Method for measuring the electron distribution function in the low temperature plasma with a high time resolution

The second derivative of the Langmuir probe characteristics was used for the determination of the electron distribution function in a low-temperature plasma. The influence of the additional probe current was suppressed by applying a sawtooth bias voltage. To avoid troubles with fast differentiation, a sampling oscilloscope was employed as a time converter. The output voltage was processed using a computer or a hybrid computer system. In the hybrid system, the first derivative of the probe characteristics was determined analogically. The latter method proved to be more advantageous when compared with the purely numerical one, the second derivative being measured over a much narrower energy interval, which results in a much lower experimental error. The time resolution of the measurements is of the order of several μsec. (J.U.). 7. figs., 5 refs