Laser Produced Positron Research at Lawrence Livermore National Laboratory

Transcription

1 Laser Produced Positron Research at Lawrence Livermore National Laboratory Present to the 2nd Conference on Extremely HighIntensity Laser Physics, September 58, 217, Lisbon Portugal Hui Chen May 24, 217 This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DEAC527NA Lawrence Livermore National Security, LLC

2 Acknowledgement: Team member and Collaborations N. Brejnholt, MA. Descalle, A. Hazi, R. Heeter, A. Kemp, G. E. Kemp, A. Link, B. Pollock, E. Marley, S. R. Nagel, J. Park, M. Schneider, R. Shepherd, M. Sherlock, R. Tommasini, S. C. Wilks, G. J. Williams Lawrence Livermore National Lab F. Fiuza, J. Sheppard SLAC D. Barnak, PY. Chang, G. Fiksel, V. Glebov, D. D. Meyerhofer, J. F. Myatt, C. Stoeckel LLE and Uni. of Rochester G. Grigori Oxford University E. d Humieres, University of Bordeaux R. Fedosejevs, S. Kerr University of Alberta F. Beg, B. Edghill, C. Krauland, C. Mcguffey, J. Peebles, MS Wei UCSD C. Kuranz, M. Manuel, L. Willingale University of Michigan A. Spitkovsky Princeton University Y. Arikawa, H. Azechi, S. Fujioka,, H. Hosoda, S. Kojima, N. Miyanaga, T. Morita, T. Moritaka, T. Nagai, M. Nakai, T. Namimoto, H. Nishimura, T. Ozaki, Y. Sentoku, Y. Sakawa, H. Takabe, Z. Zhang ILE, Osaka University P. Audebert LULI, École Polytechnique M. Hill, D. Hoarty, L. Hobbs, S. James AWE Brandon Edghill *Complete list of names are included in the publications cited Many thanks to the JLF, Omega EP, LFEX and Orion laser facilities for their support.we acknowledge the LLNL LDRD funding (ERD44 and 12ERD62, 17ERD) for this project. Jackson Williams Jaebum Park Shaun Kerr 2

3 At LLNL, we have been investigating laser produced positrons through experiments and modeling 1. Positron jet characterization: Absolute positron number and energies Emittance Yield dependence to laser & target 2. Relativistic laserplasma interaction physics: Sheath field acceleration Effect of electromagnetic field Simulation tools: Particleincell: PICLS Particle code: GEANT4; EGS4 Hydrodynamic code: HYDRA OSIRIS; LSP 3. Applications: Positron radiography APS DPP 217 Relativistic electronpositron pair plasma APS DPP 217 3

4 Majority of experiments were performed on large laser facilities with 1 ps, J to 15 J energy per shot Titan laser (LLNL) 1 ps, 35 J 5 shots/day LFEX (ILE) 24 beams 12 ps, ~.51 kj/beam Omega EP (LLE) 2 beams 1 ps up to 1.3 kj/beam Up to 16 shots/day ORION (AWE) 2 beams.51 ps, up to 5 J/beam 4

5 In each experiments, e, e+, p+ and g from gold targets were measured by various diagnostics Experimental setup at Titan Electron positron proton spectrometer EPPS raw images Escaping electrons Sheath formation Preformed plasma Shortpulse laser Protons Positrons Positron/ion Acceleration Au Target 18 o Electrons Particle energy EPPS1 EPPS2 Radiation spectrometers EPPS3 Highenergy gamma diagnostics EPPS: Chen, et al., RSI 28 Step Wedge image Gammacrystal spectrometer GCS: Seely et al. HEDP 211 Chen, et al., RSI 212 5

6 The laser intensities used experimentally were from 18 to 2 W/cm 2 Direct pair production (laser on gold target) Indirect pair production (wakefield electrons on gold target) f/8 OAP Gas Cell Parameters 3 mm He gas cell Pressure = 55 Torr n e = 9x 18 cm 3 Gas Cell Converter Target e + /e Spec Laser Parameters 8 nm, 6fs Up to J Callisto Target Chamber B. B. Pollock et al. Phys. Rev. Lett., 7:451 (211). F. Albert et al. Phys. Rev. Lett., 111:2354 (213). Williams et al. Physics of Plasmas (215) Prior experiment laser produced positrons: T. Cowan et al., Laser Particle Beams (1999) Prior references on making positrons using wakefield accelerated electrons: Gahn et al. (22) and Sarri et al., (213) 6

