Drew A. Geller

The Science and Technologies for Fusion Energy With Lasers and Direct-Drive Targets

We are carrying out a multidisciplinary multi-institutional program to develop the scientific and technical basis for inertial fusion energy (IFE) based on laser drivers and direct-drive targets. The key components are developed as an integrated system, linking the science, technology, and final application of a 1000-MWe pure-fusion power plant. The science and technologies developed here are flexible enough to be applied to other size systems. The scientific justification for this work is a family of target designs (simulations) that show that direct drive has the potential to provide the high gains needed for a pure-fusion power plant. Two competing lasers are under development: the diode-pumped solid-state laser (DPPSL) and the electron-beam-pumped krypton fluoride (KrF) gas laser. This paper will present the current state of the art in the target designs and lasers, as well as the other IFE technologies required for energy, including final optics (grazing incidence and dielectrics), chambers, and target fabrication, injection, and tracking technologies. All of these are applicable to both laser systems and to other laser IFE-based concepts. However, in some of the higher performance target designs, the DPPSL will require more energy to reach the same yield as with the KrF laser.

Continuous thermoacoustic mixture separation

The superposition of nonzero time-averaged mole flux N on a thermoacoustic wave in a binary gas mixture in a tube produces continuous mixture separation, in which one or more partially purified product streams are created from a feedstock stream. Significant product and feedstock flows occur through capillaries that are small enough to experience negligible thermoacoustic phenomena of their own. Experiments with a 50–50 helium-argon mixture show diverse consequences of nonzero flow, involving the addition of only one simple term nHN to the equation for the heavy component’s time-averaged mole flux, where nH is the mole fraction of the heavy component. A boundary condition for nH must be imposed on the equation wherever products flow out of the separation tube, but not where feedstock flows in.

Demonstrating a Target Supply for Inertial Fusion Energy

Abstract A central feature of an Inertial Fusion Energy (IFE) power plant is a target that has been compressed and heated to fusion conditions by the energy input of the driver. The technology to economically manufacture and then position cryogenic targets at chamber center is at the heart of future IFE power plants. For direct drive IFE (laser fusion), energy is applied directly to the surface of a spherical CH polymer capsule containing the deuterium-tritium (DT) fusion fuel at approximately 18K. For indirect drive (heavy ion fusion, HIF), the target consists of a similar fuel capsule within a cylindrical metal container or ’’hohlraum’’ which converts the incident driver energy into x-rays to implode the capsule. For either target, it must be accurately delivered to the target chamber center at a rate of about 5-10Hz, with a precisely predicted target location. Future successful fabrication and injection systems must operate at the low cost required for energy production (about

Saturation of thermoacoustic mixture separation

0.25/target, about 104 less than current costs). Z-pinch driven IFE (ZFE) utilizes high current pulses to compress plasma to produce x-rays that indirectly heat a fusion capsule. ZFE target technologies utilize a repetition rate of about 0.1 Hz with a higher yield. This paper provides an overview of the proposed target methodologies for laser fusion, HIF, and ZFE, and summarizes advances in the unique materials science and technology development programs.

Thermodynamic efficiency of thermoacoustic mixture separation

The theory for thermoacoustic mixture separation is extended to include the effects of a nonzero concentration gradient. New data are presented, which are in excellent agreement with this theory. The maximum concentration gradient which may be achieved in a binary mixture of gases through this separation process is intrinsically limited by the fractional pressure amplitude, by the tidal displacement, and by the size of the thermal diffusion ratio. Ordinary diffusion further detracts from the attainable final concentration gradient and can become the dominant remixing process as the cross section of the duct is increased. Rayleigh streaming also works against thermoacoustic separation, and an estimate of the molar flux from streaming is given.

