Supersonic propagation of ionization waves in an underdense, laser-produced plasma

Constantin, C.; Back, C. A.; Fournier, K. B.; Gregori, G.; Landen, O. L.; Glenzer, S. H.; Dewald, E. L.; Miller, M.C.

doi:10.1063/1.1927540

Cited by 29 publications

(11 citation statements)

References 25 publications

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“…Here, we have used T e = 2 keV for the electron temperature on axis at the time during the laser pulse when the ionization front reaches the gas-pipe wall (t ≤ 1.5 ns). This result is consistent with what was observed previously at similar laser intensities in doped-aerogel targets 44 . We find, as expected, that for these x-ray-source development experiments, which are performed with a laser energy that is more than an order of magnitude larger than what has been done previously 15 , the same enhanced laser-tox-ray conversion efficiency that results from an ionization wave propagating supersonically through the target plasma and heating the entire target's volume.…”

Section: A Supersonic Energy Depositionsupporting

confidence: 83%

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Multi-keV x-ray source development experiments on the National Ignition Facility

et al. 2010

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We report results from a five shot campaign carried out with Ar-Xe gas-filled targets at the National Ignition Facility (NIF). The targets were shot with ≈ 350 kJ of 3ω laser energy delivered with a 5 ns trapezoidal laser pulse. We report measured x-ray output from the target in different spectral bands both below and above 1.5 keV photon energies: we find yields of ≈20.5 kJ/sr with peak x-ray power approaching 4 TW/sr over all energies, as measured for the unique viewing angle of our detector, and ≈3.6 kJ/sr with peak x-ray power of 1 TW/sr for x rays with energies >3 keV. This is a laser-to-x-ray conversion efficiency of 13±1.3 % for isotropic x rays with energies >3 keV. Laser energy reflected by the target plasma for both inner and outer-cone beams is measured and found to be small, between 1-4% of the drive energy. The energy emitted in hard x rays (with energies >25 keV) is measured and found to be ≈1 J/sr. Two-dimensional imaging of the target plasma during the laser pulse confirms a fast, volumetric heating of the entire target, resulting in efficient laser-to-x-ray conversion. Post-shot simulations with a two-dimensional radiation-hydrodynamics code reproduce well the observed x-ray flux and fluence, backscattered light, and bulk target motion.

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Section: A Supersonic Energy Depositionsupporting

confidence: 83%

“…In the work in Refs. [44][45][46] the targets were all solid at room temperature, unlike the gaseous targets of the present work. The targets were all doped SiO 2 aerogels in the few mg/cm 3 density range.…”

Section: A Supersonic Energy Depositionmentioning

confidence: 99%

Multi-keV x-ray source development experiments on the National Ignition Facility

et al. 2010

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“…, file=filename3) write(7,*) header write(7,1) numeos, zbar3, abar3, rho3, n3 write(7,2) (array3(i), i=1,n3) close (7) 1 format(1x,i5,4x,1p3e15.8,3x,i5) 2 format(1p5e15. 8) stop end c ********************************************************* c EXTERNAL FUNCTION XMAXVAL function xmaxval(a,na) real*4 a(100) xmaxval=0. do i=1,na if(a(i).gt.xmaxval) xmaxval=a(i) enddo return end c ********************************************************* c UNPACK a linear array into d(nd), t(nt), p1(i,j), p2(i,j) subroutine unpack(a,d,t,p1,p2,nd,nt,incr) real*4 a(10000), d(100), t(100), p1(100,100), p2(100,100) c (0.01 is to avoid roundoff errors in integers) nd = aint(a(1)+0.01) nt = aint(a(2)+0.01) incr = 2 do i=1,nd incr=incr+1 d(i) = a(incr) enddo do i=1,nt incr=incr+1 t(i) = a(incr) enddo do j=1,nt do i=1,nd incr=incr+1 p1(i,j) = a(incr) enddo enddo do j=1,nt do i=1,nd incr=incr+1 p2(i,j) = a(incr) enddo enddo return end c ********************************************************* c PACK 2d arrays d(nd), t(nt), p1(i,j), p2(i,j) into a subroutine pack(a,d,t,p1,p2,nd,nt,incr) real*4 a(10000), d(100), t(100), p1(100,100), p2(100,100) a(1) = nd a(2) = nt SiO 2 aerogel exposed to 4-ns laser irradiation UCSD-CER-05-01 59 incr = 2 do i=1,nd incr=incr+1 a(incr) = d(i) enddo do i=1,nt incr=incr+1 a(incr) = t(i) enddo do j=1,nt do i=1,nd incr=incr+1 a(incr) = p1(i,j) enddo enddo do j=1,nt do i=1,nd incr=incr+1 a(incr) = p2(i,j) enddo enddo return end…”

