Publications

In the past three years, tremendous strides have been made in x-ray production using high-current z-pinches. Today, the x-ray energy and power output of the Z accelerator (formerly PBFA II) is the largest available in the laboratory. These z-pinch x-ray sources have great potential to drive high-yield inertial confinement fusion (ICF) reactions at affordable cost if several challenging technical problems can be overcome. Technical challenges in three key areas are discussed in this paper: (1) the design of a target for high yield, (2) the development of a suitable pulsed power driver, and (3) the design of a target chamber capable of containing the high fusion yield.

In the past thirty-six months, great progress has been made in x-ray production using high-current z-pinches. Today, the x-ray energy and power output of the Z accelerator (formerly PBFA-II) is the largest available in the laboratory. These z-pinch x-ray sources have the potential to drive high-yield ICF reactions at affordable cost if several challenging technical problems can be overcome. In this paper, the recent technical progress with Z-pinches will be described, and a technical strategy for achieving high-yield ICF with z-pinches will be presented.

In the past thirty-six months, tremendous strides have been made in x-ray production using high-current z-pinches. Today, the x-ray energy (1.9 MJ) and power (200 TW) output of the Z accelerator (formerly PBFA-II) is the largest available in the laboratory. These z-pinch x-ray sources are being developed for research into the physics of high energy density plasmas of interest in weapon behavior and in inertial confinement fusion. Beyond the Z accelerator current of 20 MA, an extrapolation to the X-1 accelerator level of 60 MA may have the potential to drive high-yield ICF reactions at affordable cost if several challenging technical problems can be overcome. New developments have also taken place at Sandia in the area of high current, mm-diameter electron beams for advanced hydrodynamic radiography. On SABRE, x-ray spot diameters were less than 2 mm, with a dose of 100R at 1 meter in a 40 ns pulse.

Recent results from light ion fusion experiments on the Particle Beam Fusion Accelerator (PBFA II) are reported. Intense proton beams have been used to drive two different types of targets. In the thermal source targets, the proton beam heated a low-density foam. The specific power deposition of the proton beam in the foam exceeded 100 TW/gm. In the spherical hydrodynamic targets, the proton beam heated a thin-walled deuterium gas-filled target directly, producing a radial convergence of the deuterium of about 6. In order to increase the specific power deposition in the target, we are developing focused lithium beams. A preformed lithium ion source has been produced using a two-step laser evaporation and ionization approach. This preformed source provides the basis for experiments being planned to reduce the divergence of the lithium beam, a critical step in demonstrating the feasibility of light ion fusion.

The first major round of target experiments driven by intense light ion beams was conducted during August and September 1991. In these experiments, intense proton beams were used to drive two different types of targets. We attempted to obtain information on the two separable issues of ion deposition and implosion hydrodynamics. Ion deposition was studied using a low density hydrocarbon foam contained within a cylindrical gold shell. Implosion hydrodynamics was studied using an ion driven exploding pusher configuration in which the ion beam heated the shell directly, exploding it both outward and inward. One of the main objectives of the experiments was to determine the extent to which we could diagnose the ion deposition and the subsequent behavior of the targets. The diagnostics included time-integrated and time-resolved x-ray pinhole cameras, time-integrated and time-resolved grazing incidence x-ray spectrometers, an 11-channel filtered x-ray diode (XRD) array, an 11-channel PIN diode array, an energy-resolved 1-dimensional imaging x-ray streak camera, a transmission grating spectrometer, an elliptical crystal x-ray spectrograph, and a bolometer. Intense beam diagnostics included an ion movie camera and an off-axis 1D slit imaging magnetic spectrograph for obtaining Rutherford-scattered ion images, momenta, and ion power densities.

Intense light ion beams are being developed to drive inertial confinement fusion (ICF) targets. Recently, intense proton beams have been used to drive two different types of targets in experiments on the Particle Beam Fusion Accelerator. The experiments focused separately on ion deposition physics and on implosion hydrodynamics. In the ion deposition physics experiments, a 3--4 TW/cm{sup 2} proton beam heated a low-density foam contained within a gold cylinder with a specific power deposition exceeding 100 TW/gm for investigating ion deposition, foam heating, and generation of x-rays. The significant results from these experiments included the following: the foam provided an optically thin radiating region, the uniformity of radiation across the foam was good, and the foam tamped the gold case, holding it in its original position for the 15 ns beam pulse width.