Electron/proton generation from solid targets and applications Farhat Beg University of California, San Diego This work was performed under the auspices of the U.S. DOE under contracts No.DE-FG02-05ER54834, DE-FC0204ER54789 and DE-AC52-07NA27344. We greatly acknowledge support of Institute for Laser Science Applications, LLNL. Committee on Atomic, Molecular and Optical Sciences Meeting The National Academy of Sciences Washington DC, April 5, 2011 1 Summary ü Short pulse high intensity laser solid interactions create matter under extreme conditions and generate a variety of energetic particles. ü There are a number of applications from fusion to low energy nuclear reactions. 10 ns ü Fast Ignition Inertial Confinement Fusion is one application that promises high gain fusion. ü Experiments have been encouraging but point towards complex issues than previously anticipated. ü Recent, short pulse high intensity laser matter experiments show that low coupling could be due to: - prepulse - electron source divergence. ü Experiments on fast ignition show proton focusing spot is adequate for FI. However, conversion efficiency has to be increased. 2 Outline § Short Pulse High Intensity Laser Solid Interaction - New Frontiers § Extreme conditions with a short pulse laser § Applications § Fast Ignition - Progress - Current status § Summary Progress in laser technology 10 9 2000 Relativistic ions 8 Nonlinearity of 10 Vacuum ) Multi-GeV elecs. V 7 1990 Fast Ignition e 10 ( e +e- Production y 6 Weapons Physics g 10 Nuclear reactions r e 5 Relativistic Plasmas n m 10 Hard X-ray Generation µ E 1 r 4 1980 = e 10 Tunnel Ionization v λ High Temperature i r 3 u Plasma Formation o 10 f Bright X-ray Generation Q Future 2 1970 n 10 o r t 1 Nonperturbative Atomic Physics c 10 High Order Nonlinear Optics e l 0 E 10 Current Technology -1 Perturbative 10 Atomic Physics Nonlinear Optics -2 10 12 14 16 18 20 22 24 10 10 10 10 10 10 10 Laser Intensity (W/cm2) • Since the invention of CPA technique, progress in this field has been astonishing • Focused intensities have increased six orders of magnitude up to 1021 Wcm-2. • Now, you can do laser physics, atomic physics, plasma physics, astrophysics and elementary particle physics in one laboratory. 4 Short pulse lasers produce extreme conditions Multi-TW laser focused to <10 µm ↓ Focused light intensity of > 1018 - 1020 W/cm2 High Field Science High Energy Density Science High electric fields Concentrated energy E ~ 1010 - 1011 V/cm Energy density in a femtosecond pulse is 109 J/cm3 Field strength is 10 to 100 times that of the electric field felt by an Corresponds to ~ 10 keV per atom at electron in a hydrogen atom solid density High electron quiver energy High brightness and pressure Uosc = 60 keV - 3 MeV Radiance exceeds that of a 10 keV black body Electron motion can become relativistic 2 Light pressure P = I/c = 0.3 - 30 Gbar (Uosc > me c = 512 keV) 5 Short pulse high intensity laser solid interaction is complex L Gremillet G Bonnaud F Amiranoff POP 9,941,(2002) !r ! 0.5g / cm3,T !12keV • Strongly depends on laserh spatial intensityh distribution, pulse shape and preplasma profile • Laser solid interaction generates! energetic particles • Beam current is in excess of! 1 GA • Azimuthal B field pinches input electrons dB/dt =curl(E) 6 Energetic particles have important applications • Fast Ignition Inertial Confinement Fusion • GeV plasma based particle accelerators • Low Energy Nuclear Physics • Proton source for medical applications • Neutron sources 7 ICF uses implosion of spherical shell to compress solid DT up to 4000x Laser ablation Thermal soft x-ray ablation Hohlraum Direct drive Indirect drive •! Drive pressure is rocket reaction from ablation •! Capsule diameter 2 mm •! Drive duration 10-8 s •! Drive energy 1 MJ " Classical ICF is prone to hydrodynamic instabilities •! Thin shells break up in flight due to hydrodynamic instabilities m µ 100 Density Temp Main Issue: Stringent symmetry Fuel 1000 gcm-3 ρr=3.0 gcm-2 requirement -3 -2 " Spark 100 gcm ρr=0.3 gcm Thermonuclear burn wave is launched by ignition spark What is Fast Ignition & Why fast Ignition? Fast Ignition ( FI) * M. Tabak et. al., Fusion Science and Technology v 49 2006 Isochoric - fast heating Heat in -11 m 2x10 s µ Indirect Drive 100 200 200 Fast Ignition 3ω to 2ω* Density Temp 10 Target Gain Target Indirect Drive Hot Spot ignition + Fuel 300 gcm-3 3ω to 2ω 1 -3 0.1 1 10 Spark 300 gcm Laser Energy (MJ) •! Higher gain and lower ignition threshold •! Less stringent symmetry requirement " •! Low energy driver suitable for IFE power plant Fast Ignition is an advanced ICF concept •!Laser hole boring and Hole boring Ignition heating by laser generated electrons