X ray and XUV phase contrast diagnostics for ELI NP

Transcription

1 X ray and XUV phase contrast diagnostics for ELI NP D. Stutman 1,2, F. Negoita 1 and D. Ursescu 1 1 ELI NP, Bucharest Magurele, Romania 2 Johns Hopkins University, Baltimore, USA CARPATHIAN SUMMER SCHOOL OF PHYSICS 2016

2 Extreme light intensity in reach at ELI NP F# HERCULES F/3 (present) F/2 Coherent addition Thin film compression 1e22 1e23 1e24 1e25 Peak intensity (W/cm2) L. IONEL, D. URSESCU, Laser and Particle Beams, 2014 Two lasers of 10 PW (200 J in 20 fs), 1 pulse per minute, synchronizable to < 100 fs

3 Day 1 ELI NP experimental directions High Field QED Extreme light intensity Nuclear physics Extreme electric fields (10 15 V/m) Extreme light pressure (10 13 bar) Multi GeV electron +10 PW laser 2x10 PW laser collision in solid Acceleration of solid density ion bunches to GeV energy Radiation reaction, B W pair production quantum vacuum QED plasma, ultra intense gamma source Day 0 Physics Commissioning experiment Extreme intensity demo through laser conversion in dense gas jet Fission fusion reactions for neutron rich nuclei Isomers, nuclear reactions in plasmas Pump probe nuclear physics experiments with two synchronized 10 PW lasers Fast ignition relevant experiments

4 Efficient acceleration of solid density ion bunches critical to nuclear physics mission at ELI NP Fission fusion scheme for producing neutron rich nuclei P. Thirolf, F Negoita et al RRP 2016 Heavy element (Pt, Au, Th, U) nucleosynthesis still a mystery Produce and study neutron rich nuclei around N=126 waiting point Fission fusion: collide 10 MeV/A fissile + light ions with solid target Solid density ion bunches to produce enough neutron rich nuclei

5 Extreme light pressure will be used at ELI NP to accelerate solid density ion bunches to GeV energies 10s of nm thick foil Radiation Pressure Acceleration (RPA) 10 PW laser Macchi et al 2013 Light pressure >10 13 atm for 5x10 22 W/cm 2 intensity Pressure accelerates ultrathin solid foil as a whole ( light sail ) Good fraction of laser energy can be converted to GeV ions

6 Heavy ion RPA with ultrathin foils looks promising at ELI NP Predicted Au ion energy for I=3x10 21 W/cm2 on 20 nm foil Conversion efficiency and maximum Au energy/nucleon as a function of intensity Petrov et al PoP 2016 Energy/A flattens with intensity, but efficiency increases rapidly

7 RPA process sensitive to pre plasma electron density profile Pre plasma N crit Esirkepov et al. NIMA 2014 S c =15 μm S c S c =20 μm 20% change in density scale length doubles proton energy Gradient between N crit (1.8x10 21 cm 3 ) and solid density essential

8 Pre plasma density profile determined by ps laser contrast Electron pressure Electron spectrum Ideal contrast S c Real Ideal Real contrast Schollmeier et al 2015 Contrast in focal spot and at full power very difficult to control Diagnostic of pre plasma density profile essential at ELI NP Requirements: penetrating probe, μm space, 0.5 ps time resolution

9 Laser contrast Main pulse pre pulses post pulses

10 Strong plasma instabilities grow on fs scale during RPA Rayleigh Taylor instability in RPA Weibel instability Electron density Proton density Kim et al 2015 Ruyer et al 2015 Rayleigh Taylor instability due to extreme density gradient Weibel instability from counter streaming electron flows No diagnostic yet for relativistic plasma instabilities Requirements: sub μm space, fs time resolution

11 Visible or UV interferometry diagnostic limited to N e <<N crit 3 interferometry C μ foil Roth J Inst 2011 Interferogram 50 TW laser N e x10 20 cm Density map N e > N crit N e < N crit µm Interferometry measures areal electron density Laser light penetrates plasma up to N crit (1.7x10 22 cm 3 for 3 Refraction however too strong much before N crit reached

12 N crit Limit of UV interferometry

13 Proton backlit radiography sensitive to density, E and B fields Sarri et al 2012 Measured Reconstructed density map MeV proton source produced by TNSA Few μm space resolution (source size) Few ps time resolution (p + velocity) Complex setup (solid target), single shot Uematsu et al 2014

14 X ray backlit radiography main diagnostic of dense plasmas Backlighter laser (few ps, 1 kj) Main laser K X ray backlighter Backlighter foil ( V, Cu, Mo) object Target plasma K X rays ~1 m Backlighter spectrum Based on X ray attenuation Spatial resolution limited by backlighter or pinhole size to >10 μm Temporal resolution > few ps Poor contrast for gradients, debris Requires kj backlighter laser energy

15 Attenuation radiography measures global density but misses steep gradients Radiographic density diagnostic of ICF capsule implosion 2.14 ns Predicted) 400 μm measured Marshall et al 2009 Koch et al 2009

