Studies of a reflex triode

The ion current of a reflex-triode has been studied as a function of the anode thickness, when a 400 kV positive pulse is applied to such an anode. The 11.4-cm-OD anode consists of solid polyethylene (or polycarbonate) film of thickness, 8, between 2 and 150 μm interwoven between 0.7 mm diameter meter wires spaced 0.7 cm apart. It is observed that the ion current increases with decreasing thickness for 12 <; δ <; 120 μm and remains practically constant for thinner films. Contrary to the predictions of a recent theoretical model, the ion current does not exhibit resonance-like behavior. For δ ≤ 25 μm, the results are in agreement with a macroscopic model, which predicts that the ratio of the ion current to the cathode current is given by 0.5 [1 + (2η + 1)^-1 (m_i/m_e)^1/2]^-1 where η is the average number of passes of a typical electron through the anode. The above theoretical estimates are based on time averages of space charge limited flows. Refinements of the theory are included in a new, one-dimensional, multi-species, particle simulation code.