Electron Beam Fusion Research Articles

Densification of plasma-sprayed titanium and tantalum coatings

Thermal spraying of corrosion- resistant coatings of titanium and tantalum is difficult; dense coatings are not produced, and oxidation of these metals increases coating porosity. In this study, oxidation during plasma spraying was reduced with a shrouding system. Porosity and oxide content also were minimized by optimizing the spraying parameters. After optimization, the coatings still had open porosity and thus were incapable of protecting the substrate material against corrosion in water solutions containing 3 % NaCl. Therefore, posttreatments for improvement of corrosion resistance were studied. Electron beam fusion produced corrosion resistance equal to or better than that of bulk commercial samples of titanium and tantalum.

Aging characteristics of electron beam and gas tungsten arc fusion zones of Al-Cu-Li alloy 2090

A transmission electron microscopy (TEM) investigation of the electron beam (EB) and gas tungsten arc (GTA) fusion zones of 2090 indicates that in both the as-welded and aged conditions, the EB and GTA fusion zones lack the volume fraction and the homogeneity of strengthening precipitates found in the base metal. In the underaged and peak-aged conditions, the δ′ phase is the primary strengthener, the volume fraction ofT 1 present being too low to be effective. TheT 1, precipitates are found either in the vicinity of other inclusions or at the dendrite boundaries. As the strength increases with postweld aging, the elongation decreases to 1 pct. The presence of the boundary phases and Cu- and Cl-containing inclusions at the boundaries leads to poor elongation. The joint efficiencies of the peak-aged EB and GTA weldments (EBWs and GTAWs, respectively) are 75 and 55 pct at 293 K and 75 and 50 pct at 77 K, respectively. Both EBWs and GTAWs have relatively low elongations.

Thermal cycling of cast iron surface by electron beam fusion treatment

The technology of cast iron surface hardening, by electron beam fusion treatment, to increase the hardness and wear resistance is very well known. This method causes the great difference of hardness between a surface layer and a base material which creates the sharp structural notch. So, an attempt was made to smooth the structural notch to improve the fusion zone properties. It was decided to use here a carbon diffusion phenomenon against the temperature gradient inside the eutectic cell of ferritic cast iron with nodular graphite. To achieve the temperature gradient, the electron beam as a quasi-linear heat source was used. Owing to a very high power density of heat source and a very short interaction time, the requested temperature gradient inside the eutectic cell was obtained (at great difference of graphite and ferrite thermal properties). As a result of such treatment, a zone of pearlitic structure around the graphite as well as beneath a ledeburitic-martensitic fusion layer was attained. Hence, the significant smoothing of structural notch was obtained.

Electron-beam enhanced fusion of binary metals and alloying in melts

Binary mixing and alloying during electron-beam fusion in bi-metal joints have been investigated and presented in this paper. In case of beam-power densities greater than about 1010 Wm−2, rapid fusion of metals is accompanied by violent agitation of the melts. The resulting mass transport in the melt is described here from an enhanced mass diffusion coefficientD =Ds(W′/a0η)1/2, whereDs is mass diffusivity in solid,W′ is beam-power density,a0 is acceleration in melt growth andη is the coefficient of viscosity. Moreover, a uniformly mixed central-widthw′ is predicted in the fusion zone (total widthw), where,w′ is significantly dependent onη andw throughW′. For these conditions, the continuity of mass transport in stationary and travel modes of the source has been solved using line and plane source models and conservation principles. The predictions from these calculations have been validated through quantitative analyses of experiments.

