Plasma and Dust Response to a magnetic Field in a magnetized dusty DC Discharge

Victor Land

June 9th 2005

Dust particles immersed in a plasma act as small probes and collect electrons 
and ions. The charged dust particles are then accelerated by a variety of 
forces, such as the electrostatic force and the ion drag force, caused by the 
deflection and collection of ions from the plasma.

In many plasma applications, for instance in Plasma Enhanced etching and 
deposition devices, magnetic fields are used to confine the plasma particles. 
Often, dust particles are found in these discharges, either as a result of 
chemical reactions in the plasma or as a result of plasma-wall interactions.

In order to get a better understanding of the response of plasma and dust to a 
change in the magnetic configuration of the discharge, the old DPX experiment 
at the Plasma Sciences Laboratory of Auburn University was rebuild to include 
an electromagnet to produce a magnetic field in the discharge.

Two setups have been created. In the first the magnetic field was oriented 
perpendicular to the electric field present in the cathode sheath in front of 
the cathode (negatively biased electrode). By applying the magnetic field a 
change in the plasma glow was observed. Using a small tray, 1 micron dust 
particles were introduced. These were then illuminated using a laser and using 
different optical techniques, the response of the dust particles to the change 
in plasma was recorded.

In the second setup a ring was placed on top of the cathode, which was thus 
also negatively biased. This created a potential well and thus a radial 
electric field. The magnetic field was oriented perpendicular to this electric 
field. We again used different optical measurements to record both the plasma 
as well as the dust response to a change in the magnetic field.

Using different probes, we also investigated the potential structure above the 
ring. Combining the measurements we come to the conclusion that the forces 
acting on the dust above the ring might strongly deviate from the classic 
balance where the downward acting gravity is balanced by an upward acting 
electrostatic force.

The results obtained will be presented in a poster at the 4th ICPDP conference 
held in Orleans France from June 13th until June 17th. During the seminar I 
will present the results and provide more background information.