High temperature of laser-compressed shells measured with Kr
34
and Kr
35
x-ray lines
B. Yaakobi, F. J. Marshall, and R. Epstein
Laboratory for Laser Energetics, University of Rochester, 250 East River Road, Rochester, New York 14623-1299
Received 4 June 1996
High electron temperatures 3–4 keV have been achieved by imploding shells filled with a deuterium-
krypton mixture on the OMEGA laser system, in agreement with hydrodynamic simulations. The temperature
was deduced from the high-energy continuum slope in the range 8–20 keV, and from the intensity ratio of
Kr
35+
to Kr
34+
x-ray lines. These results show the feasibility of obtaining higher temperatures than previously
achieved in laser implosions and studying them using spectroscopy of sub-Å x-ray lines and continuum.
S1063-651X9606611-1
PACS numbers: 52.50.Jm
The achievement of high temperatures with laser-
imploded targets is of interest for studying the physics of
laser fusion and other plasmas. Simulations 1 show that
high electron temperatures of up to 5 keV should be
achieved with laser systems such as the OMEGA system at
the Laboratory for Laser Energetics 2 using relatively thin-
shell targets. These temperatures should occur at modest
compression densities 1–5 g/cm
3
, and the ion tempera-
ture should peak above 10 keV. These simulations also show
that the addition of a small amount of krypton gas 0.03
atm to the hydrogenic fuel should produce strong emission
of Kr
35+
and Kr
34+
x-ray lines, while reducing the
compressed-fuel temperature by only a negligible amount.
We report on a series of experiments in which these predic-
tions have been demonstrated: high electron temperatures
3–4 keV were indeed measured using intense heliumlike
and hydrogenlike krypton lines as well as high-energy con-
tinuum. High ion temperatures 13 keV were likewise de-
duced from the energy spectrum of the neutrons produced by
the deuterium-deuterium DD reaction and reported earlier
3.
Results from the present experiments are shown from two
target shots for which the experimental parameters are listed
in Table I. The shells in these experiments were of CH poly-
mer and the laser pulse had a Gaussian shape of 0.6 ns full
width at half maximum. In the first shot, a Si111 diffracting
crystal was used, tuned to detect the spectral range 7–13
keV, while in the second shot a LiF200 crystal was used,
tuned to the range 12–20 keV. Figures 1 and 2 show a com-
parison between the measured and simulated spectra from
the two Kr-doped target shots listed in Table I. Figures 1a
and 2a show the uncalibrated experimental spectrum in
film density units. Figures 1b and 2b show the time- and
space-integrated simulations of the same spectra, by the hy-
drodynamic code LILAC 4. The unit keV/keV refers to
radiation energy per unit of photon energy. The simulated
spectrum is plotted on a linear scale, in line with the fact that
film density and exposure are approximately linear for these
photon energies see below. Instrumental broadening of the
lines has been included in the simulation. The wavelengths
of the krypton lines marked in Figs. 1 and 2 are known from
the literature 5. The He- line (1 s 2 p
1
P
1
-1 s
21
S
0
) is ac-
companied by lithiumlike and berylliumlike dielectronic sat-
ellites on its lower-energy side, which are barely resolved in
Fig. 1a; a high-resolution spectrum of this group of lines
was obtained using an electron beam ion trap facility 6.
FIG. 1. a Experimental spectrum from Kr-doped, DD-filled
target shot 4952; b LILAC simulation of the same spectrum. The
unit keV/keV refers to radiation energy per unit of photon energy.
The continuum slope in the range of 8–12 keV implies an electron
temperature of T
e
=3.2 keV. Instrumental broadening of the calcu-
lated lines has been included. The simulation does not include the
satellite lines on the low-energy side of the He- line.
TABLE I. Experimental parameters of the two target shots used
in the krypton spectra analysis.
Shot no.
Target
diameter
m
Target
thickness
m
DD
pressure
atm
Krypton
pressure
atm
Laser
energy
kJ
4952 870 10 10 0.03 23.6
5110 874 12.4 10 0.03 29.5
PHYSICAL REVIEW E NOVEMBER 1996 VOLUME 54, NUMBER 5
54 1063-651X/96/545/58483/$10.00 5848 © 1996 The American Physical Society