Measurements of electron emission uniformity from cathodes in high-voltage electron beam diodes

Spatial uniformity of electron emission from velvet cathodes has been measured by observing the distribution of electrons hitting the anode in a planar high-voltage diode. It is shown that unless all electrons move parallel to the diode axis, the electron distribution measured at the anode does not represent the cathode emission pattern. Here, parallel trajectories were achieved by applying a strong, uniform axial magnetic field. A 5 ns gated ICCD camera recorded light from a fast anode scintillator. The emission from two brands of velvet was found to be mostly concentrated in small spots with density of about 55/cm(2). The pixel-to-pixel standard deviation of the emission amounted to at least 16%. (C) 2003 American Institute of Physics.