Photoionization of single-charged heavy ions has been proposed recently by Rubbia (1989) as a non-Liouvillean injection scheme from the linac into the storage rings of a driver accelerator for inertial confinement fusion. The main idea of this scheme is the accumulation of high currents of heavy ions without the usually inevitable increase of phase space. Here we suggest the use of the photoionization idea in an alternative scheme: if it is applied at the final stage of pulse compression (replacing the conventional bunch compression by an rf voltage, which always increases the momentum spread), there is a significant advantage in the performance of the accelerator. We show, in particular, that this new compression scheme can potentially relax the tough stability limitations, which were identified in the heavy-ion fusion reactor study HIBALL (Badger et al. 1984). Moreover, it is promising for achieving higher beam power, which is suitable for indirectly driven fusion targets (1016 W/g, in contrast with 1014 W/g for the directly driven targets in HIBALL).

The idea of non-Liouvillean bunch compression is to stack a large number of bunches (typically 50–100) in the same phase-space volume during a change of charge state of the ion. A particular feature of this scheme with regard to beam dynamics is its transient nature, since the time required is one revolution per bunch. After the stacking the intense bunch is ejected and directly guided to the target. The present study is a first step in exploring the possibly limiting effect of space charge under the parameter conditions of a full-size driver accelerator. Preliminary results indicate that there is a limit to the effective stacking number (non-Liouvillean “compression factor”), which is, however, not prohibitive. Requirements on the power of the photon beam from a free-electron laser are also discussed. It is seen that resonant cross sections of the order of 10−15 cm2 lead to photon beam powers of a few megawatts.

Arbitrarily heavy cluster ion beams (CIB) are examined for the purpose of driving directly or indirectly an ICF compression. This paper provides an overview of cluster production, and of their interaction with cold and hot matter. Fragmentation is also considered. Concepts and ideas of interest for further investigations are identified and delineated. A connection is made with a CIB interaction experiment planned at Orsay. It is conjectured that CIB should experience enhanced stopping when compared to their atomic counterparts under similar conditions.

We have made the first observation of Kα X-ray satellites from a target heated by an intense ion beam. The satellites are produced when thermal ionization due to beam heating is accompanied by inner-shell ionization from beam ion impact. The Particle Beam Fusion Accelerator II was used to irradiate a conical aluminum target with a proton beam. The nominal beam parameters were 50–75 kJ in a 1-cm spot, 15–20-ns pulse length, and 4–5-MeV protons at peak power. An elliptical crystal X-ray spectrograph inside a 1000-kg tungsten shield was used to record the spectra. The peak ion stage reached by the aluminum target was +8. Collisional radiative calculations were performed, which indicate a peak electron temperature of 20–60 eV.

The main goals of the German program are the study of key issues of inertial fusion with intense beams of heavy ions. The completion of the new heavy-ion synchrotron and storage ring facility SIS/ESR at GSI opens new directions for experimental investigations on beam dynamics at high intensity and on beam/target interaction. In addition, new accelerator scenarios will be investigated based on non-Liouvillean beam-handling techniques.

The experimental setup developed at Orsay for studying ion beam-plasma interactions of relevance to inertial confinement fusion has been significantly improved. In this connection, the fast valves displayed on both sides of the plasma discharge play an essential role. The amount of residual gas is then reduced by a factor of 3. New and accurate results for the stopping and the effective charges of S7+ and Br6+ in the MeV/u energy range are presented.

The progress of the experimental research program at GSI for studying beam-plasma interaction phenomena is reported. Heavy-ion beams from the new accelerator facility SIS/ESR at GSI-Darmstadt are now available for experiments, and will soon deliver ≥ 109 particles per pulse in 100 ns. Focused on a small sample of matter, the beams will be able to produce a high-density plasma and to permit investigation of interaction processes of heavy ions with hot ionized matter.

For the intense beam from the new heavy-ion synchrotron (SIS), a fine-focus system has been designed to produce a high specific deposition power beam for target experiments with a beam-spot radius of 100 μm. We further discuss improvements of this lens system by nonconventional focusing devices such as plasma lenses.

Intense-beam experiments at the RFQ Maxilac accelerator at GSI have already produced the first heavy-ion-induced plasma with a temperature of 0.75 eV. New diagnostic techniques for investigating ion-beam-induced plasmas are presented. The low-intensity beam from the GSI UNILAC has been used to measure energy deposition profiles of heavy ions in hot ionized matter. In this experiment an enhancement of the stopping power for heavy ions was observed. The current experimental research program tests basic plasma theory and addresses key issues of inertial confinement fusion driven by intense heavy-ion beams.

