Electron Temperature Measurements inside the Ablating Plasma of Gas-Filled. Hohlraums at the National Ignition Facility

Transcription

1 Electron Temperature Measurements inside the Ablating Plasma of Gas-Filled Hohlraums at the National Ignition Facility M.A. Barrios 1, D.A. Liedahl 1, M.B. Schneider 1, O. Jones 1, G.V. Brown 1, S.P. Regan 2, K.B. Fournier 1, A. S. Moore 1, J. S. Ross 1, O. Landen 1, R. L. Kauffman 1, A. Nikroo 1, J. Kroll 1, J. Jaquez 3, H. Huang 3, S. B. Hansen 4, D. A. Callahan 1, D. E. Hinkel 1, D. Bradley 1 and J.D. Moody 1 1 Lawrence Livermore National Laboratory, Livermore, CA 94551, USA 2 Laboratory for Laser Energetics, Rochester, NY 14623, USA 3 General Atomics, San Diego, CA 92121, USA 4 Sandia National Laboratories, Albuquerque, NM 87123, USA Abstract The first measurement of the electron temperature (T e ) inside a National Ignition Facility (NIF) hohlraum is obtained using temporally resolved K-shell X-ray spectroscopy of a mid-z tracer dot. Both isoelectronic- and interstage- line ratios are used to calculate the local T e via the collisional radiative atomic physics code SCRAM [Hansen, et al. HEDP 3 (2007) ]. The trajectory of the mid-z dot as it is ablated from the capsule surface and moves toward the laser entrance hole (LEH), is measured using side-on x-ray imaging, characterizing the plasma flow of the ablating capsule. Data show the measured dot location is farther away from the LEH in comparison to the radiation-hydrodynamics simulation prediction using HYDRA [Marinak, et al. Phys. of Plasmas 3, 2070 (1996)]. To account for this discrepancy, the predicted simulation T e is evaluated at the measured dot trajectory. The peak T e, measured to be 4.2 kev ± 0.2 kev, is ~0.5 kev hotter than the simulation prediction. I. INTRODUCTION Indirect-drive inertial confinement fusion (ICF) experiments at the National Ignition Facility (NIF) 1 use a shaped x- ray drive to implode a cryogenically cooled deuterium-tritium (DT) fuel capsule. The x-ray drive is produced inside a laserheated high-z (typically Au) cylindrical cavity, called a hohlraum, where the capsule is suspended in the center. The hohlraum is a highly dynamic and complex environment due to the development of concurrent processes such as laser-plasma 1

2 interactions (LPI) including cross-beam energy transfer (CBET) 2,3 and backscatter 4, generation of M-band X-rays and hot electrons. Modeling this environment requires non-local thermal equilibrium (n-lte) atomic physics and non-local particle and energy transport. These processes can affect the azimuthal uniformity and magnitude of the x-ray drive experienced by the capsule, making it challenging to accurately model the hohlraum and predict the capsule performance. Experiments on NIF gas-filled hohlraums show reduced capsule velocities 5,6 and larger hot-spot shape asymmetries compared to radiation hydrodynamic (RH) simulation predictions. 7 These effects are thought to account for some of the observed reduction in neutron yield and implosion performance. Focused measurements show the reduced implosion velocities result from a 15 to 20% lower than predicted radiation drive at peak power. 8 The cause of the drive reduction, however, is not yet understood. In addition, the temporal dynamics of the LPI and CBET may be the cause of some of the observed hot-spot shape asymmetries. More recent hohlraum designs have shifted toward simpler near-vacuum/low gas fills with higher density ablators. 9 These hohlraums have a measured radiation drive closer to the RH simulation (~10% lower) predictions, and show almost no significant LPI and CBET. 10 To better understand hohlraum physics and to improve hohlraum models, it is important to characterize the plasma conditions inside the hohlraum. Of particular interest is the electron temperature (T e ) near the central region of the laser entrance hole (LEH) where laser plasma interactions, which are strongly driven by the electron temperature and density, occur. In gas-filled hohlraums plasma ablated from the capsule flows towards and into this hot region. This paper reports on the first measurements of the electron temperature near the LEH region and of the plasma flow of the ablating plasma/gas interface of the capsule inside a NIF gas-filled hohlraum, obtained by using x-ray spectroscopy and x-ray imaging of a mid-z tracer layer. II. EXPERIMENTAL TECHNIQUE Typical implosion experiments at NIF use a cylindrical hohlraum 5.75 mm in diameter and 9.42 mm long, with 3.1 mm diameter LEH s on top and bottom. Experiments described here used a 0.8X scaled version of this hohlraum in order to reach the same radiation temperature with less laser energy, therefore reducing optics use in the laser. The target used to develop the spectroscopy technique is a ViewFactor target 8,11, which uses a truncated hohlraum, as shown in Figure 1. It has a diameter of 4.69 mm, a length of 5.92 mm, and a 3.1 mm diameter LEH at the top. A 2.4 mm diameter, 25 um thick CH shell is centered 3.92 mm below the LEH and the hohlraum is truncated at full diameter, 2 mm below the center of the CH shell. The ViewFactor target was chosen to reduce the x-ray background emission from the hot Au plasma at the LEH. 11 A mid-z tracer layer was sputter-coated on top of the capsule and the center of the tracer layer, 2.72 mm directly below the LEH, is co-axially aligned with the top LEH center. The shell has a small hole drilled opposite to the tracer layer to allow the 2