7 We experimented with indirect pair production using wakefield generated electron beams Direct pair production (laser on gold target) Indirect pair production (wakefield electrons on gold target) f/8 OAP Gas Cell Parameters 3 mm He gas cell Pressure = 55 Torr n e = 9x 18 cm 3 Gas Cell Converter Target e + /e Spec Laser Parameters 8 nm, 6fs Up to J Callisto Target Chamber B. B. Pollock et al. Phys. Rev. Lett., 7:451 (211). F. Albert et al. Phys. Rev. Lett., 111:2354 (213). Williams et al. Physics of Plasmas (215) Prior experiment laser produced positrons: T. Cowan et al., Laser Particle Beams (1999) Prior references on making positrons using wakefield accelerated electrons: Gahn et al. (22) and Sarri et al., (213) 7

8 Electrons were accelerated and driven into a converter target to produce positrons 6 fs 6 J He gas cell 4 cm 4 cm e e 1.5 mm Tantalum e + Charged particle spectrometer Williams, et al. Phys. Plasmas (215) 8

9 Positron signal was not observed for either a high energy or high flux electron source Initial Electron Distributions Electrons/MeV 8 x N e = 56 pc E e = 2.8 mj N e = 5 pc E L = 6.5 J E L = J Sarri et al N e = 19 pc E e = 2.3 mj Geant4 modeling may provide explanation of null result Energy (MeV) Williams, et al. Phys. Plasmas (215) Positiveside image plate for electron source in red curve Energy (MeV) 9

10 Beam divergence is larger than expected, and is dominated by Coulomb scattering EnergyResolved Divergence of Emitted Positrons 4 < E e+ (MeV) < 6 18 < E e+ (MeV) < 2 Mean Divergence Sim w/o Coulomb Scattering Williams, et al. Phys. Plasmas (215) Initial electron divergence from LWFA sources is a negligible contribution

11 Simulation also shows that the positron beam is longer than the electron pulse due to straggling inside the target Time history of positron emission Pulse duration of positrons can be significantly longer than electron source τ e > fs τ e+ 135 fs Williams, et al. Phys. Plasmas (215) Positron Flux at Target Rear (a.u.) < E (MeV) < 6 18 < E (MeV) < Positron Breakout Time (fs) 11

12 Direct pair production was investigated extensively for laser intensities from 18 to 2 W/cm 2 Direct pair production (laser on gold target) Indirect pair production (wakefield electrons on gold target) f/8 OAP Gas Cell Parameters 3 mm He gas cell Pressure = 55 Torr n e = 9x 18 cm 3 Gas Cell Converter Target e + /e Spec Laser Parameters 8 nm, 6fs Up to J Callisto Target Chamber B. B. Pollock et al. Phys. Rev. Lett., 7:451 (211). F. Albert et al. Phys. Rev. Lett., 111:2354 (213). Williams et al. Physics of Plasmas (215) Prior experiment laser produced positrons: T. Cowan et al., Laser Particle Beams (1999) Prior references on making positrons using wakefield accelerated electrons: Gahn et al. (22) and Sarri et al., (213) 12

13 BetheHeitler process was verified as the dominant pair generation mechanisms through detailed measurements Target dependence of laserproduced positrons were measured, aided by magnetic collimation of the pair jets Positrons/SR ( ) Cu Mo Sn Ta W Au.5 Simulation Fit Z 2 ρ d A 1 (cm 2 mol) Titan Laser ~3 J, ps Scaling power, n Target ~I ~B Positron and electron jets EPP S " Y BH Z 2 ρ % $ ' # A & Electron Temperature (MeV) BetheHeitler has an effective scaling ~Z 2 n Raw Positron Data Increasing Energy Williams et al. Phys. Plasmas (216) B = 2.2 T B = 6.5 T 13

14 Quasimonoenergetic, high flux, relativistic positrons are produced in ps time scale Titan and Omega EP positron data* Sim. e+ width for ps exp. (LSP )** Positron Number/MeV/Sr number/mev (x 9 ) (x 9 ) A 2 mm target; 312J, ps B 6.4 mm target; 13J, 1ps C 2 mm target; 35 J, ps D 2 mm target; 28 J, ps E 2 mm target; 323 J, ps F 2 mm target; 812 J, ps A B C D E F 5 Titan (3 J) 15 Energy (MeV) Positron energy (MeV) 2 Omega EP (8J) 25 Positron number x 12 35x 12 Positron number FWHM ~ 8ps Time (ps) Time (ps) * More details see Chen et al., PRL 29, PRL2, HEDP 211 **Chen et al, POP 215 Pair number: 12 Peak energy: 4 3 MeV Flux duration: ~ ps E conversion>2x 4 Pair rate: ~ 22 /s Peak flux: > 25 cm 2 s 1 14

