KMS Fusion (United States)

Grid image refractometry (GIR) is proposed as a technique for determining the two-dimensional density profiles of long scale-length laser-produced plasmas. Its distinctive feature is that an optical probe beam is broken up into ‘‘rays’’ by being passed through a grid before traversing the plasma. The refraction angles of the rays are measured by imaging the plasma at two or more object planes and are integrated to yield the phase front. For cylindrically symmetric plasmas the density profile is then determined using Abel inversion. The feasibility of GIR is illustrated by an experiment in which a thick CH target was irradiated with ∼100 J of 527 nm radiation and diagnosed with a 20 ps, 263 nm probe. The resulting density profile is substantially larger than any that have previously been reported using interferometry and compares quite closely with hydrodynamic simulations.

The development of intense x-ray sources and sensitive gated detectors is needed for the diagnosis of ICF implosions. A laser plasma x-ray source, with an instantaneous power of 200–500 MW in the range 2.7–3 keV, was used to evaluate a specific detector configuration. The detector, consisting of a PET crystal and a MCP framing camera, was used to obtain radiographs of NaCl-doped targets. Applications are currently signal limited, indicating the need for brighter x-ray sources and/or more sensitive detection systems.

Thin solid samples of deuterium–tritium (DT) have been seen to sublime and redistribute within spherical inertial fusion targets due to the heat generated by beta decay. We have frozen thin DT samples within glass shells of 890 and 3750 μm diameter, and observed the evolution of the solid towards more symmetric distributions using real time holographic interferometry. Holographic interferometry provides more sensitivity than direct imaging or classical interferometry to observe the thin (10–30 μm) solid samples in these shells.

Spherical implosion experiments have been performed using shaped laser pulses at ${\ensuremath{\lambda}}_{0}$=0.53 \ensuremath{\mu}m to illuminate deuterium-filled polyvinyl alcohol (PVA) spherical shells. The deuterium fuel was cryogenically cooled to form a uniform frozen fuel layer. Plasma diagnostics included time-resolved x-ray radiography and multiframe holographic interferometry. These and other measurements in conjunction with hydrodynamic simulations establish the importance of shaped laser pulses in achieving high fuel compressions.

All advanced inertial confinement fusion (ICF) targets will be built with cryogenic thermonuclear fuel configurations. This paper reviews the ICF concept using frozen fuel, with emphasis on the conditions required for efficient energy production, some details of the implosion process, a brief discussion of certain sources of potential inefficiencies, and estimates of target fabrication requirements.

We report on the measurement of density-sensitive electric quadrupole transitions in neonlike molybdenum and silver laser-produced plasmas. These observations are unique in that they represent data which are simultaneously space and time resolved. The electron densities were determined using holographic interferometry. We test the predicted density sensitivity of the electric quadrupole transitions and find excellent agreement with calculations using a detailed, steady-state, collisional-radiative model of the neonlike charge state.

Time-resolved electron temperature and line-intensity profiles in laser-produced plasmas have been measured for the first time with an x-ray framing camera. Temperature profiles measured from the slope of the free-bound recombination continuum in AlXIII ions are significantly lower than hydrodynamic model calculations. Simultaneous interferometric density measurements are in much closer agreement with computer simulations. Spectral line-intensity profiles have also been measured and cannot be described by standard collisional radiative equilibrium models.