A temperature-modulated probe for potential measurements within electron beams

This probe, which is the most succesful of several types tried, uses a temperature-modulated tungsten emitter within the 0.050-inch diameter cylindrical probe sheath. The sensing area is a small hole near the tip of the sheath. Since this probe provides the electrons necessary for its operation, it is unaffected by other electrons--either primary or secondary. Likewise it can be used in an evacuated region with other electrons absent.