was the first FI Hole boring 10 kJ, 10 ps concept 100 kJ, 20 ps for laser to penetrate Laser •!1MeV electron range = close Lightto pressure ignition hot spot φ densebores fuel hole in coronal 1 MeV electrons •!Absorption of intense laser plasma heat DT fuel to light produces forward 10 keV 300 g/cc directed electrons •!e-beam temperature Pre-compressed scales as kT~ (I 2)0.5 -3 λ fuel 300 gcm •!kT≈1 MeV for λ=1µm laser Fast ignition at 5x1019 Wcm-2 M Tabak, S Wilks et al." Phys. Plasmas1,1626, (1994) Several options are available for igniting the fuel ElectronsLight pressure (laserbores hole in coronal plasma hole-boring)! Electrons (cone-guided)! Ignition 300 g/cc 10 kJ, ps Fast ignition 1 MeV electrons heat DT fuel to 10 keV Hole boring Hole boring Laser 1 MeV electrons heat DT fuel to 10 keV Fast ignition 10 kJ, ps 300 g/cc Ignition Light pressure bores hole in coronal plasma Protons! Ions! DT fuel C " Cone guided electron FI S Hatchett -LASNEX -2 <ρR>DT=2.2 g cm Laser 100µm Au cone Radiation - hydro simulations are very well developed for ICF and allow design optimization with good reliability " Atzeni examined the requirements for FI with an arbitrary particle beam )1.85 # " & Eign = 140% 3 ( kJ 3 $ 100g /cm ' •! Ignition requirement: !rh ! 0.5g / cm ,Th !12keV •! Parallel beam of particles was injected into uniform density sphere •! 18-20 kJ beam energy is sufficient for ignition for the beam parameter - pulse length < 20 ps ! S. Atzeni, Phys. Plas. 8, 3316 - beam intensity ~ 6-8x1019 Wcm-2 (radius ~ 20 µm) (1999)! Results from first integrated fast ignition experiment in Japan were encouraging Gekko XII Laser Facility Au cone + CD shell Neutron yield 30%! coupling" 15%! coupling! •! 2.5 kJ, 1.2 ns flat top pulse, 2 w •! 7 µm CD shell, 350 µm dia •! 1000x increase in neutron compression Imploded core yield •! 350 J, 0.5 ps ignitor pulse •! Temp. increase from 400 eV to 800 eV •! 50 µm blob was formed 50 µm from tip of the cone with a density of 50 g/cc •! Ignitor beam gave ≈ 20% energy coupling to imploded CD R Kodama et al., Nature Can we expect the same coupling at the full scale? 412(2001)798 . Recent experiments on OMEGA have shown low coupling W. Theobald, Phys. Plas. (in press) •! Short pulse laser energy is in excess of 1 kJ and pulse length is 10 ps •! 2x increase in neutron yield (1.5x107) with short pulse •! About 7% coupling significantly less than the Osaka experiment There are four main issues for cone guided electron FI M. Tabak Phys of Plasmas 1 M. Key et al. Phys of Plasmas 14 1626-1634 (1994) 055502 (2007) Short pulse laser aimed and timed to implosion Efficient deposition of electron energy in region of ρR~0.6 g cm-2 (α range), heating it to 5-10 keV! Efficient conversion: ! Elaser➔ “beam” of ~MeV electrons aimed at Efficient transport of hot assembled fuel electron energy to fuel! • Fast Ignition physics is extremely challenging • It involves relativistic laser plasma interaction with High Energy Density Plasmas 17 Laser conversion to electrons - electron source 18 Surrogate targets were used to examine the underlying physics • 1D wire geometry for current diagnosis and analysis – Experiments: Easy view of electrons (Cu-Kα fluorescence) – Modeling: 2D effects can be neglected 19 Laser prepulse can significantly modify the laser solid interaction Energy contrast levels for a FI-scale laser will be ~10-5 (i.e., 100 kJ laser = ~100 mJ – 1 J prepulse energy) § Current typical contrast levels for short pulse lasers is ~ 10-5 – 10-7 Prepulse trace from the Titan laser § These intrinsic prepulse levels are lower than what is expected at full scale, but many experiments have created artificial prepulses at relevant levels § The prepulse can form a substantial preformed plasma in front of the solid target which severely affects the interaction of the main laser with the target Increasing prepulse level into the stand-alone cone gives a large region of electron heating 150J , 0.7ps, 2"1020Wcm#2 • Well defined peak 50! µ m • Emission distributed from the tip broadly 200 µm from cone tip • Emission decreases sharply • Extends further 500 µm from over 200 µm cone tip § Total integrated Kα yield is near-identical in both cases § Peak hot electron density is 2x higher in intrinsic pp case Observation is consistent with preplasma filling the cone and hot 21 electron source away from tip of the cone Experimental data agrees well with integrated rad-hydro/PIC modeling PSC! 100 mJ Data! Time integrated K# emission! 7.5 mJ • PSC simulations show the pattern of Ka emission similar to the experiments • Simulations show well defined peak at 30-50 µm from tip for intrinsic prepulse and broader distribution centered at 150 µm for 100 mJ prepulse A.