Rutherford Appleton Laboratory

1. Vulcan Front End OPCPA System Rutherford Appleton Laboratory • Pump Laser • Stage 1 - BBO • Stage 3 - LBO • Stage 2 - BBO

2. Bandwidth ~ 50 nm @ 1053 nm OPCPA Test Bandwidth Rutherford Appleton Laboratory • Theoretical bandwidth for this system is > 250 nm (@ 1053 nm • In previous tests (limited by bandwidth of optics) we demonstrated ~ 50 nm • Actually require just 16 nm • So far first 2 stages tested (unsaturated gain of 106) • Need the 3rd stage for saturation and stability

3. Adaptive mirror Stretch 2 x 2 pass ; 4.8 ns; 16 nm 3 - stage OPCPA 2 x BBO + LBO Amplification in Vulcan (85J ; 150 mm P & Si) 3 ex NOVA 208 amplifiers (650J ; 208 mm) Expansion to 600 mm (19 m VSF) X 3.107 X 450 X 8 Pre-amp. pump 200 mJ 10 Hz Focusing on target (F3.2 OAP) Compression to 500fs (1480 l/mm) PW Scheme Rutherford Appleton Laboratory Rutherford Appleton Laboratory Oscillator 5 nJ 100fs TiSa Existing Building New Target Area

4. The Vulcan PW Facility Rutherford Appleton Laboratory Computer Schematic - 2000 Vulcan PW Facility - 2002 Energy on target 500J Pulse duration 500 fsec Intensity on target 1021 Wcm-2

5. Single electron motion Rutherford Appleton Laboratory A single electron in the laser field exhibits a figure of eight motion due to the vxB term in the Lorentz force F = -e(E+vxB) Twice every laser cycle, electrons are accelerated in the direction of k The kinetic energy the electron acquires is roughly proportional to the ponderomotive potential E k B At 1021 Wcm-2, kT 10 MeV.

6. Wave breaking of self-modulated laser wakefield demonstrated using 100 TW Vulcan facility - large energy spread. • Improved electron beam quality expected with conventional laser wakefield - long focal length optics. Self-modulated wakefield, classical wakefield and beatwave accelerators studies on the VULCAN PW facility Rutherford Appleton Laboratory Rutherford Appleton Laboratory • CPA beatwave schemes also possible and will be investigated on the PW facility

7. Accelerated electrons observed at energies up to 120 MeV Rutherford Appleton Laboratory Rutherford Appleton Laboratory • In the self modulated wakefield, stimulated Raman scatter arises from noise - generating an electron plasma wave and a down-shifted electromagnetic wave. This em wave ‘beats’ with the incident laser pulse, and the increased intensity in the beat-wave pattern enhances the plasma wave. Gradients of 1 GeV/cm have been measured. Eventually, the plasma wave breaks, generating a wide energy spread shown here. • In the classical wakefield, the laser intensity and plasma density are reduced below the threshold for stimulated Raman scatter. In this case, the ponderomotive force expels electrons from the focus, but space charge requires that they return MIK Santala et al. Phys. Rev. Lett, 86, 1227 (2001) after the laser pulse has passed. This sets up a large amplitude (GeV/cm) oscillating longitudinal electric field that can accelerate low emittance electron bunches - provided the plasma wakefield is quasi - 1 dimensional - requires PW -class lasers with long focal lengths optics.

8. Beat-wave accelerators Rutherford Appleton Laboratory • Beatwave accelerators were the first to be studied in the 1980’s • Two laser pulses of different frequencies are focused into a plasma gas. At a resonant density, the ponderomotive force of the induced beat pattern amplifies small density fluctuations arising from noise - and a large amplitude longitudinal electric field is set up. • Nd glass operating at 1mm is better than CO2 (10.6mm) as higher plasma densities are required - hence larger electric fields. • However, if the laser pulse duration is too long, the modulation instability limits the amplitude of the plasma waves that can be generated. • With chirped pulse, picosecond laser pulses, a beat-wave pattern can be induced by spectral shaping the laser pulse. The pulse duration is sufficiently short to amplify the plasma waves before the modulational instability can grow to disrupt the process. • The VULCAN PW laser will be used to study this beat-wave accelerator process.

9. Astra laser hall Beam expander The “engine” for Astra’s high energy output is the 5J frequency doubled Nd:YAG pump laser Pulse picker TiSa rod, 16mm aperture Rutherford Appleton Laboratory Astra is extremely compact, driving physics at up to 1019Wcm-2 at 10Hz with “table top” scale The final amplifier will be upgraded next year to enable full energy to be delivered to TA2

10. Astra high intensity target area Target chamber Vacuum pulse compressor Rutherford Appleton Laboratory