Fusion Microexplosion Research Articles

To Mars in Weeks by Thermonuclear Microbomb Propulsion

To reduce the radiation hazard for manned missions to Mars and beyond, a high-specific-impulse–high-thrust system is needed, with a nuclear bomb propulsion system the preferred candidate. The propulsion with small fission bombs is excluded because the critical mass requirement leads to extravagant small fission burnup rates. This leaves open the propulsion with nonfission ignited thermonuclear microexplosions, with a compact fusion microexplosion igniter (driver) and no large radiator. It should not depend on the rare isotope and only requires a small amount of tritium. This excludes lasers for ignition. With megaamperes of gigavolt proton beams and a small amount of tritium, cylindrical deuterium targets can be ignited. The proton beams are generated by discharging the entire spacecraft as a magnetically insulated gigavolt capacitor. To avoid a large radiator, needed to remove the heat from the absorption of the fast neutrons in the spacecraft, the microexplosion is surrounded by a thick layer of liquid hydrogen, stopping the neutrons and heating the hydrogen to a temperature of , which as a fully ionized plasma can be repelled from the spacecraft by a magnetic mirror.

An Eulerian MHD model for the analysis of magnetic flux compression by expanding diamagnetic fusion plasma sphere

The process of magnetic flux compression (MFC) inside a solenoid by expanding diamagnetic plasma sphere produced by an inertial fusion micro-explosions and its application as a direct energy conversion scheme to convert a part of plasma kinetic energy into pulsed electrical energy has been recently reported [1]. For a detailed analysis of this concept, an Eulerian multi-material MHD model is developed using magnetic vector potential formulation for electro-magnetic field calculations and classical volume-of-fluid method for material interface tracking. The diffusion term in the magnetic induction equation is solved implicitly while the advection terms are computed using a second-order MUSCL scheme. An iteration procedure using ADI scheme is used for the free space field calculation. In this paper, we describe the details of the new MHD model, its validation against the semi-analytical solutions (for magnetic Reynolds number ≫1) of magnetic convective-diffusion equations and application to explore the concept of MFC by expanding plasma sphere. The simulation results show that the algorithm is capable of handling complex plasma dynamics inside the MFC system. Also, the results indicate the development and the evolution of MRT like instability near the stagnation point. The magnetic field diffusion into the plasma during the expansion phase is found to be negligible.

The National Ignition Facility (NIF): A path to fusion energy

Fusion energy has long been considered a promising, clean, nearly inexhaustible source of energy. Power production by fusion micro-explosions of inertial confinement fusion (ICF) targets has been a long-term research goal since the invention of the first laser in 1960. The National Ignition Facility (NIF) is poised to take the next important step in the journey by beginning experiments researching ICF ignition. Ignition on NIF will be the culmination of over 30 years of ICF research on high-powered laser systems such as the Nova laser at Lawrence Livermore National Laboratory (LLNL) and the OMEGA laser at the University of Rochester, as well as smaller systems around the world. NIF is a 192-beam Nd-glass laser facility at LLNL that is more than 90% complete. The first cluster of 48 beams is operational in the laser bay, the second cluster is now being commissioned, and the beam path to the target chamber is being installed. The Project will be completed in 2009, and ignition experiments will start in 2010. When completed, NIF will produce up to 1.8 MJ of 0.35-μm light in highly shaped pulses required for ignition. It will have beam stability and control to higher precision than any other laser fusion facility. Experiments using one of the beams of NIF have demonstrated that NIF can meet its beam performance goals. The National Ignition Campaign (NIC) has been established to manage the ignition effort on NIF. NIC has all of the research and development required to execute the ignition plan and to develop NIF into a fully operational facility. NIF will explore the ignition space, including direct drive, 2 ω ignition, and fast ignition, to optimize target efficiency for developing fusion as an energy source. In addition to efficient target performance, fusion energy requires significant advances in high-repetition-rate lasers and fusion reactor technology. The Mercury laser at LLNL is a high-repetition-rate Nd-glass laser for fusion energy driver development. Mercury uses state-of-the-art technology such as ceramic laser slabs and light diode pumping for improved efficiency and thermal management. Progress in NIF, NIC, Mercury, and the path forward for fusion energy will be presented.

