We used Kr K{alpha} (12.6 keV) and Ag K{alpha} (22.1 keV) x-rays, produced by petawatt class laser pulses interacting with a Kr gas jet and a silver foil, to measure the integrated crystal reflectivity of flat Highly Oriented Pyrolytic Graphite (HOPG) up to fifth order. The reflectivity in fourth order is lower by a factor of 50 when compared to first order diffraction. In second order the integrated reflectivity decreases from 1.3 mrad at 12.6 keV to 0.5 mrad at 22.1 keV. The current study indicates that HOPG crystals are suitable for measuring scattering signals from high energy x ray sources (E {ge} 20 keV). These energies are required to penetrate through the high density plasma conditions encountered in inertial confinement fusion capsule implosions on the National Ignition Facility

Doeppner, T

Girard, F

Glenzer, S H

Kugland, N L

Landen, O L

Neumayer, P

Niemann, C

Doeppner, T.

Neumayer, P.

Girard, F.

Kugland, N. L.

Landen, O. L.

Niemann, C.

Glenzer, S. H.

UNT Digital Library

LLNL-PROC-403603High order reflectivity of graphite (HOPG)crystals for x ray energies up to 22 keVT. Doeppner, P. Neumayer, F. Girard, N. L.Kugland, O. L. Landen, C. Niemann, S. H.GlenzerMay 7, 2008High Temperature Plasma DiagnosticsAlbuquerque, NM, United StatesMay 11, 2008 through May 15, 2008Disclaimer  This document was prepared as an account of work sponsored by an agency of the United States government. Neither the United States government nor Lawrence Livermore National Security, LLC, nor any of their employees makes any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States government or Lawrence Livermore National Security, LLC. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or Lawrence Livermore National Security, LLC, and shall not be used for advertising or product endorsement purposes.  High order reflectivity of graphite (HOPG) crystals for x ray energies up to 22 keVT. Do¨ppner1, P. Neumayer1, F. Girard3, N. L. Kugland1,2, O. L. Landen1, C. Niemann1,2, and S. H. Glenzer11 Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551, USA2 Physics Department, Box 951547, University of California Los Angeles, Los Angeles, California, 90095, USA3Commissariat a` l’E´nergie Atomique, Boˆıte Postale 12, 91680 Bruye`res-le-Chaˆtel, France(Dated: April 30, 2008)We used Kr Kα (12.6 keV) and Ag Kα (22.1 keV) x-rays, produced by petawatt class laser pulsesinteracting with a Kr gas jet and a silver foil, to measure the integrated crystal reflectivity of flatHighly Oriented Pyrolytic Graphite (HOPG) up to fifth order. The reflectivity in fourth order islower by a factor of 50 when compared to first order diffraction. In second order the integratedreflectivity decreases from 1.3 mrad at 12.6 keV to 0.5 mrad at 22.1 keV. The current study indicatesthat HOPG crystals are suitable for measuring scattering signals from high energy x ray sources(E ≥ 20 keV). These energies are required to penetrate through the high density plasma conditionsencountered in inertial confinement fusion capsule implosions on the National Ignition Facility.PACS numbers: 52.25.Os, 52.38.Ph, 52.50.JmI. INTRODUCTIONHighly Oriented Pyrolytic Graphite (HOPG) crystalsare of particular interest for x-ray diagnostics of hot denseplasmas. Their unique crystal plane structure enablesthem to be highly efficient x-ray diffraction instruments.These type of crystals, for example, have been success-fully used in novel x-ray scattering experiments on warmdense matter [1–3] for x-ray energies of 3 to 9 keV. On theother hand, photon energies > 10 keV are required for theprobing of super-dense states of matter, as encounteredin inertial confinement fusion experiments [4]. The aimof this work is to characterize the reflectivity of HOPG inthis energy range, i.e. at 12.6 keV and 