Study of the Properties of an Anomalous Glow Discharge Generating Electron Beams in Helium, Oxygen, and Nitrogen

Resumo

The current–voltage characteristics (CVCs) and efficiency of electron beam generation in glow discharges in helium and its mixtures with oxygen and nitrogen, as well as in pure oxygen and nitrogen, are studied experimentally. Special attention is paid to creating clean conditions for a discharge operating in helium. It is shown that, under clean conditions and pressures above 10 Torr, the CVC first rapidly grows. Then, the growth slows down and the CVC begins to decrease; however, at voltages above 1.5 kV, it rapidly grows again. These features are explained via changes in the mechanisms of electron emission and electron runaway from the cathode sheath, which lead to a highly efficient (up to 85%) generation of electron beams. In the presence of molecular admixtures, the CVC changes and begins to smoothly grow, the current being substantially higher than in pure helium. In pure oxygen and nitrogen, the CVC also grows smoothly and electron beam generation is highly efficient, but its mechanism is different. In pure helium, electrons are generated primarily due to photoemission, whereas in pure oxygen and nitrogen, electron emission from the cathode is mainly caused by the bombardment by fast heavy particles. In helium mixtures with oxygen and nitrogen, other emission mechanisms can also take place.