3 hohlraum gas fill to also fill the CH shell. The tracer layers are 800 um diameter dots, nominally equal parts Mn-Co (1600Å or 3200Å thick) or Mn only (2400Å thick). The target is positioned in the NIF chamber with the CH shell centered at the target chamber center (TCC). The hohlraum is filled with 1.37 mg/cm 3 neopentane (C 5 H 12 ) gas fill to produce the same plasma electron density as a 1.6 mg/cm 3 He gas-fill used in the high-foot implosion experiments. 12 Targets were driven with ~ 600 kj of 3ω light, delivered in a 12.8 ns tailored high-foot pulse shape. 7,12,13 Because the hohlraum is truncated, the bottom outer beams (44.5 and 50 cone beams) are not used, therefore only 128 of the 192 NIF beams are used in these experiments. As the NIF laser beams hit the interior surface of the hohlraum, the laser energy is absorbed and re-emitted by the Au walls, generating a shaped x-ray drive. This drive couples to the CH shell, ablating material off its surface. The tracer dot, deposited on top of the CH shell, ablates and expands toward the hohlraum LEH, quickly equilibrating with the local plasma conditions. RH simulations using HYDRA 14, including (3200Å thick dot) and excluding the dot, were used to evaluate the T e surrogacy of the tracer dot through comparison of the resulting temperature maps of the hohlraum, at different times, for each case. Simulations indicate the tracer dot does not significantly alter the local plasma conditions. At peak emission the average T e in the location of the dot is comparable to the T e in the simulation excluding the dot, though the dot introduces a small temperature gradient of at most ±200 ev. As the expanded dot heats and is ionized, it emits characteristic K-shell emission that is recorded onto a temporally resolved x-ray spectrometer, called the NIF X-ray Spectrometer (NXS) 15. The NXS views the expanding dot co-axially aligned with the top LEH, through the thinnest dimension of the dot, as shown in Figure 1. The local T e is obtained via measured line ratios and the collisional-radiative atomic physics code SCRAM 16. SCRAM uses a hybrid approach to model level structure based on data from the flexible atomic physics code (FAC) 17. The NXS is a crystal spectrometer that records both time -resolved and time-integrated x-ray spectrum onto an x-ray streak camera 18,19 and an image plate 20, respectively. Both the time integrated and time resolved measurements use Bragg reflected rays from the same crystal; the full crystal x-ray bandwidth is recorded onto the time-integrated channel, while only a subset of the Bragg reflected rays are recorded onto the x-ray streak camera. The image plate (scanned at 25 μm/pixel) and x-ray streak camera photocathode (with varying spatial resolution between μm) are located at 1117 mm and 1188 mm from TCC. Due to differences in detector location and spatial resolution, the spectral resolution is different between the timeresolved and the time-integrated data. The NXS configuration chosen used an elliptically bent Pentaerythritol (PET) 21 crystal, recording the time resolved x-ray spectrum from ~5.5-8 kev, with spectral resolution varying between ev, and the time integrated spectrum from ~ kev, with spectral resolution varying between ev. The NXS time-integrated channel was absolutely calibrated during dedicated shots at the Omega laser facility 15,22. For every experiment an in situ 3

