[en] The U.S. Heavy Ion fusion Accelerator Research (HIFAR) program is developing an induction linac as driver for the requisite particle beams. The development of this accelerator concept is centered at the Lawrence Berkeley Laboratory (LBL). In part using its own funds, the Lawrence Livermore National Laboratory (LLNL) is developing the target physics as well as studying final beam compression, focusing and transport to the target. In addition, LLNL is investigating, with internal funding, some innovative (but higher risk) accelerator concepts for this field. (One such example is the Mirrortron accelerator). The major research efforts supported through HIFAR are concerned with the physics of these intense particle beams, the necessary accelerator technology development and the interfaces with the final target and fusion chamber requirements. The induction linac is designed to simultaneously accelerate and compress a group of parallel beams from low energy, low current (amperes), long pulse length (sub milliseconds) to the high energies (5--10 GeV), high current (10--100 kA), short pulse length (5--10 ns at peak power) required for igniting the pellet. The authors' paper provides a review of the HIFAR beam and accelerator issues, as well as a discussion of the crucial interfaces with the targets, final transport and focusing

[en] The problem of fast ion transport in inertially confined plasmas was studied using a variety of numerical techniques. Computer codes were developed which approached the problem with the aid of flux-limited, multi-group diffusion theory, particle tracking theory, and a combination of these two techniques which took advantage of the fact that they are most effective in different regions of the slowing ion energy spectrum. The problem of numerical diffusion in multi-group diffusion codes was examined with the aid of a modified code which substituted a continuous energy loss formula for the usual differencing in energy space. Results obtained using the three codes mentioned above were compared with a benchmark Monte Carlo calculation. The combined code results were found to be significantly closer to the Monte Carlo ideal than those of the individual particle tracking or multi-group diffusion codes. In order to demonstrate its flexibility, the combined code was used to model the progress of a thermonuclear burn wave in a compressed pellet of fuel material

[en] The author identifies three levels of increasing sophistication in the theory of atomic processes in dense plasmas. In the most naive work, it is assumed that atomic rates are proportional to the densities of reacting particles; e.g., electron-impact ionization varies directly as n/sub e/, three-body recombination varies directly as n/sub e/², etc. At high density, qualitatively incorrect results are predicted, such as complete recombination. A better strategy is to recompute both eigenstates and cross sections in a density-dependent model potential, such as the Debye-Hueckel or ion-sphere potentials. Calculations at this level include the most important high-density effects: pressure ionization, continuum lowering, and free-electron degeneracy. Although the results are more reasonable, this approach leaves many unanswered questions about the fundamental physics. At the third level of sophistication, attention is directed toward the discrete atomic character of the plasma environment. For each process, a rate is calculated and then averaged over the probable positions of neighboring ions. 63 references, 6 figures, 2 tables

[en] Experimental work on laser implosion and interaction at the Centre d'Etudes de Limeil-Valenton has been performed using two lasers, the P 102 laser producing 20 J on target at lambda=0.35 μm and the Octal laser producing 360 J in 280 ps and 900 J in 900 ps at lambda=1.06 μm. Experiments on plane targets allow the effect of spatial modulations of illumination on the acceleration to be studied. In addition, the optical thickness of an aluminium plasma is measured using a target with special geometry. In microballoon implosion experiments, a marked increase in neutron emission is observed when the target is coated by high-density and high-Z material. With regard to theoretical aspects, particular attention is given to interaction (resonant absorption saturation mechanisms, linear theory of Raman effects and two-plasmon effects, stimulated Brillouin scattering saturation), to transport (expansion of a plasma with two electron temperatures, self-consistent description of thermal and suprathermal electrons) and to physics out of local thermodynamic equilibrium (LTE). (author)