22.1 keV. Since theBragg angle decreases when going to higher photon ener-gies, it is necessary to use the crystals in higher diffrac-tion orders. We have characterized the performance ofHOPG in up to fifth order to ascertain their effectivenessfor use in x-ray scattering experiments, especially whenthe detection of weak signals requires high reflectivityand good spectral resolution.II. EXPERIMENTAL SETUPWe used the petawatt-class Titan laser facility atthe Lawrence Livermore National Laboratory [citationneeded] to produce Kα x-rays at 12.6 keV (Kr Kα) and22.1 keV (Ag Kα). In these experpiments, the Titanshort-pulse beam delivered a pulse energy of up to 180 Jat 1054 nm in 0.7 ps. Focusing is achieved with an f/3 off-axis parabola to a 1/e2 spot diameter of 15 µm, yieldingan intensity on target above 1020 W/cm2. To generateKr Kα x rays, the laser was focused onto a super sonicKr gas jet [5]. We aligned the laser focus close to thegas jet nozzle and near the front edge of the gas jet inorder to maximize conversion efficiency [6]. The backingpressure was kept at 90 bar to ensure the generation oflarge clusters and thus efficient laser absorption [7]. Theneutral density of the gas jet was measured off line us-ing a Lloyd’s mirror interferometer to be 8.7× 1019cm−3±10% on axis at the nozzle exit. For generating Ag Kαx rays the laser pulses were focused on a 10 µm silverfoil.The x-ray conversion efficiencies were measured oneach shot using a single hit counting CCD [8, 9] to be> 10−5 [5] and > 10−4 [8] into the full solid angle for KrKα and Ag Kα, respectively. This technique uses a CCDcamera placed far enough away from the x-ray sourcethat a series of single photon events are recorded on thedetector. Single event histogram binning [9] of the imageyields an absolute number of photon events at discreteenergies. In our setup, the single hit CCD observed thefront side of the gas jet from distance of 5 m.Laser pulse:100-300J0.7-40psImaging plateAg-foilorKr gas jetHOPGAl housing21 22 23 24 25 26energy [keV]Energy [keV]Blast shieldFilterBragg angleAg KαAg KβFIG. 1: Schematics of the experimental setup. For the KrKα setup a focal length (distance from source to HOPG) of230 mm was used. The inset shows a sample raw image for AgKα. As a reference for absolute reflectivity measurements asingle hit CCD camera and an additional HOPG spectrometerin fixed geometry (second order) were operated (not shown).2d2d 15  10  5 0 5 10 15 200.51.01.52.02  mmRear surfaceFront surface01234-4 -2 0 2 4 6 8simulationdata 4th012345-4 -2 0 2 4 6 8simulationdata 3rd01234567-4 -2 0 2 4 6 8simulationdata 2nd80%- 80%2nd order 3rd order 4th orderdistance [mm]FIG. 2: The lineshape at 22.1 keV is dominated by depth broadening which can be reproduced using Monte Carlo simulations.This method can serve as an independent means to determine reflectivity changes between different HOPG orders. [will improvestatistics of fit function]High resolution spectra of the Kα line emission wererecorded using two HOPG spectrometers. For diffractionwe used 25.4 mm × 25.4 mm × 2 mm ZYB grade HOPGcrystals (Advanced Ceramics) with a mosaic spread ofγ = 0.8 degree. The separation between the mosaic crys-tal planes is d = 0.3354 nm. While one spectrometerwas operated in second order for all the shots to serveas an additional source monitor, the primary instrumentwas used to measure the integrated HOPG reflectivitiesin various diffraction orders, see Fig. 1 for the schematicsof the setup. For detection we used imaging plates (FujiBAS-SR), which previously were absolutely calibrated at5.9 keV and 22 keV [10, 11]. In between the imaging platesensitivity can be extrapolated by the absorption prop-erties of the plates. In the gas jet setup the spectrometerwas filtered using 25 µm Mylar as blast