1. Slide 1 Please write a contribution for the ICFA Beam Dynamics Newsletter! It will provide great advertisement for XFELO workshop and all the technology advances Due March 4. Very simple to submit with MSWord template. See me or Kwang-je Kim for information.

2. Slide 2 Superconducting Accelerator Technology: Opportunities and Challenges for X-ray Oscillators George R. Neil Associate Director, Jefferson Laboratory February 2012 XFELO Workshop Pohang Korea

3. Slide 3 What is the experience base? Continuous wave SRF linacs have a broad experience base and are still growing in capability and importance for light sources as well as nuclear and high energy physics machines. Operational examples: CEBAF & 12 GeV Upgrade (80% complete) JLab IR and UV Upgrade and many under construction or proposed cERL, KEK ERL, NGLS, Cornell ERL, ILC,... Although the technology exists for CW operation at high current, improvements in many areas are desirable to reduce cost and increase performance

4. Slide 4 Existing JLab 4 th Generation IR/UV Light Source E = 130 MeV 135 pC pulses @ 75 MHz 20 μJ/pulse in 250–700 nm UV-VIS 120 μJ/pulse in 1-10 μm IR 1 μJ/pulse in THz The first high current ERL 14 kW average power Ultra-fast (150 fs) Ultra-bright (10 23 ph/sec/mm 2 /mrad 2 /0.1%BW) UV harmonics exceed FLASH average brightness (10 21 average, 10 27 peak ph/sec/mm 2 /mrad 2 /0.1%BW )

5. Slide 5 Continuous Electron Beam Accelerator The electron beam takes 5 passes through a split 1.5 km long linear accelerator before being divided in thirds and sent to targets in the End Stations. Microwaves from tubes similar to those in your microwave oven put over 1 Megawatt power into a hair diameter electron beam A helium refrigerator circulates liquid helium through the system to keep the temperature at 4 degrees above absolute zero

6. Slide 6

7. Slide 7 Assembling Niobium Cavities

8. Slide 8 Jefferson Lab’s 6 GeV electron beam accelerator (CEBAF) is in a tunnel shaped like an oval racetrack 1.5 kilometers long and 10 meters below the Earth's surface. The beam takes 5 passes through 2 linacs. It took 5 more years to build and cost ~$600M in 1990-1995. The 12 GeV Upgrade now 3/4 finished doubles the energy with only 25% more srf due to technology advances

9. Slide 9 Cornell X-ray light source Near perfect energy recovery, i.e. first and second pass 180° out of phase from each other. Moderate Gradient of 15 – 20 MV/m Requires on the order of 2 MW of linac RF power to produce 500 MW of electron beam power. Image Copied from State of the Art Design!

10. 10 NGLS approach High stability CW superconducting linac; laser heater, bunch compressors High-brightness, high rep-rate injector Beam spreader Array of independent FELs X-ray beamlines and endstations Expandable to increase capacity and capability Nominal high-level linac parameters 300 pC 1 MHz 2.4 GeV 16 MV/m 500 A 300 fs

11. 11 Laser seeded 2 color seeded Self-seeded 10 μs 10 – 100 fs HGHG FEL 100 kHz High resolution Trade-off time/energy resolution 0.1–0.6 keV (3 rd stage to 1 keV) 10 10 –10 12 ph/pulse 10 -3 –10 -4 bandwidth 10 μs 1.5– 5fs Chirped/SASE FEL 100 kHz Ultra-fast fs pulse capability 2 color 0.23–1 keV 10 10 ph/pulse ≤100 fs Three concepts are being developed for the initial X- ray lasers, based on different FEL techniques ≥1 μs 30 – 300 fs Self-seeded FEL MHz rep rate High flux 0.23–1.25 keV ~2 keV SASE 10 12 –10 13 ph/pulse ~100 W Science-driven technical design

12. 12 Maximize use of existing expertise, designs, infrastructure, industrialization Engineering developments to meet NGLS needs, reduce costs Reliable and cost-effective CW SCRF electron linac Linac approach Partner Laboratories responsibilities: SCRF Cryogenics RF power and distribution

13. 13 Experimental R&D Most NGLS technologies exist and need engineering developments R&D primarily for high rep-rate and average power, and time/bandwidth control Injector High-brightness beam at MHz rate Superconducting undulators High-field, short-period Seeded FELs Low-risk, low-cost time/bandwidth control Laser systems High average power, tunable, stable systems Beam spreader MHz rate, stable multiplexing of bunches De-chirper Passive energy chirp control Beam stops High-power, solid-state X-ray optics High average power Detectors MHz readout rate 2013: Beam characterization at gun energy 2013: Demonstration of SXRSS at LCLS 2013: 25-period planar Nb 3 Sn prototype characterized

