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The role of electron currents in Field-Reversed Mirror (FRM) dynamics has been studied through both analytic and computational means. In particular, the effects of electron currents near a magnetic field null ("0" point) is closely examined. Since the electrons are not tied to field lines in this region, they are able to partially cancel the ion current there in response to an inductive electric field and ion drag. Past workers, using a fluid description, have suggested that this cancellation may be virtually complete, making impossible the steady state operation of the FRM as well as its startup by neutral-beam injection. However, the fluid approximation is invalid near a field null. We have developed a detailed non-fluid model for the bulk dynamics of the electrons in this region. The region is treated as unmagnetized; electrons are ...
The influence of externally-imposed radial electric fields on the fusion energy output, energy multiplication, and alpha-particle ash build-up in a TFTR-sized, fusing tokamak plasma is explored. In an idealized tokamak plasma, an externally-imposed radial electric field leads to plasma rotation, but no charge current flows across the magnetic fields. However, a realistically-low neutral density profile generates a non-zero cross-field conductivity and the species dependence of this conductivity allows the electric field to selectively alter radial particle transport. The plasma burn time until reaching a given ash fraction (the "timeto-buildup") is used as a measure of plasma performance. Because the fuel species has a higher cross-field conductivity than the ash, imposition of an inward-directed field enhances fuel confinement more th...
Several crucial properties of suprathermal (>500 keV) fusion-products are explored, both in their initial phase and during their slowingdown period. A guiding center drift theory, which predicts the effect of energy loss on the motion of these suprathermals, is derived for a low-B, symmetric (non-ripple) tokamak. Velocity-space scattering is ignored. Among the important implications of this theory are: (1) the net inward drift of fusion particles during their slow-down phase, and (2) the importance of the plasma density and temperature in determiningthis drift. The effect the inward drifting has on the spatial profile for the suprathermals approaching thermal energies, on the energy distribution, and on the plasma heating profile is demonstrated for five reactor cases, ranging from near-term low-current devices to conceptual power reac...
The performance of NASA Lewis fusion experiments (SUMMA and Bumpy Torus) is compared with other experiments and that necessary for a power reactor. Key parameters cited are gain (fusion power/input power) and the time average fusion power, both of which may be more significant for real fusion reactors than the commonly used Lawson parameter. The NASA devices are over 10 orders of magnitude below the required powerplant values in both gain and time average power. The best experiments elsewhere are also as much as 4 to 5 orders of magnitude low. However, the NASA experiments compare favorably with other alternate approaches that have received less funding than the mainline experiments. The steady-state character and efficiency of plasma heating are strong advantages of the NASA approach. The problem, though, is to move ahead to experimen...
A UF6 handling system was designed for use in conjunction with the existing nuclear-pumped laser vacuum system at a nuclear reactor laboratory to perform the experiments described above. A modification to separate the gas fill system from the vacuum system and thus greatly reduce its volume is described as well as operating procedures for the first controlled nuclear pumping experiments with UF6 vapor contained in the laser cell.
The development of nuclear pumped lasers with improved efficiency, energy storage capability, and UF6 volume pumping is reviewed. Results of nuclear pumped laser experiments using a TRIGA-type pulsed reactor are outlined.
A gas handling system capable of use with uranium fluoride was designed and constructed for use with nuclear pumped laser experiments using the TRIGA research reactor. By employing careful design and temperature controls, the UF6 can be first transported into the irradiation chamber, and then, at the conclusion of the experiment, returned to gas cylinders. The design of the system is described. Operating procedures for the UF6 and gas handling systems are included.
The electron flux spectrum has been calculated over the entire range from delta-ray energies to ionization-potential energies. Estimates based on the Born approximation indicate that electron-gas atom elastic losses can be neglected. Gryzinski's (1965) classical cross sections show that electron-thermalized electron interactions can be ignored. Under those conditions the energy degradation is primarily due to the excitation and ionization of background gas.
Comment: 15 pages. Invited review for the ESO Workshop on "The Early Universe with the VLT" 1-4 April 1996
Calculations of ionization-excitation source rates in gaseous media irradiated by fission fragments and alpha particles
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