shield, and 25 µmBeryllium plus 12 µm Aluminum in front of the imagingplates. Differential filtering using 25 µm Pb was used todetermine contribution from different diffraction orders.For Ag Kα 25 µm and 400µm Aluminum were used asblast shield and imaging plate filter, respectively.III. RESULTS AND DISCUSSIONFor mosaic focusing, the Bragg relationship must besatisfied: nλ = 2d sin θB , where n is the diffraction or-der, λ is the x-ray wavelength, and θB is the Bragg an-gle. For Ag Kα θB is very small for low diffraction orders,which makes it challenging to align, and, in particular forfirst order, requires very large crystals to cover the neces-sary bandwidth. At 12.6 keV we measured all diffractionorders from one to five. In fifth diffraction order, thesignal was below the detection threshold. At 22.1 keVthe reflectivity was measured from second to fourth or-der. Fig. 2 shows the Ag Kα line shapes in second tofourth order. In general the measured line width is de-termined by a variety of factors, i.e. the natural linewidth, depth broadening, surface roughness, mosaicityof the crystal, and the source size, which was discussed,e.g., in Ref. [12]. At higher energies in general, and at22.1 keV in particular the line width is dominated bydepth broadening which appears on the high energy sideKr Kα n θB integrated Ag Kα n θB integrated(12.6 keV) reflectivity (22.1 keV) reflectivity[mrad] [mrad]1 8.4 3.7 1 4.82 17.0 1.3 2 9.7 0.473 26.1 0.21 3 14.6 0.124 35.9 0.077 4 19.6 0.0345 47.1 <0.02 5 24.8TABLE I: Bragg angles and measured integrated reflectivities30.010.11100.010.11101 2 3 4 5i nt eg rat ed  r ef l ec ti v it y [ mr ad ]HOPG order12.6 keV22.1 keVFIG. 3: Measured integral HOPG reflectivities at 12.6 keV(Kr Kα) and 22.1 keV (Ag Kα) up to 4th order. For 12.6 keVthe setup in 5th order was tested, but the signal was belowthe detection threshold.of the main line, see Fig. 2. Nevertheless, the instrumentresolution is good enough to resolve Ag Kα1 and Ag Kα2.Since the attenuation length of carbon at 22.1 keV is 15mm, the depth broadening is limited by the thicknessof the crystal. Since the energy resolution increases tohigher diffraction order, the spectral line width decreasesaccordingly. Thus decreasing the thickness of the crystalis a possibility to enhance the energy resolution of theinstrument, though sacrificing reflectivity.We performed Monte Carlo simulations to model theshape of the measured Ag Kα lines. Within this simpi-fied model the line shape depends on the mosaicity of thecrystal, the width of the crystal, the Bragg angle, the at-tenuation length in graphite, as well as the reflectivityR per unit length, which is adjusted to fit the syntheticline shape to the measured profile. For the second or-der signal in Fig. 2 the variation of the fit function withrespect to R is illustrated. The lowest diffraction orderis dominated by single reflections yielding an exponen-tial decay in the high energy side. For higher diffractionorders the probability of multiple reflections within thecrystal increases, significantly changing the shape of themeasured line. The reflectivities R(n) extracted in thisway from the simulation show the same dependence onthe diffraction order n as the measured integrated reflec-tivity. Hence at high x ray energies where the line widthis dominated by depth broadening the measurement ofthe line shape is a viable way of determining crystal re-flectivities.The measured integrated reflectivities are shown inFig. 