Overview of CLARA

1. Overview of CLARA Jim Clarke ASTeC and Cockcroft Institute ALPHA-X Workshop, May 2013

2. Update:Versatile Electron Linear Accelerator • VELA is the new name for EBTF • High brightness RF Photoinjector • Essential technology for advanced electron facilities • Light sources • Colliders • First RF Photoinjector in the UK • New tool for industry to develop new accelerator-based technologies • Healthcare • Security scanners • Water treatment • …. • Two independent beam areas available • Funded August 2011

3. VELA Beam Transport Layout Beam Injector Beam Enclosure 1 Beam Enclosure 2

4. VELA Injector

5. VELA

6. VELA Status • VELA Approval – August 2011 • VELA hardware commissioning started – Oct 2012 • RF Conditioning started – 30th Nov • 5.3 MW peak power achieved – 20th Dec • RF window vacuum leak identified – 11th Jan 2013 • RF Conditioning restarted – 21st Feb • Multipactoring observed as solenoid powered • 4.8 MW, RF window cracked – 6th March • Ceramic window fitted (Strathclyde) • RF Conditioning restarted – 19th Mar • 5.7 MW peak power achieved – 2nd Apr • First electrons – 5th Apr 2013 • Shutdown for installation of all systems

7. CLARA • Compact Linear Accelerator for Research and Applications • Major upgrade of VELA • A world class FEL test facility that can try out new ideas so they can be implemented directly into a future light source facility – we know there is a strong demand for these improvements from the NLS Science Case and direct interactions with users • In parallel we will also be able test advanced accelerator technologies • The investment in CLARA will pay for itself by reducing future risk and timescales • More importantly, it will also make any UK future light source a world beater !

8. 4th Generation Light Sources • Free Electron Lasers • Ultra high peak intensity • Very short pulses of light • Tuneable • Basic FEL unstable in intensity and wavelength • Immature as a technology, plenty of scope for improvement • Fortunately lots of ideas exist for improving FEL stability (wavelength and intensity) and to make even shorter pulses of light but very few have been tested • Can’t propose a major new facility based on an untested idea! Need test facility

9. Reviewing the field – Facilities • Currently there are only five (soon to be three?) dedicated single pass FEL test facilities worldwide, two in the US (NLCTAand SDU), one in Asia (SDUV-FEL) and two in Europe (SPARCand MAX). • Highest current priority for FELs is improving temporal coherence. • Reducing size and cost is another common theme. • An opportunity exists for a new FEL test facility looking at next frontiers. Extract from: A Review of Worldwide Test Facilities for Free Electron Lasers David Dunning, ASTeC

10. Ultimate aims of CLARA

11. Other Aims and Prerequisites Low charge single bunch diagnostics Synchronisation systems Advanced digital low level RF systems Novel short period undulators NC RF photoinjectors and seed laser systems • Generation and control of bright electron bunches • manipulation by externally injected radiation fields • mitigation against unwanted short electron bunch effects To deliver the ultimate objectives of CLARA will encompass development across many areas: High temporal coherence and wavelength stability through seeding or other methods Generation of coherent higher harmonics of a seed source Photon pulse diagnostics for single shot characterisation and arrival time monitoring

12. Goals, Opportunities and Benefits • The proof of principle demonstrations of ultra-short photon pulse generation using schemes which are applicable to X-ray FELs and with extreme levels of synchronisation. • The ability to test other novel schemes for increasing the intrinsic FEL output intensity stability, wavelength stability, or the longitudinal coherence using external seeding, self-seeding or other methods. • The ability to generate higher harmonic radiation of a seed source using EEHG, HGHG, etc. • The generation and characterisation of very bright (in 6D) electron bunches and the manipulation of the bunch properties with externally injected lasers. • The development of advanced accelerator technologies, such as a high repetition rate NCRF photoinjector, single bunch low charge diagnostics, and novel photocathode materials and preparation techniques. • The enhancement of VELA, in terms of energy, beam power, and repetition rate. • The development of vital skills within the UK accelerator community, including providing excellent opportunities for PhD students and post docs to work on a world class accelerator test facility. • To use the electron beam for other applications: ultrafast electron diffraction, plasma wakefield accelerator research, Compton scattering source of X-rays or gamma photons, and other novel acceleration schemes such as dielectric wakefield accelerators.

13. Flexible FEL Layout • 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 carefully comparing the various schemes and their detailed requirements – we do not anticipate testing them all! • We are designing in this flexibility from the start.

