The Heavy-Ion Fusion Systems Assessment project is nearing completion of a two-year effort. The resulting system modelwill be used to set directions for future target design work.

Major uncertainties in target design were studied using thecost of electricity as a figure of merit. Net electric power was fixed at 1000 MW to eliminate large effects due to economies of scale. The system is relatively insensitive to target gain, factors of three changes in gain resulting in 8 to 12% changes in electricity cost. Possible increased peak power requirements pose only a small cost risk, but require many more beamlets for transport. A shortening ofthe required ion range causes both cost and beamlet difficulties. A factor of 4 decrease in the required range at a fixed driver energy increases electricity cost by 44% and raises the number of beamlets to 240. Finally, the heavy ion fusion system can accommodate large increases in target costs. Thus, to address the major uncertainties, target design should concentrate on requirements for ion range andpeak driver power.

Analytical study of the linear stability of one-dimensional double layers in nonmagnetized plasmas based on the solution of the Vlasov–Poisson system is presented. Electromagnetic effects are not included. A self-consistent equilibrium electrostatic potential Φ0(z) that monotonically increases from a low level at z = − ∞ to a high level at z = + ∞ is assumed. We model this potential as a piecewise continuous function of z and we assume that Φ0(z) has constant values for − ∞ z ≤ 0 and L ≤ z < ∞, L being the thickness of the double layer. The BGK states for the Vlasov–Poisson system provide an explicit expression for the velocity distribution of the reflected electrons required for the particular double layer configuration. The stability of the double layers is studied via the linearized Vlasov and Poisson equations using the WKB approximation.

Multiple-pass amplifiers were configured from Nd:glass rods using polarization and angular coupling techniques. Very high gain (>600) single beam triple-pass booster stages and high gain (30 or 15) single or double-beam double-pass amplifiers were combined to construct a very cost effective high-power (50 GW) pulsed laser system. These techniques were also effectively applied to smaller compact high repetition-rate systems.

Diode experiments that trigger the anode plasma formation by external radiation have been carried out with the goal of producing a pure beam of metallic ions. The anode of a race-track-type MID, which is coated with a sodium film in situ by vapor deposition, is synchronously irradiated by radiation emitted from a vacuum diode. Pure beams of Na+ are extracted only under operation with the radiation trigger. The current density reaches the Child–Langmuir limit.

Polarization dependent light absorption in laser produced plasmas of small focal diameters (28 μm full 1/e2 width) has been investigated simultaneously in five different channels of observation: specular reflection of the laser light, second harmonic (2ω) generation, charge and velocity distribution of the emitted ions and ablation pressure to the target. The experiments have been performed using a Nd-YAG mode locking pulse (λ = 1·06 μm, λ = 45 ps) which has been focused onto plane, thick plexiglass (C8H5O2) n disks to intensities up to 1014 W/cm2. As a result of the small focal spot size, a very small density scale length of 0·6 μm is derived from the resonance curves, consistently, for all channels of diagnostics.

Previous work on the evolution of weak double layers in a hydrogen plasma has been extended to include H+ and O+ with relative drift. It has been shown (Bergmann & Lotko 1986) that the relative drift between hydrogen and oxygen ions due to a quasistatic parallel electric field gives rise to a strong linear fluid instability which dominates the ion acoustic mode at the bottom of the auroral acceleration region. This ion–ion instability can modify ion distributions at lower altitudes and the subsequent nonlinear evolution of weak double layers at higher altitudes in the ion acoustic regime. We have found that ion hole formation can occur for smaller relative electron-ion drifts than seen in previous simulations, due to the hydrogen-oxygen two-stream instability. This results in local modification of the ion distributions in phase space, and a partial filling of the valley between the hydrogen and oxygen peaks, which would be expected at higher altitudes on auroral field lines. It is shown that the observed velocity diffusion does not necessarily preclude ion hole and double layer formation in hydrogen in the ion acoustic regime. These simulation results are consistent with the experimentally measured persistence of separate hydrogen and oxygen peaks, and the observation of weak double layers above an altitude of 3000 km on auroral field lines.

Theoretical treatments of the stopping power are reviewed and problems necessary to extend these treatments to high temperature and high density materials are discussed. Physically important parameters which govern the stopping power properties are indicated. The average equilibrium charge for a gaseous medium is one of the important parameters in the stopping power and the charge-exchange processes involved are discussed. The effective charge is described in terms of a relation between the average equilibrium charge and the effective charge. The atomic energy levels for high density and high temperature matter are also included in the stopping power formula.

Actual calculations of the stopping power are made for Pb ions passing through the HIBLIC-target. Range profiles are estimated for Xe and U ions in an ionized Al target for temperatures T = 0 to T = 1290 eV using the Brueckner, Senbetu & Metzler (1982) theory based on a dielectric response function. Results are compared with those of Northcliffe & Schilling (1970), Ziegler (1980), and Hubert et al. (1980). In order to include dynamic local-field corrections in the dielectric function, a model is proposed similar to a two component plasma.

Sensitivity analysis is a powerful first-order mathematical technique that identifies the major reactions, the effects of errors in rate constants, pressure effects, and temperature effects in a plasma chemistry type model. Several methods of sensitivity analysis have been discussed in the literature. This paper describes the successful implementation of the state transition matrix method to the sensitivity analysis of a plasma chemistry model using both e-beams and ions for excitation. The ion excited plasma study is important to the field of nuclear-pumped lasers. This model examines 8 species and 37 reactions.

Inertial confinement fusion using light ion beams requires fast rise time, high power drivers. One technique to enhance a conventional pulsed power generator is to use a plasma erosion opening switch (PEOS) between the generator and the ion diode. Ideally, the PEOS conducts current until a current threshold is reached, then rapidly opens and delivers the inductively stored energy to the load on a short time scale. Experiments at the Naval Research Laboratory (NRL) used a PEOS to improve the Gamble II current rise time from 60 ns to 10 ns at 1 MA. Load voltages over 4 MV have been obtained (>2× the matched load voltage).

