HR: 0800h
AN: SM41A-1165    [Abstracts]
TI: Inhomogeneous sheath as the cause of collisionless energy absorption: the effect on spherical probes*
AU: * Walker, D N
EM: dwalker@ccf.nrl.navy.mil
AF: Plasma Physics Division Naval Research Laboratory, 4555 Overlook Avenue, Washington, DC 20375 United States
AU: Fernsler, R F
EM: fern@ppd.nrl.navy.mil
AF: Plasma Physics Division Naval Research Laboratory, 4555 Overlook Avenue, Washington, DC 20375 United States
AU: Blackwell, D D
EM: davidb@ccf.nrl.navy.mil
AF: Plasma Physics Division Naval Research Laboratory, 4555 Overlook Avenue, Washington, DC 20375 United States
AU: Amatucci, W E
EM: amatucci@ccf.nrl.navy.mil
AF: Plasma Physics Division Naval Research Laboratory, 4555 Overlook Avenue, Washington, DC 20375 United States
AU: Messer, S J
EM: messer@ccs.nrl.navy.mil
AF: NRC-NRL Postdoctoral Assoc. Naval Research Laboratory, 4555 Overlook Avenue, Washington, DC 20375 United States
AB: We are continuing interpretation of spherical probe data gathered from a network analyzer¹. The analyzer allows an investigation of impedance characteristics by providing the reflection coefficient obtained when applying a low level RF signal to the probe near floating potential or negatively DC-biased in a low pressure plasma. The plasma impedance in the sheath surrounding the object becomes "resistive", and energy absorption is observed experimentally, even though the plasma is effectively collisionless. We will demonstrate theoretically how this behavior arises by solving Maxwell's equations together with cold fluid equations. The solutions obtained indicate that the plasma resistance is inversely proportional to the plasma density gradient evaluated at the location where the plasma frequency is equal to the applied frequency, consistent with earlier work which concentrated mostly on planar probes. New experimental results show clearly the absorption phenomena for the spherical probe based on the network analyzer measurements. Energy absorption is a function of the applied frequency and is generally seen at frequencies below the ambient plasma frequency. Using a derived density profile we compare theory to experiment. *Work supported by ONR ¹Blackwell, DD, DN Walker, WE Amatucci, SJ Messer, Phys. Plasmas, 12(9) ,TBD , 2005
DE: 2494 Instruments and techniques
DE: 2794 Instruments and techniques
DE: 2799 General or miscellaneous
DE: 9820 Techniques applicable in three or more fields
SC: SPA-Magnetospheric Physics [SM]
MN: Fall Meeting 2005