private communication.2Y. Wang, M. Borland, Proc. PAC07, 3444-3446, (2006),.www.jacow.org.
18A. Nassiri Crab Cavities for Light Sources April 23, 2008 - Shanghai
X-ray Slicing Results (2.4-m U33, 10keV)
Two slits at 26.5 m
– Vertical slit is varied from ±100 mm to ±0.010 mm
– Fixed horizontal slit of ±0.25 mm (E. Dufrense)
19A. Nassiri Crab Cavities for Light Sources April 23, 2008 - Shanghai
Results for Constant 1% Transmission
24-bunch mode has a slight edge due to smaller emittance
Effect of emittance increase is clear in comparison of 2 MV and 4 MV results
No compelling reason to go above 4 MV
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Details of X-ray Slicing Results for Hybrid Mode1
Slits: H=0.5 mm, V=0.2 mm1M. Borland, private communication.2007.
2nd harmonicradiation
back-chirp back-chirp
Back-chirppulses haveabout 2.5%of the intensityof the centralpulse.
21A. Nassiri Crab Cavities for Light Sources April 23, 2008 - Shanghai
Details of X-ray Slicing Results for 24 Bunch Mode
Slits: H=0.5 mm, V=0.2 mm
2nd harmonicradiation
Back-chirppulses haveabout 0.02%of the intensityof the centralpulse and arenot seen here.
22A. Nassiri Crab Cavities for Light Sources April 23, 2008 - Shanghai
Summary of Tolerances1
Quantity Driving Requirement 24-bunch Hybrid
Common-modevoltage
Keep intensity and bunch length variationunder 1%
±1% ±1%
Differential voltage Keep emittance variation under 10% ofnominal
±0.44% ±0.43%
Common-modephaserelative to buncharrival
Constrain intensity variation to 1% ±10 deg ±10 deg
Differential phase Keep centroid motion under 10% ofbeam size
±0.07 deg ±0.09 deg
Rotational alignment Emittance control ~1 mrad ~1 mrad
Tolerance on timing signal from crab cavity to users: ±0.9 deg
1M. Borland, “Long-Term Tracking, X-ray Predictions, and Tolerances,” SPX Cavity Review, 8/23/07.
23A. Nassiri Crab Cavities for Light Sources April 23, 2008 - Shanghai
Transient Short Pulse
via
Beam Manipulation
24A. Nassiri Crab Cavities for Light Sources April 23, 2008 - Shanghai
Transient Short Pulse Generation via Beam Manipulation
Studied various transient alternate short pulse schemes (i.e., pulsed) that manipulate beam and rely on radiation damping to restore emittance, bunch length. Potentially useful for beam and beamline diagnostics development, possibly experiments (during machine intervention/studies).
Synchrobetatron coupling W. Guo et al., Phys. Rev. ST Accel. Beams 10, 020701 (2007)
– Chirp is produced via a magnet kick: A sin(x + (z)), rather than deflecting cavity: A(z) sin(x + )
– Beam tilt (y-t) in ID, rather than (y’-t) as with deflecting cavity Rf phase modulation
G. Decker et al., Phys. Rev. ST Accel. Beams 9, 120702 (2006)
– Bunch length actually compressed – no tilt
– Bunch shape oscillation at 2x synchrotron frequency Quarter-integer betatron resonance
W. Guo, private communication, M. Borland, private communication, 2005
– Same chirp as deflecting cavity, except build-up over several turns using resonant excitation at frequency: 8frf + 0.25frev
– Drive at much lower power: ~1 MV
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Comparison: Transient short pulse generation
Pulse compression
achieved
Repetition rate limit
Pro Con
Synchro-betatron
3x (avg)
6.5x (w/o jitter)
~40 Hz (1 kHz
possible with fast kickers)
Available hardware
Bunch current limited to few mA; sensitive to tune jitter &
wakefields
Rf phase modulation
2x ~40 Hz Available hardware,
should allow ~50
mA
Limited pulse compression
Quarter-integer
resonance
TBD
(simul. 50x)
~20 Hz Same as RT
deflecting cavity
Needs hardware
Slide courtesy K. Harkay; Figs. courtesy B. Yang, G. Decker, M. Borland
26A. Nassiri Crab Cavities for Light Sources April 23, 2008 - Shanghai
Technology Options
