In order to study the influence of working coefficient on the development characteristics of initial electrons in gas switch gap under DC-withstanding process

a picosecond ultraviolet pulsed laser was used to generate initial electrons in the switch gap. The currents which were generated by the motion and growth of electrons were measured to abtain the influence of working coefficient on the development characteristics of initial electrons under condtitons of the gap distance of 5 mm

the gas pressure from 0.1 to 0.4 MPa

and the working coefficient from 50% to 75%. The experimental results show that the working coefficient has a significant influence on the development of initial electrons

and there is a threshold of working coefficient which produces the effective ionization on electrons. The threshold has a slight growth but remains in the range of 63%±3% with the pressure changing from 0.1 to 0.4 MPa. And the threshold is consistent with the working coefficient when the value of effective ionization coefficient is zero. When the working coefficient increases further

new generations of electron avalanches will emerge in the gap and the discharge process will continue to develop.As a result

it is helpful for improving the DC-withstanding stability of gas switch to set the working coefficient near the effective ionization threshold.