Study of matter in extreme conditions using 4th generation FEL light sources

Transcription

1 Study of matter in extreme conditions using 4th generation FEL light sources Sam Vinko Department of Physics Clarendon Laboratory University of Oxford Workshop on Science with Free Electron Lasers Shanghai, 21 August 2011

2 Outline Matter in extreme conditions (MEC) Unique match of free-electron lasers and MEC science FLASH: XUV FEL at DESY, Germany LCLS: X-ray FEL at SLAC, USA MEC science at FELs: flagship experiments First experiments on FLASH and LCLS Conclusions 2

3 Matter in extreme conditions occurs widely in nature Hot Dense Matter (HDM) supernova, stellar interiors, accretion disks plasma devices, laser produced plasmas, Z- pinches directly and indirectly driven inertial fusion Γ = V Coulomb E Kinetic Warm Dense Matter (WDM) cores of large planets systems that start solid and end as a plasma X-ray driven inertial confinement fusion 3

4 Matter in extreme conditions occurs widely in nature Necessity to study these systems in a controlled, laboratory environment to understand their properties: Equation of state over a large range of temperature, pressure, density Radiative and transport properties, opacity Material properties of WDM & HDM High energy-density (HED) systems are intrinsically unstable if unconfined confinement is an issue: inertial, magnetic, gravitational creating samples challenging: high energy deposition needed on the time scale of confinement samples small, with large gradients in temperature, density Probing HED also challenging volumetric probe needed, must penetrate dense systems intense enough to beat interaction cross sections, life-time time scales direct accurate measurement techniques not always available 4

5 MEC studies with XUV and X-ray FEL radiation 1. XUV and X-ray wavelengths are well-suited for MEC studies: Photon energies above plasmon energies allow volumetric energy deposition through single-electron photo-excitation and photo-ionization Resulting energy deposition mechanism is straightforward and simple to measure Optical laser excitation ω < ω p XUV and X-ray laser excitation ω > ω p ω < ω p is typically ev (UV) 5

6 MEC studies with XUV and X-ray FEL radiation 2. FEL short pulse lengths allow for inertial confinement approach: create and study the system before it blows up Simple, no additional confinement needed Requires ultrafast heating and probing techniques Relevant time scales determined by hydrodynamic expansion (> 10 ps) Strongly coupled and dense systems in principle simple to create and probe Probing on ultra-short time scales yields snapshots of the system temporal resolution 3. High photon flux (>10 12 photons per pulse) allows high energy deposition Intensties >10 17 W cm -2 have been achieved at XUV wavelengths Intensties >10 18 W cm -2 have been achieved at X-ray wavelengths Large photon numbers enable probing using photon-hungry techniques 4. Practical: tailor the source to each experiment Continuous wavelength range, versatility, high repetition rate, variable pulse length, etc. 6

7 4th generation FEL light sources Peak brightness 9 orders of magnitude higher than 3rd generation synchrotrons short bunch duration ( sub 100 fs); lots of photons per bunch (!10 12 ); tunable wavelength Hard X-ray FELs: LCLS at SLAC, USA : nm, 2009 SCSS at SPring-8, Japan : nm, 2011 European X-FEL at DESY, Germany: 0.1-6nm, 2015 Swiss-FEL at PSI : 0.1-7nm,

8 FLASH - Free electron LAser in Hamburg SASE single-pass FEL; tunable photon energy range ev (fundamental); pulse repetition rate 10 Hz; single-bunch / multi-bunch mode; ~50 μj average energy; ~ fs pulse length; achieved intensities ~10 17 Wcm 13.5 nm A. Nelson et al., Optics Express 17, (2009). 8

9 LCLS - Linac Coherent Light Source SASE single-pass FEL; tunable photon energy range: 500 ev 12 kev (fundamental); pulse repetition rate 120 Hz; ~1-3 mj average pulse energy; bandwidth 0.3% variable pulse length: <10 fs fs focusing optics ~10 18 Wcm -2 provided 9

10 LCLS - Matter in Extreme Conditions Endstation 10

11 MEC research with FELs Creating Warm Dense Matter Generate ~ 10 ev solid density matter Measure the equation of state XFEL 10 µm solid lower Z sample 100 µm short pulse probe laser Creating Hot Dense Matter Generate ~ 100ʼs ev solid density matter Generate hot, dense, high-pressure matter with the FEL solid high Z sample XFEL 6 µm short pulse probe laser L > absorption length Plasma spectroscopy of Hot Dense Matter Use high energy laser to create uniform HED plasmas Measure collision rates, redistribution rates, ionization kinetic XRSC CH Al FEL tuned to a resonance Probing High Pressure phenomena Use high energy laser to create steady high pressures Produce shocks and shockless high pressure systems Diagnostics: Diffraction, Small-angle, Diffuse scattering XFEL High Energy Laser Scattering Diagnostic development for dense matter Thomson scattering from solid density plasmas Measure ne, Te, ni, <Z>, f(v) XFEL back scattered signal ~ 100 µm dense heated sample forward scattered signal 11

