The relaxation of two-temperature electron–ion systems is investigated. We apply a quantum kinetic approach which is suitable to treat strong electron–ion coupling and avoids any ad hoc cut-off procedures. A comparison with the usual Landau–Spitzer formula gives good agreement for Coulomb logarithms larger than three, whereas larger relaxation rates were found for strongly coupled plasmas. It is shown that the Landau–Spitzer theory can be greatly improved considering hyperbolic orbits. Numerical results for the energy transfer rates and the temporal behavior of the electron temperature are shown.

Results are presented for a theoretical model, known as the ion model (IM), recently elaborated to calculate the radiative opacity of a hot dense plasma. The density functional theory is used to obtain the general set of self-consistent field equations that describe the state of the whole ensemble of plasma atoms and ions. Theoretical features of the Hartree–Fock–Slater model, the detail configuration account, and the IM are considered. The IM is used for optimal selections of compound chemical compositions for laser and heavy ion target designs.

One approach being explored as a route to practical fusion energy uses heavy ion beams focused on an indirect drive target. Such beams will lose electrons while passing through background gas in the target chamber, and therefore it is necessary to assess the rate at which the charge state of the incident beam evolves on the way to the target. Accelerators designed primarily for nuclear physics or high energy physics experiments utilize ion sources that generate highly stripped ions in order to achieve high energies economically. As a result, accelerators capable of producing heavy ion beams of 10 to 40 MeV/amu with charge state 1 currently do not exist. Hence, the stripping cross sections used to model the performance of heavy ion fusion driver beams have, up to now, been based on theoretical calculations. We have investigated experimentally the stripping of 3.4 MeV/amu Kr+7 and Xe+11 in N2; 10.2 MeV/amu Ar+6 in He, N2, Ar, and Xe; 19 MeV/amu Ar+8 in He, N2, Ar, and Xe; 30 MeV He+1 in He, N2, Ar, and Xe; and 38 MeV/amu N+6 in He, N2, Ar, and Xe. The results of these measurements are compared with the theoretical calculations to assess their applicability over a wide range of parameters.

Correlations of Doppler shifted line shapes with time-of-flight spectra of fast ions has been established for nanosecond-laser pulses. Fast ion energies of different velocity groups have been established in the large interval of Iλ2 = 4 × 1012–5 × 1016 W/cm2 μm2. The obtained scaling relations differ markedly from those reported by Gitomer et al. (1996).

The aim of the presented experiments is to study the transport of a heavy ion beam in a high-current plasma channel. The discharge is initiated in NH3 gas at pressures between 2 and 20 mbar by a line-tuned CO2 laser. A stable discharge over the entire electrode gap (0.5 m) was achieved for currents up to 60 kA. Concerning the ion beam transport, the magnetic field distribution inside the plasma channel has to be known. The ion-optical properties of the plasma channel have been investigated using different species of heavy ions (C, Ni, Au, U) with 11.4 MeV/u during six runs at the Gesellschaft für Schwerionenforschungs-UNILAC linear accelerator. The high magnetic field allowed the accomplishment of one complete betatron oscillation along the discharge channel. The results obtained up to now are very promising and suggest that, by scaling the discharge gap to longer distances, the beam transport over several meters is possible with negligible losses.

The longitudinal dynamics of drift compression and pulse shaping for a space-charge-dominated heavy ion fusion beam is studied. A nonperiodic quadrupole lattice is designed for a beam undergoing drift compression, and an adiabatically matched solution is found for the transverse envelope equations in the nonperiodic lattice.

The numerical simulation of the driving beams in a heavy ion fusion power plant is a challenging task, and simulation of the power plant as a whole, or even of the driver, is not yet possible. Despite the rapid progress in computer power, past and anticipated, one must consider the use of the most advanced numerical techniques, if we are to reach our goal expeditiously. One of the difficulties of these simulations resides in the disparity of scales, in time and in space, which must be resolved. When these disparities are in distinctive zones of the simulation region, a method which has proven to be effective in other areas (e.g., fluid dynamics simulations) is the mesh refinement technique. We discuss the challenges posed by the implementation of this technique into plasma simulations (due to the presence of particles and electromagnetic waves). We present the prospects for and projected benefits of its application to heavy ion fusion, in particular to the simulation of the ion source and the final beam propagation in the chamber. A collaboration project is under way at Lawrence Berkeley National Laboratory between the Applied Numerical Algorithms Group (ANAG) and the Heavy Ion Fusion group to couple the adaptive mesh refinement library CHOMBO developed by the ANAG group to the particle-in-cell accelerator code WARP developed by the Heavy Ion Fusion–Virtual National Laboratory. We describe our progress and present our initial findings.