15 Positrons are accelerated to s of MeV, which far exceed their birth energy Positron peak energy vs laser energy 35x 3 Sheath acceleration of protons Positron Peak energy (MeV) y=9+x Measurements Birth peak energy (from GEANT4*) Laser energy (J) Sheath acceleratio n Shortpulse Laser Au Target Sheath Field Snavely, et al., PRL 2 Wilks, et al., PoP 21. p+ p+ p+ Proton Acceleration * Chen, et al, Phys. Plasmas 215 * Particle code GEANT4 was developed by CEAN (www. geant4.cern.ch) This feature is unique and it is the result of intense laser target interaction 15

16 Detailed positron spectrum reveals physics in sheath acceleration E&P pectra at 3 laser energies 9 ps laser; Au target (1mm x 2mm dia.) Black 247 J Green 8 J Red 15J Number/keV/sr 8 7 e 6 e+ * Chen, et al, Phys. Plasmas Energy (kev) 4 5x 3 16

17 Detailed positron spectrum reveals physics in sheath acceleration E&P pectra at 3 laser energies Time evolution of the spectrum (LSP) 9 ps laser; Au target (1mm x 2mm dia.) Black 247 J Green 8 J Red 15J Number/keV/sr 8 7 e 6 e+ * Chen, et al, Phys. Plasmas Energy (kev) 4 5x 3 Shaun Kerr, APS DPP

18 Laser produced relativistic pairs form jets at the back of the target e+ and e angular distributions Jets simulated by LSP* Normalized Number of Positrons 1..5 Data Fit EGS e+ Target normal Laser direction Ral. number of electrons e 4 4 Angle (degree) EPPS RCF Fit EGS Angle (Degrees) Chen et al., PRL 2 *Tony Link Jet angular spread: 3 degrees. The jets are shaped by the E and B fields of the target. Its direction is controlled by the laser parameters and target. 18

19 The emittance of laserpositrons is comparable to, or smaller, than that obtained on large accelerators Measured positron emittance Simulated positron emittance using LSP Positron emittance (mm.mrad) Accelerator (SLAC) Positron energy (MeV) Exp. on Titan & OMEGA EP, in collaboration with SLAC Chen, Sheppard, Gronberg et al., POP 213 Our pairs can be called a jet; as they are not sufficiently collimated to be a beam. 19

20 We found that the pair yield scales as ~E 2 based on data from Titan, EP and Orion experiments Positron number ~ E 2 Norm. positrons ~ I laser 1.1 8x 9 6 Positron number/sr 4 2 Orion (1ps) Titan (1, ps) Omega EP (ps) Number of positrons per KJ laser energy Titan (1 ps) Titan ( ps) Orion (1ps) Omega EP (ps) Laser energy (J) Laser intensity (W/cm2) Chen, Fiuza, Sentoku et al. PRL, 215 Chen, Link, et al, PoP, 215 Myatt, et al. PRE 29 Positron number shows a ~E 2 dependence for both 1 ps and ps shots. 2

21 Relativistic, nonneutral electronpositron plasma jets have been produced Parameter Exp. Value* T //.5 4 MeV T.21 MeV n e+ ~ 1113 cm 3 n e ~ 1215 cm 3 t Jet 5 3 ps *Chen, et al. PRL 2; HEDP 211; POP 214 The most obvious needs are to (1) increase the density of the pair jets and (2) reduce the electron/positron density ratio. 21

22 We have demonstrated effective collimation of laserproduced relativistic electronpositron pair jets e & e+ spectra after collimation MIFEDS setup on OMEGA EP Coil Exp. setup Positron number/mev/sr Numbers/MeV/Sr Radius (mm) 8 6 Bfield lines Particle trajectory 2 4 Distance to beam source (mm) 6 Shot with Bfields by MIFEDS Electrons Electrons Positrons Positrons Positrons Ref. shot (no Bfields) Particle energy(mev) (MeV) Energy Chen, Fiksel, Barnak, et al., POP 214 The effective divergence of the beam reduced from 3 deg FWHM to 5 deg; The charge (e/e+) ratio in the beam reduced from ~ to 5. 22

