Experimental Studies of a Deep, Negative, Electrostatic Potential Well in Spherical Geometry

Steady electron injection produced a stable, negative electrostatic potential well at the center of a hollow, open, 6.35‐cm‐diam spherical anode. Even though the primary electron source was localized, electron flow became spherically symmetric at anode currents of the order of 10 mA for anode potentials up to 1.0 kV. Well defined and reproducible oscillations were observed over a lower current range. These oscillations ceased and certain collector characteristics abruptly changed at currents which varied as $V^{\frac{3}{2}}$ , suggesting space charge saturation. An electron beam probe verified the presence of the well and measured its depth. The data showed correlation with a simple model and demonstrated the ease with which such wells can be produced.