Showing papers on "Perveance published in 1974"

Plasma‐induced field emission and the characteristics of high‐current relativistic electron flow

Abstract: The results of a comprehensive diode study conducted using a pulsed high‐current electron accelerator are reported Time‐dependent analysis of right‐cylindrical graphite cathodes has shown evidence of the field emission character of the cold‐cathode diode The effects of cathode whiskers or microprojections on the diode response have been observed Within a few nanoseconds after the voltage is applied to the diode, the whiskers explode to form cathode flares The observed diode perveance throughout the remainder of the pulse can be explained in terms of the expansion of the plasma cathode formed by the merger of many cathode flares Cathode plasma velocities ranged from approximately 2 to 3 cm/μsec The observed diode behavior was consistent with that predicted by previous studies of high‐voltage vacuum breakdown

Theory of potential-well formation in an electrostatic confinement device

Abstract: A theoretical model is developed to describe the behavior of an ion‐injection electrostatic confinement device. It is assumed that there is a shallow potential well in the center. Distribution functions, which are consistent with atomic processes occurring and with mechanisms leading to particle angular momentum, are obtained for ions and electrons. Using these distribution functions, Poisson's equation is solved to obtain potential and density profiles. By varying the experimental parameters, the conditions needed to go from a shallow potential well to a deep potential well are studied. The most important problems are found to be nonspherical focusing through grid construction asymmetry, and neutralization by electrons. Deeper wells are produced by increasing ion perveance, improving spherical symmetry, and reducing pressure.

Method and apparatus for extracting well-formed, high current ion beams from a plasma source

Abstract: A well-formed ion beam having a high current is extracted from an ion plasma by a low perveance ion extraction system including focus and extraction electrodes, the extraction electrode having an ion exit aperture and being axially spaced from the focus electrode a distance of at least several times the diameter of the ion exit aperture. A voltage differential is applied between the electrodes to define a plasma sheath at the ion source aperture, and the ion beam is extracted from the plasma sheath.

Modulator circuit for high power linear beam tube

Abstract: A high power linear beam tube; to be modulated, such as a high-power klystron, has its cathode directly connected with the depressed collector electrode of a modulator tetrode tube and its anode connected to the accelerating electrode of the tetrode modulator tube. The modulator tetrode tube includes a gridded convergent flow linear beam electron gun and a mirror image, substantially 100 percent depressed collector. The control grid is non-intercepting grid with and provides a voltage gain of 20 to 50 and a relatively high-power gain, as of 20 to 40 db. The electron gun includes a massive non-intercepting accelerating anode disposed between the control grid and the depressed collector. When the beam traverses the accelerating anode to the depressed collector, the collector is lowered toward cathode potential, causing an equivalent current to flow in the thermionic diode load. The beam perveance of the load tube is preferably substantially equal to the perveance of the electron gun of the tetrode modulator tube.

Low perverance ion beam extraction from an electron bombardment discharge

Abstract: Ion beams extracted from an electron bombardment (Penning) discharge by low perveance, single aperture Pierce electrode configuration, are compared with the beam properties predicted by a space charge computer program. For a 1 mm diameter source aperture, and an electron perveance of 1 x 10$sup -8$ AV/sup - $sup 3$/$sub 2$/, the measured and computed results are in good agreement. When this configuration was scaled up to have a 4 mm diam source aperture the extracted current was as much as 40 percent higher than predicted by the calculated electron perveance of 1 x 10$sup -8$ AV/sup -$sup 3$/$sub 2$/. In the case of an electrode configuration with a calculated electron perveance of 3.5 x 10$sup -8$ A/V/sup $sup -3$/$sub 2$/, that was also scaled to a 4 mm diameter source aperture, the extracted current was also 40 percent higher than predicted. In the latter case at 70 kV a maximum beam current of 4.3 mA (or argon) could be extracted with 0.8 A of discharge current. Plasma sheath instabilities occurred at currents above approximately 2 times the calculated perveance. (auth)

Instabilities in Self-Focused Electron Beams

Abstract: The appearance of large amplitude oscillations and attenuation of beam current have been observed in high perveance electrically self-focused beams. These phenomena are shown to be due to instabilities produced by the interaction of the beam with its self-generated plasma. The critical current which must be exceeded for the instabilities to appear and the frequencies of the oscillations have been related to beam and background parameters and the dimensions of the experimental system.