Cygnus dose symmetry
The Cygnus Dual Beam Radiographic Facility consists of two identical radiographic sources each with a dose rating of 4 Rad at 1 m, and a 1 mm diameter spot size. The development of the rod pinch diode was responsible for the ability to meet these criteria. The rod pinch diode in the Cygnus machines use a 0.75 mm diameter tungsten tapered anode rod extended through a 9 mm diameter cathode aperture. When properly configured, the electron beam born off the aperture edge can self-insulate and pinch onto the tip of the rod creating an intense, small x-ray source. The Cygnus sources are utilized as the primary diagnostic on experiments which are single-shot, high value events. In such an application there is an emphasis on reliability and reproducibility. The azimuthal quality and reproducibility of the Cygnus sources will be analyzed using lithium fluoride thermoluminescent dosimeters. Photogrammetry will be used to quantify the precision of the rod pinch diode build (i.e. the centeredness of the anode rod). One goal of these tests will be investigation of the relationship of dose symmetry to anode rod position (i.e. the correlation of off-center dose to an off-center anode rod).
Experimental Comparison of 2-3MV X-Ray Sources for Flash Radiography
High-brightness flash x-ray sources are needed for penetrating dynamic radiography for a variety of applications. Various bremsstrahlung source experiments have been conducted on the TriMeV accelerator (3MV, 60 {Omega}, 20 ns) to determine the best diode and focusing configuration in the 2-3 MV range. Three classes of candidate diodes were examined: gas cell focusing, magnetically immersed, and rod pinch. The best result for the gas cell diode was 6 rad at 1 meter from the source with a 5 mm diameter x-ray spot. Using a 0.5 mm diameter cathode immersed in a 17 T solenoidal magnetic field, the best shot produced 4.1 rad with a 2.9 mm spot. The rod pinch diode demonstrated very reproducible radiographic spots between 0.75 and 0.8 mm in diameter, producing 1.2 rad. This represents a factor of eight improvement in the TriMeV flash radiographic capability above the original gas cell diode to a figure of merit (dose/spot diameter) > 1.8 rad/mm. These results clearly show the rod pinch diode to be the choice x-ray source for flash radiography at 2-3 M V endpoint.
Explosive emission of electrons
A review of papers devoted to study and use of the emission of electrons from a metal in contact with plasma clusters formed on explosion of micropoints on a cathode under the influence of thermionic field emission current of high density. A systematic discussion is given of questions of thermionic field emission of electrons from the metal, energy dissipation in cathode micropoints, explosive evaporation of the points, and formation of localized plasmas–cathode flares, which stimulate a rapid increase in electron emission from the cathode. A discussion is given of questions associated with study of the removal of cathode material in the operation of cathode flares and also with the investigation of the parameters of the plasma and the kinetics of its dispersion. The laws governing the removal of electrons from the cathode flare plasma are discussed, as well as the mechanism of electron emission from the metal to the cathode flare plasma. A separate section is devoted to the use of explosive emission in high-current electron accelerators and pulsed x-ray sources. The role of this phenomenon in initiation of electrical discharges in vacuum and gas is also discussed.