Plasmas of high reproducibility that are suitable for beam-plasma experiments are generated by a pulsed-power z-pinch discharge. The z-pinch device is designed as a plasma target for the investigation of ion beam-plasma interactions. The dynamic plasma state is characterized by the electron density, the electron temperature, and the magnetic field distribution, which are observed using time-resolved diagnostics. For z-pinch discharges in hydrogen, average electron densities of up to (2.6 ± 0.1) × 1018 electrons/cm3 were measured interferometrically. Electron temperatures in the range 2–7 eV are determined by time-resolved spectroscopy. The reproducibility of the electron density of the z-pinch discharge in terms of shot-to-shot fluctuations is estimated to be better than 3%. This is a favorable condition for performing beam-plasma experiments.

Recent direct-drive implosion experiments on the GEKKO XII laser with plastic hollow shell targets demonstrated compressed densities of ∼600 g/cm3 (∼600 times liquid density) at a temperature of ∼0.3 keV. The highly compressed core plasmas are indicated to be strongly coupled (average Coulomb energy/thermal energy ≈5) and partially degenerate (thermal energy/Fermi energy ≈0.3). The diagnostic method based on the secondary nuclear fusion reactions is presented to prove the electron degeneracy in the highly compressed core plasma. The yield ratio of the secondary DT neutrons to the primary DD neutrons in such highly compressed core plasmas was calculated with inclusion of the strong Coulomb-coupling effects, the varied degrees of the electron degeneracy, and the electronic shielding effects. It was found in our calculations that there is a significant dependence of the yield ratio on the compressed core density. For the plastic targets at the electron temperature of ∼0.3 keV, the yield ratio increases from 9 × 10−4 to 8 × 10−3 for densities from 10 to 1000 g/cm3. The preliminary experiments using deuterated plastic hollow shell targets suggested that the enhancement of the yield ratio provided evidence of the electron degeneracy.

We develop a renormalized technique to evaluate the stopping power for a test ion traversing a hot classical plasma. We show that the linear description of energy loss begins to break down at a distance much greater than the classical distance of closest approach. The close-collision contribution to the stopping power is on the same footing as that for distant collision. As a new result, we show the existence of nonanalytical terms in addition to the usual Z2 contribution to the stopping power.

The charge state and the level populations of ionic projectiles that are stopped in hydrogen plasma are calculated in the average ion model. It is shown that in available experimental systems the parameters can be chosen such that the end of the range will occur inside the plasma column. The predicted narrow region over which recombination occurs can be used as a check on plasma stopping-power theory and as a direct measurement of the range, using spectroscopic diagnostics.

Until now a theoretical derivation of scaling laws for the effective charge Zeff of heavy ions penetrating matter has been lacking, although for cold gaseous targets there are well-established empirical relations of the form Zeff/Zp = f (up/ZpγZtδ), where vp and Zp are, respectively, the velocity and nuclear charge of the projectile ion, Zt, is the nuclear charge of the target atoms, and γ and δ are the scaling exponents. We show that the scaling exponents may be derived from an investigation of loss and capture rates. The treatment is based on the Bohr-Lamb criterion. This very crude criterion yields γ = 2/3. Our analysis allows the formulation of a modified criterion, yielding γ = 0.528 for cold gas, which deviates by only 2% from the often-used empirical Betz formula. The dependence on Zt, in cold gas is oscillatory and cannot be described by a simple exponent δ. The treatment is also applied to a fully ionized plasma, resulting in Zerf/Zp = f (upZt0.27/Zp1.39).

General aspects of the excitation of matter with heavy-ion beams are discussed. Lasers in the wavelength region between 1 and 3 μm in rare-gas mixtures pumped with 1.9-GeV xenon, 100-MeV sulphur, 3.6-MeV argon, and 3.3-MeV helium ions are described as examples for lasers pumped by heavy-ion beams. The beam power ranges from a few watts (dc) to about 1 MW during short pulses of about 1-ns length. Optical gain can be measured with an intracavity method. Data on the shape of the volume excited by a 100- MeV 32S beam are shown. An experimental setup for time-resolved optical spectroscopy in a wide wavelength region between a few nanometers and about 700 nm is described. Emission spectra of rare gases excited by heavy-ion beams are discussed and optical gain on ion lines and excimer bands is estimated for different target and beam parameters. Collisional processes in the target gas were studied by time-resolved optical spectroscopy. Population densities of selected 3p levels in Ne I, II, and IV and rate constants for collisional depopulation of excited levels were determined. Experiments planned at the heavy-ion synchrotron SIS at Gesellschaft für Schwerionenforschung in Darmstadt are discussed.