[en] Power concentration has been the principal concern for inertial confinement fusion with light-ion beams. Recently a proof-of-principle experiment on ion focusing has been completed on Proto I and indicates that the Particle Beam Fusion Accelerator II (PBFA-II) beam should be focusable for high intensity targets to study ignition. The results are now being scaled to PBFA I. The theoretical stability of the electron sheath in the diode has been examined, and the growth rates are typically 5% of the electron cyclotron frequency. A new spectroscopic diagnostic has been developed to measure the electric fields and ion velocity distributions in the diode. Recent experiments with glow-discharge cleaning have shown that the ion species can be controlled and that the purity can be improved substantially. Plasma erosion opening switches will compress the power pulse to match the target acceptance time on PBFA II. Experiments with these switches on single-module accelerators show power gain. Currents of 5 MA have been interrupted in 20 ns in other experiments. The high voltage lithium ion option has been chosen for PBFA II, and the Applied-B diode has been selected as the first diode for the first shot on PBFA II in January 1986. (author)

[en] In modelling the steady-state flow of a collisionless plasma or an ion beam from a source region into a source free area, by means of the Poisson-Vlasov set of equations, a non-physical build-up of positive charge occurs a short distance away from the discharge point that soon acts to impede further flow out of the source. Such an occurrence is seldom observed in the laboratory and the question of what is the appropriate electron model to mitigate this effect, has been of concern for some time now

[en] We present a calculation of the time dependent charge state of a heavy projectile traversing a finite temperature target. The calculation uses an average-atom model to integrate the rate equations

[en] More precise stopping power models for use in ICF target design need to be developed. The light ion beam ICF program is now moving into a phase where ''ad hoc'' scaling of certain key physics parameters in the stopping power models is no longer sufficient. Our goal is to predict ion ranges in ICF targets to within about 10-20%. A verified stopping power model is also essential in diagnosing target irradiation intensities; such data can only be inferred by target response. Presently, our area of primary concern involves calculating the stopping power of the bound electrons of partially ionized atoms. One bound electron stopping power model that we are investigating uses the local oscillator model along with Hartree-Fock-Slater atomic charge density profiles to calculate I(Z,q,E), a generalized average ionization potential for the target electrons. This method is being studied systematically to look for deficiencies in the underlying physics model, especially at low projectile velocities. Another procedure uses the Generalized Oscillator strength model to calculate the bound electron stopping. Experimental measurements of enhanced stopping power in ICF plasmas at the 0.3 TW/cm² level have been reported by the Naval Research Laboratory. Further experiments at Sandia are aimed at extending this data base both to higher ionization states and to higher-Z targets using a 1.2 TW/cm² proton beam on the PROTO-I accelerator

[en] The next-generation fusion devices based on the tokamak confinement concept are expected to emphasize steady-state operation. Such future reactors may include designs like the International Thermonuclear Experimental Reactor (ITER) and that of the recent International Tokamak Reactor (INTOR) program. Effective means of non-inductive plasma current drive would therefore be necessary. This paper describes a neutral beam concept for a current drive system (which will heat the plasma as well) that is based on negative ions and has a beam energy > 1 MeV. Such systems, at much lower power levels, are also being considered for alpha diagnostics. Preliminary physics calculations show that the plasma core current necessary for stability enhancement can best be achieved in these future reactor-like machines with tangentially injected beams having energies ranging from 1 to 4 MeV. Further study and experiments will better define the optimum energy. Studies of how to accomplish beams of this energy led to the system described in this paper

[en] A method is suggested for investigation of the laser beam mutual coherence function Γ(x₁,x₂,τ)which is based on analysis of a Fourier-transformed speckle field produced as a result of the interaction between the radiation and a statistical Gaussian diffuser. By means of the suggested method the coherence properties of high-power laser beams have been studied at different stages of the pulse amplification in the Delfin-1 installation designed for experiments on the laser fusion. It is shown that, if the radiation from the master oscillator of the installation is practically fully coherent all over the beam, the halfwidth of the Γ(x₁,x₂) function is reduced to 0.1-0.2 of the beam diameter as the pulse amplification proceeds. This phenomenon is caused by nonlinear effects arising in the active medium at the flux density of ∼ 1 GW/cm². A dependence of theΓ(x₁,x₂) function on the spectral composition of the laser radiation has been also investigated