/spl alpha/-/spl gamma/ transition properties of an RF discharge in argon

Summary form only given. This report shows that the /spl alpha/-form range of existence possesses not only the right-hand boundary (conventional one at larger pressures-[Yatsenko, N.A.-Zh. Tekh. Fit., 1981, V. 51, p.1195]) but also a left-hand one (to the left of the RF discharge extinguishing curve minimum). Figure shows the extinguishing curve of the RF discharge in argon (L=2.2 cm, f=13.56 Mhz) and the /spl alpha/-/spl gamma/ transition curve. At low p secondary electrons fly through the electrode sheath without collisions gaining the energy /spl epsiv//sub e//spl ap/eU/sub sh/ (U/sub sh/ is the voltage across the sheath). When U/sub sh//spl ges/U/sub 1/ (U/sub 1/ is the ionization potential of the argon atom by an electron impact), a beam of fast electrons penetrates the plasma from the sheath ionizing on its way the gas atoms. The RF discharge transits to a /spl gamma/regime. Therefore at low pressures the /spl alpha//spl gamma/ transition curve coincides with the RF discharge extinguishing curve.