Features of the α-γ transition in a low-pressure rf argon discharge

It is found that the region for the stable existence of the aregime of a radio-frequency (rf) discharge is bounded not only on the moderate-pressure side, but also on the low-pressure side. One feature of the α-γ transition in a low-pressure rf discharge is that the criterion for breakdown of the electrode sheath is not satisfied. It is shown that at low pressures the α-γ transition of an rf argon discharge takes place abruptly and exhibits hysteresis. At intermediate pressures the α-γ transition is continuous and lacks jumps; negative differential conductivity appears, double layers form, and nonmonotonic behavior of the plasma density is observed at the center of the discharge. The role of stochastic (collisionless) electron heating in sustaining an rf discharge at intermediate gas pressures is discussed.