4 calibration is derived by comparison of the absolute time-integrated data and a temporal integral of the time-resolved data. Data were taken on a 10 ns sweep window, using a 250 μm slit in front of a CsI photocathode, resulting in a temporal resolution of ~ 80 ps. The x-ray streak camera timing relative to NIF is determined by cross-timining the data with an absolutely timed diagnostic, timed to within ±15 ps, that has a similar line-of-sight. A streaked spectrum for a 1600 Å Mn-Co dot is shown in Figure 2 (a), with the delivered laser pulse shape shown at the bottom of the image as the solid line. Bright Mn and Co line emission is observed above the x-ray background emission from the Au free-bound continuum. Line emission dominated by the helium-like He α y (1s 2-1s2p 3 P 1 ), He α w (1s 2-1s2p 1 P 1 ), and hydrogen-like Ly α (1s-2p) transitions are recorded for both Mn and Co. To measure line power (J/ns), the local x-ray continuum is first subtracted from the spectrum at each time step after filter transmission corrections and the in situ calibration is applied. The power in each line is then obtained from the calibrated time-resolved spectrum by integration over energy bounds defined by the full-width of a particular line feature of interest. Note that due to the spectral resolution of the instrument there is spectral blending between the main line features of interest (H- and He-like) and satellites. The contribution to the total line power from the satellites, at temperatures reached in these experiments, although small, is included in the SCRAM simulations. Note that for Mn-Co dots there is also spectral blending of the Mn He β (1s 2-1s3p) line emission at kev with the brighter Co He α w (1s 2-1s2p 1 P 1 ) transition at kev. The latter is also accounted for in the SCRAM simulations. Results are shown in Figure 2 (b), for data averaged in time over 800 ps. This averaging time reduces the temporal modulations in the emission flux from the streak data noise, while still preserving temporal evolution information on a hydrodynamic time-scale. The He α emission for both ion transitions follows the main laser drive, while the Ly α emission does not increase until the laser reaches maximum power, with peak emission observed at the end of the main drive, consistent with predictions from RH simulations. The various line ratios used in this analysis have different dependences on the electron temperature (see Figure 3). Model spectra from 0-D SCRAM are calculated on a 54-point temperature grid ranging from kev with a 0.1 kev spacing. All are evaluated with the electron density fixed at n e =10 21 cm -3, since line ratios for observed K-shell emission of Mn and Co are negligibly sensitive to density in this regime. SCRAM spectra are processed the same way measured data is analyzed. The x-ray continuum contribution is subtracted from the modeled spectrum and the line emission is integrated over the same energy bounds as the data (i.e. integrating over main line plus satellites), to provide a relation between a specific measured line ratio and T e, as shown in Figure 3. A two-material tracer layer was used in order to have access to both interstage and isoelectronic line ratios. The tracer materials were chosen such that line ratios would be sufficiently sensitive for temperatures in the 3 to 5 kev range, but would not emit at photon energies close to the Au M- or L-shell emission, while having a ΔZ=2 to provide a sensitive isoelectronic 4