Ionization distributions and radiation spectra of a dense plasma driven by intense ion beams are studied by solving stationary rate equations. Expressions for the rate coefficients are derived. Optically thin plasmas of hydrogen and carbon are considered neglecting hydrodynamic motion. Results on level populations versus temperature, on power balance and equilibrium states, and also on emission spectra are given. In particular, the transition from beam-determined plasma states to thermal equilibrium states is discussed. Beam parameters are chosen close to those in experiments now being planned.

A time-dependent collisional radiative model, based on a five-charge state at any spacetime point in the plasma, is elaborated in order to follow the basic atomic physics processes in a plasma undergoing ionization and recombination. This model can either be used independently or be included in a magnetohydrodynamics code of a transient plasma. In the latter case, the efficiency of the model makes it particularly useful in saving computing time of hydrodynamic codes developed in connection with ion-driven fusion.

The main objective of this work is to find analytical formulas for the oscillator strength f of hydrogen-like ions. It is well known that f is proportional to the energy of the transitions between eigenstates (ΔE), and to the square of the R matrix. Therefore, the problem of calculating f can be reduced to finding analytical expressions for both parameters, ΔE and R. Hence these expressions would be in accordance with quantum results based on more sophisticated calculations.

Frequency-dependent opacities are determined for high-Z plasma taking into account splitting of the energy levels with orbital quantum number l. The energy levels are calculated with the help of the screened hydrogenic model generalized by Perrot for l splitting. Oscillator strengths for bound-bound and bound-free transitions are computed from hydrogenic wave functions with two different screened nuclear charges. The average atom model is used to determine the plasma state, with provision for continuum lowering and pressure ionization. Explicit results for extinction coefficients of gold plasma with ρ = 0.1 g/cm3 and T = 100−500 eV are compared with calculations neglecting l splitting. Considerably enhanced absorption at lower photon energies (50–300 eV) is obtained when taking l splitting into account. Planck and Rosseland mean opacities are also calculated and compared with data contained in the SESAME opacity library. Remarkable agreement is found without any artificial line broadening or band smearing.

We present results from non-LTE line radiation transport calculations for high-temperature, optically thick plasmas with densities ∼1016-1020 ions/cm3. The calculations are based on an escape probability radiative transport model in which the atomic rate equations are solved self-consistently with the radiation field. Steady-state ionization and excitation populations are determined by detailed balancing of atomic processes, with photoexcitation effects included. Atomic data are computed using a combination of Hartree-Fock, semiclassical impact-parameter, and distorted-wave calculations. Our results indicate that the reabsorption of line radiation significantly alters the level populations and reduces the radiation flux from several types of fusion-related plasmas. We also compare our results with those obtained from multigroup radiation diffusion calculations, and discuss the ramifications of our results for ICF target chamber plasmas.

A formulation of radiative transfer is discussed describing energy flow in a turbulent mixture in the vicinity of a Rayleigh–Taylor unstable interface, as might be extant in an ICF pellet. Included in this discussion are (1) the method of smoothing and the Liouville master equation approaches in the case of Markovian statistics as the description of the fluid mixing, (2) the use of asymptotics to derive various limiting descriptions of the Markov model, (3) the use of the theory of alternating renewal processes to obtain an integral equation formulation for non-Markovian statistics, and (4) the reduction of this non-Markovian integral formulation to integro-differential equations of the generic transport form, with statistical effects represented by pseudoscattering terms.

We present a theoretical approach to the thermodynamic properties of nonideal plasmas consisting of neutral atoms, multiply charged ions, and free electrons. Starting with the free energy, we describe the ionization equilibrium of this system by a coupled set of mass action laws (Saha equations). Our model of interaction takes into account Coulomb forces between all charged particles and hard-core forces between all heavy particles and the electrons. The influence of multiple ionization and different interaction parts on plasma composition, mean charge, and equation of state is discussed for xenon. Finally, we show the potential occurrence of the plasma phase transition.