Progress towards realization of a laser IFE solid wall chamber

The high average power laser (HAPL) program aims at developing laser inertial fusion energy (Laser IFE) based on lasers, direct drive targets and a solid wall chamber. The preferred first wall configuration is based on tungsten and ferritic steel as armor and structural materials, respectively. A key concern is the survival of the first wall under the X-ray and ion energy deposition from the fusion micro-explosion. The HAPL design and R&D effort in the chamber and material area is focused toward understanding and resolving the key armor survival issues. This includes modeling and experimental testing of the armor thermo-mechanical behavior in facilities utilizing ion, X-rays and laser sources to simulate IFE conditions. Helium management is addressed by conducting implantation experiments along with modeling of He behavior in tungsten. This paper summarizes the HAPL chamber activities. The first wall/armor configuration and design analysis are described, key chamber issues are discussed, and the R&D to address them is highlighted.

Threats, design limits and design windows for laser IFE dry wall chambers

The High Average Power Laser (HAPL) program is carrying out a coordinated effort to develop inertial fusion energy based on lasers, direct-drive targets and a dry wall chamber. The dry wall must accommodate the ion and photon threat spectra from the fusion micro-explosion over its required lifetime. This paper summarizes the current HAPL strategy on the armor/first wall configuration based on tungsten and ferritic steel as preferred armor and structural materials, respectively. The thermal performance of an example fully dense tungsten armor configuration on a ferritic steel first wall is described showing the basis for separating the high energy accommodation function of the armor from the structural function of the first wall. Example design operating windows for the armor, first wall and blanket are presented based on different requirements and constraints. The possibility of utilizing an engineered porous armor is discussed. Key chamber wall and armor issues are summarized.

Mini-fission–fusion explosive devices (mini-nukes) for nuclear pulse propulsion

Nuclear pulse propulsion demands low-yield nuclear explosive devices. Because the critical mass of a fission explosive is rather large, this leads to extravagant fission devices with a very low fuel burn-up. For non-fission ignited pure fusion microexplosions the problem is the large ignition apparatus (laser, particle beam, etc.). Fission ignited large fusion explosive devices are for obvious reasons even less desirable. A third category (mini-nukes) are devices where the critical mass of the fission explosive is substantially reduced by its coupling to a DT fusion reaction, with the DT fusion neutrons increasing the fission rate. Whereas in pure fission devices a reduction of the critical mass is achieved by the implosive compression of the fissile core with a chemical high explosive, in the third category the implosion must at the same time heat the DT surrounding the fissile core to a temperature of ⩾ 10 7 K , at which enough fusion neutrons are generated to increase the fission rate which in turn further increases the temperature and fusion neutron production rate. As has been shown by the author many years ago, such mini-nukes lead to astonishingly small critical masses. In their application to nuclear pulse propulsion the combustion products from the chemical high explosive are further heated by the neutrons and are becoming part of the propellant.

Thermal Loading of a Direct Drive Target Rarefied Gas

In an inertial fusion energy (IFE) power plant, each fusion micro-explosion (~10 Hz) causes thermal and structural loads on the IFE reactor wall and driver optics. The loading on the wall must remain sufficiently low to ensure that economic and safety constraints are met.One proposed method for decreasing the intensity of the wall loading is to fill the reaction chamber with a gas, such as Xe, at low density. The gas will absorb much of the radiation and ion energy from the fusion event, and then slowly release it to the chamber wall. Unfortunately the protective gas introduces major heat loads on the direct drive target. The thermal loading of a target, during injection, largely determines the viability of that target upon reaching chamber center. Thus, the density of the gas must be carefully selected to ensure that a target will survive injection.The objective of this work is to quantify and characterize the heat flux resulting from the interaction of the target and the protective gas. The loading of the target is modeled using DS2V, a commercial DSMC (Direct Simulation Monte Carlo) program. Using DS2V, this work explores the effect of the protective gas density, temperature, sticking (condensation) and accommodation coefficients on the heat flux to the target.

