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

Overview of CLARA

Jim Clarke ASTeC and Cockcroft Institute

ALPHA-X Workshop, May 2013

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

VELA Beam Transport Layout

BeamEnclosure 1

BeamEnclosure 2

Beam Injector

VELA Injector

VELA

VELA StatusVELA Approval – August 2011VELA hardware commissioning started – Oct 2012RF Conditioning started – 30th Nov5.3 MW peak power achieved – 20th DecRF window vacuum leak identified – 11th Jan 2013RF Conditioning restarted – 21st FebMultipactoring observed as solenoid powered4.8 MW, RF window cracked – 6th MarchCeramic window fitted (Strathclyde)RF Conditioning restarted – 19th Mar5.7 MW peak power achieved – 2nd AprFirst electrons – 5th Apr 2013Shutdown for installation of all systems

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 !

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

Reviewing the field – Facilities• Currently there are only five (soon to be three?) dedicated single pass FEL

test facilities worldwide, two in the US (NLCTA and SDU), one in Asia (SDUV-FEL) and two in Europe (SPARC and 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

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.• In this context “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). A SASE FEL normally generates pulses that are dictated by the electron bunch length, which can be orders of magnitude larger than the cooperation length.

Ultimate aims of CLARA

Other Aims and Prerequisites

To deliver the ultimate objectives of CLARA will encompass development across many areas:

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 effectsHigh temporal coherence and wavelength stability through seeding or other

methodsGeneration of coherent higher harmonics of a

seed source

Photon pulse diagnostics for single shot

characterisation and arrival time monitoring

Low charge single bunch

diagnostics

Synchronisation systems

Advanced digital low level RF systems Novel short period

undulators

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.

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.

EXAMPLES OF FEL SCHEMES ON CLARASINGLE 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

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

Parameters

The parameters have now been broken down to cover 5 different operating modes. This helps us understand which parameters we need simultaneously.

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

25

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 SEU gun and an SEU linac with an XEU linearizing 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.

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

CLARA Layout

Gun

2m linac

EBTF exploitation

area

4m linac

Bunch Compressor

Laser Heater 4m

linacs

4th Harmonic Cavity

TDC1

TDC2

FEL modulator

Further exploitati

on line

FEL radiators

FEL afterburner

Dump

Photon Diagnostic

s

70MeV

250MeV

Total Length ~ 90m

Impact on VELA

Impact on VELA

• 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

CLARA Front End

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)

Next Steps

CDR now being draftedTDR will follow

CLARA funding still to be securedSwissFEL linacs released Jan 2015If procurement starts April 2014 then could install in first half of 2016CLARA first commissioning – mid 2016

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