Dual-element switching in Pierce guns

In aperture gridded Pierce guns, it has been found that focus electrode voltage over anode potential for full beam cutoff increases linearly with anode perveance. By simultaneously switching both the focus electrode and an electrically isolated anode negative with respect to ground, full beam cutoff can be achieved at significantly lower voltage. The relationship between cutoff voltage and perveance can be used to quantify the gain from dual-element switching.