Physical behaviour of electron-beam fusion heat transfer and deep penetration in metals

A simple model of fusion and deep penetration in metals under electron-beam interactions and energy transfer, is described in this paper. In this model, electrons in the beam penetrate a depth S and cause melting there, during which thermal-conduction melting occurs in a further depth zi in the beam direction. Hence, in the first discretized-fusion step, fusion depth D1 = S + z1, and total fusion depth in j steps, h = Σi = 1j (S + zi). Also, thermal conduction from a line source from the surface to the cavity bottom, causes sideways melting. In general, thermal-conduction melting f is given as f=[f0q0V'4π2x0Tmemp(−R02/k0t)] where, f0 is a dimensionless variable dependent on the beam and metal, q0 and V′ are source-strength and source-travel parameters, x0 is a unit distance, Tm is the melting point, R0 is a distance variable, k0 = K/ϱc is the thermal diffusivity, K is the coefficient of thermal conductivity, ϱ is the metal density and c is the specific heat. The sideways melting in succeeding steps add up to the initial melt width, to give the final width. Also, for metals K >K0(= 100J m−1 K−1s−1), meltings zi and f are reduced by (K0/K)1/2, due to large-scale thermal losses outwards. Using the present model, fusion profiles and penetrations for various conditions of the beam and metals were investigated through numerical calculation and are validated through experiments.

Increasing the life of alloy steels by fusion of their surface with an electron beam

1. After electron-beam treatment a uniform finely dispersed structure with cellular distribution of the carbide phase is formed in the fused zone. The sizes of the cells and the carbides depend upon the electron-beam fusion conditions. 2. Electron-beam fusion of the working surface of the experimental lot of R6M5 steel punches made it possible to increase their life by 2.5–3 times.

Electron beam fusion, energy compression, and the absolute instability

Absolute electron beam-plasma instability is suggested as a means of energy compression for pellet and liner inertial confinement fusion systems.

Pellet and Pellet-Blanket Neutronics and Photonics for Electron Beam Fusion

Pellet and Pellet-Blanket Neutronics and Photonics for Electron Beam Fusion

A Study of the Double-Focusing Diode

Applying a co-axial Marx generator with rectangular pulse across a constant load for the study of double-focusing-diodes, an impedance reduction and an increase in anode plasma density are observed. To achieve electron beam fusion, low-impedance diodes of impedance less than 1 Ω have been researched. The reduction of impedance accompanied by electron-beam double-focusing is important. It may be speculated that electron reflexing after focusing is required to lower the impedance and to increase the anode plasma density.

Characteristics of Co-Axial Marx Generator and Its Application to Electron Beam Fusion

A co-axial Marx generator with a short rise time of pulse less than 4 nsec, and ∼40 nsec flat top duration was successfully constructed. For the attainment of electron beam fusion, the requirements for the beam source are a rise time of less than 1 nsec, an impedance of less than 0.01 Ω and an inductance of less than several nH/MV. The co-axial Marx generator can be considered to be the most important tool for these purposes. We analyzed this rectangular output pulse of the co-axial Marx generator and applied it to electron beam fusion.

Long self-magnetically insulated power transport experiments

Energy and power transport in a self-magnetically insulated triplate transmission line are examined. The experiments are done on the MITE accelerator (2 MV, 0.4 MA, 40 ns), which is one module of the electron beam fusion accelerator, EBFA I. The transport efficiency is very sensitive to the injection geometry. An abrupt transition at the beginning of the line causes ∼40% power losses through an apparent instability. The growth length of the instability is ∼53 cm in a line with a vacuum wave impedance Z0=7.6 Ω. A second loss mechanism is associated with an azimuthal asymmetry in the self-magnetic field near the injection region. Both loss mechanisms were avoided by properly shaping the input to the transmission line and 90% energy transport and ∼100% power transport were achieved.

Data Acquisition and Processing on Electron Beam Fusion Accelerators

This report is a review of the hardware and software components of the custom data acquisition facility developed for the Sandia electron beam fusion research program. The facility contains a Modcomp II minicomputer system, Tektronix transient digitizers, conventional oscilloscopes, and an image digitizer. Commercial equipment is utilized as much as possible. Special interfaces were designed for the transient and image digitizers. Careful cable shielding techniques are used to overcome the severe noise environments. The Modcomp multi-task operating system allows two simultaneous users. Special applications programs have been developed for data acquisition and reduction. The facility is currently operational, and a duplicate of this system will be built to support the next generation accelerator EBFA (Electron Beam Fusion Accelerator).

Electron beam fusion?

