Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, OX11 0QX, UK. Telephone: (44) Fax: (44) International Conference on Frontiers in Diagnostic Technologies (CFDT1) Frascati, Italy th November 2009 Particle energies in a laser/fusion environment David Neely 1,2, J Collier 1, M Dunne 1, P McKenna 2 and J. M Perlado 3 1 Central Laser Facility, STFC, Oxfordshire, UK 2 University of Strathclyde, Glasgow, Scotland 3 Instituto de Fusión Nuclear (DENIM)/ETSII/ Universidad Politécnica Madrid,

Fast Ignition and HiPER Electron transport Ion Fast Ignition ? Introduction Ultra-high Intensity- “relativistic”

Fast Ignition approach to laser fusion “Fast Ignition” approach of HiPER provides the bridge between laser fusion demonstration (NIF, LMJ) and the route to power production Significantly smaller (cheaper) capital plant investment System model predicts cheaper electricity Allows academia & industry to take lead role Unique capabilities for a broad science programme Ignite the fuel directly using e-beam, ion-beam or KE from multi-PW laser interaction ILE Osaka target picture

Recent sensitivity modelling (Atzeni, Honrubia et al) with kJ e g/cm2 range

Inertial Fusion Energy distribution Data M Perlado X- Rays (Energy)Ions (Energy) Spectra (J. Perkins) Central Ignition -Dir. Drive -Indirect Drive 1,5% 18% 24% 7% 154MJ 438MJ Shock Ignition -Dir. Drive1,5%24%48MJ HEAT DEPOSITION IN WALL Energy is deposited in the first mm. Neutrons just deposit around 3% of energy Fluka Thermo-mechanical response Atomic particles Implantation Sputtering Debris/Shrapnel ANSYS Debris/Shrapnel - Only data available from M. Tobin Effect of Ions on wall – Experiments Pulsed Ion Damage to IFE First- Wall Materials - Lessons for MFE Plasma Facing Materials – Effect of Ions on wall – Model We estimated the ablation process using ACORE (Ablation Code for Reactor)- Norimatsu We estimate the cluster formation/condensation ACONPL - Norimatsu SRIM

Environment and Fusion technology John Perkins’ calculations ARIES web page Heat deposition with FLAIR -Time dependence Heat Transport with ANSYS Sputtering with SRIM HiPER Work Package 8 M Perlado

Neutron first wall damage Damage Rate in typical CTR materials MaterialDPA per MW/m 2 per Year 316 SS Mo8 SiC30 Al17 Characterized by Displacement per Atom (DPA) ~ DPA / (MJ/m 2 ) Typical DPA For neutron flux energy deposition to ICF Chamber wall: 1.91 x 10 3 MJ/m 2 Accumulative DPA < Magnetic and Laser Fusion devices face similar material challenges

2. PW beamlines: >70kJ in 10ps 2  (how?) 1.Implosion energy: 300 kJ in 5ns 10 m chamber 3  ? Baseline specifications 3. Parallel development of IFE building blocks Target manufacture DPSSL laser Reactor designs

Fast Ignition and HiPER Electron transport in Laser Fusion Ion Fast Ignition ? Introduction Ultra-high Intensity- “relativistic”

Fast Ignition requirements Freeman et al., Fusion Science and Technology, 49, 297 (2006) Requirements for energy delivered to pellet: Energy ~15 kJ Spot size ~35 μm Pulse duration <20 ps (hydrodynamic disassembly time) Cone enables laser to be delivered within 200  m of core without interacting with coronal plasma

e-delivery (Honrubia & Atzeni studies) … Indicates: 300 kJ implosion laser 70 – 100 kJ ignition laser Assuming cone to blob ~ 100  m divergence ~ 30º half-angle f ~ 0.4  m code accuracy

Previous experimental work: I = 5 x W/cm 2 Lancaster et al., PRL 98, (2007) Green et al., PRL 100, (2008) Target thicknesses ~100 µm Diagnostics: K  emission XUV emission Shadowgraphy

Ion emission to diagnose electrons Ion detector: Film currently used Scintillator developments required Ion emission: proportional to high energy n e proportional to t e

Ion emission to diagnose electrons Comparison to other techniques: CTR: High energy electrons; thin targets Kα imaging: <100 keV electrons; Optical probe: Limited accessible plasma density Spatial and energy resolved measurements of the Multi-MeV ions provide a diagnostic of the electron sheath at the target rear surface, and hence the electron transport through the target.

