1. 1 NGLS Concept Outline and Near-Term Tasks John Corlett FNAL March 15, 2012

2. 2 Motivation: Coherent X-rays with high repetition rate, unprecedented average brightness, ultrafast pulses Weak pulses at high rep rate Today’s storage ring x-ray sources ~ nanoseconds ~ picoseconds ~nanojoule Tomorrow’s x-ray laser sources ~ microseconds ~ attoseconds to femtoseconds Intense pulses at high rep rate ~0.1 millijoule Intense pulses at low rep rate ~ milliseconds ~ femtoseconds Today’s x-ray laser sources ~millijoule … …

3. 3 Approach CW superconducting linac, laser heater, bunch compressor High-brightness, high rep-rate gun and injector Beam spreader Array of independent FELs X-ray beamlines and endstations High average power electron beam distributed to an array of FELs from high rep- rate injector and CW SCRF linac NGLS offers significant advances over current capabilities: More photons per unit bandwidth More photons per second Shorter pulses Controlled trade-off between time and energy resolution

4. 4 High repetition rate soft X-ray laser array o Up to 10 6 pulses per second o Average coherent power up to ~100 W Spatially and temporally coherent X-rays (seeded) o Ultrashort pulses from 250 as – 250 fs o Narrow energy bandwidth to 50 meV Tunable X-rays o Adjustable photon energy from 280 eV – 1.2 keV −higher energies in the 3 rd and 5 th harmonics o Polarization control o Moderate to high flux with 10 8 – 10 12 photons/pulse Expandable o Capability o Capacity Capabilities

5. 5 Three initial FEL beamlines to span the science case Seeded or self-seeded 2 color seeded SASE or self-seeded 10 μs 5 – 150 fs High resolution ~Time-bandwidth limited 10 11 – 10 12 ph/pulse 10 -3 – 5x10 -5 bandwidth High-resolution spectroscopy Diffract-and-Destroy (with harmonics) 10 μs 0.25 – 25fs Ultra-fast Sub-fs pulses 2 color 10 8 ph/pulse Multidimensional spectroscopy ≤1 μs 5 – 250 fs Highest rep rate High flux 10 11 - 10 12 ph/pulse 100 W Diffract-and-Destroy (at highest rate) Photon correlation spectroscopy

6. 6 Accelerator Systems R&D priorities High repetition rate –Injector “APEX” –Beam spreader Advanced FEL operation –Modeling and optimization –Seeding approaches –Seed lasers –Superconducting undulators Developing partnerships SCRF RF power

7. 7 Superconducting accelerator design Linac cost drivers −Cryomodules −Cryogenic plant −RF power −Civil construction  CW SCRF linac and harmonic cavities to accelerate and manipulate high repetition rate, high brightness, high average power electron beam  The cryomodule design has a strong influence on conventional facilities  Cryomodule acceleration energy, stability and reliability are key machine parameters  Cryogenics plant and delivery and cryomodules are inseparable systems  Plan to adopt features of existing designs – state-of-the-art

8. 8 RF frequency 1.3 GHz V cavity ≈ 14 MV Cavity tuning excursion ±25 Hz  Beam <15° R/Q 1036 Ω Cavity length 1.038 m Q o 1x10 10 I beam 1 mA SCRF linac power requirements (CD-0) 7 cavities per CM 450 kW wall-plug power for RF systems 290 kW wall-plug power for cryo-systems Want Higher gradient Higher Q 0 Smaller cavity detuning Lower current?

9. 9 Cryomodule optimization (main linac) Current cryomodule concept uses “TESLA” cavities in JLAB-style housing Cold/warm transitions on each cryomodule Distribute 5 K liquid, cool to 1.8 K at cryomodule Warm magnets & diagnostics Design questions Operating gradient increased to ~16 MV/m Q 0 ≥ 2x10 10 HOM power dissipation and absorption Field emission Number of cavities within a single module Shield temperature and arrangement Power coupler design Tuner type and access Selection and sizing of cryogenic circuits Minimization of acoustic noise Warm to cold transitions

10. 10 First draft due May 16 Preparations for a CDR

11. 11 Linac optimization and CDR FNAL could help provide input on SCRF and cryoplant topics: Selection of linac technology Cryomodule type (individual / strings) Number of cavities within a single module Frequency choice Operating gradient Operating temperature Q o HOM power dissipation and absorption Field emission Shield temperature and arrangement Power coupler design Tuner type and access Selection and sizing of cryogenic circuits Minimization of acoustic noise Warm to cold transitions Harmonic cavities & cryomodules Cryoplant size Cryogen distribution RF power and distribution LLRF and controls Timing distribution Beam-based feedback Optimized operational parameters