5 line ratio. Tracers were chosen to have an ionization distribution with both helium-like and hydrogen-like ions. The He α w lines are used because they are bright thereby requiring less dopant material, making the dot less perturbative. For the Mn and Co He α lines the optical depths at line center are ~10-20 for these experimental conditions. However, the dot acts as a translucent medium, where the photons undergo scattering and eventually make it out of the emitting volume to the detector For the He α w transitions, at the plasma conditions (T e, n e ) relevant to these experiments, the line destruction mechanisms are negligible and the decay probability of the He α w upper excited level to ground differs negligibly from 1. Line transport calculations using a Monte-Carlo approach show that line scattering will cause deformation of the line profile, without perturbing line fluxes. 26 For non-spherical emitting volumes like the dot tracer used in these experiments, multiple line scattering leads to anisotropy effects where there is an angular dependence on the line brightness, since the photons preferentially escape the thinner dimension more often. 26,29 The degree of anisotropy can vary between excited levels and materials. For isoelectronic line ratios, line transport effects are similar since the same excited level is compared for two materials that vary only in Z. Differences in the strength and anisotropy distribution between the two lines is negligible, as found in detailed Monte-Carlo simulations 26. Additionally, the isoelectronic line ratio enables reducing model uncertainty since the same excited level is calculated in the atomic physics code for both materials, and there is also a partial cancellation of time dependent effects. 30 To verify the latter, steady-state and time-dependent calculations were run using FLYCHK 31, where the time dependent density and temperature profiles were obtained from RH simulations using HYDRA (see Section III). The resulting line intensities for helium-like and hydrogen-like states for both Mn and Co were virtually the same. No time dependent corrections are included in the current T e analysis using either isoelectronic or interstage line ratios in this work. Nonetheless, a more thorough time-dependent analysis using SCRAM is ongoing and will be discussed in a future publication. If time-dependent effects are impacting the interstage line ratio, the different equilibration rates between the Heand H-like ionization means the present steady-state analysis will tend to underpredict the T e during the temperature rise and overpredict T e when the temperature decays after the laser pulse turns off. Because the isoelectronic line ratio comparison is made between two different materials, the T e estimated from it is sensitive to target stoichiometry and the spectrometer calibration. For the experiments described here, the Mn-Co dot composition was measured to within 4% by fitting K-shell absorption edges of a stack of films corresponding to sections of the mask used during coating of the tracer dot on the CH shell. For every target the measured stoichiometry and error is included in the SCRAM table used to relate emission ratio to T e (see Figure 3). In the case of interstage line ratios differences in line-of-sight enhancement caused by geometric anisotropy need to be accounted for between the different ionization states being compared. In particular, the He-like w line is more likely to 5

6 escape toward the face-on detector, where the dot is thinner, than the H-like lines, which are less optically thick at temperatures below 5 kev. No anisotropy corrections are included in the line ratios presented here, and the present isotropic analysis will tend to underpredict the peak temperature. Using interstage line ratios presents the advantage that they are independent of the target stoichiometry since different ionization excited levels are compared for a given tracer element, and are typically less sensitive to calibration uncertainty since lines are often close in energy. Including both time dependence and anisotropy effects in the interstage ratio error analysis (not done here) would increase the uncertainties for temperatures below 4 kev. The dot dynamically samples the local plasma conditions over the region of its expanded volume, as it moves toward the LEH. Consequently, it is equally important to diagnose the location of the dot. To provide a line-of sight for the expanding dot, a 250μm 2300μm aperture was cut on the side of the hohlraum wall (see Figure 1). On the opposite side of the hohlraum a second aperture, 400μm 2000μm, was cut to prevent emission from the Au wall from impeding the measurement of the dot emission. High-density-carbon (HDC) windows, 80 μm thick, are used to fill the apertures to prevent premature closure of the aperture before data is recorded. The HDC window dimensions were 150μm 2200μm for the front window, and 300μm 1900μm for the back window, leaving a 50μm gap around the HDC window and the aperture it sits in. Mylar strips, 6μm thick, bond to the HDC and Au to keep the HDC window in place. The full imaging system uses a pinhole array with either 20- or 35-μm diameter pinholes at a 2X magnification. Data is recorded onto a gated x-ray detector (GXD) 32,33, with spatial resolution of ~50 μm/pixel. The instrument is absolutely timed relative to the NIF laser to within ±50 ps. Gated x-ray images of the dot are broadband with photon energies above ~5 kev, and are temporally integrated over ~100 ps. The entire side window is imaged at discrete times over ~2.3 ns, timed to measure the dot emission during the main drive. Adjacent images on a given framing camera strip are taken every 68 ps. For each image the window bounds are identified [see Figure 4 (a)] and the bottom of the window is used as a reference to provide absolute units relative to TCC. Target metrology provides the initial Z position of the capsule and its radius. Parallax in the data is corrected for in the analysis. The dot location is identified by integrating the signal in the window width for every window length position and fitting a Gaussian profile to determine the centroid and width of the expanded dot, as shown in Figure 4 (b) for a frame at t=10.7 ns. The dot location is known to within ± 19 μm. III. EXPERIMENTAL RESULTS 6