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APS operating modes, 100 mA
1.59 s
1x1 (16 mA)
8x7 (86 mA)
1.3 s
Deflecting cavity rf voltage
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Cavity Design Evolution – A“ warm” system
June 05*
Nov 07* V. Dolgashev, SLAC
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APS Short-Pulse X-Ray Normal-Conducting Cavity Design*
Frequency 2.815 GHz
Deflecting Voltage 2 MV
Peak Power 2.8 MW
Working Mode Qo 12000
Rt / Q 117
Iris Radius 22 mm
Phase Advance π
Structure Length w/o beam pipes
11.17 cm
Duty Factor 0.147%
Pulse Rate 1.0 kHz
Kick / (Power) 1/2 1.19 MV/MW1/2
Beam Current 100 mA
Input coupler
Rectangular damping waveguide
Water header
Normal-conducting 3-cell cavity with damping waveguide and dual input couplers
Damping material is attached to each damping waveguide flange
Tuning pins Ridged
damping waveguide
*In collaboration with V. Dolgashev (SLAC)
30A. Nassiri Crab Cavities for Light Sources April 23, 2008 - Shanghai
Coupler
Coupler
DamperFlange
DamperFlange
DamperFlange
Slide courtesy: L. Morrison
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Two-Sector Layout
Sector 6, section 6 Sector 7, Girders 1 through 5 Sector 7, section 6
Upstream end ID chamber
Downstream end ID chamber
Gate valve
Gate valve
32A. Nassiri Crab Cavities for Light Sources April 23, 2008 - Shanghai
APS 2.8 GHz Superconducting Single-Cell Deflecting Cavity1
Frequency (GHz) 2.815
Deflecting Voltage 4 MV * 2
Qo (2K) 3.8 * 109
G 235
RT / Q ( m) 37.2
Beam Radius 2.5 cm
No. Cavities 12 * 2
Operation CW
Beam Current (mA) 100
Esp/Vdefl (1/m) 83.5
Bsp/Vdefl (mT/MV) 244.1
HOM dampers
LOM/ HOM damper
Input Coupler / HOM damper
Compact single-cell cavity / damper assembly
Deflecting cavity
Waveguide damper replaces KEK coaxial coupler
1 In collaboration with JLab and LBL
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Deflecting Cavity Layout - Schematic
B B T1T1 B
2920 mm
VV
8000 mm
4592.7 mm
T2 ID VC
P P
T2
190 mm190 mm
107.3 mmSpace available for cryo-modules + bellows
Created:1/16/08Rev: 00
4100 mm
12 cavities + cryomodule
Gate valve Bellows
Thermal intercept
400 mmBellows
2
3
34A. Nassiri Crab Cavities for Light Sources April 23, 2008 - Shanghai
Conclusions Short X-ray pulse generation at the synchrotron light sources will open up new
frontiers in time domain science using X-ray techniques to study structural dynamics included but not limited to:
– Condensed Matter, Chemical and Biological, Gas Phase Dynamics Both normal-conducting room-temperature and SRF options are feasible, with
the advantages of SRF being:
– Not limited to SR bunch train fill patterns
– Higher flux and higher repetition rates up to CW Tracking studies have been performed for pulsed and CW system For CW system
– Presented studies cover only single-particle dynamics Emittance growth for 4 MV is acceptable
– Present results start from base of 20 pm, which seems to be minimum presently achievable
– We stay under 50 pm (2% coupling)
– Little benefit from going to higher voltages We can achieve below 2 ps FWHM with ~1% of nominal intensity
35A. Nassiri Crab Cavities for Light Sources April 23, 2008 - Shanghai
Acknowledgements
V. Dolgashev (SLAC)
R. Rimmer (JLab)
H. Wang (JLab)
P. Kneisel (JLab)
L. Turlington (JLab)
Derun Li (LBL)
J. Shi ( Tsinghua University- Beijing), PhD Candidate
B. Adams, A. Arms, N. Arnold, T. Berenc, M. Borland, T. B. Brajuskovic, D.
Bromberek, J.Carwardine, Y-C. Chae, L.X. Chen, A. Cours, J.Collins, G. Decker, P.
Den Hartog, N. Di Monti, D. Dufresne, L. Emery,M. Givens, A. Grelick, K. Harkay,
D. Horan, Y. Jaski, E. Landahl, F. Lenkszus, R. Lill, L. Morrison, A. Nassiri, E.
Norum, D. Reis, V. Sajaev, G. Srajer, T. Smith, X. Sun, D. Tiede, D. Walko, G.
Waldschmidt, J. Wang, B. Yang, L. Young
Collaborators