Estimates of the Time-dependent Current in Bi-polar Child-Langmuir Diodes with Ion Charge Stripping
Abstract
The Immersed-B electron beam diode^1 has been proposed as a means of generating high dose, small spot, pulsed, x-ray radiation. It is a bi-polar, space-charge limited diode comprised of a cylindrical needle point cathode immersed in a large (10-50 Tesla) solenoidal magnetic field. Experimental data obtained at Sandia National Laboratories (SNL) demonstrates rapidly collapsing diode impedances for geometries which produce current densities ≥ 50 kA/cm^2 on the anode. Charge stripping of ions emitted from the anode has been proposed as a possible mechanism for the observed impedance collapse^2. We present a simple time-dependent (0-d) model for the current history of a bi-polar, Child-Langmuir diode when ions emitted from the anode are allowed to ionize (strip) while traversing the A-K gap of the diode. It is found that the diode can undergo explosive current growth on a timescale 1/α which is inversely proportional to the ion-ion ionization frequency. The time rate of change of the impedance scales as -α (V/I_e), where V (I_e) is the initial diode voltage (electron current). Comparison to data taken on the RITS-3 accelerator at SNL will also be presented. 1. M.G. Mazarakis et al Appl. Phys. Lett 70, 832 (1997) 2. D.R. Welch et al, these proceedings.
- Publication:
-
APS Division of Plasma Physics Meeting Abstracts
- Pub Date:
- October 2003
- Bibcode:
- 2003APS..DPPFO3008O