Theoretical and numerical analyses are given for direct- and indirect-driven reactor targets, from which 3-GJ fusion output energy is released. For a reactor target, which has a large radius and long implosion time, supersonic flow of imploding D–T fuel in the converging nozzle (in sphere) is important for adiabatic compression of fuel. For a direct-driven target, pellet gain depends much upon the region where the beam deposits its energy. Phase mixing is also important to increase the absorption rate of irradiating laser light. When a strong light with a phase is concentrated on a small region of target surface, collective electron motion on the target surface radiates electromagnetic waves, which reduce the electron motion. When beam irradiation on the target is not uniform, an indirect-driven target must be used because a direct-driven target is weak for nonuniform irradiation. For an indirect-driven reactor target, which requires a long implosion time, expansion of radiator and absorber layers causes the decrease in radiation temperature. There is the optimum target structure with respect to the aspect ratio (radiation gap distance).

The results of 1-D numerical study are reported for a class of simple D-T targets driven by the beams of heavy ions. A simple target is defined as a uniform spherical metallic shell with the frozen D-T deposited on its inner surface and the D-T gas in the central cavity. Optimum target parameters have been found for several combinations of the three relevant driver parameters—the input energy Ein, the beam pulse duration tin, and the beam ion energy Eb. A simple box pulse profile was assumed. As a central set of driver parameters around which most of the calculations have been done, the values Ein = 6.12 MJ, tin = 17 ns, and Eb = 20 GeV have been adopted. It was found that all the targets from the class under consideration ignite uniformly over the entire fuel mass. Maximum energy gains amount to Gopt = 80–100. The physical picture of the target performance is analyzed in detail.

The possibility of heavy-ion beam-pumped ion lasers is demonstrated by observation of optical gain on the 476.5-nm Ar II 4p–4s ion laser transition in argon gas excited by 2.5–ns pulses of 110–MeV 32S ions with repetition rates up to 156 kHz. The particle energy per pulse was about 20 μJ. The projectiles were stopped in the target at pressures between 5 and 35 kPa. The beam from an argon ion probe laser operated at 476.5 nm was used to determine gain amplitude and time structure from a measured transient increase of the probe laser intensity when target excitation by the ion beam was present. The maximum gain observed was (0.5 ± 0.1) x 10-3 at a target gas pressure of 5 kPa. The optical gain observed in argon is consistent with calculations based upon an analysis of spectroscopic studies of rare gas targets excited by heavy-ion beams.

A new technique to achieve smooth laser irradiation profiles on laser fusion targets is evaluated numerically and experimentally. In this technique, smoothing is obtained by using a spectral dispersing optic and a random-phase plate placed in front of a focusing lens employing the broad-bandwidth of KrF lasers. Experimental results and numerical calculations agree well, verifying that this simple optical system is effective for smooth irradiation on targets.

We describe the properties of the exploding foil neon-like germanium soft X-ray lasers having wavelengths of 19–28 nm and gain length product of more than 10. The measured X-ray intensity of lasing lines from an exploding foil target has been explained with the results of the plasma hydrodynamic code from the viewpoint of suitable condition of electron density and temperature for creating population inversion.

The conditions for an experiment are being discussed in which the hydrodynamic efficiency could be measured and an optimum thermonuclear target design worked out that could be performed on a single-channel accelerator facility producing a 209Bi ion beam of ∼100 GeV per nucleus. As numerical simulations show, the expected values of the hydrodynamic efficiency are 5–10%, while the optimization of the target-beam system could be performed by compressing D-T gas in a conical cavity and registering some 109-1011 neutrons per shot.

In an earlier preliminary design study, we proposed a novel nuclear-pumped laser-driven (NPL) inertial confinement fusion (ICF) power reactor that represents an important variation on the “neutron feedback” concept for ICF. This NPL-driven ICF concept also included an advanced, DT-seeded, D3He-fueled pellet and magnetic protection of the first wall of the reactor chamber. Advantages that were demonstrated for this approach included increased efficiency for laser-to-target energy coupling, increased efficiency for thermalto-electric energy conversion, and reduced neutron activation and waste. The coupling efficiency is enhanced because a nuclear-pumped flashlamp is directly pumped by fission fragments from uranium micropellets within the lamp medium. The thermal conversion efficiency is greater because a large fraction of the ICF pellet&s fusion yield is in charged Finally, the fraction of the fusion yield carried by neutrons is significantly reduced in comparison with pure D-T-fueled pellets; thus, neutron-induced activity in the first wall is decreased and safety is increased. The initial study indicated these factors could result in a required driver energy of 5 MJ (vice 10 MJ currently projected) and a pellet gain of only 50 (vice 100 currently projected) for a feasible l,000-MWe power reactor operating with approximately six pellets per second. The current study includes a refined analysis of an NPL-driven ICF power reactor of this type. A cylindrical design for the fission/NPL blanket is selected as a “natural” geometry for pumping the NPL. Required enrichments and criticalities are then predicted for the multiplication of the fusion neutron yield needed to pump the NPL. Based upon these results, we report a more detailed parametric study of the efficiencies for converting neutron, X-ray, and plasma yields from advanced ICF pellets into electrical and optical energy flows required in this concept. We also examined breeding tritium in a lithium blanket layer. Results from these studies help define topics and parameter spaces for further research on this unique reactor concept.

