Introduction to CLARA Jim Clarke ASTeC, Cockcroft Institute

FELs in the UK ASTeC has an established track record in FEL design, simulation, and optimisation –4GLS –ALICE –NLS –Advanced concepts –SwissFEL, NGLS We now also have practical hands-on experience in the UK for the first time with the success of ALICE FEL

Recent FEL Publications 1.B. W. J. M c Neil & N. R. Thompson. X-ray Free-Electron Lasers. Nature Photonics, 4:814–821, B. W. J. M c Neil, N. R. Thompson, D. J. Dunning & B. Sheehy. High harmonic attosecond pulse train amplification in a Free Electron Laser. Journal of Physics B: Atomic, Molecular & Optical Physics, 44 (2011) M. D. Roper, N. R. Thompson & D. J. Dunning. A time-preserving soft X-ray monochromator for a FEL source: Design optimization using Genesis simulations and wavefront propagation. Journal of Modern Optics, 58, 16 (2011) D. J. Dunning, N. R. Thompson & B. W. J. M c Neil. Design study of an HHG-seeded harmonic cascade free-electron laser. Journal of Modern Optics, 58, 16 (2011) P. H. Williams, D. Angal-Kalinin, D. J. Dunning, J. K. Jones, & N. R. Thompson. A Recirculating Linac Free-Electron Laser Driver. Physical Review Special Topics – Accelerators and Beams, 14, (2011) 6.D. J. Dunning B. W. J. M c Neil, N. R. Thompson & P. H. Williams. Start-to-end modelling of a mode-locked optical klystron free electron laser amplifier. Physics of Plasmas, 18, (2011) 7.E. Kur, D. J. Dunning, B. W. J. M c Neil, J. Wurtele & A. A. Zholents. A Wide Bandwidth Free-Electron Laser with Mode Locking Using Current Modulation. New Journal of Physics 13 (2011) K. B. Marinov & S. I. Tzenov. Nonlinear density waves in the single-wave model. Physics of Plasmas 18, , S. I. Tzenov & K. B. Marinov. Nonlinear waves and coherent structures in the quantum single-wave model. Physics of Plasmas 18, (2011) 10.S. I. Tzenov & K. B. Marinov. Hydrodynamic approach to the free electron laser instability. Physics of Plasmas 18, , N. R. Thompson, D. J. Dunning, J. A. Clarke, M. Surman, A. D. Smith, Y. Saveliev, & S. Leonard. First Lasing of the ALICE Infra-Red Free-Electron Laser. Submitted to NIM A 12.B. W. J. McNeil & N. R. Thompson. Cavity resonator free electron lasers as a source of stable attosecond pulses, Europhysics Letters 96 (2011) 54004

National FEL Facility The NLS was put on hold in Dec 2009 for “3 to 5 years” –“The NLS project would have very high impact. It would have a major lead in both a national and international context. It would be a unique, world leading facility in the area of biological imaging and would open up exciting new research areas and develop new communities.” – STFC Science Board Report, Dec Currently a major new national-class facility does not appear to be on the horizon During the NLS design study it became clear that: –There are potential new technologies which could make a significant positive impact to the capital cost of the facility –There are untested FEL schemes which could significantly improve the performance of the facility Designing these technologies and concepts into the baseline of NLS was not possible as they were (and still are) unproven

ASTeC Strategy ASTeC has decided to make use of NLS being “on- hold” to prove some of the key new concepts and technologies –This will ensure that any future UK FEL national facility will have world leading performance A new single pass FEL test facility is proposed – CLARA This has been discussed at the STFC Accelerator Strategy Board –“A fundamental frontier of science is to measure structural dynamics in real time, and so a priority for this science is a national programme to develop the techniques and technologies to push the performance of short pulsed light sources beyond the present state of the art.” – STFC Operating Plan

CLARA Compact Linear Advanced Research Accelerator A national FEL test facility that can try out many of the new FEL concepts so they can be implemented directly into a future light source facility In parallel we will also be able test more advanced accelerator technologies The relatively small investment required for CLARA could pay for itself in the money we will save in the capital cost of a future light source More importantly, it will also make any national future light source a world beater !

Ultimate Aim of CLARA To develop a normal conducting test accelerator able to generate longitudinally and transversely bright electron bunches and to use these bunches in the experimental production of stable, synchronised, ultra short photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation of light source facilities. –Stable in terms of transverse position, angle, and intensity from shot to shot. –A target synchronisation level for the photon pulse ‘arrival time’ of better than 10 fs rms is proposed. –“ultra short” means less than the FEL cooperation length, which is typically ~100 wavelengths long (i.e. this equates to a pulse length of 400 as at 1keV, or 40 as at 10 keV).

Other Aims and Prerequisites To lead the development of low charge single bunch diagnostics, synchronisation systems, advanced low level RF systems, and novel short period undulators. To develop skills and expertise in the technology of NC RF photoinjectors and seed laser systems. To develop novel techniques for the generation and control of bright electron bunches –manipulation by externally injected radiation fields –mitigation against unwanted short electron bunch effects (e.g. microbunching and CSR). To demonstrate high temporal coherence and wavelength stability of the FEL, for example through the use of external seeding or other methods. To develop the techniques for the generation of coherent higher harmonics of a seed source. To develop new photon pulse diagnostic techniques as required for single shot characterisation and arrival time monitoring.