7 Figure 5 shows the measured trajectory of the dot collected over two identical shots, shown as the dark and light blue diamonds. Measured uncertainty, as described in Section II, is within the height of the symbols shown. Data are compared to post-shot RH simulations using HYDRA, shown as the red circles. The target geometry is used as input in the simulations and includes the truncated (open end down) hohlraum, capsule, and tracer dot. The simulations shown here use a flux limiter of 0.15, typically used in simulations for NIF experiments to approximate the non-local heat transport in the hohlraum. 34 The measured incident laser power is used; power loss primarily from stimulated Raman scattering (SRS at about 8%) and a smaller fraction from stimulated Brillouin scattering (SBS at about 2%) is not explicitly included in this simulation. Drive multipliers, used to match the measured drive, were also omitted from the simulation. 35 Data show the predicted HYDRA trajectory overestimates the distance traveled by the dot toward the LEH, where the difference in position between data and simulation decreases as a function of time. The dot position from the original location (capsule top) is lower than simulated by a ~ 35% difference 36 at the beginning of the main drive, and a ~16% difference at the end of the main drive. Though the data and simulation follow a similar trend where a decrease in acceleration is observed toward the end of the drive, the measured dot velocity is higher than predicted by simulations. These results indicate discrepancies between physical processes in the hohlraum and simulations using HYDRA 35 occur earlier in time, affecting the x-ray drive that couples into the ablation region. T e data was taken over five shots using different dot designs, as previously described. T e temporal profiles were reproducible within ± ev for interstage and ± ev for isoelectronic line ratios. Statistical errors are calculated for each line feature as a function of time. Statistical errors include contributions from counting statistics in the streak data (less than ±0.5%), uncertainty in the measured filter transmission (±6-7%), and statistical errors in the local continuum background subtraction. The error in the filter thickness is random because different filters are used on different shots. The error from the local continuum subtraction is a larger contributor for line emission with poorer signal-to-noise ratio. At peak emission these are: ±2% for Mn and Co He α emission, ±7 % for Mn Ly α emission, and ±15% for Co Ly α emission. The statistical uncertainty for each line emission is used to calculate the error in any particular line ratio. The line ratio error is propagated through the corresponding SCRAM table to obtain the statistical error in T e. For interstage line ratios this error varies between ± ev, while for isoelectronic line ratios it ranges between ± ev. The lower sensitivity dlog(r)/dt e of the isoelectronic line ratios, R, amplifies the T e uncertainty. The systematic error in T e was calculated from the relative uncertainty between the lines used for each ratio. For interstage line ratios using He-like and H-like transitions, the instrument off-line calibration and in situ calibration contribute ±7% and ±0.5%. For isoelectronic line ratios of Mn and Co He-like transitions, the instrument off-line calibration and in situ calibration contribute ±9% and ±1.5%. Additionally, uncertainty in the measured Mn-Co dot stoichiometry is included as a 7

8 systematic uncertainty, for each dot batch, and only affects the isoelectronic line ratios. Note this is included as a systematic uncertainty because multiple targets are made from the same coating run and therefore have the same error in stoichiometry. The ±4% measurement uncertainty in target stoichiometry translates to a T e error of ± ev in the temperature ranges relevant to these experiments, as shown in Figure 3. Propagating all of the systematic uncertainties through the corresponding SCRAM table, results in a total systematic uncertainty of ±70 ev and ±600 ev for interstage and isoelectronic ratios. Figure 6 (black curve) shows the T e temporal profile obtained from averaging identical shots. The dotted gray curve at the bottom of each plot shows the requested laser pulse shape. The shaded green region represents the statistical uncertainty and the shaded light purple region represents the total measurement uncertainty where random and systematic errors are added in quadrature. Both line ratios follow similar temporal profiles, where peak T e is observed at the end of the main drive. Resulting peak T e agrees within 200 ev between interstage line ratio [(Mn Ly α )/(Mn He α(y+w) )], Figure 6 (a), and isoelectronic line ratio [(Co He α(y+w) )/(Mn He α(y+w) )], Figure 6 (b), with peak temperatures of 4.3 and 4.1 kev. T e from interstage and isoelectronic line ratios was averaged over 5 and 3 shots respectively. The T e prediction from the HYDRA simulation is shown as the dashed red curve, where the simulation T e is evaluated at HYDRA s predicted dot trajectory, and solid red curve, where the simulation T e is evaluated at the measured dot trajectory. This correction shifts the simulated temperature down by ~ ev. Although the increasing temperature predicted by the simulation agrees with the trend in the measured data, the measured peak T e is hotter compared to the simulation by ~ ev. Assuming the hohlraum plasma fill density is the same in the experiment and the simulation, a rough estimate shows that increasing the hohlraum plasma fill temperature by ev everywhere represents about 15 kj in this sub-scale (80% size) target. In a full-scale hohlraum this increase in temperature would translate to 60 kj of energy not contributing to the hohlraum drive. This might partially explain the measured lower x-ray drive reported previously. 8 The data in Figure 6 identifies a discrepancy in the rate-of-rise to the peak, the peak value, and the rate-of-fall in the simulated T e. Estimates of the mid-z ionization balance equilibration time show that the slower temperature rise and fall in the data cannot be due to a slow response of the mid-z tracer to a faster responding local plasma T e. Active investigations are working on understanding these differences in the context of heat, particle, and radiation transport in the hohlraum. These T e measurements now provide additional experimental constraint on the physics used in the models. IV. CONCLUSIONS X-ray spectroscopy and side imaging of a mid-z tracer dot are used to dynamically sample the plasma T e inside the hohlraum and track the plasma flow as the tracer layer ablates and expands toward the LEH. Temperature measurements are obtained via various line ratios and SCRAM tables, all which agree within 200 ev for peak T e. Measured T e shows these 8

