Deflecting Cavities for Light Sources - sinap.ac.cn
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 Scientific Case Scheme Expected Performance and Tolerances Transient Schemes Technology Options Conclusions A. Nassiri Shanghai Crab Cavities for Light Sources April 23, 2008 - 2
Scientific Case A. Nassiri Shanghai Crab Cavities for Light Sources April 23, 2008 - 3 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 Nan
o Milli Single Molecule Motion 10-11 10-12 10-13 10-14 Pico 10-15 Femto Sec. X-ray Techniques PS Source Storage Ring Sources Period of Moon Radiative Decay Radicals
Rotational Motion Vibrational Motion Internal Conversion & Intersystem Crossing Spectr. Predissociation Reactions and Reactions Proton Transfer A. Nassiri Shanghai 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 Crab Cavities for Light Sources Biological April 23, 2008 - 4 A New Era of Ultrafast X-ray Sources APS Concept LCLS: 120Hz
SPPS 10Hz Photo courtesy: D. Reis, UM A. Nassiri Shanghai Crab Cavities for Light Sources April 23, 2008 - 5 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 A. Nassiri Shanghai Crab Cavities for Light Sources April 23, 2008 -
6 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 A. Nassiri Shanghai Crab Cavities for Light Sources April 23, 2008 - 7 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) A. Nassiri Shanghai Crab Cavities for Light Sources April 23, 2008 - 8 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 A. Nassiri Shanghai Crab Cavities for Light Sources April 23, 2008 -
9 Scheme A. Nassiri Shanghai Crab Cavities for Light Sources April 23, 2008 - 10 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). A. Nassiri Shanghai Crab Cavities for Light Sources April 23, 2008 - 11
Expected Performance and Tolerances A. Nassiri Shanghai Crab Cavities for Light Sources April 23, 2008 - 12 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 rf 2 y ,e 2
y ,rad 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. M. Borland, Phys. Rev. ST Accel Beams 8, 074001 (2005). 1 A. Nassiri Shanghai Crab Cavities for Light Sources April 23, 2008 - 13 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 M. Borland, private communication, 2004. M. Borland, Phys. Rev. ST Accel Beams 8, 074001 (2005). 1 2 A. Nassiri Shanghai Crab Cavities for Light Sources April 23, 2008 - 14 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 M. Borland, private communication,2004. M. Borland, Phys. Rev. ST Accel Beams 8, 074001 (2005). 3 V. Sajaev, private communication, 2005. 4 M. Borland and V. Sajaev, Proc. PAC 2005, 3886-3888, (2005), www.jacow.org. 1 2 A. Nassiri Shanghai Crab Cavities for Light Sources April 23, 2008 - 15 Comparison of Emittance Growth for Pulsed, CW
1 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 Y. Wang, M. Borland, Proc. PAC07, 3444-3446,www.jacow.org, (2007). A. Nassiri Shanghai Crab Cavities for Light Sources April 23, 2008 - 16 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 L. Emery, private communication. Y. Wang, M. Borland, Proc. PAC07, 3444-3446, (2006),.www.jacow.org. 1 2 A. Nassiri Shanghai
Crab Cavities for Light Sources April 23, 2008 - 17 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) A. Nassiri Shanghai Crab Cavities for Light Sources April 23, 2008 - 18 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 A. Nassiri Shanghai Crab Cavities for Light Sources
April 23, 2008 - 19 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. 1 Slits: H=0.5 mm, V=0.2 mm M. Borland, private communication.2007. A. Nassiri Shanghai Crab Cavities for Light Sources April 23, 2008 - 20
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 A. Nassiri Shanghai Crab Cavities for Light Sources April 23, 2008 - 21 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 1 M. Borland, Long-Term Tracking, X-ray Predictions, and Tolerances, SPX Cavity Review, 8/23/07. A. Nassiri Shanghai Crab Cavities for Light Sources April 23, 2008 - 22 Transient Short Pulse via Beam Manipulation A. Nassiri Shanghai Crab Cavities for Light Sources
April 23, 2008 - 23 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 A. Nassiri Shanghai Crab Cavities for Light Sources April 23, 2008 -
24 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 A. Nassiri Shanghai Crab Cavities for Light Sources April 23, 2008 - 25 Technology Options A. Nassiri Shanghai Crab Cavities for Light Sources April 23, 2008 - 26 APS operating modes, 100 mA Deflecting cavity rf voltage 8x7 (86 mA) 1.59 s 1x1 (16 mA) 1.3 s A. Nassiri
Shanghai Crab Cavities for Light Sources April 23, 2008 - 27 Cavity Design Evolution A warm system June 05* Nov 07 * V. Dolgashev, SLAC A. Nassiri Shanghai Crab Cavities for Light Sources April 23, 2008 - 28 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 Working Mode Qo Rt / Q 2 MV 2.8 MW Water header 12000 Tuning pins 117 Iris Radius 22 mm Phase Advance 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 Rectangular damping waveguide Damping material is attached to each damping waveguide flange * A. Nassiri Shanghai Ridged damping waveguide Crab Cavities for Light Sources In collaboration with V. Dolgashev (SLAC)
April 23, 2008 - 29 Damper Flange Damper Flange Coupler Coupler Damper Flange Slide courtesy: L. Morrison A. Nassiri Shanghai Crab Cavities for Light Sources April 23, 2008 - 30 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 A. Nassiri Shanghai Crab Cavities for Light Sources April 23, 2008 - 31 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 A. Nassiri Shanghai Crab Cavities for Light Sources April 23, 2008 - 32 Deflecting Cavity Layout - Schematic 8000 mm 190 mm
Space available for cryo-modules + bellows 107.3 mm ID VC V T1 B T2 190 mm 4592.7 mm 2920 mm 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 A. Nassiri Shanghai Crab Cavities for Light Sources April 23, 2008 - 33 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 A. Nassiri Shanghai Crab Cavities for Light Sources April 23, 2008 - 34 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 A. Nassiri Shanghai Crab Cavities for Light Sources
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