12. 12 Technology Readiness Assessment and R&D planning Assess technical maturity for each system or component at level ~3 in the NGLS WBS ~50 items Determine Critical Technology Elements (CTEs) Essential, unique capabilities, incomplete requirements definition Prioritized list of CTEs will guide R&D plan FNAL could help provide input on SCRF TRA and R&D needs WBSWBS NameTRLDictionaryReferences and comments from proponents 1.1.4VHF RF Electron Gun 3The gun cavity is a resonant RF structure that supports the cathode, and the electric field that accelerates the photoelectrons, in a UHV environment. The gun RF system provides ~100 kW CW power at 187 MHz. A prototype gun is operational in APEX, has demonstrated design RF power capability, and is undergoing further tests for vacuum, long- term reliability, etc. [1] "Schemes and challenges for electron injectors operating in high repetition rate X-ray FELs", Fernando Sannibale, Daniele Filippetto & Christos F. Papadopoulos, Journal of Modern Optics, Volume 58, Issue 16, 2011, Special Issue: Development and Technical Challenges of Next Generation Free Electron Lasers, pages 1419-1437 1.1.4.3Photocathode3 – 5Mounted inside the VHF RF gun cavity, and illuminated by the drive laser, the photocathode provides the electrons for the accelerator. CsTe photocathodes operate in accelerator environments and are used at FLASH, Fermilab, etc. at average repetition rates lower than NGLS. Alkali antimonides have been successfully demonstrated in tightly controlled laboratory environments; emittance under field, field emission, laser and beam damage are not yet tested. APEX will test cathodes, and demonstrate efficiency, lifetime, and reliability, under NGLS conditions. TRL 4 seems to be to be just about right. We have done the lab kluge, tested a concept (TRL4), but we have not done 1st test in reasonable lab environment simulating gun conditions. Also in TRL 4, initial proof of concept.....we have proved the concept for QE and emittance, but not any other parameter (emittance under field, field emission, laser and beam damage). All in all, your rating of 3-5 is probably right; some bits are done and proven, others aren't. Is it OK to leave it like this, ie. 3-5. Some significant part we are still vulnerable if reviewed and need to ramp up efforts in the next year to get through at TRL 4 issues. [1] Vecchione et al, APL 99, 034103 (2011) 1.1.5Drive Laser System 5The drive laser system provides photon pulses at a wavelength matched to the work-function of the photocathode material, with sufficient energy per pulse to emit the required number of electrons, and with the appropriate temporal and spatial shape to control beam dynamics of the emitted electrons. For CsTe photocathodes, operating laser systems exist at high repetition rate in burst mode, e.g. at FLASH. For alkali antimonides, lasers of required power are commercially available. What is needed are controls and filtering, and diagnostics, to provide spatial and temporal characteristics specific to NGLS needs, in a CW 1 MHz system. Transverse (position) and longitudinal (timing) feedback systems are also needed to achieve the pulse to pulse stability required. APEX will test these systems, which may be different depending on photocathode materials. All the subsystems have been proven to work separately, and most of them have also been proven in the system an accelerator environment. Fiber laser (oscillator + amplifier) systems (ref.[1]) with the similar wavelength, energy per pulse and repetition rate are commercially available. The TRL also depends on energy per pulse needed, which in turn depends on the choice of cathode material. The challenge resides on interfacing the drive laser with the accelerator satisfying all the tight tolerances requested by user facility. Longitudinal pulse shaping of high rep. rate lasers has already been proven (ref. [2]), but further improvements will be required to get better results. Time and space stability tolerances require feedbacks on the system. The high repetition rate opens the door to high bandwidth feedbacks and can in principle make it very stable. Such systems are state of the art and could be implemented and proven already in the APEX laser. In conclusion, it can be said that all the subsystems are state of the art, but the new challenge of building a very stable laser of a future user facility, decreases the level of readiness down to 5. References [3] and [4] below describe similar high repetition rate laser systems, giving a sense of the level of complexity. [1] see for example: http://www.calmarlaser.com/products/fiber_laser/cazadero.php [2] I. Bazarov et. al., Phys. Rev. ST Accel. Beams 11, 040702 (2008) [3] Ingo Will, Horst I. Templin, Siegfried Schreiber, and Wolfgang Sandner, "Photoinjector drive laser of the FLASH FEL," Opt. Express 19, 23770-23781 (2011) [4] D.G. Ouzonov, I. Bazarov, B. Dunham and C. Sinclair, "The Laser System for the ERL Electron Source at Cornell University", Proceedings of PAC07, Albuquerque, New Mexico, USA. 1.1.6Buncher Cavity5The buncher cavity supports a resonant RF field, that provides an energy chirp to the weakly relativistic electron bunches output from the gun, thereby producing bunching in the downstream beam. A similar system has operated for the ALS harmonic cavities, and at the Cornell ERL prototype. RF power coupler modifications are required for NGLS needs. The buncher RF system provides ~10 kW CW power at 1.3 GHz. The design of the buncher we are using is based on the existing ALS 3rd harmonic cavity with two significant modifications: the buncher is active (coupler added) and it is scaled from 1.5 to 1.3 GHz. So probably that makes it more a 4 than a 5, but I don't have a strong preference

