EMITTANCE MEADUREMENTS BASING ON PROBE-SLIT METHOD FOR A HIGH CURRENT GRID-CONTROLLED PULSE ELECTRON GUN

Single slit and probe method has been used for measuring the beam emittance of an electron gun. Amovable slit 0.1mm wide is used for sampling .A probe 0.1mmin diameter parallel to the slit and moving at a constant velocity, is used to catch the beam through the slit. Using geometrical relation, the divergence r₁' and r₂' of the beam through the slit can be calculated.
In our device, the distance between the slit and the probe is 59mm, the angle resolution is 3.4mrad, and the maximum system acceptance is 6.4× 10^-1cm·rad. A mechanism is designed to adjust the depth of parallelism between the slit and probe in order to improve the measurement accuracy. There is water cooled structure in the slit plate, which can bear higher beam power. With fine shielding and rational second- electron suppressor, the current of the order of 10^-10 A has been clearly measured. The relative error of the measured phase plots is about 8%.
The system is useful to study the effects on the emittance, of electron energy, the grid pulse voltage, cathode temperature, pulse current intensity.