12 Creating Warm Dense Matter FEL creates rapidly and uniformly heated high energy-density matter isochores (constant volume) 104!"#$%&'(#)*#+&,-*&#./+(0(/+ classical plasma! = 1 isentropes (constant entropy) WDM created by isochoric heating will isentropically expand: sampling WDM phase space Using foams allows more complete sampling Temperature (ev) dense plasma Density ( g/cm3)! = 10! = 100 high density matter

13 Creating Hot Dense Matter!"#$%123#4%&!.-5&62%$#+%&7&89:8; <%+3%*#5/*%&#0'&!*%$$/*% 2(+/.#B-0$&6C1D&E/.B4-'%&7&E!>; <%+3%*#5/*%&#0'&!*%$$/*% =%*$/$&<(+%&#0'&23#4% )((((*(#"34+1(5(%"&67",(89!7( :;;(/01(2 <=39,(7=%9>=+!&3(39+"(6=%%"-$=+,-(!=(:; A& &+,(C(DE&% C;;(+#(1=3,2!796A+"--(9-(=+"(&E-=%$4=+(3"+1!72 FG (K06# C?(LM:(A"B()%917!* HIJI&8%%&%5&#.I 13

14 Plasma spectroscopy on Hot Dense Matter!,-.#&',+./0.1"#.)2 Schematic experiment NO CL&M+&9. ;M:(P# =($(K.%&.#$%* 5&N&OP&.#$%*&(**#'(#5%$&9.&'-5 NO 9. FGH(!'+",(!=(:QRJ("B SE-"%."("#9--9=+(89!7 (TU%&V(-!%"&A(6&#"%& 5&N&FOO&3$P&Q?8&&(**#'(#5%$&3.#$+#!"#$%&'()*+ 107 He-like n = H-like 1s3l 1s2l Emission after pump before pump 1s 2 He-like H-like XFEL pump Energy (ev)

15 Probing high pressure phenomena 8U82&VQ?8&$"-4S&%T3%*(+%05 laser creates shock in a single crystal BL beams create ns divergent x-rays angular x-ray spread samples crystal planes provides critical data on dynamics at high pressure laser creates shock in a polycrystal XFEL is fs-scale monochromatic source grains in the polycrystal diffract the beam low divergence! nm-scale fs diffraction of real solids 15

16 Scattering Intensity Diagnostic development: X-ray Thomson scattering Proof-of-principle experiments on Be by H.J. Lee, A. Kritcher, T. Döppner, G. Gregori, S. H. Glenzer et al. Back Scattering q = 125 at LLE Forward Scattering q = 40 at LLNL 6 ratio of electron to ion feature: n e = 3.3x10 23 cm -3 1 Ion elastic scattering peak 4 2 Red wing gives T e = 53 ev plasmon peak plasmon peak Energy (kev) red wing provides fits to Te = 53 ev; ratio of electron to ion (elastic) peak gives mean ionization <Z> = 3.1; At high resolution ion feature provides Ti Energy (kev) ratio of plasmon peak intensities yields Te 12 ev; plasmon peak position yields ne 3 x cm -3 16

17 First Experimental Results 17

18 Creating Warm Dense Matter on FLASH Gas monitor detector Gas attenuator Aperture Fast shutter 13.5 nm Multilayer coated off-axis parabola 3 mm Target samples: Al, Mg, Si3N4 Photodiode Target stage scans through focus 4 µm Al filter 18

19 Saturable absorption in Aluminium L-edge Electron configuration in atomic aluminium: (µm -1 )! p s 2 2s 2 2p 6 3s 2 3p 1 K L M " ff 4* * 4 5* E phot K-edge at 92 ev two absorption channels: bound-free excitation of L-electrons: σ = 27 μm-1 (CXRO tables online free-free excitation of the valence band: σ = 0.2 μm-1 (S.M. Vinko et al., HEDP 5, (2009)) 19

20 Saturable absorption in the XUV "%-&%%&3" $31$6,27(-38$7 9:;$1&-$"#27(<2#2=(>&""$8 97$,#13"(#$-;$12#?1$ $()$4/ 0.1 1x x x x x10 17!"#$"%&#'()*+,-./ 1 electron per atom excited core hole life time ~ 40 fs Nagler et al. Nature Physics 5, 1341 (2009) 20

