4500 eV

1. a) b) Time resolved inner-shell spectroscopy of laser produced plasmas using a HOPG crystal in Von Hamos geometry R. L. Weber1, M. Notley2, B. Fell2, R. R. Freeman1, L. Van Woerkom1, A. J. Mackinnon3, R. Dickson3, D. Hey3,4, F. Khattak5, E. Garcia Saiz5, D. Riley5, S.N. Chen6, F. Beg6, G. Gregori1,7 1 The Ohio State University, 191 West Woodruff Ave, Columbus, OH 43210 2 Central Laser Facility, CCLRC Rutherford Appleton Laboratory, Chilton, Oxfordshire OX11 0QX UK 3 Lawrence Livermore National Laboratory, Livermore, CA, 94551 4 University of California, Davis, CA 95616 5 Dept of Mathematics and Physics, Queens University of Belfast, Belfast, UK 6 University of California, San Diego, CA 92093 7 Clarendon Laboratory, University of Oxford, Oxford OX1 3PU UK K-a K-a 4.5 4.75 5.0 4.5 4.75 5.0 1.0 2.0 He-a 5000 eV 4500 eV 1.0 0.5 0.0 0.0 Spectral line-outs of K-a show differences in time during plasma recombination (time w.r.t. start of pulse). Experimental Setup: Instrument Setup: The time response of the cathode estimated at ~60 ps from Eq. 2 [5] Novel Von-Hamos HOPG Bragg spectrometer was used to provide time resolved spectra around the Ti He-a line. Spectral resolution of ~ 0.6 keV and clever adjustment of the crystal allowed detection of K-a, He-a and K-b lines of Ti. The temporal resolution of the cathode is sufficient to observe K-a and He-a emission. An estimated time resolution attributable to the crystal is 2 ps. In Eq. (3) tc is resolution te is the extinction depth (200µm) for HOPG. Source to cathode distance was 542 mm dispersion is given by Eq. (1) [4] Pulse characteristics: - 1.5 ps, 100 J, 1053 nm, focused to ~1018 W/cm2 - 1 ns, 100 J, 527 nm, focused to ~1015 W/cm2 Results: Time resolved images of the x-ray emission from Ti foils and sandwiched Al/Ti/Al foils, in the region between 4.4 and 5.0 keV, show well resolved of K-a, He-a and K-b lines. Inhomogeneities in the CsI photocathode are clearly visible at the highest sweep speed. This results from a non-uniform deposition of the CsI on the CH substrate. Despite such effects, emission lines remain prominent. Due to extreme pin cushioning some of the data required transformation as shown: When irradiating Al/Ti/Al foils with the short pulse laser one can adjust the position of the crystal to record the evolution of the Ti K-b line. Due to the fixed length of the photocathode it is not possible to simultaneously record K-a and K-b. Here we compare the temporal evolution of K-b with varying target size and laser energy. For the case of short-pulse illumination, Ti K-a emission is clearly visible for about 300 ps after the start of the pulse. b) With a laser energy of ~ 25 J we looked at 1 x 1 mm vs .25 x .25 mm target. K-b K-b Time (ns) Time (ns) A similar comparison was then made with a laser energy of ~ 50 J K-b K-b Energy (keV) The FWHM of the K-b line is ~ 20 eV, which is in good agreement with the calculated value. References [1] K. Eidmann et al., J. Quant. Spectrosc. Radiat. Transfer, 65, 173 (2000) [2] S.B. Hansen et al., Phys. Rev. E, 72, 036408-1 (2005) [3] J.D. Lindl, Inertial Confinement Fusion, Springer-Verlag, New York, 1998 [4] A. Pak et al Rev Sci Instrum., vol 75, No 10, 3747, Oct 2004 [5] B.L. Henke et al., J. Appl. Phys. 52(3), 1509, 1981 [6] Missalla et al., Rev. Sci. Instrum., 70, 1288, 1999 Energy (keV) This work was partially funded by the US DOE by the University of California Lawrence Livermore National Laboratory under contract no. W-7405-ENG-48 and by the US Office of Fusion Energy Science.