Magnetic Control of Low-Pressure Discharges.
Abstract
In low pressure discharges, operated in electronegative gas mixtures to the right of the Paschen curve minimum, the discharge resistance can be increased by application of transverse magnetic fields. This effect allows the use of a magnetically controlled glow discharge as an opening switch with submicrosecond opening time, or to shorten the recovery time considerably if it is used as a closing switch. The application of a magnetic field transverse to an electric field in a low pressure discharge causes a shift in the electron energy distributions towards lower energies. This shift affects the transport and rate coefficients, and consequently the resistance of the discharge. In order to model magnetically controlled glow discharges Monte Carlo codes are used to determine the rate and transport coefficients in He:SF6 gas mixtures. With the obtained values the equilibrium electric field strength E/N for the positive column of the discharge was calculated. In a 20% SF6/80% He mixture the electric field rises linearly with a slope of about 1 (kV/cm)/Tesla. Besides steady-state characteristics the transient dynamic response of the positive column to the change of the magnetic field was calculated. A typical time scale for the plasma response is tens of nanoseconds. To study magnetically controlled discharges experimentally a coaxial discharge system was built which allows application of axial magnetic fields up to 1.2% Tesla. Measurements of the discharge voltage and current in an 80% He 20% SF6 mixture at a pressure of 8 torr were performed at varying magnetic field intensities. The discharge voltage was found to increase with increasing magnetic field as predicted by our model.
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 01, 1986
- Accession Number
- ADA171928
Entities
People
- Karl H. Schoenbach
Organizations
- Old Dominion University