16 Plasma instabilities measurable only above 10 μm scale Radiographic imaging of Rayleigh Taylor instability in ICF capsule Smalyuk et 2009 Limited spatial and temporal resolution, need for kj backlighter debris, preclude conventional K attenuation radiography at ELI NP

17 Wave phase effects (refraction) stronger than attenuation for X rays passing through sharp density gradients Phase shift and attenuation coefficients in CH (cm 1 ) Phase shift α N e dl 10 1 Attenuation µ µrad X ray energy (kev) Refraction measures directly electron density gradient

18 object X ray wave z x Phase shift

19 Refraction radiography better diagnostic of small scale plasmas than attenuation radiography Simulated radiographs of 25 µm thick CH shell with 8 kev, 5 μm backlighter Attenuation image Refraction angle image 250 μm

20 Measurements confirm predictions Attenuation image Refraction angle image 2 mm CH rod 0.1 mm CH filament 20 kev X rays

21 Ultra small angle scatter (USAXS) probes density inhomogeneity on sub μm scale USAXS (multiple-refraction) Clear acrylic L sub µm L µrad Acrylic doped with sub-µm boron particles Beam broadened in angle Sub μm density perturbations without sub μm radiographic resolution Plasma instabilities, turbulence

22 X rays over a few kev can penetrate typical ELI NP target plasmas without suffering excessive refraction or attenuation Refraction, USAXS cause µrad deflection and broadening of the probe X ray beam µm, fs resolution needed for ELI NP plasmas How to measure X ray refraction (also attenuation and scatter)? How to make µm, fs resolution X ray backlighter (probe beam)?

23 Talbot grating interferometer simultaneously measures X ray refraction, attenuation, and USAXS X-ray source Source grating Beam-splitter phase grating Analyzer grating Detector pixel Grating period ~few μm Talbot distance ~1 m Sample Pfeiffer et al Nature 2006 Works through Talbot effect <0.1 µrad angular resolution, insensitive to X ray spectrum shape Can be made 2 D

24 Talbot effect grating Talbot distance ~10 cm for 10 kev X rays and few μm period gratings

25 Talbot X ray gratings made in gold (MicroWorks Inc) 20 μm 50 μm Up to 10 x 10 cm area

26 Simultaneous refraction + attenuation + USAXS images using phase stepping when multiple exposures possible Attenuation Refraction USAXS Pixel intensity object Grating position ( phase ) Phase stepping 20 kev mean energy Grating imperfections compensated by subtracting images w/o object

27 Moiré deflectometry when only one exposure possible (laser) Moiré fringes object Moire deflectogram (20 kev) Refraction image from Moire deflectometry 1 mm Stutman et al RSI 2011 Valdivia et al JAP 2013 Sinusoidal fringe profile replaces phase stepping Refraction + attenuation + USAXS Refraction image from 30 exposure phase stepping

28 Talbot deflectometry enables high resolution, accurate electron density diagnostic PMMA tube Be rod 3 mm Be rod Valdivia et al JAP 2013 Spatial resolution backlighter size

29 Sub μm scale density structure from USAXS 8 kev Talbot deflectometry of wood splinter (0.1 1 μm filaments) Moiré image Attenuation image Loss of fringe contrast Valdivia et al AO µm Talbot X ray technique very well suited to ELI NP diagnostic needs Can be applied also with XUV light, to probe plasma around N crit 1 µm spot (spatially coherent), few fs duration, 5 15 kev backlighter to apply method at ELI NP

30 LWFA betatron source makes μm, fs X ray backlighter LWFA betatron X ray emission (Corde et al 2013) Gas target Betatron backlit radiography main beam detector 1 µm Fs backlighter beam gas jet dipole magnet 5 15 kev X rays TW laser into He gas jet 1 µm, few fs, tunable, directional, no debris 5 15 kev peaked spectrum matches interferometer response

31 X ray deflectometer contrast matches betatron spectrum Talbot deflectometer fringe contrast (%) Betatron spectrum X ray energy (kev)

32 Single shot, µm/fs resolution phase contrast radiography demonstrated with betatron X ray backlighter 3 meters He gas jet object filter 80 TW/30 fs Magnet electrons 10 µm nylon wire Fourmeaux et al 2011

33 Betatron X ray backlighter at ELI NP Secondary target heating beam Backlighter beam split from main beam Remote detector for reduced plasma and background 10 PW acceleration beam TW XUV coherent backlighter for N e < 10 N crit HHG in solid target (plasma mirror) for XUV

34 Direct measurement of density gradient possible at ELI NP N e /N crit Profile C foil Moiré fringes N e gradient from FTM analysis

35 Single grating 2 D deflectometry ideal diagnostic for ELI NP Object fringe image Reference fringe image 2 meters Talbot pattern 2 D beam splitter Target Object fringe perturbation (15 µm dia. C sphere at 2m) backlighter 2 D Talbot pattern directly resolvable by CCD detector produced at large distance with single phase grating (no photon loss)

36 Summary X ray or XUV phase contrast imaging can provide much needed plasma density profile and instability diagnostic Betatron X ray backlighter or solid target HHG XUV backlighter for micron/fs spatial resolution First experiments in second year of operation at ELI NP np.ro/jobs