Nonlinear wave interaction in a magnetron plasma

Oscillations in the frequency range 10 <f < 300 MHz were measured using a Langmuir probe in a magnetron plasma. Dual probes were used to obtain wave number information. Three distinct peaks were observed that obeyed the nonlinear selection rule omega=omega (0)-omega (1), where omega (0) is the pump frequency, and omega and omega (1) are the decay frequencies. The phase velocity of the highest frequency wave (f=262 MHz) was consistent with beam plasma oscillations driven by secondary electrons from the target. The nonlinearly driven lower frequency wave had a phase velocity enabling efficient Landau damping. The resulting transfer of energy from the secondary electrons to the waves to the bulk electrons may explain the enhanced ionization of sputtered material observed in some high power density magnetron discharges. (C) 2000 American Institute of Physics. [S0003-6951(00)00648-3].