Section: Discussionmentioning

confidence: 99%

“…These experiments build on previous experiments that show aerogel targets can be volumetrically heated by a laser [7,8]. This illumination geometry is similar to the one-sided illumination, previously used at the Omega laser.…”

Section: Analysis Of Datamentioning

confidence: 99%

“…Fortunately, a significant advance in target fabrication has led to the production of silica aerogels with densities as low as 2 mg/cc that can be doped with mid-Z elements. Recent experiments have measured supersonic heat wave propagation in these aerogels, indicating that they are volumetrically heated before significant hydrodynamic motion affects the plasma, as was found for the gas-filled targets [7,8]. Thus, the density of the target is chosen to ensure volumetric heating, while the Z and concentration of the dopant are chosen for the desired wavelength and optical depth of the emission to be studied.…”

Section: Introductionmentioning

confidence: 99%

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Final Report LDRD 04-ERD-019 Development of absolute spectroscopic diagnostics for non-LTE plasmas

Scott¹

2010

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Overview:This project sought to further our understanding of non-Local Thermodynamic Equilibrium (NLTE) processes by providing benchmark data to validate computational models. This has been a difficult regime to study in the laboratory, where experimental scales produce strong gradients while interpretation requires well-characterized uniform plasmas. It has also been a difficult regime to simulate, as evidenced by the large discrepancies in predictions of NLTE spectra for fixed plasma properties. Not surprisingly, discrepancies between data and calculations of recombining laser-produced plasmas have been in evidence since the 1980's. The goal here was to obtain data of sufficient accuracy to help resolve these discrepancies and enable better modeling of the NLTE processes that are integral to high-energy density experiments.Advances in target fabrication, diagnostic development and simulation capabilities provided the foundations for this project. Uniform plasmas were to be achieved by using aerogel foams of low enough density (~mg/cm 3 ) and thickness (~mm) to be volumetrically heated by a laser. The foams were doped with Ti to provide K-and L-shell emission and recombination spectra during the experiments. A new absolutely calibrated transmission grating spectrometer provided absolute temporal measurements at 18 frequencies, in addition to a CCD image of the timeintegrated spectrum. Finally, atomic models of varying degrees of sophistication and detail, combined with NLTE radiation transport and hydrodynamics, were used to simulate the experiments and understand the observed spectra.We give here a summary of the main achievements, challenges and results of this project. Details are available in the documents included as appendices. Summary:The first set of experiments was performed on the NIKE laser at NRL in March, 2004, with the goals of evaluating the performance of the diagnostics and the achieved plasma uniformity. By varying the laser parameters, we determined the required parameters for creating L-shell emission and were able to obtain K-shell (He-like) Ti. Pinhole x-ray images of the K-shell emission showed transverse plasma uniformity depended upon the target quality. Not all targets had acceptable quality, as it proved difficult to fabricate targets of the desired thickness (½ mm).Using thicker targets also adversely affected the production of uniform conditions through the plasma, as the plasma was expected to have a moderate optical thickness (~few) to the laser radiation at early times during the laser pulse. Large differences in predictions of target 1 performance by different codes were traced to the differences in the calculation of laser absorption, and this is discussed at length in the reports from UCSD.The first absolutely calibrated, time resolved L-shell emission spectra (from 4 to 26 Å) were also obtained in this series of experiments. The spectral resolution was not sufficient to match any individual spectral features. However, combined with the time resolution, it was sufficient to de...

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Characterization of heat-wave propagation through laser-driven Ti-doped underdense plasma

Tanabe

Nishimura

Ohnishi

et al. 2010

High Energy Density Physics

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Supersonic propagation of ionization waves in an underdense, laser-produced plasma

Cited by 29 publications

References 25 publications

Multi-keV x-ray source development experiments on the National Ignition Facility

Multi-keV x-ray source development experiments on the National Ignition Facility

Final Report LDRD 04-ERD-019 Development of absolute spectroscopic diagnostics for non-LTE plasmas

Characterization of heat-wave propagation through laser-driven Ti-doped underdense plasma

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