The electron emission experiments on PZT cathode were done under high pressure of 410

-3

Pa and low pressure of 1.4 Pa. The number of collected electrons was given by integrating the curve line of collected current. The ratio of collected electrons under low pressure and high pressure is 0.193 3 and it can be drawn that many electrons emitted from the cathode were lost under low pressure.The reasons why electrons were lost were analyzed based on the theory of molecular motion and plasma discharge. The probability of electrons which can reach anode after collision with the gas molecular can be calculated through theory of molecular motion. The value are respectively 89.58% and 99.97% under low and high pressure

thus the ratio is 0.896 1 which is far away from the ratio calculated from collected current. Only a little fraction of the emitted electrons were lost due to the collision with the gas molecular

but more due to the plasma discharge through the grid electrode as the plasma should be considered under low pressure. The time that the grid electrode was covered by the plasma is 23.8 ns based on plasma discharge theory

which is near to the periodic time 20 ns observed from the waveforms of the collected current. Thus it can be testified that the palsma discharge is the main reason for the losing of electrons under low pressure by the above results.