Based on these experiments and theoretical predictions, a PEOS system has been incorporated into the PBFA II experiment at Sandia National Laboratories (SNL). The PEOS on PBFA II is ultimately to provide a 6 to 8-MA, 30-MV pulse with 10-ns rise time into an “applied B” ion diode. This is a large extrapolation of present experiments. The PEOS system on PBFA II is described here and theoretical predictions are given.

The discussion of parallel electric fields in the earth's magnetosphere has undergone a notable shift of emphasis in recent years, away from wave-generated anomalous resistivity towards the more large-scale effects of magnetic confinement of current carrying plasmas. This shift has been inspired in large part by the more extensive data on auroral particle distribution functions that have been made available, data that may often seem consistent with a dissipation-free acceleration of auroral electrons over an extended altitude range.

Efforts to interpret these data have brought new vigor to the concept that a smooth and static electric field can be self-consistently generated by suitable pitch-angle anisotropies among the high-altitude particle populations, different for electrons and ions, and that such an electric field is both necessary and sufficient to maintain the plasma in a quasi-neutral steady state. This paper reviews and criticizes certain aspects of this concept, both from a general theoretical standpoint and from the standpoint of what we know about the magnetospheric environment. It is argued that this concept has flaws and that the actual physical problem is considerably more complicated, requiring a more complex electric field, possibly including double layer structures.

Numerical simulations of proton stopping lengths in aluminum slab plasmas have been done using a modified version of the MEDUSA-KA code and compared to other published computations. Simulations have been performed for proton beam parameters consistent with future experiments on the KALIF light ion accelerator at KfK including carbon contamination of the beam. These simulations show that proton range shortening should be evident in KALIF experiments and that the carbon contamination must be removed to allow interpretation of the data.

Ultrahigh axial magnetic fields have been compressed and measured in a gas-puff Z pinch. A 0·5-MA, 2–cm-radius annular gas-puff Z pinch with a 3-minute repetition rate was imploded radially onto an axial seed field, causing the field to compress. Axial magnetic field compressions up to 180 and peak magnetic fields up to 1·6 MG were measured. Faraday rotation of an argon laser (515·4 nm) in a quartz fiber on axis was the principal magnetic field diagnostic. Other diagnostics included a nitrogen laser interferometer, x-ray diodes, and magnetic field probes.

The magnetic field compression results are consistent with simple snowplow and self-similar analytic models, which are presented. The axial magnetic fields strongly affect the Z pinch dynamics. Even small axial fields help stabilize the pinches, some of which exhibit several stable radial bounces during a current pulse.

The method of compressing axial fields in a gas-puff Z pinch is extrapolable to the order of 100 MG. Scaling laws are presented. Potential applications of ultrahigh axial fields in Z pinches are discussed for x-ray lasers, inertial confinement fusion, and collimated sources of gamma radiation.

The conference has shown some important advances toward the solution of problems required for inertial fusion. We can tentatively categorize as solved, or nearly solved, the following problems: Marx prefires, Marx jitter, gas-switch prefires, gas-switch jitter, power combination of multi-modules, high-current beam divergence (in barreltype, Applied-B/MID diodes), and preheat. In addition, there are a set of mature problems with promising solutions: pulsed power accelerator efficiency, ion sources, and the electron kinetics of an extractor ion diode. Newer problems that were addressed at the meeting but still require considerable work include: impedance control of efficient ion diodes, diagnostics for both beams and targets, the further development of target design tools and their experimental verification, targetfabrication processes to make the nearly perfect targets required for inertial fusion, channel formation and beam transport in those channels at the power levels required for fusion, and pulse-shaping.

A theoretical and experimental study of line broadening and merging is presented and suggested for diagnosis of high density laser plasmas. For densities larger than 1022 cm−3 the hydrogenlike sequence is reduced to four lines for the emitter ion with ZE = 9. The perturbation effects on the latter come mainly from the interaction with plasma ions and electrons (Stark effect, multipolar interactions, ionization by tunnel effect, polarization line shift …).

We present experimental results on three dynamic properties of very strong double layers observed in a triple plasma device. First, it is observed that when an inductance of sufficient size is inserted in series with the external bias supply used to produce the double layer, disruptions in the plasma current occur accompanied by disruptions in the double layer potential. Second, it is observed that with all external reactances reduced as much as possible, a sort of jitter-motion occurs in the position of the double layer around its equilibrium position. Third, when the external bias supply is pulsed, the initial potential distribution is observed to have an essentially uniform slope, as in the case of a vacuum capacitor. The disruption phenomenon may be explained in terms of the behavior of the potential structure as a function of the bias voltage and this explanation is discussed along with the experimental evidence for its validity. A comparable understanding of the other two phenomena has not been achieved, but in both cases there are qualitative differences between the behavior reported here and what has been observed in Q-machines and these differences are discussed.

In a triple plasma device, the injection of electron current from the source chamber to the target chamber causes the formation of a potential double layer. At a low current density, the space charge of the injected current produces a virtual cathode-type potential double layer. This double layer is stable and various wave instabilities are observed to associate with this double layer. As the current density is increased, the double layer becomes unstable and a moving double layer results. As the current density is increased further, the enhanced ionization causes the neutralization of the space charge of the electron beam and the ‘beam plasma discharge’ is ignited.

For inertial confinement fusion (ICF) research, theories and simulations will continue to play an important role because research must cover all the sciences and technologies for extracting fusion energy. Experimental research is mainly concentrated on driver technology at the present stage.