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.

The actual situation with respect to the use of an RF linac driver for heavy ion inertial fusion (HIF) is discussed. At present, there is no high current heavy ion linac under construction. However, in the course of linac projects for e−, p, d, or highly charged ions several developments were made, which may have some impact on the design of a HIF driver. Medium- and low-β superconducting structures suited for pulsed high current beam operation are actually designed and investigated at several laboratories. A superconducting 40 MeV, 125 mA cw linac for deuteron acceleration is designed for the Inertial Fusion Material Irradiation Facility (IFMIF). The Institute for Applied Physics (IAP) is developing a superconducting 350-MHz, 19-cell prototype CH-cavity for β = 0.1. The prototype cavity will be ready for tests in 2004. A superconducting main HIF driver linac would considerably reduce the power losses. Moreover, it would allow for an efficient linac operation at a higher duty factor.

The 1.4-AMeV room-temperature High Current Injector HSI at Gesellschaft für Schwerionenforschung (GSI) has been in routine operation for more than 2 years now. With a mass-to-charge ratio of up to 65, a current limit of 15 mA for U4+, and an energy range from 2.2 AkeV up to 1.4 AMeV, this linac is suited to gain useful experience on the way toward the design of a HIF RF driver. The status and technical improvements of that A/q ≤ 65, 91-MV linac are reported. Beam dynamics calculations for Bi1+-beams show that powerful focusing elements at the linac front end are the bottleneck with respect to a further increase in beam current. Besides superconducting and pulsed wire quadrupoles, the potential of the Gabor-plasma lenses is investigated.

In this work, we first presents a review of the work that research teams have developed in collaboration in order to determine the optical properties of plasmas during the recent years, and showing the achievements reached. The second part of this paper is devoted to one of these improvements, which is to include reabsorption of the radiation in the calculations of dense optically thick plasmas in non-LTE conditions. Two models recently developed for this purpose are presented. The quantitative study was focused on aluminum plasmas, which was obtained recently at LULI experiments.

In 1982 to 83 a preliminary conceptual design of a heavy-ion-driven inertial fusion (HIF) system, called HIBLIC-I (Heavy Ion Beam and LIthium Curtain) was worked out (The Working Group on ‘HIBLIC-I’ 1984). Its principal aims are: (i) to find out the critical issues in this approach to fusion power plant, (ii) to assess its feasibility and (iii) to promote good collaboration between different fields (such as accelerator physics, plasma science and reactor technology) and of different institutions in Japan. (Obayashi 1981; Hirao 1982).

High-energy electron radiography (HEER) has been proposed for time-resolved imaging of materials, high-energy density matter, and for inertial confinement fusion. The areal-density resolution, determined by the image intensity information is critical for these types of diagnostics. Preliminary experimental studies for different materials with the same thickness and the same areal-density target have been imaged and analyzed. Although there are some discrepancies between experimental and theory analysis, the results show that the density distribution can indeed be attained from HEER. The reason for the discrepancies has been investigated and indicates the importance of the uniformity in the transverse distribution beam illuminating the target. Furthermore, the method for generating a uniform transverse distribution beam using octupole magnets was studied and verified by simulations. The simulations also confirm that the octupole field does not affect the angle-position correlation in the center part beam, a critical requirement for the imaging lens. A more practical method for HEER using collimators and octupoles for generating more uniform beams is also described. Detailed experimental results and simulation studies are presented in this paper.

Experimental and theoretical studies on the evolution of shock waves in air plasma induced by laser spark have been carried out. The systematic study of the shock wave has been performed experimentally and 1-D numerical code of radiation hydrodynamics (1-DRHC) has been used to simulate the later stage of laser spark in air. The numerical results on the propagation of shock waves and the expansion of hot plasma are presented and subsequent results on the first divergent and convergent shock waves are found to be in good agreement with the experimental data.

We studied the formation of the collector ion flow in magnetically insulated diodes (MID) with plate-, sphere-, and cone-shaped cathodes. The ions are formed as a result of the ionization of residual gas by electron bombardment and are focused into the cathode plasma region. This effect can negatively influence diode operation in the microsecond range of pulse duration.

Ti electrodes were directly deposited at different positions on diamond-like carbon (DLC) films to form horizontal and longitudinal electric fields on their surfaces. The ID/IG ratio increased with the sp3 content in the membrane when the DLC film was laser-irradiated and the electric field intensity was 0 V/cm. The bias electric field intensity increased from 0 to 1000 V/cm, and the corresponding laser-induced damage threshold (LIDT) increased. The three-dimensional damage morphology of the DLC film with two different electrode structures was observed when the electric field intensity was 220 V/cm. Two types of electrode structures were observed in the Raman spectra under an electric field intensity of 110 V/cm and laser energy densities of 0 and 1.56 J/cm2. Results showed that the horizontal bias field had a more obvious influence than the longitudinal electric field on the decrease of the sp3–sp2 hybridization, preventing the formation of sp2 clusters, thereby slowing down the graphitization process of DLC. Applying the bias field to the DLC film could slow down the DLC film graphitization process and improve the LIDT of the DLC film.

The formation conditions of a cryogenic target with a quality fusion cryolayer were found. The special device for the injection of the cryotarget into the ICF focus was devised.