Fusion–fission–fusion fast ignition plasma focus

A crucial advancement in the problem for the controlled release of energy by nuclear fusion appears possible by an autocatalytic fusion–fission–fusion microexplosion, where the deuterium–tritium (DT) fusion reaction of a dense magnetized DT plasma placed inside a thin liner made up of U238, Th232 (perhaps B10) releases a sufficient number of 14 MeV fusion neutrons which by fission reactions in the liner implode the liner on the DT plasma. The liner implosion increases the DT plasma density and with it the neutron output accelerating the fast fission reactions. Following the fast fission assisted ignition, a thermonuclear detonation wave can propagate into unburnt DT to reach a high gain. The simplest way for the realization of this concept appears to be the dense plasma focus configuration, amended with a nested high voltage magnetically insulated transmission line for the heating of the DT. The large magnetic field needed for the α-particle entrapment of the DT fusion reaction is here generated by the thermomagnetic Nernst effect, amplifying the magnetic field of the plasma focus current sheet.

Autocatalytic fission–fusion microexplosions for nuclear pulse propulsion

Autocatalytic fission–fusion microexplosions, mutually amplifying fission and fusion reactions, are proposed for propulsion. Autocatalytic fission–fusion microexplosions can be realized by imploding a shell of uranium 235 (or plutonium) onto a magnetized deuterium–tritium (DT) plasma. After having reached a high temperature, the DT plasma releases fusion neutrons making fission reactions in the fissile shell increasing the implosion velocity which in turn increases the fusion reaction rate until full ignition of the DT plasma. To implode the fissile shell a small amount of high explosive and to magnetize the DT plasma a small auxiliary electric discharge are required. In comparison to nuclear bomb pulse propulsion, the energy released per pulse is much smaller and the efficiency higher. And in comparison to laser- or particle-beam-ignited fusion microexplosions, there is no need for a massive fusion ignition driver.

Analytic optimization of ion-driven hohlraums

An analytic model of ion beam driven hohlraums is presented which is used to determine the optimal hohlraum design parameters. It is shown that the radiation intensity within the hohlraum can exceed the average ion intensity driving the hohlraum. This “greenhouse effect” significantly lowers ion beam intensity requirements for driving a fusion microexplosion.

Nova target physics program and the Nova upgrade laser

Recent advances in ICF target design and performance have made possible the achievement of ignition and gain with 1–2 MJ laser drive energy, as against the 5–10 MJ necessary to achieve high gain in the earlier designs. Ignition and propagating burn can be achieved at the lower energy by increasing the hohlraum temperature and, thereby increasing the pressure driving the imploding fusion capsule. Nova experiments continue to address the target physics of radiatively driven targets, such as laser-plasma interaction physics, the efficiency of laser light conversion to X-rays, hohlraum characterization and design, hydrodynamic stability, and implosion physics. Recent experiments on Nova have also demonstrated 1.3 times higher hohlraum temperature than previously predicted. This latter demonstration is the key achievement leading to the Nova Upgrade proposal. These combined results, together with those from experiments to study the interaction of high-power laser light with target plasmas, indicate that the capsule drive and symmetry conditions required for ignition and net gain can be achieved with a properly designed upgrade of the existing Nova facility. Success in the Nova Upgrade objective would firmly establish target and driver requirements for achieving high yield and high gain and would support a decision to construct a Laboratory Microfusion Facility (LMF) for defense applications and an Engineering Test Facility (ETF) for energy applications by the end of the first decade of the next century. Nova Upgrade experiments would focus on the target physics necessary to determine the minimum driver energy required to achieve ignition and high-gain laser fusion. The thermonuclear yield produced (up to 20 MJ) would be used to study the effects of fusion microexplosions on potential LMF and ETF reactor chamber materials. This information would permit development of the most efficient and least costly designs for the LMF and the ETF.

