In inertial confinement fusion (ICF), the possibility of ignition or high energy gain is largely determined by our ability to control the Rayleigh-Taylor (RT) instability growth in the target. The exponentially amplified RT perturbation eigenmodes are formed from all sources of the target and radiation non-uniformity in a process called seeding. This process involves a variety of physical mechanisms that are somewhat similar to the classical Richtmyer-Meshkov (RM) instability (in particular, most of them are active in the absence of acceleration), but differ from it in many ways. In the last decade, radiographic diagnostic techniques have been developed that made direct observations of the RM-type effects in the ICF-relevant conditions possible. New experiments stimulated the advancement of the theory of the RM-type processes. The progress in the experimental and theoretical studies of such phenomena as ablative RM instability, re-shock of the RM-unstable interface, feedout and perturbation development associated with impulsive loading is reviewed.

Along with laser-indirect (X-ray)-drive and magnetic-drive target concepts, laser direct drive is a viable approach to achieving ignition and gain with inertial confinement fusion. In the United States, a national program has been established to demonstrate and understand the physics of laser direct drive. The program utilizes the Omega Laser Facility to conduct implosion and coupling physics at the nominally 30-kJ scale and laser–plasma interaction and coupling physics at the MJ scale at the National Ignition Facility. This article will discuss the motivation and challenges for laser direct drive and the broad-based program presently underway in the United States.

We performed integrated experiments on impact ignition, in which a portion of a deuterated polystyrene (CD) shell was accelerated to about 600 km/s and was collided with precompressed CD fuel. The kinetic energy of the impactor was efficiently converted into thermal energy generating a temperature of about 1.6 keV. We achieved a two-order-of-magnitude increase in the neutron yield by optimizing the timing of the impact collision, demonstrating the high potential of impact ignition for fusion energy production.

The Nike krypton fluoride laser ͓S. P. Obenschain, S. E. Bodner, D. Colombant, et al., Phys. Plasmas 3, 2098 ͑1996͔͒ is used to accelerate planar plastic foils to velocities that for the first time reach 1000 km/s. Collision of the highly accelerated deuterated polystyrene foil with a stationary target produces ϳGbar shock pressures and results in heating of the foil to thermonuclear temperatures. The impact conditions are diagnosed using DD fusion neutron yield, with ϳ10 6 neutrons produced during the collision. Time-of-flight neutron detectors are used to measure the ion temperature upon impact, which reaches 2-3 keV.

We present experimental results and simulations that study the effects of thin metallic layers with high atomic number (high-Z) on the hydrodynamics of laser accelerated plastic targets. These experiments employ a laser pulse with a low-intensity foot that rises into a high-intensity main pulse. This pulse shape simulates the generic Report Documentation PageForm Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. We present experimental results and simulations that study the effects of thin metallic layers with high atomic number (high-Z) on the hydrodynamics of laser accelerated plastic targets. These experiments employ a laser pulse with a low-intensity foot that rises into a high-intensity main pulse. This pulse shape simulates the generic shape needed for high-gain fusion implosions. Imprint of laser nonuniformity during start up of the low intensity foot is a well-known seed for hydrodynamic instability. We observe large reductions in hydrodynamic instability seeded by laser imprint when certain minimum thickness gold or palladium layers are applied to the laser-illuminated surface of the targets. The experiment indicates that the reduction in imprint is at least as large as that obtained by a 6 times improvement in the laser uniformity. We present simulations supported by experiments showing that during the low intensity foot the laser light can be nearly completely absorbed by the high-Z layer. X-rays originating from the high-Z layer heat the underlying lower-Z plastic target material and cause large buffering plasma to form between the layer and the accelerated target. This long-scale plasma apparently isolates the target from laser nonuniformity and accounts for the observed large reduction in laser imprint. With onset of the higher intensity main pulse, the high-Z layer expands and the laser light is transmitted. This technique will be useful in reducing laser imprint in pellet implosions and thereby allow the design of more robust targets for high-gain laser fusion. Prescribed by ANSI Std Z39-18 2 shape needed for high-gain fusion implosions. Imprint of laser nonuniformity during start up of the low intensity foot is a well-known seed for hydrodynamic instability. We observe large reductions in hydrodynamic instability seeded by laser...