3. In general, the signal strength descreases to-wards higher diffraction orders by two orders of mag-nitude. Even though the absolute values differ the slopeis very similar at 12.6 keV and 22.1 keV. The highestreflectivity is observed at 12.6 keV in first order with3.7 mrad. This value agrees with previous measurementsat ∼ 5 keV and ∼ 8 keV [12]. At 22.1 keV the reflectivityis measured to be lower by a factor of 2 to 3 compared to12.6 keV. Nevertheless, the integrated reflectivity is stillup to about a factor of 5 times higher than for commonlyused less mosaic crystals such as LiF or PET [13] makingthem suited for the detection of weak signals, as requiredin x-ray Thomson/Compton scattering experiments toprobe dense and warm states of matter.AcknowledgmentsWe would like to thank the staff of the Jupiter LaserFacility for their support. This work was performed un-der the auspices of the U.S. Department of Energy by theLawrence Livermore National Laboratory, through theInstitute for Laser Science and Applications, under con-tract DE-AC52-07NA27344. The authors also acknowl-edge support from Laboratory Directed Research and De-velopment Grants No. 08-LW-004 and 08-ERI-002.[1] S. H. Glenzer, G. Gregori, R. W. Lee, F. J. Rogers, S. W.Pollaine, and O. L. Landen. Demonstration of spectrallyresolved x-ray scattering in dense plasmas. Phys. Rev.Lett., 90(17), 2003.[2] G Gregori, SH Glenzer, HK Chung, DH Froula, RW Lee,NB Meezan, JD Moody, C Niemann, OL Landen,B Holst, R Redmer, SP Regan, and H Sawada. Measure-ment of carbon ionization balance in high-temperatureplasma mixtures by temporally resolved x-ray scattering.J. Quant. Spectr. Rad. Trans., 99(1-3):225, 2006.[3] S. H. Glenzer, O. L. Landen, P. Neumayer, R. W. Lee,K. Widmann, S. W. Pollaine, R. J. Wallace, G. Gregori,A. Ho¨ll, T. Bornath, R. Thiele, V. Schwarz, W. D. Kraeft,and R. Redmer. Observations of plasmons in warm densematter. Phys. Rev. Lett., 98(6), 2007.[4] J. D. Lindl, P. Amendt, R. L. Berger, S. G. Glendin-ning, S. H. Glenzer, S. W. Haan, R. L. Kauffman, O. L.Landen, and L. J. Suter. The physics basis for ignitionusing indirect-drive targets on the national ignition facil-ity. Phys. Plasmas, 11(2):339, 2004.[5] N.L. Kugland, C.G. Constantin, C. Niemann, P. Neu-mayer, H.-K. Chung, T. Do¨ppner, A. Kemp, S.H. Glen-zer, and F. Girard. 12.6 kev kr kα x-ray source for highenergy density physics experiments. submitted to Rev.Sci. Instrum., 2008.[6] N.L. Kugland et al. submitted to Appl. Phys. Lett., 2008.[7] T. Ditmire, R. A. Smith, J. W. G. Tisch, and M. H. R.Hutchinson. High Intensity Laser Absorption by Gases4of Atomic Clusters. Phys. Rev. Lett., 78:3121–4, 1997.[8] H. S. Park, D. M. Chambers, H. K. Chung, R. J. Clarke,R. Eagleton, E. Giraldez, T. Goldsack, R. Heathcote,N. Izumi, M. H. Key, J. A. King, J. A. Koch, O. L. Lan-den, A. Nikroo, P. K. Patel, D. F. Price, B. A. Reming-ton, H. F. Robey, R. A. Snavely, D. A. Steinman, R. B.Stephens, C. Stoeckl, M. Storm, M. Tabak, W. Theobald,R. P. J. Town, J. E. Wickersham, and B. B. Zhang. High-energy k alpha radiography using high-intensity, short-pulse lasers. Phys. Plasmas, 13(5), 2006.[9] B.R. Maddox et al. submitted to Rev. Sci. Instrum., 2008.[10] N. Izumi, R. Snavely, G. Gregori, J. A. Koch, H. S. Park,and B. A. Remington. Application of imaging plates tox-ray imaging and spectroscopy in laser plasma experi-ments (invited). Review of Scientific Instruments, 77(10),2006.[11] N. Izumi. private communication.[12] A. Pak, G. Gregori, J. Knight, K. Campbell, D. Price,B. Hammel, O. L. Landen, and S. H. Glenzer. X-ray linemeasurements with high efficiency bragg crystals. Reviewof Scientific Instruments, 75(10):3747, 2004.[13] F. J. Marshall and J. A. Oertel. Framed monochromaticx-ray microscope for icf (invited). Review of ScientificInstruments, 68(1):735, 1997.

High order reflectivity of graphite (HOPG) crystals for x ray energies up to 22 keV

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High order reflectivity of graphite (HOPG) crystals for x ray energies up to 22 keV

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