9 hohlraum plasmas reach peak temperatures of ~4.2 kev. In contrast to the data, initial HYDRA simulations over predict the distance the tracer layer travels toward the LEH, and underpredict the measured peak T e by about 500 ev. An elevated measured temperature compared to simulations could be caused by re-absorption of outgoing SRS, inhibited heat flow to the Au wall arising from ion acoustic wave turbulence, hydrodynamic instabilities, or possibly other physics processes. 34 A hotter temperature measured at ~2 mm from TCC likely indicates a hotter temperature at the LEH. Having a hotter plasma temperature at the LEH changes the hohlraum dynamics significantly, in addition to affecting LPI and CBET. Measuring plasma conditions (T e, plasma flow and drive) inside the hohlraum constrains the simulations and provides an experimental platform to test different model parameters and hypotheses. To fully characterize plasma conditions, future work is planned to measure the temperature closer to the LEH where most of the LPI occurs, and where differences in models are most dramatic. Having demonstrated the viability of using x-ray spectroscopy as a means to measure plasma conditions for NIF hohlraums, this platform can be adapted to test conditions in full-scale cryogenic targets, and further push the current understanding of the dynamic processes that drive different hohlraum designs. In general, data analysis shows that systematic experimental uncertainties (from material stoichiometry and spectrometer calibration) are more pronounced for the isoelectronic line ratio analysis, while systematic uncertainties in the emission processes (due to geometric/opacity and time-dependent effects) are more pronounced for interstage ratios. The authors would like to thank the engineering, target fabrication, and operations teams at the National Ignition Facility who made these experiments possible. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA G.H. Miller, E.I. Moses, and C.R. Wuest, Opt Eng 443, (2004). 2 P. Michel, S.H. Glenzer, L. Divol, D.K. Bradley, D. Callahan, S. Dixit, S. Glenn, D. Hinkel, R.K. Kirkwood, J.L. Kline, W.L. Kruer, G.A. Kyrala, S.L. Pape, N.B. Meezan, R. Town, K. Widmann, E.A. Williams, B.J. MacGowan, J. Lindl, and L.J. Suter, Phys. Plasmas 17, (2010). 3 J.D. Moody, P. Michel, L. Divol, R.L. Berger, E. Bond, D.K. Bradley, D.A. Callahan, E.L. Dewald, S. Dixit, M.J. Edwards, S. Glenn, A. Hamza, C. Haynam, D.E. Hinkel, N. Izumi, O. Jones, J.D. Kilkenny, R.K. Kirkwood, J.L. Kline, W.L. Kruer, G.A. Kyrala, O.L. Landen, S. LePape, J.D. Lindl, B.J. MacGowan, N.B. Meezan, A. Nikroo, M.D. Rosen, M.B. Schneider, D.J. Strozzi, L.J. Suter, C.A. Thomas, R.P.J. Town, K. Widmann, E.A. Williams, L.J. Atherton, S.H. Glenzer, and E.I. Moses, Nat. Phys. 8, 344 (2012). 4 J.D. Moody, P. Datte, K. Krauter, E. Bond, P.A. Michel, S.H. Glenzer, L. Divol, C. Niemann, L. Suter, N. Meezan, B.J. MacGowan, R. Hibbard, R. London, J. Kilkenny, R. Wallace, J.L. Kline, K. Knittel, G. Frieders, B. Golick, G. Ross, K. Widmann, J. Jackson, S. Vernon, and T. Clancy, Rev. Sci. Instrum. 81, 10D921 (2010). 9

