A new way reduce control electrode current in DC operated CFAs

This paper describes a new method to reduce control electrode (CE) current in DC operated CFAs. The method-which has a patent pending-involves the introduction of an auxiliary electrode behind the traditional CE. When the gap between the cathode and CE is properly designed, current in the rotating hub of the CFA can be diverted into this gap and collected on the auxiliary electrode-which is at anode potential. We have demonstrated that up to 50% of the current that would have normally been collected on the CE, can be diverted and collected on the auxiliary electrode-substantially reducing the CE current. Since the auxiliary electrode is at ground or anode potential, no additional power supplies are required to operate the CFA. There are two embodiments of this idea that have been tested at CPI. In the first, the gap between the auxiliary electrode and the cathode forms a cutoff magnetron so that all electrons entering the gap get collected on the auxiliary electrode. In the second embodiment, the gap is not cutoff but the gap is tapered to produce an axial electric field component that pulls electrons in an axial direction, parallel to the magnetic lines, and into the auxiliary electrode. This second method is required if a cutoff gap would be too small for reliable DC voltage standoff.