HR: 1340h
AN: SM23A-0483    [Abstracts]
TI: Plasma Impedance Measurements Using a Small Spherical Probe$^{1}
AU: * Walker, D N
EM: dwalker@ccf.nrl.navy.mil
AF: Plasma Physics Division, Naval Research Laboratory, Washington, DC 20375 United States
AU: Blackwell, D D
EM: daveb@ccf.nrl.navy.mil
AF: SFA, Inc., 9315 Largo Drive West Suite 200, Landover, MD 20774 United States
AU: Amatucci, W E
EM: amatucci@ccf.nrl.navy.mil
AF: Plasma Physics Division, Naval Research Laboratory, Washington, DC 20375 United States
AU: Fernsler, R F
EM: fern@ppd.nrl.navy.mil
AF: Plasma Physics Division, Naval Research Laboratory, Washington, DC 20375 United States
AU: Messer, S J
EM: messer@ccs.nrl.navy.mil
AF: NRL-NRC Postdoctoral Associate, Naval Research Laboratory, Washington, DC 20375 United States
AB: Using the response of a spherical probe to a swept RF signal generated with a network analyzer, we have begun a study of plasma impedance properties in the large Space Physics Simulation Chamber (SPSC) at the Naval Research Laboratory. From a measurement of the ratio of reflected to incident power we characterize plasma impedance as a function of the probe driving frequency which is much lower than frequencies for detectable electromagnetic radiation. We demonstrate the measurement of electron density and compare results to those of a Langmuir probe. As the capacitive and inductive responses of the plasma are adiabatic, it is only in the presence of a dissipation mechanism that the driving energy can be extracted as work. In plasmas where the total electron collision frequency, $\nu_{e}$, is on the order of or larger than the plasma frequency, $\omega_{p}$, the dissipation often occurs through collisions. In the case of collisionless plasmas the sheath-plasma resonance, which occurs at fractions of $\omega_{p}$, up to $\omega_{p}$/2, is a possible dissipation mechanism. We present observations of energy transfer under collisionless conditions and compare this to predictions of a kinetic approach. $^{1}$Work supported by ONR and DARPA
DE: 7831 Laboratory studies
DE: 7853 Spacecraft/atmosphere interactions
DE: 7855 Spacecraft sheaths, wakes, charging
DE: 7899 General or miscellaneous
SC: SPA-Magnetospheric Physics [SM]
MN: 2004 AGU Fall Meeting