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, Shanghai Outline Scientific Case Scheme Expected Performance and Tolerances Transient Schemes Technology Options Conclusions

3A. Nassiri Crab Cavities for Light Sources April 23, Shanghai Scientific Case

4A. Nassiri Crab Cavities for Light Sources April 23, Shanghai Time Scales: Physical, Chemical, and Biological Changes Nano Pico Femto Milli 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 MotionFundamental 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 MotionPhotosynthesis Biological 10 6 Period of Moon PS Source X-ray Techniques Storage Ring SourcesX-ray FELs Sec.

5A. Nassiri Crab Cavities for Light Sources April 23, 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, 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, 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 fs –Rep-rate kHz –Low flux % 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, 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,  t 1,  t 2,  t 3 ….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 angular increment with undulator sources (few % bandwidth) X-ray pulse ns laser pulse

9A. Nassiri Crab Cavities for Light Sources April 23, 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 photons/pulse for single image acquisition Single-pulse acquisition will allow study of fast, irreversible processes X-ray energy: few% bandwidth at 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, Shanghai Scheme

11A. Nassiri Crab Cavities for Light Sources April 23, Shanghai Deflecting cavity introduces angle-time correlation into the electron bunch, “crabbing” the beam. B x 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, Shanghai Expected Performance and Tolerances

13A. Nassiri Crab Cavities for Light Sources April 23, Shanghai Estimating X-ray Pulse Duration X-ray pulse length can be estimated assuming Gaussian distributions 1 Emittance growth matters because it increases the minimum achievable pulse duration. Electron beam energy Deflecting rf voltage & frequency Unchirped e-beam divergence (typ. 2-3  rad) Divergence due to undulator (typ. ~5  rad) For 4 MV, 2800 MHz (h=8) deflecting system, get ~0.6 ps 1 M. Borland, Phys. Rev. ST Accel Beams 8, (2005).

14A. Nassiri Crab Cavities for Light Sources April 23, Shanghai Emittance Growth 1,2 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 1 M. Borland, private communication, M. Borland, Phys. Rev. ST Accel Beams 8, (2005).

15A. Nassiri Crab Cavities for Light Sources April 23, Shanghai Reducing Emittance Growth 1,2,3,4 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 1 M. Borland, private communication, M. Borland, Phys. Rev. ST Accel Beams 8, (2005). 3 V. Sajaev, private communication, M. Borland and V. Sajaev, Proc. PAC 2005, , (2005),

16A. Nassiri Crab Cavities for Light Sources April 23, Shanghai Comparison of Emittance Growth for Pulsed, CW Starting vertical emittance is 13 pm (0.5% coupling) 10-k turn tracking results with parallel elegant 1 “1 kHz” shows hybrid bunch emittance only “CW” is for 24-bunch mode, all bunches are affected 1 Y. Wang, M. Borland, Proc. PAC07, , (2007).

17A. Nassiri Crab Cavities for Light Sources April 23, Shanghai Comparison of Emittance Growth Starting vertical emittance is 20 pm (0.8% coupling) 1 10-k turn tracking results with parallel version of elegant 2 Hybrid-mode results are for intense bunch only 1 L. Emery, private communication. 2 Y. Wang, M. Borland, Proc. PAC07, , (2006),.

18A. Nassiri Crab Cavities for Light Sources April 23, 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, 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

20A. Nassiri Crab Cavities for Light Sources April 23, Shanghai Details of X-ray Slicing Results for Hybrid Mode 1 Slits: H=0.5 mm, V=0.2 mm 1 M. Borland, private communication nd harmonic radiation back-chirp Back-chirp pulses have about 2.5% of the intensity of the central pulse.

21A. Nassiri Crab Cavities for Light Sources April 23, Shanghai Details of X-ray Slicing Results for 24 Bunch Mode Slits: H=0.5 mm, V=0.2 mm 2nd harmonic radiation Back-chirp pulses have about 0.02% of the intensity of the central pulse and are not seen here.

22A. Nassiri Crab Cavities for Light Sources April 23, Shanghai Summary of Tolerances 1 Tolerance on timing signal from crab cavity to users: ±0.9 deg 1 M. Borland, “Long-Term Tracking, X-ray Predictions, and Tolerances,” SPX Cavity Review, 8/23/07.

23A. Nassiri Crab Cavities for Light Sources April 23, Shanghai Transient Short Pulse via Beam Manipulation

24A. Nassiri Crab Cavities for Light Sources April 23, 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, (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, (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: 8f rf f rev –Drive at much lower power: ~1 MV

25A. Nassiri Crab Cavities for Light Sources April 23, Shanghai Comparison: Transient short pulse generation Pulse compression achieved Repetition rate limit ProCon 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 HzAvailable hardware, should allow ~50 mA Limited pulse compression Quarter- integer resonance TBD (simul. 50x) ~20 HzSame 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, Shanghai Technology Options

27A. Nassiri Crab Cavities for Light Sources April 23, Shanghai APS operating modes, 100 mA 1.59  s 1x1 (16 mA) 8x7 (86 mA) 1.3  s Deflecting cavity rf voltage

28A. Nassiri Crab Cavities for Light Sources April 23, Shanghai Cavity Design Evolution – A“ warm” system June 05 * Nov 07 * V. Dolgashev, SLAC

29A. Nassiri Crab Cavities for Light Sources April 23, Shanghai APS Short-Pulse X-Ray Normal-Conducting Cavity Design * Frequency2.815 GHz Deflecting Voltage2 MV Peak Power2.8 MW Working Mode Q o R t / Q117 Iris Radius22 mm Phase Advanceπ Structure Length w/o beam pipes cm Duty Factor0.147% Pulse Rate1.0 kHz Kick / (Power) 1/ MV/MW 1/2 Beam Current100 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, Shanghai Coupler Damper Flange Damper Flange Damper Flange Slide courtesy: L. Morrison

31A. Nassiri Crab Cavities for Light Sources April 23, Shanghai Two-Sector Layout Sector 6, section 6 Sector 7, Girders 1 through 5Sector 7, section 6 Upstream end ID chamber Downstream end ID chamber Gate valve

32A. Nassiri Crab Cavities for Light Sources April 23, Shanghai APS 2.8 GHz Superconducting Single-Cell Deflecting Cavity 1 Frequency (GHz)2.815 Deflecting Voltage4 MV * 2 Qo (2K)3.8 * 10 9 G235 R T / Q (  m) 37.2 Beam Radius2.5 cm No. Cavities12 * 2 OperationCW Beam Current (mA)100 E sp /V defl (1/m)83.5 B sp /V defl (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

33A. Nassiri Crab Cavities for Light Sources April 23, Shanghai Deflecting Cavity Layout - Schematic BBT1 B 2920 mm VV 8000 mm mm T2 ID VC PP T2 190 mm mm Space available for cryo-modules + bellows Created:1/16/08 Rev: mm 12 cavities + cryomodule Gate valve Bellows Thermal intercept 400 mm Bellows

34A. Nassiri Crab Cavities for Light Sources April 23, 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, 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