Paramagnetic dust particles in rf-plasmas with weak external magnetic fields

Abstract

Experimental studies on dusty plasmas containing systems of (super-)paramagnetic dust particles are presented. In our experiments, external (homogeneous as well as inhomogeneous) magnetic fields in the mT range are applied to study the effect on single particles or few-particle systems that are trapped inside the sheath region. The behavior of the paramagnetic dust particles is considerably different than that of dielectric plastic particles, which are widely used in dusty plasmas. It is revealed that especially non-magnetic contributions play an important role in the interaction between superparamagnetic particles. Figure 3. Top view camera snapshots of two-dimensional paramagnetic dust particle systems at a neutral gas pressure of 10 Pa. (a) Dust layer without external magnetic field, and (b) at maximum homogeneous magnetic field (≈1.15 mT). New J. Phys. 16 (2014) 043026 M Puttscher and A Melzer 7 New J. Phys. 16 (2014) 043026 M Puttscher and A Melzer 10

The magnetized dusty plasma experiment (MDPX)

“…How is the dust grain charge affected by the magnetic field? However, in the majority of experiments, including those studies involving weakly magnetized plasmas (Kaw et al 2002;Vasil'ev et al 2007;Pilch et al 2008;Puttscher and Melzer 2014;Tadsen et al 2014), the dust grain charge most frequently inferred from measurements of the plasma parameters and using various charging models to estimate the value of the charge. How are the inter-dust forces modified by the magnetic field?…”

“…There have been a number of different measurements of the dust particle charge in unmagnetized dusty experiments such as the direct collection of unconfined grains after falling through a plasma (Walch et al 1995), modulation of the particle clouds (Trottenburg et al 1995), a normal mode analysis for strongly coupled dust clusters (Melzer et al 2001), or measurements of the decrease of the total free electron charge in the plasma (Barkan et al 1994;Thomas and Watson 2000). However, in the majority of experiments, including those studies involving weakly magnetized plasmas (Kaw et al 2002;Vasil'ev et al 2007;Pilch et al 2008;Puttscher and Melzer 2014;Tadsen et al 2014), the dust grain charge most frequently inferred from measurements of the plasma parameters and using various charging models to estimate the value of the charge. Given the challenges associated with probe measurements in strong magnetic fields, as discussed briefly in Sec.…”

Comparative study of the surface potential of magnetic and non-magnetic spherical objects in a magnetized radio-frequency discharge

“…An experimental work of Melzer et al (2019) shows a reduction in the dust charge at low magnetic field (B < 0.02 T) and nearly constant value up to B > 5 T. In their work, the charge on micron-sized dust grains is extracted by a normal mode analysis of the dust cluster in the magnetized rf plasma. A similar rf discharge configuration and normal mode analysis technique were used to get the charge on micron-sized paramagnetic particles at low B-field (B < 0.01 T) and observed a nearly constant value of the dust charge (Puttscher & Melzer 2014). The inconsistencies in the numerically, as well as experimentally, observed values of the dust charge leave many open questions on the charging mechanism of spherical particles (magnetic and non-magnetic) in a magnetized plasma.…”

Dust vortex flow analysis in weakly magnetized plasma

“…In laboratory experiment, dynamics of both para magnetic and diamagnetic (Melamine-formaldehyde or MF) particles was investigated in the presence of gradient in magnetic field by Puttscher and Melzer [20], finding that only para-magnetic particles responded to magnetic field gradient. An interesting dynamics of diamagnetic particles was however also reported by Puttscher and Melzer [21] which is governed by an ambipolar electric field generated due to magnetized drifting electrons.…”