Short Pulse Schemes: Slicing + Wavelength Selection E.L. Saldin et al., Opt. Comm., 237, 153, (2004). E.L. Saldin et al., Opt. Comm., 239, 161, (2004). CLARA CONFIG. e-beam Laser seed

Short Pulse Schemes: Energy Chirped Beam + Tapered Undulator E.L. Saldin et al., Phys. Rev. STAB, 9, , (2006). CLARA CONFIG. e-beam Laser seed

Short Pulse Schemes: Modelocking N. Thompson and B. Mc Neil, Mode-Locking in a Free Electron Laser Amplifier, Phys. Rev. Lett., 100, , (2008). e-beam Laser seed CLARA CONFIG.

Seeding and Harmonic Generation Schemes e-beam Laser seed e-beam Laser seed e-beam Laser seed e-beam Laser seed EEHG Single Stage HGHG Single Stage HGHG with a split modulator Cascaded Harmonic Generation e-beam Laser seed Cascaded Harmonic Generation + Afterburner

Flexible FEL Layout Chicane (1m long) Diagnostic/Matching Section Modulator Undulator (1.5m long) Radiator Undulator (2.5m long) e-beam Laser seed 0m3m6m9m12m15m18m21m By implementing a flexible FEL layout, especially in the modulator region, it will be possible to test several of the most promising schemes. We are currently starting to carefully compare the various schemes and their detailed requirements – we do not anticipate testing them all ! We aim to design in this flexibility from the start.

Modulator / Radiator Example Configurations Provisional

Selection of Energy/Undulator Period If we define... – Shortest wavelength – Longest wavelength – Minimum gap – Minimum undulator parameter a w...this then defines the undulator period and required beam energy to tune over this wavelength range in a single undulator Longest wavelength is at minimum gap and shortest wavelength is at maximum gap (min a w ) We know we might want resonant interactions with – 800nm + harmonics – OPA at ~ 5um – HHG at 100nm – 50nm So these are the wavelengths of interest... Need to set energy/period to give us access to these wavelengths and some tunability across them

Example: 8mm Gap, a w > Tune from OPA at 5um to Ti:Sa at 800nm: 96MeV / 38mm Tune between 3 rd and 5 th Harmonic of Ti:Sa: 170MeV / 24mm 3 Resonance with HHG at 100nm, no tunability: 190MeV / 19mm 4 Resonance with HHG at 50nm, no tunability: 268MeV / 19mm 5 Tune between 100nm and 50nm: 315MeV / 26mm At 100MeV, minimum wavelength is 370nm At 200MeV can just reach 100nm

Emittance Requirement 4 For FEL at 50nm with 200MeV beam, need normalised emittance < 1.5mm-mrad

100 pC 50 MeV NB. head of bunch to the right ParameterABunits Emittance mm mrad Bunch length15323fs Peak current A Energy spread58187keV Energy4850MeV Example Bunches (Velocity Bunched) Linac 2 Linac 1Gun Linac 3 Linac 4 5 MeV 50 MeV Work In Progress

Example FEL Output (Velocity Bunched) Linac 2 Linac 1GunGun Linac 3 Linac 4 5 MeV 50 MeV 240MeV z = 11.6m FWHM = 20fs z = 11.6m Single Spike SASE

FEL PARAMETERS Beam Energy250 MeV Minimum Gap6 mm (provisional) Radiator Period29 mm (provisional) Radiator Tuning nm (2 nd to 8 th harmonic of Ti:Sa + HHG) Bunch Charge pC Emittance0.2 – 2.0 mm-mrad Seed Sources5-20µm OPA + 800nm Ti:Sa nm HHG Afterburners To reach 50 nm in 1 st harmonic, novel undulator technology ModulatorsStrong R 56 to enable EEHG

Conceptual Layout

CLARA Layout Work In Progress EBTF (Under Construction Now)

Superconducting Undulators ASTeC has led a UK initiative to develop SCUs for several years A recent highlight was the practical demonstration of a 4m long helical undulator for the ILC positron source –11.5 mm period, 0.86 T on axis, 4m long, 4.2 K Now the team is focussed on designing and fabricating a planar undulator with Diamond Light Source –15 mm period, 1.29 T on axis, 2m long, 3° phase error, 1.8 K –Applicable to FELs and storage rings –Installation into DLS due in 2014 D. J. Scott et al, PRL, 107, (2011)

Variable Polarization Undulators B r = 1.3T, Period = 32mm, gap = 8 mm FEL for NLS (APPLE-2) required 2.25 GeV, if APPLE-4 could be used then would only need 1.9GeV (15% lower Energy) Machine energy is a major cost driver! (DELTA)

High Repetition Rate NC RF The NLS baseline operating rep rate was 1.1 kHz, utilising a NCRF photoinjector –Modified FLASH/XFEL gun, 1.3 GHz, 50 MV/m –Cooling water channels improved for better cooling efficiency EBTF/CLARA gun will be 3 GHz EBTF gun cavity (Strathclyde/LAL) will operate at 10 Hz repetition rate Scaled NLS model gun cavity being fabricated by DLS now could be tested up to 400 Hz with CLARA –Gun RF modulator and PI laser specified for up to 400Hz CLARA linac is not specified at present, frequency choice and repetition rate needs to be selected

Next Steps for CLARA Select the basic parameters (2011) Firm up the conceptual layout (2011) Detailed accelerator design (2012) Selection of FEL schemes (2012) Secure the funds... (2012?) Build up CLARA... (2012 – 2014?) Run CLARA... (2015 – ???)

Acknowledgement Many thanks to colleagues from ASTeC, Technology Department (STFC), Strathclyde University, SwissFEL, LAL, the Cockcroft Institute, the John Adams Institute, and Diamond Light Source for their contributions to this talk and the CLARA project in general