Title :
Measuring electron densities in highly collisional plasmas using a 110 GHz interferometer
Author :
Kelly, K.L. ; Scharer, J.E. ; Laroussi, M. ; Block, R. ; Schoenbach, K.
Author_Institution :
Dept. of Electr. & Comput. Eng., Wisconsin Univ., Madison, WI, USA
Abstract :
Summary form only given, as follows. A 110 GHz interferometer is used to measure electron densities in a highly collisional plasma. The plasma is formed and maintained with a helical coil driven at 13.56 MHz. In this regime, the background pressure approaches atmospheric pressure, and the collisionality is of the order /spl nu//sub e-n//spl ap/10/sub 9/-10/sup 13/. Probe measurements in this pressure range are inaccurate and unreliable due to complicated effects that electron-neutral collisions have in the sheath. It is necessary to operate an interferometer at a frequency high enough that the dominant characteristic frequency is the operating frequency (/omega>/spl nu//sub e-n/) yet low enough that small phase changes can be detected as a wave passes through the plasma. In this experiment, plasma dimensions are of the order 5-10 cm. In addition, the inelastic nature of collisions in this experiment make it necessary to interpret small phase changes with great care. A model has been developed help in that interpretation. Typical operating parameters are pressures of 1-700 Torr, applied magnetic field of 0-1000 Gauss, operating gasses of nitrogen, oxygen, argon, and air, and input RF power levels of 100-3000 Watts.
Keywords :
electron density; plasma collision processes; plasma density; plasma diagnostics; plasma probes; radiowave interferometry; 0 to 1000 gauss; 1 to 760 torr; 100 to 3000 W; 110 GHz; 13.56 MHz; Ar; N/sub 2/; O/sub 2/; air; atmospheric pressure; background pressure; dominant characteristic frequency; electron densities; electron-neutral collisions; helical coil; highly collisional plasma; highly collisional plasmas; input RF power levels; interferometer; operating frequency; operating parameters; probe measurements; sheath; Atmospheric measurements; Atmospheric-pressure plasmas; Coils; Density measurement; Electrons; Frequency; Plasma density; Plasma measurements; Plasma properties; Plasma waves;
Conference_Titel :
Plasma Science, 2000. ICOPS 2000. IEEE Conference Record - Abstracts. The 27th IEEE International Conference on
Conference_Location :
New Orleans, LA, USA
Print_ISBN :
0-7803-5982-8
DOI :
10.1109/PLASMA.2000.854821