Composition dependence of ion diffusion coefficients in gas mixtures at arbitrary field strengths

Expressions for the diffusion coefficient of ions in gas mixtures are obtained from momentum transfer theory, and are given in terms of the diffusion coefficients and drift velocities of the ions in the pure component gases. Blanc's law holds exactly at all field strengths if the mean free time between collisions is independent of velocity (Maxwell model), but otherwise there may be either positive or negative deviations from Blanc's law at high fields. Such deviations are of comparable magnitude for the diffusion coefficients and the mobility, but are not identical. Specific cases of inverse-power potentials are treated in further detail, and some numerical examples are given for rigid-sphere interactions

Composition dependence of ion transport coefficients in gas mixtures

A simple momentum-transfer theory for the composition dependence of ion mobilities and diffusion coefficients in gas mixtures at arbitrary field strengths is corrected, extended, and compared with a similar theory based on momentum and energy transfer, and with results based on direct solution of the Boltzmann equation by Kihara's method. Final equations are recommended for predicting composition dependences, given only results on ion mobilities and diffusion coefficients in the pure component gases

Revised theory of transient mass fluctuations

Abstract Several publications during the last 10 years by Woodward and colleagues have indicated a theory, based on general relativity, that has: (1) predicted transient mass fluctuations; (2) cited a specific embodiments where a net average force would be present; (3) suggested a few ways that this theory might be tested in the laboratory; and (4) have reported such test results incorporating these embodiments. In this paper we show that: (1) the average force predicted by Woodward occurred only because of a neglected term in a product derivative, and that when the neglected term is correctly returned, the average force vanishes; (2) this vanishment of the average force occurs for arbitrary forcing functions, not just the sinusoidal one considered by Woodward; (3) the transient mass fluctuation, predicted by Woodward, was developed in a theory which neglected local gravitational and electrodynamic forces which are several dozen orders of magnitude greater; (4) a less incomplete theory considering local gravitational forces produces a vastly smaller transient mass fluctuation

Extraction induced emittance growth for negative ion sources

Nonlinear emittance growth produced by ion extraction is considered by a 3-D analysis in a Vlasov-Poisson-Boltzmann formulation. Phenomena considered include: presheath effects, including electron depletion, electron sheath accumulation (for large transverse magnetic fields), nonlinear sheath fields (obtained by a self-consistent solution with an assumed quasi-equilibrium positive ion distribution and at least one Vlasov distribution), nonlinear fringe fields produced by the accelerator-extractor itself obtained self-consistently with item 3 above, nonlinear space charge of the beam itself, and beam in conjunction with extracted electrons. For specific volume negative ion source configurations, an investigation of the contribution of aberrations caused by an electron trap and electron accumulation in the extraction sheath are studied. Either of these effects can contribute significantly to the beam emittance, possibly dominating the contribution of the negative ion temperature in the source. 2 refs., 10 figs

Determination of ICRF antenna fields in the vicinity of a 3-D Faraday shield structure

A three-dimensional (3-D) magnetostatic analysis developed at Oak Ridge National Laboratory has been used to calculate the electromagnetic transmission properties of representative Faraday shield designs. The analysis uses the long-wavelength approximation to obtain a 3-D Laplace solution for the magnetic scalar potential over one poloidal period of the Faraday shield, from which the complete magnetic field distribution may be obtained. Once the magnetic field distributions in the presence and absence of a Faraday shield are known, the flux transmission coefficient can be found, as well as any change in the distributed inductance of the current strap. The disturbed capacitance of the strap can be found from an analogous 3-D electrostatic calculation, enabling the phase velocity of the slow-wave structure to be determined. Power dissipation in the shield may be estimated by equating the surface current on a perfect conductor with the surface magnetic field and using the surface current in conjunction with the finite conductivities of the shield materials to obtain the power distribution to eddy current heating. 4 refs., 5 figs., 1 tab

Modified calutron negative ion source operation and future plans

Negative ion generation has advanced rapidly by employing the concept of surface ionization. The modified calutron has proven to be a successful tool to explore these concepts and provide solutions to the many problems which must be evaluated. Many features of the SITEX (Surface Ionization with Transverse Extraction) ion source are ideally suited to this exploration. Some of these features are; a ribbon-like plasma, electron control by transverse magnetic fields and the ability to separate the Cs oven parameters from those which control the positive ion generation

ORNL positive ion neutral beam program

The neutral beam group at Oak Ridge National Laboratory has constructed neutral beam generators for the ORMAK and PLT devices, is presently constructing neutral beam devices for the ISX and PDX devices, and is contemplating the construction of neutral beam systems for the advanced TNS device. These neutral beam devices stem from the pioneering work on ion sources of G. G. Kelley and O. B. Morgan. We describe the ion sources under development at this Laboratory, the beam optics exhibited by these sources, as well as some theoretical considerations, and finally the remainder of the beamline design

Electrostatic ion thruster optics calculations

Two- and three-dimensional ion thruster optical calculations including both source and exhaust plasmas are performed. These calculations include both a self-consistent ion source extraction plasma sheath and an explicit computation of the primary ion optics including sheath and electrode induced aberrations. A study determining the effects of beam space charge, accelerator geometry, and properties of the downstream plasma sheath on the position of the electrostatic potential saddle point near the extractor electrode is made. Results of the electron blocking potential barrier height as a function of electrode thickness and secondary plasma processes are described