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12 31 H.-K. Chung, M.H. Chen, W.L. Morgan, Y. Ralchenko, and R.W. Lee, High Energy Density Phys. 1, 3 (2005). 32 J.A. Oertel, R. Aragonez, T. Archuleta, C. Barnes, L. Casper, V. Fatherley, T. Heinrichs, R. King, D. Landers, F. Lopez, P. Sanchez, G. Sandoval, L. Schrank, P. Walsh, P. Bell, M. Brown, R. Costa, J. Holder, S. Montelongo, and N. Pederson, Rev. Sci. Instrum. 77, 10E308 (2006). 33 L.R. Benedetti, J.P. Holder, M. Perkins, C.G. Brown, C.S. Anderson, F.V. Allen, R.B. Petre, D. Hargrove, S.M. Glenn, N. Simanovskaia, D.K. Bradley, and P. Bell, Rev. Sci. Instrum. 87, (2016). 34 M.D. Rosen, H.A. Scott, D.E. Hinkel, E.A. Williams, D.A. Callahan, R.P.J. Town, L. Divol, P.A. Michel, W.L. Kruer, L.J. Suter, R.A. London, J.A. Harte, and G.B. Zimmerman, High Energy Density Phys. 7, 180 (2011). 35 O.S. Jones, C.A. Thomas, P.A. Amendt, G.N. Hall, N. Izumi, M.A. Barrios, L.F. Berzak Hopkins, H. Chen, E.L. Dewald, D.E. Hinkel, A.L. Kritcher, M.M. Marinak, N.B. Meezan, J.L. Milovich, J.D. Moody, A.S. Moore, S.M. Sepke, D.J. Strozzi, and Turnbull, D. P., Sumbitted IFSA 2015 Conf. Proc. (2016). 36 Percent difference is defined here as, 100 * Data- Simulation /Simulation Figure Captions Figure 1: (color online) Dot spectroscopy targets use a truncated hohlraum with a side slit that permits observation of the expanded dot. The dot tracer layer is deposited on top of the capsule and expands toward the LEH. Figure 2: (color online) (a) Streaked X-ray spectrum from a 1600 Å thick Mn-Co tracer dot, He- and H-like emission is recorded for both Mn and Co. (b) The time-resolved line emission, integrated over the line width, is obtained after the streaked spectrum is calibrated and the local x-ray continuum is subtracted. Shaded regions represent total error in measured line power. Figure 3: (color online) Relationship between line ratio and T e as derived by SCRAM model (spectra were evaluated from kev with an n e = cm -3 ) for an interstage and an isoelectronic line ratio. The shaded orange region for the isoelectronic line ratio depicts uncertainty due to target stoichiometry measurements for the Mn-Co tracer dots. Figure 4: (color online) A side slit on the hohlraum enables tracking the location of the tracer layer as it expands toward the LEH. (a) Images recorded at different times are processed to identify the slits bounds. Here the vertical direction corresponds to the position Z along the hohlraum axis, where the LEH is above the top edge of the slit bounds. (b) For each image, the location of the dot is fitted using a Gaussian profile, recording both the location and expansion of the tracer layer. 12

13 Figure 5: (color online) Measured dot trajectory (blue diamonds) compared with HYDRA simulation (red circles) shows the simulation over predicts the location of the tracer layer as it moves toward the LEH. Figure 6: (color online) Measured average electron temperature (black solid curve) using an interstage line ratio (a), averaged over 5 shots, and an isoelectronic line ratio (b), averaged over 3 shots. The total error, including both random and systematic uncertainty, is shown as the shaded purple region; the random error contribution is shown as the green shaded region. The dashed gray line corresponds to the requested laser pulse shape. Red lines are the predicted T e from HYDRA simulations, using nominal simulation dot trajectory (dashed) and evaluating T e at the measured dot trajectory (solid), Peak T e measured by these ratios agree within 200 ev, and occurs at the end of the main drive. 13

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