Study of two-dimensional Debye clusters using Brownian motion

Journal Article · Thu Jun 15 00:00:00 EDT 2006 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.2215475· OSTI ID:20787346

Sheridan, T E; Theisen, W L ^[1]

---

1. Department of Physics and Astronomy, Ohio Northern University, Ada, Ohio 45810 (United States)

A two-dimensional Debye cluster is a system of n identical particles confined in a parabolic well and interacting through a screened Coulomb (i.e., a Debye-Hueckel or Yukawa) potential with a Debye length {lambda}. Experiments were performed for 27 clusters with n=3-63 particles (9 {mu}m diam) in a capacitively coupled 9 W rf discharge at a neutral argon pressure of 13.6 mTorr. In the strong-coupling regime each particle exhibits small amplitude Brownian motion about its equilibrium position. These motions were projected onto the center-of-mass and breathing modes and Fourier analyzed to give resonance curves from which the mode frequencies, amplitudes, and damping rates were determined. The ratio of the breathing frequency to the center-of-mass frequency was compared with theory to self-consistently determine the Debye shielding parameter {kappa}, Debye length {lambda}, particle charge q, and mode temperatures. It is found that 1 < or approx. {kappa} < or approx. 2, and {kappa} decreases weakly with n. The particle charge averaged over all measurements is -14 200{+-}200 e, and q decreases slightly with n. The two center-of-mass modes and the breathing mode are found to have the same temperature, indicating that the clusters are in thermal equilibrium with the neutral gas. The average cluster temperature is 399{+-}5 K.

• OSTI ID: 20787346
• Journal Information: Physics of Plasmas, Vol. 13, Issue 6; Other Information: DOI: 10.1063/1.2215475; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
AMPLITUDES
ARGON
BROWNIAN MOVEMENT
CENTER-OF-MASS SYSTEM
DAMPING
DEBYE LENGTH
ELECTRON TEMPERATURE
FOURIER ANALYSIS
HIGH-FREQUENCY DISCHARGES
ION TEMPERATURE
PARTICLES
PLASMA
PLASMA CONFINEMENT
RADIATION TRANSPORT
RESONANCE
THERMAL EQUILIBRIUM
THERMODYNAMICS
TWO-DIMENSIONAL CALCULATIONS
YUKAWA POTENTIAL