A Novel Macro-Particle Filter for Non-Metal Vacuum ARC Plasmas

Abstract

Summary form only given. Vacuum arcs are typically used to form metal plasmas that are nearly 100% ionized, which can then be used to create various types of coatings. The difficulty in forming coatings using an arc plasma is that these devices are also prodigious sources of "macro-particles", or micrometer-sized molten droplets of cathode material that emanate from the arc at high velocity. Removing these particles from the plasma stream is an important facet of any coating scheme that employs a vacuum arc. For the most part, these filtering schemes use magnetic fields to steer the plasma to the substrate while removing line of sight to the cathode. This approach is very effective at removing the macro-particles, but with significant losses in plasma flux. When non-metal, or semi-conducting cathodes such as boron or carbon, are used in a vacuum arc the macro-particles are observed to "bounce" off nearby surfaces multiple times. This renders many filtering schemes ineffective. A novel macro-particle filter designed to remove "bouncy" particles from a vacuum arc plasma will be discussed. The filtering scheme is based on the venetian-blind filter first reported by Ryabchikov, that uses a magnetic field formed by a series of linear current carrying blades to deflect the plasma while removing line-of-sight from the cathode to the substrate. The filter in this case uses a magnetic field formed by two, current carrying linear blades oriented to remove line-of-sight from the cathode and to keep reflected particles from reaching the substrate. Unlike other schemes using linear blade filters, the field from the blades is coupled to a magnetic field formed by external field coils. This results in a unique field structure that guides the plasma around the blades while removing virtually all of the particles. It also results in a relatively high-efficiency when compared to other filtering schemes and has been tested successfully using boron and carbon vacuum arcs. Data on the effectiveness of this filtering scheme will be reported