14. Slide 14 Standard Approach for X-ray FELs Accelerate off-crest in L1 to induce a phase-energy correlation along the bunch Use harmonic RF to linearize the longitudinal phase space (Extract energy from beam) Implement a laser heater (LH) to increase intrinsic energy spread (optional) Partially compress the bunch in BC1 Intermediate acceleration in L2 Fully compress the bunch in BC2 Accelerate to final energy and de-chirp in L3 C. Tennant, IPAC 2011

15. Slide 15 Combination Recirculator and Linac C. Tennant, IPAC 2011 1.Inject beam at E inj 2.Accelerate through linac (f L1 ) to induce a phase-energy correlation along the bunch 3.Perform the first bunch compression and linearization in recirculator arcs 4.De-chirp the beam through linac on the second pass by running near zero- crossing (f L2 ) 5.Accelerate on-crest through the afterburner (f L3 ) 6.Perform the final bunch compression

16. Slide 16 Linac configuration C. Tennant, IPAC 2011 Recirculation can make sense for cost savings if the charge/peak is sufficiently low that CSR is not an issue in emittance degradation: example is CEBAF (1 pCoul) Energy recovery starts to make economic sense for currents above ~1 mA: example is the JLab IR Demo (10 mA)

17. Slide 17 Cost drivers & technical risk Linac cost drivers: –Cryomodules –RF –Cryogenics –Tunnel Technical risks –Field emission –BBU –Emittance degradation (e.g. coupler kicks) –Wakefields & image currents (e.g. chamber heating) –Trip rate & reliability TunnelRF powerCryomodulesCryogenic plant 0 10 20 30 40 50 relative cost [%] Matthias Liepe, ERL 2009 Cornell University, Ithaca New York

18. Slide 18 Technical risk Technical risks –Field emission: onset at some gradient, individual cavity dependent, must degrade operating point for CW –BBU: average current and transport design dependent –Emittance degradation: e.g. coupler kicks –Wakefields & image currents: e.g. chamber heating –Trip rate & reliability: gradient dependent

19. Slide 19 Cost drivers Linac cost drivers: –Cryomodules: engineer for reliability, ease of assembly (~ $4-5M per 100 MeV +$10M to engineer first one) –RF: would like many cavities per rf source but cost & difficulty of amplitude and phase control usually leads to single source per cavity: (klystrons $6/Watt, solid state $10/watt, but worth it. $50k/source control) –Cryogenics: scales as P 0.7 but component size limits at about 5000W at 2K. Must provide cooling power margin, requirement depends on (gradient) 2 and Q 0 of srf cavities. ($40-50M for 5kW @ 2K) –Tunnel: local cost of construction, site dependent, length (maximum energy) dependent

20. Slide 20 Cost drivers Linac cost drivers: –60 Cryomodules = $300M –RF: $150k/cavity x 8 cavity/cryomodule x 60 = $72M –Cryogenics:. Need 6 x $40-50M for 5kW = $300M –Tunnel: local cost of construction, site dependent, length (maximum energy) dependent –Plus beam transport, diagnostics, controls, undulators, optics, end stations…. Total probably > $1B

21. Slide 21 Linac/ERL Cost Trades Courtesy T. Powers

22. Slide 22 Cost Optimization (WORK IN PROGRESS T. Powers) For cryogenic plant costs  Temperature and frequency dependence of BCS losses  Frequency dependence of residual resistance.  Increased cost of cryo plant at lower temperature  Decreased wall plug efficiency at lower temperature. 2.5 GeV, CEBAF Upgrade Cavities Includes  Cryomodules costs  Cryo plant costs  Inner Cryomodule Girders  RF system costs  Civil Construction costs  Controls costs  10 year Power costs Courtesy T. Powers

23. Slide 23 Cornell approach for 100 mA ERL Slides by Mattias Liepe and Georg Hoffstaetter at NGLS workshop Sept. 2012 (See also excellent review of HOM damping options) Choices: – f=1.3GHz, T=1.8K, Q=2.E10 – 7-cells/cavity – beam pipe absorbers – Modified Tesla-type cryomodule Gives roughly the same answer as to optimum gradient

24. Slide 24 Cost optimization: cavity gradient 10152025 135 140 145 150 155 160 165 total SRF construction cost (Linac, tunnel, cryo) cost [arb. Units] field gradient [MV/m] 0510152025 10 9 11 cavity Q 0 Q 0 field gradient [MV/m]  Average operation at 16 MV/m Lowest reasonable field for (a) good stability, (b) low background, (c) safety for Q0 drop. Cornell approach for 100 mA ERL Mattias Liepe and Georg Hoffstaetter

