Microparticles in a Collisional Rf Plasma Sheath under Hypergravity Conditions as Probes for the Electric Field Strength and the Particle Charge

We used microparticles under hypergravity conditions, induced by a centrifuge, in order to measure nonintrusively and spatially resolved the electric field strength as well as the particle charge in the collisional rf plasma sheath. The measured electric field strengths demonstrate good agreement with the literature, while the particle charge shows decreasing values towards the electrode. We demonstrate that it is indeed possible to measure these important quantities without changing or disturbing the plasma.

Figure 1

CCD camera images of a microparticle, confined within the plasma sheath under several hyper-gravity conditions.

Figure 2

Equilibrium position of the microparticle as function of $g^{*}$ together with a fourth-order fit through the data points.

Figure 3

Deviation of the extrapolated electrode potential form the measured electrode bias potential.

Figure 4

Obtained profiles for the electric field and the particle charge as function of the position in the sheath. The plotted error bars are mainly due to uncertainty in the Langmuir probe measurements.

Figure 5

Resonance frequency curve determined from the $E(z_E)$ and $Q_p(z_E)$ profiles in Fig. 4 compared with independently performed measurements of the microparticle’s resonance frequency.