The Heavy Ion Fusion Virtual National Laboratory High Current Experiment (HCX) is exploring transport issues such as dynamic aperture, effects of quadrupole rotation, and the effects on the beam of nonideal distribution function, mismatch, and electrons, using one driver-scale 0.2 μC/m, 2–10 μs coasting K+ beam. Two- and three-dimensional simulations are being done, using the particle-in-cell code WARP to study these phenomena. We present results which predict that the dynamic aperture in the electrostatic focusing transport section will be set by particle loss.

Between the accelerator and fusion chamber, the heavy ion beams are subject to a dramatic but vital series of manipulations, some of which are carried out simultaneously and involve large space charge forces. The beams' quality must be maintained at a level sufficient for the fusion application; this general requirement significantly impacts beam line design, especially in the considerations of momentum dispersion. Immediately prior to final focus onto a fusion target, heavy ion driver beams are compressed in length by typically an order of magnitude. This process is simultaneous with bending through large angles to achieve the required target illumination configuration. The large increase in beam current is accommodated by a combination of decreased lattice period, increased beam radius, and increased strength of the beamline quadrupoles. However, the large head-to-tail momentum tilt (up to 5%) needed to compress the pulse results in a very significant dispersion of the pulse centroid from the design axis. General design features are discussed. A principal design goal is to minimize the magnitude of the dispersion while maintaining approximate first order achromaticity through the complete compression/bend system. Configurations of bends and quadrupoles, which achieve this goal while simultaneously maintaining a locally matched beam-envelope, are analyzed.

This article extends previous numerical studies of the stability properties of intense nonneutral charged particle beams with large temperature anisotropy (T⊥b >> T∥b) to allow for nonaxisymmetric perturbations with ∂/∂θ ≠ 0. The most unstable modes are identified, and their eigenfrequencies, radial mode structure, and nonlinear dynamics are determined.

A longitudinal compression is indispensable in a final stage of the heavy ion driver system using a particle accelerator. For the beam compression, an induction buncher applies the bunching voltage so as to make a considerable velocity tilt between the head and the tail of the beam bunch. However, the velocity tilt induces mismatch oscillation of the beam envelope due to the nonconformity between the beam particle velocity and the confinement force of the lens system. At the first step of design works for the beam transport line, the initial phase advance is decided to avoid resonance lines on the tune diagram. However, as the phase advance changes in the buncher by the velocity tilt, the beam bunch reenters in the resonance condition under certain circumstances. The transport region for avoiding the resonance condition is discussed on a phase diagram, as a function of the phase advance and the velocity tilt.

Recently the “fast ignition” method in the ICF problem was considered (Caruso & Pais, 1996). It allows increasing a target gain factor and raising reliability of the burning process. Since the required power of the irradiating beam in this method is unattainable for the traditional type of heavy ion driver with the energy of ions ≤10 GeV, the powerful laser is considered as a possible driver only. Here we investigate the fast ignition method for a system constituted from the directly irradiated cylindrical target and a powerful heavy ion driver of the charge-symmetric type (Koshkarev, 1993) in which the ions with energy ≈100 GeV and mass ≈200 are used. The actual design of a powerful heavy ion driver with the required characteristics is outside the purpose of this article. However some consideration will be given to exploring whether such a performance is within the realm of reasonable extrapolations of the present state of the art.

A detailed understanding of the physics of space-charge-dominated beams is vital in the design of heavy ion inertial fusion (HIF) drivers. In that regard, low-energy, high-intensity electron beams provide an excellent model system. The University of Maryland Electron Ring (UMER), currently being installed, has been designed to study the physics of space-charge-dominated beams with extreme intensity in a strong focusing lattice with dispersion. At 10 keV and 100 mA, the beam from the UMER injector has a generalized perveance as much as 0.0015, corresponding to that of proposed HIF drivers. Though compact (11 m in circumference), UMER will be a very complex device by the time of its completion (expected 2003). We present an update on the construction as well as recent experimental results.