Beta-layering in foam-lined surrogate IFE targets

The acoustic power loss in the thermoacoustic mixture-separation process is derived, including the contributions due to a nonzero gradient in concentration. The significance of the gradient-dependent term is discussed. The limiting thermodynamic efficiency of the separation is calculated. Under reasonable circumstances, the efficiency approaches 10(-2) nHnL(delta m/m(avg))2, where nH and nL are the mole fractions of the two components of the mixture, and delta m/m(avg) is the fractional difference between the molar masses of the two components. This efficiency is of the same order of magnitude as that of some other, more conventional separation methods.

Thermoacoustic enrichment of the isotopes of neon

Abstract Solid deuterium-tritium (the symbol DT is used here to represent the equilibrium mixture of 50% deuterium and 50% tritium, having the molecular composition: 25% D2, 50% deuterium tritide molecules, and 25% T2) (DT) is nucleated from DT-wetted foam and subsequently forms a uniform layer by the beta-layering phenomenon. Compared to DT frozen on smooth metal surfaces, the surface roughness of the inner-lying pure DT solid-vapor interface is substantially lower at all modal values higher than ~10, possibly due to the small-grain-size polycrystalline nature of the solid. For thick layers, deleterious effects are observed, notably the formation of DT-rich vapor voids in the foam matrix and the subsequent propagation of these voids into the pure solid DT layer.

Thermoacoustics and thermal dissociation of water

The enrichment of the neon isotopes in a thermoacoustic device is demonstrated. Because the thermal diffusion ratio of neon is small, an apparatus longer than a wavelength was necessary in order to easily observe the separation. The device was modular and extensible, so that arbitrarily large separations could in principle be obtained. The acoustic duct was a series of multiple, identical quarter-wavelength modules with side-branch drivers. In this way, waveforms close to that of a traveling wave were maintained in the duct, despite the high acoustic attenuation caused by the duct’s small diameter and large length. The concentrations of the isotopes were measured at one end of the duct using a quadrupole mass spectrometer. For the operating frequency of 227 Hz, the maximum separation gradient obtained was 0.43%/m, and mole fluxes at zero gradient as high as 3 nmol/s were observed. Effects of turbulence, though not observed, are also discussed, and the scaling properties of this method are compared with th...

Stick-slip behavior in a continuum-granular experiment

Near 2600 K, 10% of water molecules are thermally dissociated at atmospheric pressure, with a reaction time constant below 1 ms. Such temperatures can be reached with focused sunlight. To use this endothermic reaction for the production of hydrogen, the hydrogen must be separated from the oxygen at high temperature, because they would quickly recombine to form water again, if the unseparated mixture were simply returned to lower temperatures. We have considered thermoacoustic mixture separation for this purpose. Our calculations show that the thermal‐diffusion ratios are high enough to yield steadily flowing streams of hydrogen‐enriched steam and oxygen‐enriched steam in a separation channel less than a wavelength long. However, the thermoacoustic power density in 1‐bar steam is low, so the required apparatus would be large, needing alot of expensive and fragile high‐temperature material, such as calcia‐stabilized zirconia. Our estimates show that this approach to solar hydrogen production would be approximately 30 times more expensive than solar‐Stirling electricity generation driving traditional water electrolysis. [Work supported by DOE Office of Science.]

Overview of recent tritium target filling, layering, and material testing at Los Alamos national laboratory in support of inertial fusion experiments

We report moment distribution results from a laboratory experiment, similar in character to an isolated strike-slip earthquake fault, consisting of sheared elastic plates separated by a narrow gap filled with a two-dimensional granular medium. Local measurement of strain displacements of the plates at 203 spatial points located adjacent to the gap allows direct determination of the event moments and their spatial and temporal distributions. We show that events consist of spatially coherent, larger motions and spatially extended (noncoherent), smaller events. The noncoherent events have a probability distribution of event moment consistent with an M(-3/2) power law scaling with Poisson-distributed recurrence times. Coherent events have a log-normal moment distribution and mean temporal recurrence. As the applied normal pressure increases, there are more coherent events and their log-normal distribution broadens and shifts to larger average moment.