1. R & D for particle accelerators in the CLF Peter A Norreys Central Laser Facility STFC Fellow Visiting Professor, Imperial College London

2. Brief introduction to laser wakefield accelerators ASTRA laser Dream beam Photon acceleration ASTRA GEMINI laser specifications first results electron beam control for FEL’s VULCAN 10 PW laser specifications bunch charge betatron emission

3. 1PW = 10 15 W Power = Energy= 500 J = 1  10 15 W pulse duration 500 fs To maximise the intensity on target, the beam must be focused to a small spot. The focal spot diameter is 7  m and is focused with an f/3.1 off-axis parabolic mirror Intensity = Power = 1 x 10 21 W cm -2 Focused area Laser characteristics Amplifier diffraction gratings

4. A single electron in an intense infinite plane polarised laser field exhibits a figure of eight motion due to the vxB term in the Lorentz force F = -e(E+vxB) At relativistic intensities, electrons are accelerated in the direction of the propagation direction k twice every laser cycle. The kinetic energy the electron acquires is roughly proportional to the ponderomotive potential energy U p Electron motion in an intense laser field 10 16 Wcm -2 10 18 Wcm -2 10 21 Wcm -2 U p 1 keV0.4 MeV14 MeV Intensity on target

5. Perturbing ‘object’ passes through a medium which is displaced from equilibrium The medium then returns creating oscillations Areas of high and low electron density create extreme electric fields High intensity laser pulse Laser wakefield acceleration Gas Jet Electron density

6. Electron acceleration Laser pulse Wakefield Projection of electron density Electron injection Plasma electrons are trapped and accelerated by the laser’s wakefield Collaboration between Oxford, RAL, IST Lisbon, University of Strathclyde, UCLA, and Imperial College London

7. Astra laser Single Beam Titanium Sapphire laser system 10 TW optical pulse at 10Hz / 25TW at 1Hz Operated to 2 target areas Experiments in Laser-Plasma Physics

8. Advantages of laser wakefield accelerators Laser Plasma Accelerators have 10,000 higher electric field than conventional accelerators Implies kilometer’s to centimeters reduction in size for same electron energy - attractive Until 2004, they had produced broad range of energies which severely limited applications Quasi mono-energetic electrons up to 100 MeV were produced for the first time at RAL Capilliary discharge experiments later extended this to 1 GeV at LBNL and 200 MeV at RAL. IC / RAL / Strathclyde / UCLA collaboration S.P.D.Mangles et al Nature, 431, 535 (2004) Astra Target Area 2

9. Photon acceleration x – ct (m) Initial photon distribution Final photon distribution Wakefield Scaled electron density Photon frequency (rad/s) Image taken from simulations using a dedicated wave-kinetic code Photon bunching in a wakefield

10. Modulational instability 20 nm overall shift: ionisation blueshift 5 nm peak separation: photon acceleration Stokes separation would have been: 30-40 nm Modulation of a laser spectrum by its own wakefield in a long (180 fs) -pulse experiment

11. Theory and simulations Analytic theory predicts additional peak splitting on top of Stokes splitting with 3-5 nm separation Simulations for 5, 10, 20, 40 bar backing pressure do not show peak splitting, but do show widening of the fundamental peak with wakefield amplitude and background density wakefield amplitudebroadening of fundamental peak

12. Astra-Gemini facility Dual Beam Petawatt Upgrade of Astra (factor 40 power upgrade) 10 22 W/cm 2 on target irradiation 1 shot every 20 seconds Opened by the UK Science Minister (Ian Pearson MP) Dec 07 Significantly over-subscribed. Assessing need for 2 nd target area. Ian Pearson, MP Minister of State for Science and Innovation, Dec 2007

13. South Beamline of Gemini has been commissioned Achieved target energy, spot size and almost pulse duration Pulse duration ~ 45 fs (TBP 0.35) Gemini Target Chamber TIME SPECTRUM TIME 40 fs 34 nm

14. 10 weeks of user access to Gemini Target Area successfully completed Imperial College Electron acceleration experiment Systems are generally working well Gemini First User Experiment

17. Rapid Progress Subsequent work by IC team has shown that with good control of laser parameters, reproducibility can be obtained. Unoptimised laser beam Improved Laser Quality Effect of laser contrast ratio on electron beam stability in laser wakefield acceleration experiments S P D Mangles, A G R Thomas, et al., PLASMA PHYSICS AND CONTROLLED FUSION 48 (12B): B83-B90 Sp. Iss. SI, DEC 2006

18. Taylored density gradients produce small energy spread bunches 10 TW beam focused on far edge of gas jet Bunches of 0.76 +/- 0.02 MeV generated Simulations indicate beams with 0.2 MeV energy spread with GeV energy and beyond may be possible

19. 8 Beam CPA Laser 3 Target Areas 3 kJ Energy 1 PW Power Vulcan facility Increased complexity, accuracy & rep-rate

20. ‘New’ Target Area New 10PW Target Area TAW TAP View of the lower floor 4m diameter chamber, 2.5m high Short F, 45 degree optic to maximise space Long F optic possible on N-S axis - affects final beam positioning. New 10 PW Area TAW

21. Revolutionary bunch charge Taken to the 10PW level, 3D PIC simulations show that this can accelerate 2-40nC of charge. 40nC at 1GeV 14nC at 4 GeV 2nC at 10GeV Images courtesy of L.Silva

22. Betatron radiation A 12 GeV beam with 1 nC charge will emit intense betatron radiation while accelerated while only losing 0.2% of its energy Images courtesy of L.Silva

23. Thank you for Listening