1. Rutherford Appleton Laboratory Three mechanisms interact to cause ion acceleration in PW laser interactions Relativistic electrons expelled by the ponderomotive pressure of light wave. To overcome the attractive electric field of the ions, E e > E c. The Coloumb energy E c is approximately E c 2 2 ne 2 l s R Later the ions move due to Coloumb repulsion. E i 4 2 ne 2 R 2 R laser lsls Inductive electric field caused by the rapid change in the B field that accelerates ions and decelerates electrons. The energy gained by this process is E i 8 e 2 n R 2

2. Rutherford Appleton Laboratory Sophisticated 3D simulations performed by Prof. S.Bulanov and co-workers has revealed that for linear polarisation case the ion energy is p x = 0.61m i c Conclusion: at intensities 3 10 21 Wcm -2, ~10 12 protons are accelerated with energies of several hundred MeV 3D computer simulations of ion acceleration process

3. Rutherford Appleton Laboratory PIC simulation S.V.Bulanov et al JETP Lett 71, 407 (2000) a 0 2 I 2 PIC simulation T.Zh.Esirkepov et al JETP Lett 70, 82 (1999) a 0 I 2 Prospects for GeV proton acceleration using PW lasers

4. Rutherford Appleton Laboratory The energy gain over the interaction length in a plasma wakefield is When I 2 >> 10 18 Wcm -2 m 2, the radiation pressure is so large nearly all electrons are expelled from the photon wave-envelope, generating a snow- plough in which the electron momentum gain is provided the laser pulse fully interacts with the plasma (i.e. not diffracted) Accelerating gradients 200 TeV/cm at 10 26 Wcm 2 Wakefield acceleration

5. Nd:glass 20 fs seed laser stretched to 400 ps 1000ps 527 nm 3400 J SHG LBO 1.5 cm KDP 3.8 cm 4452 J 41 % LBO 1.4 cm KDP 1.1 cm KDP 0.8 cm 3400 J 44 % 46 % 0.2 mJ4 J Output signal and pump intensity profiles 100 PW Intensity profile after compression (0.3 J/cm 2 ) Rutherford Appleton Laboratory Ideas for EW lasers (Dr I.N.Ross)

6. Rutherford Appleton Laboratory Future Upgrade Options Given Some Technology Development SHG PumpDielectric Gratings 1μm Output50cm KDP F/1 Focusing 0.3 EW10 25 W/cm 2 THG Pump Dielectric Gratings 0.5μm Output 50cm KDP F/1 Focusing 0.6 EW 10 26 W/cm 2 Multi OPCPA >1 EW >10 26 W/cm 2

7. Rutherford Appleton Laboratory The VULCAN PW upgrade is nearly completion - first experiments to university users scheduled November 2002 - laser wakefield accelerator studies >100 MeV protons and >1GeV heavy ions expected Future upgrades to multi-PW levels are being actively pursued The CLF is investigating new designs for average and peak power lasers required for accelerator and fusion applications Summary