13. 13 Developing cost and schedule estimate Revisit cost estimate developed for CD-0 independent cost review FNAL could help provide input for SCRF and cryoplant costs

14. 14 Summary schedule (for planning purposes) FY CD-0CD-1CD-2/3aCD-3bCD-4b 11 12 13 14 15 16 17 18 19 20 21 22 CD-4a 23 TB D Conceptual design Preliminary Design Procurement / Construction R&D Installation Commissioning

15. 15 NGLS DESIGN STUDY AND ACCELERATOR R&D TEAM B. Austin, K.M. Baptiste, D. Bowring, J.M. Byrd, J.N. Corlett, P. Denes, S. DeSantis, R. Donahue, L. Doolittle, P. Emma, D. Filippetto, G. Huang, T. Koettig, S. Kwiatkowski, D. Li, H. Nishimura, T.P. Lou, H.A. Padmore, C. Papadopoulos, C. Pappas, G. Penn, M. Placidi, S. Prestemon, D. Prosnitz, J. Qiang, A. Ratti, M. Reinsch, D.S. Robin, F. Sannibale, R. Schlueter, R.W. Schoenlein, A. Sessler, J.W. Staples, C. Steier, C. Sun, T. Vecchione, M. Venturini, W. Wan, R. Wells, R. Wilcox, J. Wurtele

16. 16 SCRF discussions Present LBNL concepts for SCRF systems in NGLS Agenda: –Corlett - NGLS concept –Emma - linac physics design –Wells - cryomodules and layout –Koettig - cryogenics –Byrd - HOM power and damping –Bowring - harmonic cavities –Doolittle - optimizations

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18. 18 Repetition rate 1 MHz Charge per bunch from ~10 pC to ~1 nC Emittance <10 -6 mm-mrad (normalized) Electric field at the cathode ≥~10 MV/m (space charge emission limit) Beam energy at the gun exit ≥~500 keV (space charge control) Bunch length ~100 fs to ~10 ps for handling space charge effects, and for allowing different modes of operation Compatible with magnetic field control within the gun (emittance exchange and compensation) 10 -11 Torr vacuum capability (cathode lifetime) Accommodates a variety of cathode materials High reliability for user operations Injector design goals – APEX gun The gun is the most challenging component LBNL approach uses a CW VHF cavity

19. 19 APEX gun: high-brightness MHz electron source APEX cavity is successfully RF conditioned

20. 20 Normal conducting High power dissipation in structure walls Operate in pulsed mode for highest gradient E.g. 120 Hz SLAC linac (2.9 GHz) ~ 20 MVm -1 Superconducting Capability to operate CW Supports high beam power Options for beam recirculation and energy recovery ≲ 20 MVm -1 a goal for CW operations e.g. CEBAF 12 GeV upgrade Choice of SCRF linac SLAC linac EUXFEL

21. 21 CD-0 SCRF power requirements NGLS CD-0 SCRF parameters are conservative 13.5 MVm -1 (14 MVm -1 for linearizer) Q o = 1x10 10 (5x10 9 for linearizer) Strongly impacts costs, or scope

22. 22 SCRF linac power requirements

23. 23 Cryomodules (harmonic cavities) Harmonic cavities cryomodule concept uses the Fermilab design modified for CW operation (Nikolay Solyak) CW heat dissipation #cells per cavity HOM’s & damping

24. 24 Cryosystem Cryoplant size (1 vs 2 units) –Estimated load exceeds capabilities of existing single units Installed capacity 4.5 kW @ 2K ➞ ~4.5 MW system –Cost roughly scales with number of cryoplants Operating temperature (affects Q 0, cryoplant and distribution costs) Cryomodule segmentation (single vs string) has implications on space utilization, transportation, installation Pressure stabilization of helium baths in cryomodules and optimization of controls for the cold compressors Real time monitoring of cryomodule performance