Two concepts have been applied to the classical problem of accelerators for the ignition of indirectly driven inertial fusion. The first is the use of non-Liouvillian stacking based on photoionisation of a singly charged ion beam. A special FEL appears the most suited device to generate the appropriate light beam intensity at the required wavelength. The second is based on the use of a large number of (>1000) beamlets–or “beam straws”–all focussed by an appropriate magnetic structure and concentrated on the same spot on the pellet. The use of a large number of beams–each with a relatively low-current density–elegantly circumvents the problems of space charge, making use of the non-Liouvillian nature of the stopping power of the material of the pellet. The present conceptual design is based on a low-current (〈i〉 ≈ 50 mA) heavy-ion beam accelerated with a standard LINAC structure and accumulated in a stack of rings with the help of photoionisation. Beams are then extracted simultaneously from all the rings and further subdivided with the help of a switchyard of alternate paths separating and synchronising the many bunches from each ring before they hit the pellet. Single beam straws carry a reasonable number of ions: Beams and technology are directly relatable to the ones presently employed, for instance, at the CERN-PS. Space-charge-dominated conditions arise only during the last few turns before extraction and in the beam transport channel to the reaction chamber. In a practical example, we aim at a peak power of 500 TW delivered to the pellet for a duration of 10–15 ns. High-energy (10 GeV) beam straws of Ba doubly ionised ions are concentrated on several (four) focal spots of a radius of about 1 mm. The power density deposited on these tiny cylindrical absorbers inside a hermetic “hohlraum” is about 2.5 × 1016 w/g. These conditions are believed to be optimal for X-ray conversion, i.e., with an estimated conversion efficiency of about 90%.

The radiation transport effect on pellet implosion and the Rayleigh-Taylor (R-T) instability are studied in a light-ion beam (LIB) inertial confinement fusion (ICF) by numerical simulation and analytic work. First, we present the nonuniformity-smoothing effect of the radiation transport on implosion symmetry in an LIB ICF fuel pellet. The 2-D implosion simulation shows that the initial nonuniformity can be smoothed out well in an LIB ICF pellet; for example, the initial nonuniformity of 6% is smoothed to 0.07% during the implosion phase. In addition, linear analyses for the R-T instability under nonuniform acceleration in space and under radiation are also performed: The nonuniform acceleration field in space does not change the growth rate (γ) of the R-T instability. However, this nonuniformity may suppress the growth itself of the R-T instability. Radiation may reduc the growth rate (γ).

Atomic modeling of high-Z partially ionized plasma is essential for simulating radiation hydrodynamics of laser-produced plasma. A collisional-radiative model based upon an average atom model is used to calculate plasma opacity and emissivity. Because line radiations are most dominant in such plasma, the detail configuration accounting (DCA) for electronic state is required. We propose a statistical method to carry out the DCA with the use of the average population of bound electrons. Further modeling of line group made of the same transition from ions in different change states is discussed by considering the detail structure (hierarchy) of the line group.

The control of the extracted beam quality of a nuclear-pumped laser is a major issue. One possible control method involves changing the spatial power deposition profile, which is a function of the gas pressure and the pumping mechanism. Thus, we proposed a combined He-3 and wall coating (e.g., B-10 or U-235) technique. Then, the pump power deposition profile can be adjusted by varying the He-3 partial pressure. To examine this technique, measurements are being performed with an in-core cell by imaging the radiation-induced fluorescence onto a linear diode array located some distance from the cell. Results from these measurements are presented and other related issues such as gas dynamics, index of refraction effects, and efficient beam extraction from a large-volume cavity are discussed.

