Collective ion acceleration in a vacuum diode

Recent experiments in a “Luce-Type¹” vacuum diode have been made utilizing time-resolved spectroscopic measurements of anode plasma expansion velocity by line broadening and Doppler shift techniques, electrostatic and magnetic probe measurements of space charge potential well movement, time of flight Faraday cup measurements, and nuclear activation ion energy measurements. Preliminary results using a 3 MeV, 90 KA, 40 nsec electron beam from the FX-75 accelerator show mean proton energies between 5–10 MeV with an energetic tail in excess of 30 MeV with corresponding 10–20 KA peak ion current and 5–10 nsec pulse width. Ion beam current modulation has been observed as a result of the typical diode current modulation due to accelerator waveguide reflections. A brief discussion of a modified one-dimensional ion emission law² is given and the results will be compared to the Olson model³ for gas ionization neutralization.