Transcript Deflecting Cavities for Light Sources

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
Outline
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Scientific Case
Scheme
Expected Performance and Tolerances
Transient Schemes
Technology Options
Conclusions
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Scientific Case
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Time Scales: Physical, Chemical, and Biological Changes
Atomic Resolution
Transition States and
Reaction Intermediates
IVR and Reaction
Products
106
10-3 10-8
10-9
Femto-chemistry
10-10
10-11
Nano
Milli
Single Molecule Motion
10-12
10-13
10-14 10-15 Sec.
Femto
Pico
X-ray Techniques
PS Source
Storage Ring Sources
Period
of Moon
Radiative Decay
Rotational Motion
Vibrational Motion
Internal Conversion & Intersystem Crossing
Radicals
Spectr.
Predissociation
Reactions
and
Reactions
Proton
Transfer
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Harpoon
Reactions
Abstraction, Exchange &
Elimination
Protein Motion
X-ray FELs
Vibrational
Relaxation
Collisions
in Liquids
Norrish
Reactions
Dissociation
Reactions
Fundamental
Physical
Chemical
Diels-Adler
Charge Recomb.
Photosynthesis
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Biological
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A New Era of Ultrafast X-ray Sources
APS Concept
LCLS: 120Hz
SPPS 10Hz
Photo courtesy: D. Reis, UM
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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 subpicoseconds 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
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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
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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
X-ray pulse
– Slow variable: crystal angular setting
– Fast variable: pump-probe delay time, t
• For each crystal orientation collect:
– No laser, t1, t2, t3….Laue frames
ns laser pulse
 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)
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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
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Scheme
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Crabbing Scheme
 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).
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Expected Performance
and
Tolerances
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Estimating X-ray Pulse Duration
 X-ray pulse length can be estimated assuming Gaussian distributions1
Electron beam
energy
 t , xray  E
Vh  a
Deflecting
rf voltage &
frequency
 id
2  2
y ,e y ,rad
 rf
Unchirped e-beam
divergence (typ.
2-3 rad)
For 4 MV, 2800 MHz
(h=8) deflecting
system, get ~0.6 ps
Divergence due
to undulator (typ.
~5 rad)
 Emittance growth matters because it increases the minimum achievable pulse
duration.
1M.
Borland, Phys. Rev. ST Accel Beams 8, 074001 (2005).
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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.
2M.
Borland, private communication, 2004.
Borland, Phys. Rev. ST Accel Beams 8, 074001 (2005).
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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.
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.
2M.
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Comparison of Emittance Growth for Pulsed, CW


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
1Y.
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
Wang, M. Borland, Proc. PAC07, 3444-3446,www.jacow.org, (2007).
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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.
2Y.
Emery, private communication.
Wang, M. Borland, Proc. PAC07, 3444-3446, (2006),.www.jacow.org.
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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)
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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
2nd harmonic
radiation
back-chirp
back-chirp
Back-chirp
pulses have
about 2.5%
of the intensity
of the central
pulse.
1M.
Slits: H=0.5 mm, V=0.2 mm
Borland, private communication.2007.
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Details of X-ray Slicing Results for 24 Bunch Mode
2nd harmonic
radiation
Back-chirp
pulses have
about 0.02%
of the intensity
of the central
pulse and are
not seen here.
Slits: H=0.5 mm, V=0.2 mm
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Summary of Tolerances1
Quantity
Driving Requirement
24-bunch
Hybrid
Common-mode
voltage
Keep intensity and bunch length variation
under 1%
±1%
±1%
Differential voltage
Keep emittance variation under 10% of
nominal
±0.44%
±0.43%
Common-mode
phase
relative to bunch
arrival
Constrain intensity variation to 1%
±10 deg
±10 deg
Differential phase
Keep centroid motion under 10% of
beam size
±0.07 deg
±0.09 deg
~1 mrad
~1 mrad
Rotational alignment Emittance control
 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.
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Transient Short Pulse
via
Beam Manipulation
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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
Synchrobetatron
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
Quarterinteger
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
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Technology
Options
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APS operating modes, 100 mA
Deflecting cavity rf voltage
8x7 (86 mA)
1.59 s
1x1 (16 mA)
1.3 s
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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*
Normal-conducting 3-cell cavity with
damping waveguide and dual input couplers
Frequency
Input
coupler
2.815 GHz
Deflecting Voltage
Peak Power
2 MV
2.8 MW
Working Mode Qo
Rt / Q
Water
header
12000
Tuning
pins
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
Beam Current
1.19 MV/MW1/2
100 mA
Ridged
damping
waveguide
Rectangular
damping waveguide
Damping material is attached to
each damping waveguide flange
*In
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Crab Cavities for Light Sources
collaboration with V. Dolgashev (SLAC)
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Damper
Flange
Damper
Flange
Coupler
Coupler
Damper
Flange
Slide courtesy: L. Morrison
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Two-Sector Layout
Sector 6, section 6
Upstream end
ID chamber
Sector 7, Girders 1 through 5
Sector 7, section 6
Downstream end
ID chamber
Gate valve
Gate valve
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APS 2.8 GHz Superconducting Single-Cell Deflecting Cavity1
Input Coupler /
HOM damper
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
Deflecting
cavity
LOM/ HOM
damper
HOM
dampers
Waveguide damper replaces
KEK coaxial coupler
Compact single-cell cavity / damper assembly
1
In collaboration with JLab and LBL
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Deflecting Cavity Layout - Schematic
8000 mm
190 mm
190 mm
4592.7 mm
2920 mm
Space available for cryo-modules + bellows
107.3 mm
ID VC
V T1 B T2
T2 B
P
B T1 V
P
12 cavities +
cryomodule
Gate
valve
Bellows
3
2
Bellows
400 mm
Thermal
intercept
4100 mm
Created:1/16/08
Rev: 00
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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
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Acknowledgements
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
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
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