Session 7P - Plasma Applications and Plasma Technology.
POSTER session, Thursday morning, November 14
Exhibit Hall - Concourse Level, Adam's Mark
A microwave-heated plasma device, employing a planar magnetron configuration for enhancing plasma density, has been built to produce a continuous stream of directed hyperthermal neutrals. Magnetrons are characterized by strongly curved magnetic fields which are shaped to 'trap' fast electrons near the cathode. In a conventional magnetron a large cathode bias, -200 to -1000 V, is used to accelerate secondary electrons emitted from the cathode and thus sustain the plasma. For this application the desired cathode bias is less than -100 V, and thus the plasma must be sustained by other methods. Our choice is electron cyclotron resonance heating, which allows even positive 'cathode' biases. Langmuir probes have been used to characterize this plasma system over a wide array of parameters: position, pressure, cathode bias, microwave power and magnetic field strength. Typical parameters are: T_e \, hot \simeq 15 \, eV, T_e \, bulk \simeq 5 \, eV, n_i \simeq 3 \times 10^10 \, cm^-3, V_p \simeq 20 \, V while V_f drops steeply near the cathode from 10 to -50 V. In addition a \sim 35 \, eV electron beam has been observed near the cathode. Detailed analysis of the Langmuir probe data will be presented and discussed.