The U.S. Heavy Ion Fusion Virtual National Laboratory is continuing research into ion sources and injectors that simultaneously provide high current (0.5–1.0 A) and high brightness (normalized emittance better than 1.0 π-mm-mr). The central issue of focus is whether to continue pursuing the traditional approach of large surface ionization sources or to adopt a multiaperture approach that transports many smaller “beamlets” separately at low energies before allowing them to merge. For the large surface source concept, the recent commissioning of the 2-MeV injector for the High Current eXperiment has increased our understanding of the beam quality limitations for these sources. We have also improved our techniques for fabricating large diameter aluminosilicate sources to improve lifetime and emission uniformity. For the multiaperture approach, we are continuing to study the feasibility of small surface sources and a RF-induced plasma source in preparation for beamlet merging experiments, while continuing to run computer simulations for better understanding of this alternate concept. Experiments into both architectures will be performed on a newly commissioned ion source test stand at Lawrence Livermore National Laboratory called STS-500. This stand test provides a platform for testing a variety of ion sources and accelerating structures with 500-kV, 17-μs pulses. Recent progress in these areas is discussed as well as plans for future experiments.

Activities of research and development on repetitive induction voltage modulators in the Tokyo Institute of Technology–High Energy Accelerator Research Organization group are presented along with a discussion of the magnetic response of ferro-magnetic materials to fast magnetization and a transient beam loading in the modulators. The modulator is composed of independently driven modules switched by field effect transistors. To make waveform control, the induced voltages are stacked and synthesized in the induction unit. A proof-of-principle experiment shows that the module elements are successfully operated up to megahertz levels with good reproducibility. For the evaluation of magnetic core response, magnetic characteristics are investigated over a wide range of parameters, and an empirical core loss scaling is derived at minor-hysteresis loops. Using the prototype induction module, we have also investigated the effect of beam loading. Results indicate that the effect depends not only on the impedance of the driving circuit but on nonlinearity of the magnetic-core response. This means that the response of the induction modulator depends on the time scale of domain motion and operating point in the B-H plane of magnetic materials. Based on the progress of the component technology in the induction accelerator and database of magnetic materials, a system design has been developed.

Temporal evolution of X-ray spectra of lead plasma produced by a CO2 laser pulse with energy of 100 J and a duration of 15 ns has been measured using a six-channel X-ray polychromator. The polychromator registered the radiation intensity in the range from 180 to 1850 eV. Plasma temperature was determined by comparison of measured results with radiation spectra obtained by numerical simulation. The values of electron temperature are in good agreement with results of hydro simulations.

The heavy ion fusion program is developing single aperture superconducting quadrupoles based on NbTi conductor, for use in the High Current Experiment at Lawrence Berkeley National Laboratory. Following the fabrication and testing of prototypes using two different approaches, a baseline design has been selected and further optimized. A prototype cryostat for a quadrupole doublet, with features to accommodate induction acceleration modules, is being fabricated. The single aperture magnet was derived from a conceptual design of a quadrupole array magnet for multibeam transport. Progress on the development of superconducting quadrupole arrays for future experiments is also reported.

Beams for heavy ion fusion are likely to require at least partial neutralization in the reactor chamber. Present target designs call for higher beam currents and smaller focal spots than most earlier designs, leading to high space-charge fields. Focusing is complicated by beam stripping in the low-pressure background gas expected in chambers. One method proposed for neutralization is passing an ion beam through a plasma before the beam enters the chamber. In this article, the electromagnetic particle-in-cell code LSP is used to study the effectiveness of this form of preneutralization for a range of plasma and beam parameters. For target chamber pressures below a few milliTorr of flibe gas, preneutralization is found to significantly reduce the beam emittance growth and spot size in the chamber.

A review of structural materials choices under irradiation in fusion environments is presented. Results on the neutron source term and the intensities in the structural materials as a function of pulse time, energy, and protection is given. The role of multiscale modeling for understanding the basic physics in irradiated materials is explained, and simulations of metals under pulse irradiation and SiC are reported.

The emissions to the atmosphere, by a heavy ion inertial fusion reactor in accidental and normal operations, are in form of tritium gas with two chemicals forms of tritium: HT and HTO. Emissions of 100% HT have been analyzed in this work, and their consequences in the dosimetry. The primary phase of the emission depends on the atmospheric conditions. As a consequence, the tritium is dispersed far from the source. The HT can be oxidized in the stratosphere or in the surface by microbiological action to convert it to HTO, and back to the air in a reemission process or penetrate into the subground. In the form of HT, the effective dose equivalent (EDE) is important in the case of intake (inhalation, skin absorption, or ingestion), because tritium is a beta emitter of low energy and the dose by external uptake is not considerable. Thus, the dose by ingestion contributes the most to the total dose in the case of HT rather than HTO. It constitutes 98% of the total EDE, in contrast with the contribution to the total dose by HTO, which is only 40%.