25. Slide 25 Effect of operating temperature Cryogenic losses strongly depend on temperature below Tc Optimum operating temp ultimately set by residual resistance NEW LIGHT SOURCE (NLS) PROJECT SCIENCE CASE AND OUTLINE FACILITY DESIGN www.newlightsource.org Editors: J Marangos, R Walker and G Diakun, Science and Technology Facilities Council (STFC)

26. Slide 26 2K and 4K JLab Cryogenic Development 3x Power Reduction 20-25% Power Reduction 2008 12 GeV PED Dana Arenius Large machines are getting more efficient Difference between 2K and 4K does not make up for BCS losses

27. 108 MV, 20 MV/m, 7-cell cavities Compare with original CEBAF cryomodule specification 20 MV, 5 MV/m, 5-cell cavities CEBAF Upgrade Cryomodule Upgrade made possible by advances in SRF

28. Summary : Heat Load Estimates per cryomodule 2 K50 K (shield) Static73 W362 W (mainly FPC and HOMs) Includes u-tubes (10 W @ 2K, 30 W @ 50 K) Dynamic382 W188 W (cavity, FPC, and HOM RF losses) Total455 W550 W Coupler Cooling~ 1 gram/sec cool outer conductors

29. Slide 29 Cost vs. Number of Cells per Cavity Matthias Liepe, ERL 2009 Cornell University, Ithaca New York 0246810 0 0.5 1 1.5 2 2.5 3 normalized cost Cells per Cavity construction 10 yr operation Monopoles >6 cells per cavity desirable, if OK with BBU limit –Q and R/Q of HOMs will increase with number of cells –Risk of trapped modes with very high Q increases as (number of cells) 2 Become sensitive to fabrication errors

30. Slide 30 Estimated residual resistance vs frequency Residual Resistance Data From Cavity Production Projects at Jefferson Lab Gianluigi Ciovati, Rongli Geng, John Mammosser, and Jeffrey W. Saunders IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 21, NO. 3, JUNE 2011 C100 EP But: Note the wide spread

31. Slide 31 Matthias Liepe, ERL 2009 Cornell University, Ithaca New York Cooling Power for Dynamic Cavity Losses for given E acc (still quite optimistic) (dream…) Benefit from lower temp & freq. No advantage to lower freq? Ideally the optimum frequency and temperature depend on residual resistance. In reality ???

32. Slide 32 Residual resistance shows large scatter G. Ciovati SNS med  SNS high  C50C100

33. Slide 33 Possibilities for future improvements New designs with better damping, fewer ports, better packing factor, higher shunt impedance New processes for higher Q 0 New materials may lead to higher operating temperature New developments in RF power may increase efficiency, lower cost Simpler cryomodules may reduce capital outlay

34. Slide 34 ANL-08/39 BNL-81895-2008 LBNL-1090E-2009 SLAC-R-917 ANL-08/39 BNL-81895-2008 LBNL-1090E-2009 SLAC-R-917 Average Brightness vs Photon Energy LCLS 1.5 Å, 4.2 x 10 22 High Rep Rate Injectors SRF Xray Cavity

35. Slide 35 600 MeV, 2 pass acceleration 200 pC, 1 mm mrad injector Up to 4.68 MHz CW repetition rate Recirculation and energy recovery 10 nm fundamental output, 10 nm/H harmonic 50 fs-1000 fs near-Fourier-limited pulses JLAMP FEL designed for unparalleled average brightness of 10-100 eV photons Baseline: seeded amplifier operation using HHG HGHG amplifier + oscillator capability THz Wiggler for synchronized pump/probe

36. Slide 36 CW operation gives high average brightness in both fundamental and harmonics 4 th Gen 3 rd Gen 2 nd Gen JLAB-UV FEL JLAB-THz UV harm NLS Infrared FELs FLASH LCLS XFEL JLAMP harm JLAMP

37. Slide 37 JLAMP in the Light Source Landscape JLAMP delivers important parameter space un-addressed in hard X-ray proposals, with chemical selectivity to measure atomic structure at the nano- scale, measurement of dynamics on the attosecond timescale of electron motion, and imaging JLAMP NGLS LCLS JLAMP harmonics JLAMP NGLS Ultimate LS JLAMP harmonics FLASH LCLS

38. Slide 38 Many of the slides for this background summary were developed by other people and presented at other workshops. I am grateful for all their contributions to the field and hope they do not mind me providing advertisement for their great work. Thanks to Mattias Liepe, Georg Hoffstaetter, Chris Tennant, Bob Rimmer, Tom Powers, Dana Arenius, Gianluigi Ciovati, Rongli Geng, John Mammosser, and Jeffrey W. Saunder and the NGLS Collaboration