23 The positron scaling indicates that ARC energy may provide very high positron yield Positron number/sr ARC energy results in high e+ yield Titan_number_1ps_635 Orion_number_1ps Titan_numb_ps EP_posNum 'fit_titan&ep_number_ps' 'fit_titan&orion_number_1ps' ARC To determine the actual yield, we need: (1) Laser intensity; (2) Pulse contrast; (3) Focal quality. Furthermore, ARC is unique relative to the Titan, Omega EP and Orion lasers: Titan parabola f/3 Omega EP f/2 Orion f/3 NIF ARC f/ Laser energy (J) The long focal length parabola is favored by wakefield acceleration experiments; its effect to laser plasma interaction needs to be determined. ARC results Hui Chen, APS DPP 217 We have been awarded NIF Discovery Science shot time using ARC these questions will be answered soon. 23

24 Date Published Primary Author Laser Energy/J Intensity/ Wcm $% 9/14/215 E. Liang Texas Petawatt ~ 3 %+ Pulse Duration/fs Target Diamet er /mm % Au: Disk/Rod 24.5/2 Pt: Disk/Rod 24.5/2 3 Thickness /mm Best e + /e ratio Best e + Number Best e + Density Dominant Production Method.15/4 15%/37% ~ BetheHeitler/Direct 3 cm $4 Process.16/46 33%/52% ± % /23/2 C. Gahn TableTop at ATLAS Pb 2 (slab) ~2 8 BetheHeitler/Indirect Process 3/15/217 Yonghong Yan XingGuang ᴵᴵᴵ laser facility 2 ~2 9 8 Ta ±.3 BetheHeitler/Direct 9 str $ Process 3/12/217 Yuchi Wu XingGuang ᴵᴵᴵ laser facility str $ 3/7/216 Tongjun Xu Petawatt at Shanghai Institute of Optics and Fine Mechanics 6/2/213 G. Sarri HERCULES at Center for Ultrafast Optical Science 4/23/215 G. Sarri ASTRAGEMINI at Rutherford Appleton Laboratory Cu and Pb 22 48% 3.5 > 3 BetheHeitler/Indirect % cm $4 Process.8 6 > 3 Cu, Sn, Ta and Pb 12/23/29 H. Chen Titan at the Jupiter Laser Facility 1225 ~1 %+ 7 Au, Ta, Sn, Cu, Al 7/1/2 H. Chen Titan at the Jupiter Laser Facility and OMEGA EP at the Laboratory for Laser Energetics 4/24/214 H. Chen OMEGA EP at the Laboratory for Laser Energetics 1/31/213 H. Chen Titan at the Jupiter Laser Facility and OMEGA EP at the Laboratory for Laser Energetics ? cm $4 BetheHeitler/ ± 4 Pb 54 49% of the cm $4 BetheHeitler/Indirect beam is e B Process s $ BetheHeitler/Direct Process 5 %+ Process Au ~ 4 BetheHeitler/Direct 83 ± 3 5 > Au = DE D F BetheHeitler/Direct Process Magnetic Collimation > 12/6/216 G. Williams Titan at the Jupiter Laser Facility Cu, Mo, Sn, Ta, W, Au Brandon Edghill, APS DPP Au 1 + % per bunch BetheHeitler/Direct Process BetheHeitler/Direct Process Target Dependence /21/215 G. Williams Calisto at the Jupiter Laser Facility Ta None Measured above background BetheHeitler/Indirect Process 24

25 At LLNL, we have been investigating laser produced positrons through experiments and modeling ü Pair jet characterization: Absolute positron number and energies Emittance Yield dependence to laser & target ü Relativistic laserplasma interaction physics: Sheath field acceleration Effect of electromagnetic field Simulation tools: Ø Particleincell: PICLS ü Particle code: GEANT4; EGS4 Ø Hydrodynamic code: HYDRA ü OSIRIS; LSP Ø Applications: Positron radiography APS DPP 217 Relativistic electronpositron pair plasma APS DPP

26

27 A relativistic pair plasma by pair confinement? In theory mirror machine works for both charges A doublecoil system will form a mirror field The first step: one coil has been demonstrated Bfields Exp. setup Coil Radius (mm) 8 6 Bfield lines 4 2 coil Gibson et al, PRL 196 Pedersen et al, J. Phys. B 23 Myatt, et al, PRE 29 coil Particle trajectory 2 4 Distance to beam source (mm) 6 Chen et al. PoP (214) Theory and preliminary simulations show that using mirror fields, it is possible to trap MeV electrons and positrons produced from the lasersolid interactions. 27

28 Detailed positron spectrum reveals physics in sheath acceleration Positron spectra at 3 laser energies Time evolution of the spectrum (LSP) 9 ps laser; Au target (1mm x 2mm dia.) Black 247 J Green 8 J Red 15J Number/keV/sr 8 7 e 6 e+ * Chen, et al, Phys. Plasmas Energy (kev) 4 5x 3 Shaun Kerr, APS DPP