HERMES II (High Energy Radiation Megavolt Electron Source) was developed as a gamma ray simulator. However, it had a radiation pulse width of 60 ns. As a result, the second derivative of the dose was too small, compared to the dose, to drive important inductive effects in electronic circuits. While at Sandia National Laboratories, Dr. McClenahan led the project that successfully developed a short pulse diode for HERMES II.

The short pulse diode consists of a 4-cm diameter, conical, hollow cathode that injects an annular beam into a 5-cm beam tube. The entire diode is immersed in a weak magnetic field. This unique geometry causes the low-voltage, low-current portion of the beam to strike the wall. Only the high-voltage, high-current portion reaches the high atomic number converter at the end of the beam transport tube. This diode produces a 20 ns radiation pulse, and it is far cheaper than developing a new, short-pulse simulator.

The Triaxial Diode was a research project to investigate low impedance diode concepts for high-power, low-voltage, pulsed accelerators. Dr. McClenahan led the project at Sandia National Laboratories. The experimental and theoretical effort resulted in a diode that produced an annular beam that did not pinch on axis. Such a beam results in a more nearly uniform radiation dose over a larger area than a conventional, pinched beam. The triaxial concept has been incorporated into the diodes used on the premier X-ray simulators in the United States.

The pentaxial diode, developed for SPEED, takes the triaxial-diode concept one step further. The pentaxial diode consists of two nested triaxial diodes. With the pentaxial diode, SPEED delivered a uniform, low-voltage, X-ray dose to a relatively large area. The pentaxial diode was the first diode successfully fielded on SPEED. Using the pentaxial diode, SPEED became an important X-ray simulation tool at Sandia.

Subsequently, Sandia extended the nested triaxial diode concept to three nested triaxial diodes. Using this diode, Saturn became the premier X-ray simulator in the world.

RHEPP (Repetitive, High-Energy, Pulsed Power) is a project at Sandia National Labs to develop intense radiation sources for a variety of applications, including infectious waste sterilization. Dr. McClenahan was responsible for developing suitable electron emitters for the project. Conventional, cold cathodes rarely perform consistently for a large number of shots. Typically, they emit fewer electrons on each successive shot, until they hardly emit any electrons at all. Thermionic cathodes maintain consistent emission levels for indefinite periods; nevertheless, they rarely generate a high enough current density to satisfy most high-power, pulsed-beam requirements. Dr. McClenahan developed a cathode that emits high-current-density electron beams and continues to operate at high repetition rates for extended periods without significantly changing its emission characteristics. One such cathode ran continuously at 300 shots per second for seven hours, and it showed no significant change in emission.

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