Ballistic propagation and focusing of intense light-ion beams requires (1) close limits on allowable beam divergence (∼5 mrad) and (2) gas-filled magnetic lenses that must function effectively even if deleterious self-fields are generated during the passage of the beam through the lens. An alternative to ballistic focusing was suggested some years ago in which magnetically compressed light-ion rings capable of delivering 3–4 MJ in a pulse of ∼1 ns are transported to the target in a tube. This concept is reexamined in light of recent work on the creation of ion rings and magnetic compression of stabilized liners. The physics issues of (1) magnetic compression, (2) transport of ion rings in a tube, and (3) the interaction of the ring with the target will be explored to evaluate the feasibility of this scheme.

A practical, visible nuclear-pumped laser (NPL) has been sought at the University of Illinois and other laboratories for a number of years. Yet, the results from successful visible NPLs to date have not been fully satisfactory, e.g., the threshold pumping power is too high for conventional applications. Progress in recent studies of 3He-Ne-H2 as a candidate NPL operating in the visible region at 585.3 nm on the 2P1,-1S2 Ne transition is described. We obtained lasing on the above transition for 3He-Ne-H2 concentrations of 1,140, 588, and 412 torr, respectively, with the laser cavity placed in the beamport of the University of Illinois TRIGA reactor. The threshold thermal neutron flux is 1014 n/cm2-s, corresponding to a threshold pumping power of 5 W/cm3.

Intense light-ion beams are being developed for investigations of inertial confinement fusion (ICF). This effort has concentrated on developing the Particle Beam Fusion Accelerator II (PBFA II) at Sandia as a driver for ICF target experiments, on design concepts for a high-yield, high-gain Laboratory Microfusion Facility (LMF), and on a comprehensive system study of a light-ion beam-driven commercial fusion reactor (LIBRA). This article reports on the status of design concepts and research in these areas.

The present review is of the experimental investigations on laser-plasma interaction being carried out in past years at IAE. Experiments were conducted on the “Mishen” facility. The laser system of Mishen consists of two channels with output beam parameters as follows: the main beam—output energy 100–200 J (λ = 1.054 μm) in 3-ns pulse, divergence ∼2 × 10-4 rad, contrast ratio ∼106, power density at the target surface ∼1013–1014 W/cm2; the diagnostic beam–output energy 10–20 J (λ = 1.054 μm) and 5–10 J (λ = 0.53 μm) in 0.3-ns pulse, divergence ∼10-4 rad, power density 1013 - 1014 W/cm2. Our aim in this experiment is to study the different aspects of the ICF processes in flat geometry. The main issues of our studies are hydrodynamic aspects, including acceleration efficiency, high-velocity impact in cascade targets, hydrostability, and X-ray physicsconversion efficiency, heat transfer, and X-ray-driven targets.

Lasing in atomic iodine pumped with incoherent, nuclear-stimulated XeBr* fluorescence is reported. These experiments represent the first demonstration of a nuclear flashlamppumped laser of any type. The fluorescence of XeBr* under nuclear pumping is also discussed.

A parameter study of implosion, burn, and gain of D–T ignitor/D3He fuel pellets is presented for a D3He inertial confinement fusion reactor. It is found from burn simulation that attaining a quasi-isobaric state with a temperature of 4 keV and pR value of 2.5 g/cm2 for the D–T ignitor and 0.8 keV and 9.5 g/cm2 for the D3He main fuel would suffice to obtain a pellet gain of ∼40–50 required for the D3He reactor. With 30-MJ laser irradiation and the coupling efficiency of 10%, the density of the target is assumed to be imploded to 5,000 times the liquid density. However, in the implosion simulation to realize the above configuration it is found that after void closure the central hot D–T ignitor region is ignited, while the bulk of the D3He main fuel is still imploding with high velocities. This preignition of the D–T ignitor leads to a low compression of the main fuel and prevents the D–T/D3He pellet from obtaining the required pellet gain. The pellet gain obtained is only ∼3.

In pulse-power technology, a transformer-type accelerator is a good candidate for a highvoltage pulse generator suitable for repetitive operations. In this article, a reverse-conducting thyristor has been used as a switching element in a primary circuit and good operations have been obtained. A dual-resonant mode and the mode proposed by Reed, preferable to the former in the sense of voltage gain, have been investigated experimentally. A voltage gain of 25% increase compared to that of the dual-resonant mode operation has been obtained. Two different types of transformers, a spiral and a Tesla type with various turn ratios, were constructed and the characteristics of each type when applied to the same circuit have also been investigated in detail. As a result, it has been made clear that the stray capacitance of the secondary winding restricts the upper limit of the turn ratio to get the large voltage multiplication.