Electron beam fusion?

In-depth heating by an intense relativistic electron beam

The dynamic response of a planar target irradiated by a tightly pinched intense relativistic electron beam is found to be very sensitive to in-depth heating by the beam due to x-ray deposition and to diode voltage fluctuations. We find that voltage fluctuations are primarily responsible for the observed wave structure preceding the large-amplitude shock wave while x-ray deposition affects the response to a lesser extent. The implications of these results for electron-beam fusion target and accelerator designs are noted.

Ablation-driven targets for electron-beam fusion: Density problem with very low-Z ablators

The behavior of DT-filled implosion targets with very low-Z (carbon) ablators irradiated by 1-MeV electrons is compared to that with intermediate- and high-Z ablators. The inner part of the pusher is of lower entropy due to decreased bremsstrahlung heating. The DT is shielded from compression until later in the energy pulse, when it is more strongly compressed. However, thicker ablators transfer less energy to the pusher; hence, diamond-carbon ablators perform better than graphite-carbon. Precompression of graphite-carbon with a laser does not reduce the minimum power required for break-even, but does lead to increased gain above break-even.

Considerations in the Design of Electron-Beam-Induced Fusion Reactor Systems

Electrical power generation by controlled fusion may provide a partial solution to the world's long-term energy supply problem. Achievement of a fusion reaction requires the confinement of an extremely hot plasma for a time long enough to allow fuel burnup. Inertial confinement of the plasma may be possible through the use of tightly focused, relativistic electron beams to compress a deuterium-tritium (D-T) fuel pellet. A power balance analysis applied to a conceptual electron-beam fusion power plant indicates that energy gains of between 5 and 16 are required from the fuel pellet for economic feasibility. To deliver an average power of 100 MW(e), the reactor must operate at a pulse rate of approximately 35 Hz, assuming an electron-beam energy of 1 MJ per pulse. The use of a fusion-fission hybrid reactor substantially relaxes the pellet gain requirement, and allows break-even plant operation at near unit pellet gain. Calculations show that x rays and ions will comprise an important part of the total energy release (30 percent for a pellet gain of 7.9). The x-ray radiation has an approximate 350-eV blackbody spectrum. The energy of ions from the gold shell surrounding the D-T fuel lies between 100 and 500 keV. Consideration ofmore » the response of diode and first-wall materials to the incident x-ray and ion fluxes shows that wet walls of lithium or tin over niobium are not desirable, due to spallation or other stress wave damage, engineering complexity, and excessive materials usage and cost. A solid wall protected by a graphite cloth shield offers the maximum protection to the surrounding blanket structure.« less

Authors

Authors

Radiation Patterns from Electron Beam Fusion Targets

Time-integrated x-ray pinhole photographs of gold spheres and hemispheres irradiated by focused intense relativistic electron beams have exhibited radiation patterns with a distinct, brightened edge or halo. This report describes Monte Carlo electron-photon transport calculations which were performed to analyze this halo effect. A locally 1-D model of the spherical targets is presented and is used to obtain information concerning the spectral variation of the radiation pattern. These results indicate that a complete model, including film response and effective pinhole size, is required for proper quantitative comparison.

Targets for Electron-Beam Fusion

I have performed computer simulations of high-density, spherical shells containing DT gas, irradiated by pulsed electron beams. For these targets, (1) the optimal shells are thick enough that few electrons reach their inner surface, (2) the low-level bremsstrahlung which penetrates the shell significantly affects the target performance, (3) breakeven requires about ${10}^{15}$ W deposited for 5 nsec. This represents a considerable improvement over the behavior of bare DT spheres; further improvements may reduce the power to ${10}^{14}$ W.

ELECTRON BEAM STORAGE DEVICES FOR CONTROLLED FUSION

The following topics are briefly discussed: (1) electrical energy storage: current status, (2) confinement of unneutralized plasma, (3) energy storage with an intense relativistic electron beam, (4) electrostatic heating of a tokamak, (5) electron beam formation, (6) stability problems, and (7) fusion with high-density pellets. (MOW)