Thermal Temperature Measurements of Inertial Fusion Implosions

L. C. Jarrott, B. Bachmann, T. Ma, L. R. Benedetti, F. E. Field, E. P. Hartouni, R. Hatarik, N. Izumi, S. F. Khan, O. L. Landen, S. R. Nagel, R. Nora, A. Pak, J. L. Peterson, M. B. Schneider, P. T. Springer, and P. K. Patel

Phys. Rev. Lett. 121, 085001 – Published 22 August 2018

Abstract

Accurate measurement of the thermal temperature in inertially confined fusion plasmas is essential for characterizing ignition performance and validating the basic physics understanding of the stagnation conditions. We present experimental results from cryogenic deuterium-tritium implosions on the National Ignition Facility using a differential filter spectrometer designed to measure the thermal electron temperature from x-ray continuum emission from the stagnated plasma. Furthermore, electron temperature measurements, used in conjunction with the Doppler-broadened DT neutron spectra, allow one to infer the partition of energy in the hot spot between internal energy and unconverted kinetic energy.

Received 20 April 2018
Revised 14 May 2018

DOI:https://doi.org/10.1103/PhysRevLett.121.085001

Physics Subject Headings (PhySH)

Indirect drive Inertial confinement fusion

Plasma Physics

Authors & Affiliations

L. C. Jarrott^*, B. Bachmann, T. Ma, L. R. Benedetti, F. E. Field, E. P. Hartouni, R. Hatarik, N. Izumi, S. F. Khan, O. L. Landen, S. R. Nagel, R. Nora, A. Pak, J. L. Peterson, M. B. Schneider, P. T. Springer, and P. K. Patel

Lawrence Livermore National Laboratory, Livermore, California 94550, USA

^*jarrott1@llnl.gov

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Vol. 121, Iss. 8 — 24 August 2018

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Images

Figure 1
Titanium differential filter spectrometer diagnostic layout. (Left) Bremsstrahlung x-ray emission from the hot spot at a characteristic temperature, leaves the hot spot (dotted black line) and is attenuated by the fuel shell and remaining ablator (solid black line). It then passes through the differential filters of 270, 550, and $920 μ m$ , with each filter allowing a different mean x-ray energy to pass through as shown by the normalized sensitivity. (Middle) The x-ray signal from each filter is then deposited onto IP film. The IP signal from each filter is then used to reconstruct the x-ray emission spectra escaping the hot spot and passing through the fuel shell and ablator. (Right) Monte Carlo analysis of a particular cryogenic experiment on the NIF using uncertainties associated with filter thickness $err (F)$ , optical depth $err (O)$ , IP spectral response $err (I)$ , and signal error $err (S)$ are sequentially added in quadrature and used to create a distribution of best-fit inferred x-ray electron temperatures.
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Figure 2
Ion and electron temperature measurements from a recent cryogenic DT implosion on NIF. The bottom axis shows the polar viewing angle for each diagnostic. All five NTOF diagnostics infer a higher hot-spot temperature compared to the x-ray electron temperature measurement by as much as 900 eV, similar to previous speculation of the temperature overprediction.
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Figure 3
Comparison of emissivity-weighted electron temperature, neutron-weighted electron temperature, and neutron-weighted ion temperature from simulation. (a) Neutron-weighted electron temperature plotted against emissivity-weighted electron temperature showing weighting differences of measurements. Red and blue lines correspond to fit to simulation database and analytic solution Eqs. (4) and (6). (b) Neutron-weighted ion temperature plotted against neutron-weighted electron temperature showing species temperature differences. (c) Neutron-weighted ion temperature plotted against emissivity-weighted electron temperature which is used to compare TiDFS measurements to NTOF measurements and extract RKE.
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Figure 4
Comparison of the emissivity-weighted electron temperature inferred from x-ray continuum measurements with neutron-weighted ion temperature measurements inferred from NTOF ion velocity variance measurements. A zero-RKE contour of the relation between the x-ray electron temperature and the neutron-weighted ion temperature is shown in dark blue to illustrate expected differences in $T_{i}^{NW}$ and $T_{e}^{EW}$ .
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