Ultrahigh intensity lasers can potentially be used in conjunction with conventional fusion lasers to ignite inertial confinement fusion (ICF) capsules with a total energy of a few tens of kilojoules of laser light, and can possibly lead to high gain with as little as 100 kJ. A scheme is proposed with three phases. First, a capsule is imploded as in the conventional approach to inertial fusion to assemble a high-density fuel configuration. Second, a hole is bored through the capsule corona composed of ablated material, as the critical density is pushed close to the high-density core of the capsule by the ponderomotive force associated with high-intensity laser light. Finally, the fuel is ignited by suprathermal electrons, produced in the high-intensity laser-plasma interactions, which then propagate from critical density to this high-density core. This new scheme also drastically reduces the difficulty of the implosion, and thereby allows lower quality fabrication and less stringent beam quality and symmetry requirements from the implosion driver. The difficulty of the fusion scheme is transferred to the technological difficulty of producing the ultrahigh-intensity laser and of transporting this energy to the fuel.

Diffusive x-ray-driven heat waves are found in a variety of astrophysical and laboratory settings, e.g. in the heating of a hohlraum used for ICF, and hence are of intrinsic interest. However, accurate analytic diffusion wave (also called Marshak wave) solutions are difficult to obtain due to the strong non-linearity of the radiation diffusion equation. The typical approach is to solve near the heat front, and by ansatz apply the solution globally. This works fairly well due to "steepness" of the heat front, but energy is not conserved and it does not lead to a consistent way of correcting the solution or estimating accuracy. We employ the steepness of the front through a perturbation expansion in E = b/(4+a), where the internal energy varies as TB and the opacity varies as T". We solve using an iterative approach, equivalent to asymptotic methods that match outer (away from the front) and inner (near the front) solutions. Typically E < 0.3. Calculations are through first order in E and are accurate to-lo%, which is comparable to the inaccuracy from assuming power laws for material properties. We solve for supersonic waves with arbitrary drive time history, including the case of a rapidly cooling surface, and generalize the method to arbitrary temperature dependence of opacity and internal energy. We also solve for subsonic waves with drive temperature varying as a

We describe the injtial experiments to study the Z-pinch-drjven hohlraum ligh-yield jnertjal confinement fusion (ICF) concept of Hammer and Porter [J. H. Hammer et al., Phys. Plasmas, 6, 2129]. We show that the relationship between measured pinch power, hohlraum temperature, and secondary hohlraum coupling ("hohlraurn energetic") is well understood from O-D semi-analytic, 2-D viewfactor, and 2-D radiation magneto-hydrodynamics models. These experiments have shown the highest x-ray powers coupled to any Z-pjnch driven secondary (2655 TW), indicating the concept could scale to fusion yields of 400 MJ. We have also developed a novel, single-sided power feed, double-pinch driven secondary that meets the pinch simultaneity requirements for polar radiation symmetry. This source wjll perrnjt investigation of the pinch power balance and hohh-aum geometry requirements for ICF reIevant secondary radiation symmetry, leading to a capsule implosion capability on the Z accelerator [R. B.Spielman. er al.. Phys. Plasmas. 5,2105Plasmas. 5, (1998].

Calculations are presented for a high yield inertial fusion design, employing indirect drive with a double-ended z-pinch-driven hohlraum radiation source. A high current (∼60 MA) accelerator implodes z pinches within an enclosing hohlraum. Radial spoke arrays and shine shields isolate the capsule from the pinch plasma, magnetic field, and direct x-ray shine. Our approach places minimal requirements on z-pinch uniformity and stability, usually problematic due to magneto-Rayleigh–Taylor instability. Large inhomogeneities of the pinch and spoke array may be present, but the hohlraum adequately smooths the radiation field at the capsule. Simultaneity and reproducibility of the pinch x-ray output to better than 7% are required, however, for good symmetry. Recent experiments suggest a pulse shaping technique, through implosion of a multishell z pinch. X-ray bursts are calculated and observed to occur at each shell collision. A capsule absorbing 1 MJ of x rays at a peak drive temperature of 210 eV is found to have adequate stability and to produce 400 MJ of yield. A larger capsule absorbs 2 MJ with a yield of 1200 MJ.

The application of a novel but practical technique for central fuelling of reactor-grade tokamak plasmas by compact torus (CT) plasma rings driven by a coaxial accelerator is examined. It is emphasized that this is the only advanced method of controlled and localized deep penetration fuelling which can be developed in the near term and which is already applied in a currently operating experimental system. Assessment of the dynamics of the CT as it traverses the plasma requires quantification of several interrelated constraints, including ring decay, tilting, field line reconnection, deceleration in the external field gradient and ring expansion/contraction. A self-consistent, radial zoning scheme is employed to model the transport of the CT to the desired plasma deposition point. It is demonstrated that the injection velocity requirements are usually dominated by CT tilting and reconnection with the external toroidal field of the tokamak. The implications for CT fuel transport around the reconnection point are then examined. The application of this formalism to the TIBER Engineering Test Reactor permits the parameterization of fuelling requirements in terms of injection velocity, fuel mass, penetration distance, CT dimensions and repetition rate. The hardware implications for near-term applications are also assessed.