21 Saturable absorption in Aluminium L-edge Electron configuration in atomic aluminium: (µm -1 )! p s 2 2s 2 2p 6 3s 2 3p 1 K L M " ff 4* * 4 5* E phot K-edge at 92 ev two absorption channels: bound-free excitation of L-electrons: σ = 27 μm-1 (CXRO tables online free-free excitation of the valence band: σ = 0.2 μm-1 (S.M. Vinko et al., HEDP 5, (2009)) 21

22 Saturable absorption in the XUV %$#")"$# 8&9).*"$# Experimental Data, binned Theoretical transmission, 15fs pulse Theoretical transmission, 35fs pulse Experimental Data, binned Theoretical transmission, 15fs pulse Theoretical transmission, 35fs pulse Transmission x x x x x x !"%",()+:"21";. Intensity (W/cm2) Transmission x x x x x x10 17 Intensity (W/cm 2 ) Transmission Experimental Data, binned Cold transmission in the low intensity limit: - 52nm Al oxide: 16% - 52nm Mg + 20 nm Al + oxide: 10% - 83 nm SiN: 65% Effective measure of the core-hole fraction! 0 1x x x x x10 17 Intensity (W/cm2) 22

23 Creation of WDM saturable absorption enables the creation of far more homogeneous systems attenuation lengths are longer they are linear instead of exponential 50 Standard absorption Saturated absorption Sample Depth (nm) Temperature (ev) Time (fs)

24 Probing Warm Dense Matter on FLASH: L-shell spectroscopy XY1#T($&3#*#K-.(4&+(**-*Z L&++ Q892R&\&]C&%= 23%45*-+%5%* 1&3-$(B-0%'&#5&[#*(-/$&#0).%$ <#*)%5&$#+3.% 1&$4#0&5"*-/)"&,-4/$ 1&!EE9Z&9.Z&2(:&III 6UUDZ&'(-'%; 24

25 Probing Warm Dense Matter on FLASH: L-shell spectroscopy L-shell photo-excitation Radiative recombination Solid, crystalline aluminium ^_ Q?8&3"-5-0&%T4(5%'&#&81$"%.&4-*%&$5#5% ^_N&]C&%= Emitted photons map the occupancy of the valence band 25

26 Emission spectra from Warm Dense Aluminium Intensity / Energy 3 5.1!10 15 W/cm 2 3.4!10 15 W/cm 2 9.3!10 14 W/cm 2 1.5!10 14 W/cm 2 4.3!10 13 W/cm 2 2.0!10 13 W/cm W/cm 2 Al IV emission lines T=1.1 ev T=0.9 ev T=0.8 ev T=0.4 ev Energy (ev) Scanned 3 orders of magnitude in intensity Fluorescence overlaps with atomic emission lines from dilute plasma Valence band emission takes place ~40 fs after the first arrival of FEL pulse Measures the average temperature and density immediately after the pulse Vinko et al., PRL 104, (2010) Temperature (ev) classical plasma! = 1 dense plasma! = 10! = 100 high density matter Density ( g/cm3) 26

27 Conclusions Creating of Warm dense systems with XUV FEL sources very promising Saturable absorption helps to create homogeneous samples; tailoring XUV beam characteristics to material properties is essential XUV fluorescence spectroscopy gives insight into electronic structure of dense plasmas; experimentally still challenging (resolution, weak signal) but combined with advanced analysis techniques (DFT-MD) yields a wealth of information immediate goals: proof of principle pump-probe spectroscopy Creating Hot Dense Matter with X-ray FELs First results of high-intensity X-ray-matter interaction presented spectroscopy promising probe technique, but significant care needed in deducting physical plasma parameters: spectra are not directly representative of the charge state distribution of the system Emission spectra extremely sensitive to IPD model: large experimental dataset useful to benchmark models and extract the IPD function for a well-defined system Ongoing research on LCLS: bright future ahead First Thomson scattering experiments conducted (Dec 2010) First homogeneity of created HDM studies by Fourier Domain Interferometry (Feb 2011) First X-ray diffraction from shocked samples conducted (June 2011) First plasma spectroscopy of laser heated samples (as we speak) Dedicated MEC endstation to start user operation early next year 35

28 Acknowledgements Peak Brightness Collaboration (see all authors of Nature Physics 5, p693 (2009), PRL 104, , (2010) Oxford: Orlando Ciricosta, Justin Wark LLNL: Richard Lee SLAC: Bob Nagler LBNL: Phillip Heimann, Byoung-ick Cho IAEA: Hyun-Kyung Chung 36