Brillouin backscattering instability is investigated in inhomogeneous collisional plasma. The slow-coupling equations for the instability in a medium with linear density ramp are obtained. For large inhomogeneity scale length, the homogeneous growth rate is found to be modified by a factor of

[1/square root(2) times square root(ω02/ (ω02 + νe2) + ω0/square root(ω02 + νe2))]

For the convective instability, the amplification factor is found to be

[Λ = (|γB0|2/2β)(ω02/ω02 + νe2)]

The presence of collisions leads to a reduction in both the growth rate and the amplification factor, where the threshold intensity for the instability to occur increases.

A two-dimensional particle-in-cell simulation is carried out to study the focusing effects of the long proton beam propagating in background plasmas. It is found that the smooth beam, with the long length and the small density gradient profile, is focused to high density. The sharp beam, with long length and the large density gradient profile, is modulated into many high density and periodic short beam pulses due to the wakefield induced by the beam. In addition, increasing the plasma density and adopting the non-uniform plasmas are the effective ways to reduce the wakefield.

A new method of experimental measurement of the imploded mass of laser-imploded shell targets is proposed. This method is based on simultaneous measurements of the velocity spectrum of the neutral atom flux emitted from the imploded part of the target, and the total energy carried by them. A semiconductor diode with a shallowly located p – n junction was used as the low energy neutral particle detector. By means of the time of flight method neutral atom fluxes with velocities υ ∼ (0·6 − 1·8) × 107cm/s were registered in experiments carried out on the 6-beam laser system “Delfin”.

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.

Rare gas or lead clusters of several hundreds to many thousands of atoms per cluster were irradiated by intense laser pulses producing peak intensities up to 1017W/cm2. Fast, highly charged fragment ions were observed by means of standard TOF mass spectrometry as well as a magnetic deflection TOF device (MDTOF). Charge states of up to Xe30+ or Pb18+ were detected with maximum kinetic energies reaching far beyond 100 keV for Xe. A strong dependence of the charging and heating process on the laser pulse duration was found. While the resulting ionic fragment spectra are qualitatively similar for rare gas and lead clusters, the kinetic energies for the metal clusters seem to be significantly lower.

A steady-state analytical model is used to calculate the operational parameters of a coaxial-type, self-magnetically insulated ion-beam diode, called a plasma focus diode (PFD). The electrons are described by nonlaminar flow with a constant radial density distribution instead of the density profile determined self-consistently by one-dimensional laminar flow. The calculated results were compared with the experimental results obtained at the peak power, and good agreement was obtained between them. From the theoretical understanding of the PFD we obtained the scaling relations of diode impedance and the ion-current efficiency and used them to discuss the possible ways to increase the coupling efficiency and the ion-current efficiency and to reduce the instabilities in the diode operation.

For very high intensity accelerators, not only beam power but also space charge is a concern. Both aspects should be taken into consideration for any analysis of accelerators aiming at comparing their performances and pointing out the challenging sections. As high beam power is an issue from the lowest energy, careful and exhaustive beam loss predictions have to be done. High space charge implies lattice compactness making the implementation of beam diagnostics very problematic, so a clear strategy for beam diagnostic has to be defined. Beam halo is no longer negligible. Its dynamics is different from that of the core and plays a significant role in the particle loss process. Therefore, beam optimization must take the halo into account and beam characterization must be able to describe the halo part in addition to the core one. This paper presents the advanced concepts and methods for beam analysis, beam loss prediction, beam optimization, beam diagnostic, and beam characterization especially dedicated to very high intensity accelerators. Examples of application of these concepts are given in the case of the IFMIF accelerators.

The article reviews experiments on flash X radiography of laser-accelerated foils. The spatial resolution, sensitivity, spectral range, and signal-to-noise ratio of measurements were carefully optimized and characterized. The method was used at the Mishen facility to measure a distribution of mass ablative rate across the focal spot and for observation of the transverse plasma flows during the drive laser pulse.

A model for nonlocal α particle transport is implemented in a one-dimensional radiation hydrodynamics code and applied for typical directly and indirectly driven ICF target simulations. Ignition criteria are compared for four configurations; spherical, cylindrical, planar with a central hot spot, and another planar configuration with a hot spot on one side. This last planar configuration is then used for fast ignitor studies, since it is able to simulate hot spot formation by direct laser heating and free expansion towards the incoming beam. Ignition requirements as a function of laser intensity and pulse length, taking into account the relationship between intensity, hot electron temperature, and range, are then determined.

Experiments have been performed at the Central Laser Facility, Rutherford Appleton Lab., UK. using novel techniques in which laser produced plasmas have been diagnosed by measurements of the charged thermonuclear reaction products. Two types of experiment are being reported here. Firstly, thermonuclear alpha particles from an exploding pusher target have been used to determine the growth of the Rayleigh–Taylor instability in a separate laser driven planar foil. The resulting alpha particle range loss distributions provide a direct measurement of the foil thickness distribution and hence the instability. The R–T instability has been observed in a number of foils with range losses varying between almost zero to over lOμm. Secondly, a thermonuclear particle backlighting technique has been used in the measurement of the stopping power of hot plasma for different materials. The ratio of plasma stopping power to that of the cold material is measured and compared to a value obtained from theoretical modelling. The solid state nuclear track detector CR–39 has been used as a diagnostic for these experiments. A sophisticated image analysis system has been developed to enhance and improve data recovery.