U N C L A S S I F I E D LA-UR Short-pulse ion acceleration exceeding scaling laws from flat foils and “Pizza-top Cone” targets at the Trident laser facility Kirk Flippo P-24, Los Alamos National Laboratory November 3 rd, 2006 FIW, Cambridge, MA
LA-UR Colleagues and Collaborators B. M. Hegelich, J. A. Cobble, J. C. Fernández, D. C. Gautier, R. Johnson, J. Kline, S. Letzring, T. Shimada P-24, LANL Jörg Schreiber Department für Physik, Ludwig-Maximilians-Universität München and Max-Planck-Institut für Quantenoptik, München, GERMANY Marius Schollmeier Darmstadt University of Technology, Institute of Nuclear Physics GSI, Darmstadt, GERMANY B. Albright, M. J. Schmitt, L. Yin X-1-PTA, LANL G. Korgan, S. Malekos NanoJems R. Schulze MST-6, LANL S. Gaillard, J. Rassuchine, M. Bakeman, N. Le Galloudec, T.E. Cowan, Nevada Terawatt Facility, University of Nevada, Reno Ron Perea MST-7
LA-UR Outline Intro and overview of acceleration mechanisms TNSA and the Maxwellian spectra Flat Cu target results Pizza-top cone target results Recent Scaling Laws and comparison with current best scaling laws
LA-UR Proton Acceleration Experiment Setup: Oblique View from 67-degrees to target parallel 67-degrees Short Pulse Protons RCF Target Rear-side Normal Target Top View Target RCF Ion Beam Short Pulse To Thomson Parabolas Holes for TP Access RCF Plane Rear-side Plane
LA-UR Pre-pulse Pre-plasma Pre-pulse Brief Overview of Laser-Ion Acceleration Target Normal Sheath Accelerations (TNSA) E p+p+ e-e- rear side p + e-e- target sp laser front side p + Reflected sp laser Pre-plasma target refluxing e - Reflected sp laser target e-e- e-e Preplasma Formation Hot e - Generation… e-e- … and hot e - Recirculation Ion Acceleration p+p+ p+p+ p+p+ Cold return current e - p+p+ CH & H 2 O E E p+p+
LA-UR A Closer Look: Heavier Ions are Accelerated Too E p+p+ e-e- p+p+ p+p+ p+p+ target N x+ C x+ If the target forms Oxides, Nitrides, and/or Carbides these constituents will be accelerated along with the protons O x+ B. M. Hegelich et al. PRL 89, (2002), B. M. Hegelich et al. POP 12, (2005)
LA-UR Vanadium Ablation Experiment: Actual Laser Heating Shot (no ablation, no Photoshop ® ) ~1 mm 1 cm
LA-UR Laser accelerated ions typically exhibit a Maxwellian spectrum usually with a cuttoff LULI, solid target, Hegelich et al., PRL 89 (2002) RAL, gas target Wei et al., PRL 93 (2004) LLNL, PW, solid target Snavely et al., PRL 85 (2000) LLNL, cluster target Ditmire et al., PRA 57 (1998) MPQ, Ti:S solid target, Schneider, Hegelich et al., APB 79 (2004) Jena, water droplet target, Karsch, Hegelich et al., PRL 91 (2003) CUOS, solid target Maksimchuk et al. PRL (2000)
LA-UR Protons from Flat Foils and Pizza Cone Targets Diagnosed with RCF stacks Proton Beam
LA-UR Flat Copper Foil Target RCF up to 23.2 MeV I=1.1x10 19 W/cm 2,19.6 J, 670fs (expected ~13 MeV) 1.2 MeV Bragg Peak = 22.5 MeV 23.2 MeV HD RCF MD RCF Beam decreases in size with higher proton energies
LA-UR Flat Copper Foil Spectrum I=1.1x10 19 W/cm 2,19.6 J.14 J in protons, ~.75% conversion efficiency
LA-UR Typical Pizza-Top Cone Target Dimensions and material information of a typical target. The target dimensions vary. The Critical Dimension is the inside converging apex and ranges from 4um to 20 um in diameter. The inner target surface may have an adhesive layer less than 200A. The area in between the gold, at the flat foil, may consist of SiO2. Typical target angle at a cross section of ~50um. However, target angle becomes sharper as you approach the apex
LA-UR Image from the rear side of the RCF stack with LANEX imaging plate showing beam > 35 MeV Target holder Cone target Proton Beam RCF stack with Lanex on back Laser
LA-UR Pizza-Top Cone Target Beam > 30 MeV I= 1 W/cm 2, 19 J, 605 fs High energy beam diameter does not change as drastically with energy as in the flat foil case 1.2 MeV Bragg Peak = 5 MeV 26.8 MeV HD RCF CR-39 HD RCF MeV HS RCF Lanex 30+ MeV
LA-UR Cut-off extrapolated from flat foils Pizza-Top Cone Target Spectrum > 30 MeV I= 1 W/cm 2, 19 J, 605 fs Beam seen exiting RCF stack on LANEX was greater than 30 MeV Scanner RCF imaging spectroscopy gives ~.5 J in protons measured, ~2.5% conversion eff. !
LA-UR Proton energy from cones is dependent on the top to neck ratio
LA-UR Thinner targets improve the maximum energy of protons and the energy conversion efficiency of cones. From J. Fuchs et al., Nature Physics 1, 199 (2005) 15 um Cone target um Cu target um Cone target 15 um Cu target 5 um Cu target 35 um Cu target Trident: =600 fs, I=1 W/cm 2 If analysis is done via the method in the paper
LA-UR The proton maximum energy and conversion efficiency correspond to over 3 times the measured intensities. From J. Fuchs et al., Nature Physics 1, 199 (2005) Cone target Cu target 10 Cu target Cone target ( laser = 320 fs for protons > 4 MeV) Trident: =600 fs, I=1 W/cm 2
LA-UR For the measured pulse duration both the proton maximum and the energy conversion efficiency is enhanced. From J. Fuchs et al., Nature Physics 1, 199 (2005) Cu target Cone target Cu target Cone target Trident: =600 fs, I=1 W/cm 2 >3.5 times above model in energy and almost 5 times in Intensity
LA-UR Comparison between fluid-model predictions and previously published data of similar conditions 20-μm-thick targets and a 10 μm FWHM laser spot size. Number of protons in a 1 MeV bin around 10 MeV From J. Fuchs et al., Nature Physics 1, 199 (2005) Cu target Cone target Cu target Cone target
LA-UR Conclusions Protons from flat foils have been recorded up to 26.8 MeV, which is several times the energy for the thickness, > 3.5 times above scaling for a given pulse duration, and scaling as an experiment with 3 times the intensity on target. Protons from cone targets have been observed above 30 MeV and extrapolated to >35 MeV, and much higher efficiency (~2x) and ~5 times the number than a flat foil! Above scaling law energies and efficiencies are due to improved laser condition monitoring, especially pre-pulse levels (contrast). Recent RCF calibration using Bragg-peak energies indicates the higher dE/dx for a given particle can lead to a greater OD. A different calibration would have a significant impact on the total conversion efficiency numbers due to a difference in total numbers and Maxwellian temperatures.
LA-UR Backup Slides
LA-UR Proton Energy Dependence on Pulse Duration for Constant Intensities
LA-UR Flat Foil and Cone Spectra Show Different Temperature Behaviors