 Evidence of collimation of fast electrons in solid targets by self- generated B-field observed using proton emission Collimation of fast electron transport Yuan…McKenna., submitted (2009)

Expected proton energies from simulation Mora 2003 plasma expansion model is used to calculate proton energy using electron density output from LEDA Excellent agreement between simulations (with magnetic field) and experiment

Simulations with 2-D hybrid LEDA code Electron refluxing within thin targets perturbs B-field structure Ne no B field Ne with B field Simulations by Alex Robinson (RAL)

Fast Ignition and HiPER Electron transport Ion Fast Ignition ? Introduction Ultra-high Intensity- “relativistic”

Proton Fast Ignition M. Roth et al., Phys. Rev. Lett. 86, 436 (2001) M. Temporal, et al., Phys. Plasmas 9, 3098 (2002). Requirements: E protons (3 to10 MeV) ~15 kJ E Laser ~100 kJ (for η Laser →proton~15%) I Laser 2 ~10 20 W.cm -2.  m 2 t protons <20 ps Φ protons ~35 μm -focusing How does conversion efficiency scale with laser parameters? Focusing – need to deliver the energy in a radius ~15 μm How to prevent preheating of source foil? Knowledge of ion stopping in plasmas Proton foil Proton foil without re-entrant cone ? Laser

Lateral effects – defocus drive beam Lateral effects dominate when  >  l v hot  ef =  l +  /v hot Beam angular profile modified Refluxing increases when  >> (L + d )

Optimising flux with foil thickness Thinner foils result in Increased proton flux Vulcan PW 1 ps 1054 nm illumination Intensity 4x10 19 Wcm -2 As the focal spot size is 60 microns Lateral spreading is not expected to have a significant effect on electron surface density Flux loss must be associated with transport losses through foil

Comparison with previous studies Defocus reduces intensity - proton energy Defocus enables thin targets – higher efficiency Robson et al, Nature Physics 3, 58 (2007)

Grismayer and Mora (PoP ) showed some spectral modification due to low intensity pre-pulse. What about a high intensity ( Wcm -2 ) pre-pulse? Studied this with Vlasov and PIC codes in 1D. Low Intensity pre-pulse xx x x nini nini vivi vivi High Intensity pre-pulse Protons have non-negligible velocity due to first pulse in high intensity case Spectral control using multi pulses

Two-stage Mechanism As the hotter pulse arrives → surge in protons across carbon Front → “wave breaking” + peak in proton density 186μm = rear surf.

Integrated dose dual-pulse Pulse ratio mid10 19 Wcm -2 reduces low energy ~1.2MeV increases high energies 1.2MeV3.2MeV4.5MeV5.5MeV RCF Beam images Fast Ignition relevant proton energies

Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, OX11 0QX, UK. Telephone: (44) Fax: (44) Co-workers J Collier, P Foster, R Evans, S Hawkes, A Robinson, M Streeter, C Spindloe, M Tolley Central Laser Facility, STFC P McKenna, D C Carroll University of Strathclyde F. Nurnberg, M. Roth, M Guentner, K Harres GSI, University of Darmstadt M Zepf, B Dromey, K Markey, S Karr, Queens University of Belfast C-G Wahlström Lund Laser Centre, Sweden Y T Li, M H Xu Beijing National Laboratory

Conclusion Ion emission as an electron transport diagnostic Provides spatial information on hot electron transport Refluxing effects on many present experiments a limitation Ion spectral control - dual-pulse and planar Simple optical control mechanisms- high efficiency First results indicate mechanism effective Ion source for probing Detector developments Fast Scintillators and transducers required High resolution neutron and  -ray imaging required EMP, neutron,  -ray and radiation hardened developments needed

Central Laser Facility Rutherford Appleton Laboratory (1200 staff) Science and Technology Facilities Council Oxfordshire, U.K. Astra Ti:Sapphire 40 fs, 0.5 J Vulcan Nd:Glass 700 fs, 400 J

Dual-pulse timing Intensity on target mid Wcm -2 Lower pre-pulse must come earlier

Proton scaling with defocus Defocus results in Reduced intensity Lower maximum proton energy Vulcan PW 1 ps 1054 nm illumination 2 micron think Al targets Lower energy protons suited for Fast Ignition Secondary heating