Analysis and experiments in support of inertial confinement fusion reactor concepts

Cost-effective and safe containment of high-yield inertial confinement fusion (ICF) microexplosions in near-term laboratory microfusion facilities (LMF) and longer-term reactors requires an understanding of the interaction of target-generated x rays and ionic debris with surrounding buffer gases and the first solid surface that faces the target. The microfireball plasma created when a target explodes in a gas atmosphere of 1–10 Torr is not in local thermodynamic equilibrium. The plasma state must be determined by coupling the radiation field to the atomic level population calculation in order to correctly predict the surface emission of the plasma. Conditions similar to those predicted for ICF target chambers can be simulated using the SATURN x-ray simulator facility [Proceedings of the 2nd International Conference on Dense Z-Pinches, AIP Conf. Proc. 195 (AIP, New York, 1989), p. 3]. Aluminum and graphite samples that represent possible first wall materials were tested in SATURN. Coated aluminum samples and four-directional graphite weaves in a carbon matrix survived the tests.

Liquid Momentum Removal Using Rod Arrays Applied to the HYLIFE ICF Reactor

This work related to the multiple liquid-lithium-jet blanket concept of the High Yield Lithium Fusion Energy (HYLIFE) reactor. The fusion microexplosion would result in part of the liquid lithium being propelled toward the vacuum chamber wall where the resulting impact would cause high peak hoop stresses. In an attempt to reduce these peak stresses, it was proposed to set up an array of bars between the vacuum vessel first wall and the liquid jets so that part of the liquid momentum would be removed as the liquid passed through the bars. The bars would have a shorter lifetime than the vacuum vessel due to the liquid impact so that they should be considered as a type of sacrificial and replaceable first-wall shield. Results for the momentum removal during the initial transient impact were taken from the literature. These results were then nondimensionalized and used in combination with the steady-state results from our experiments to estimate the percentage of liquid momentum removed from large liquid slugs. For example, for the staggered array with a rod-to-liquid slug diameter ratio of approx. 0.08, the fractional momentum removed approaches approx. 12% for long liquid slugs. The results from this initial scoping study are encouragingmore » when applied to the HYLIFE reactor since, for ferritic and austenitic steels, the rather flat fatigue curves at a higher number of stress cycles suggest that a small decrease in the peak stress could significantly increase the fatigue life of the vacuum vessel.« less

Laser-fusion reactor materials problems resulting from fusion microexplosion emissions

Many materials problems that have been identified in laser-fusion reactor (LFR) concepts are similar to those anticipated for magnetically confined thermonuclear reactor designs, although LFR engineering and design options are different. The characteristics of a typical fusion-pellet microexplosion are discussed, and conceptual alternatives for containing pellet microexplosions are reviewed. Fusion pellet microexplosions occur within a few picoseconds, and energy is deposited in structural and blanket regions in about 1 μs. Thus, the effects of cyclical strain and shock phenomena pose unique materials problems for LFRs. In addition, optical elements (i.e., mirrors) are exposed to the products of fusion pellet microexplosions and possibly to other cavity materials. The most critical requirements for experimental data are investigations of the effects of pulsed, high-intensity neutron irradiation on fatigue stress limits and on the optical properties of mirror surfaces.

Laser-fusion reactor materials problems resulting from fusion microexplosion emissions☆

Laser-fusion reactor materials problems resulting from fusion microexplosion emissions☆

THEORETICAL ASPECTS OF COLLECTIVE ION ACCELERATION IN RELATIVISTIC ELECTRON BEAM DEUTERATED POLYETHYLENE TARGET INTERACTION*

The principal objective of this research has been to develop a 1-MJ plasma focus, which when operated in a low-density mode is expected to produce 10- nsec, 5-MA small diameter relativistic electron bursts. They will be used in fusion microexplosion studies to heat and compress solid targets in an effort to obtain significant thermonuclear yield. Some results on deuterated polyethylene are presented. (MOW)

An Alternative Thermonuclear n-Capture Path to the Superheavy Island

Thermonuclear neutron-capture approaches to heavy transuranium element synthesis are investigated. Certain feature of capture experiments using thermonuclear macro-explosives are re-analyzed in view of recent results of nuclear shell-structure theory and theoretical developments in laser-energized fusion micro-explosions. The micro-explosion conditions for prompt multiple neutron capture are estimated for the simplest moderation techniques. We speculate on some practical neutor-capture paths to the superheavy island, especially a hybrid approach, using both macro-and micro-explosion events.