14. EXAMPLES OF FEL SCHEMES ON CLARA SINGLE SPIKE SASE100pC tracked bunch compressed via velocity bunching SLICING + CHIRP/TAPERShort pulse generation using an energy chirped electron bunch and a tapered undulator E. L. Saldin et al, Phys. Rev. STAB 9, 050702, 2006 MODE-LOCKINGMode-locked amplifier FEL using the standard CLARA lattice with electron beam delays between undulatorsN. R. Thompson and B. W. J. McNeil, Phys. Rev. Lett. 100, 203901, 2008 MATCHED MODE-LOCKINGElectron beam delays matched to the rms electron bunch length to distinguish a single spike from the pulse train Plots courtesy of Ian Martin and Neil Thompson

15. Slicing Scheme Example • Few-cycle seed laser is used to modulate the electron beam energy to an amplitude greater than the natural bandwidth of the FEL. • By tapering the gap of the undulator, only the sections of the electron bunch where the energy chirp is correctly matched to the undulator taper will experience high FEL gain. CLARA Example: 50 mm, 10 mJ, 500 fs seed laser

16. Parameters The parameters have now been broken down to cover 5 different operating modes. This helps us understand which parameters we need simultaneously. 25 • FEL output wavelengths from 400nm to 100nm • Can make use of 800nm laser for harmonic generation experiments • Can use well established laser diagnostics for single shot pulse length measurements • No need for long photon beamlines, can deflect by 90 degrees

17. RF Frequency & Rep Rate • The current VELA gun (ALPHA-X) and the DLS 1 kHz gun are both SEU • There is significant effort within Europe on advanced RF guns using SEU • CLARA will have an SEUgun and an SEUlinac with an XEUlinearizing cavity • Higher rep rates (>100 Hz) will be useful for • Industrial applications • Feedback systems for stabilization • Sharing pulses amongst multiple facilities • Technology demonstration and leadership • A future national facility • CLARA has a maximum energy specified to be 250 MeV but it is not necessary (or even important) to attain this energy at the highest rep rates • The vast majority of industrial users will be satisfied with 100 MeV • We have proposed that CLARA should have a repetition rate of 400 Hz but at a reduced linac gradient (and so beam energy). The infrastructure (eg RF modulators, lasers) should therefore be capable of up to 400 Hz operation. Full beam energy should be possible at 100 Hz.

18. High Repetition Rate NCRF Initial EBTF gun cavity (ALPHA-X) will operate at up to 10 Hz repetition rate High Rep Rate Gun Development Scaled to S-band FLASH/XFEL gun cavity fabricated by DLS could be tested at up to 400 Hz with EBTF/CLARA (no RF pick up) New design is being generated and compared against DLS solution CLARA Linac Assuming use of 3 x SwissFEL Injector linac structures (100 Hz @ 20 to 25 MeV/m, 400Hz @ 10MeV/m, 4.3 m long) A study on practical realisation of high gradient, 20 to 25 MeV/m, 400 Hz linac structures has carried out by AES – solution proposed looks feasible and realistic X-Band RF Source Collaboration initiated with CERN Development of low cost RF source for linearising cavity

19. CLARA Layout 4th Harmonic Cavity Further exploitation line Photon Diagnostics Gun 4m linac FEL afterburner Laser Heater 2m linac 4m linacs 70MeV 250MeV Bunch Compressor TDC2 FEL radiators TDC1 FEL modulator Dump EBTF exploitation area Total Length ~ 90m

20. Impact on VELA

21. Impact on VELA CLARA Front End • CLARA axis is offset by 1m from VELA • VELA photoinjector laser/RF system used by CLARA gun (VELA gun cavity initially as well) • Existing VELA beamline will stay in place (after first 5m) • CLARA will then feed VELA at up to 25MeV (cf 5MeV) • Option for new themionic gun for VELA available if required

22. Other Opportunities • Time Resolved Electron Diffraction • Grant proposal submitted for ultrafast electron diffraction • Will be incorporated into existing VELA for demo experiments, aiming to incorporate within CLARA later • Plasma accelerator research • see next talk • THz source for science • Compton fs gamma or X-ray source • High energy beamline for industrial exploitation • Dielectric Wakefield Acceleration Experiments • Exotic storage rings (eg optical stochastic cooling, non-equilibrium light source, integrable optics lattice)

23. Next Steps • CDR now being drafted • TDR will follow • CLARA funding still to be secured • SwissFEL linacs released Jan 2015 • If procurement starts April 2014 then could install in first half of 2016 • CLARA first commissioning – mid 2016

25. Acknowledgement Many thanks to colleagues from ASTeC, Technology Department, 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