Arc discharges are common in welding and lightning storms but what about about in altered gravity conditions?
How often does that really come up? Not often, unless we ever send manned missions into space again, and it may be relevant in the design of ion thrusters used for spacecraft propulsion so let's do some science.
Jiří Šperka of Masaryk University in Czech Republic and Dutch colleagues studied the behavior of a special type of arc discharge, so-called glide arc, in varying hypergravity conditions, up to 18 G. In their paper, they demonstrate how the plasma channel of this glide arc discharge moves due to external forces of buoyancy in varying gravity conditions. Though electric discharges can be affected by gravity, the electromagnetic forces between charged particles are typically much stronger than any gravitational forces. Therefore, in order to understand this effect, the authors designed an experimental device to perform measurements on atmospheric pressure glide arc helium plasma under the forces of hypergravity.
They changed the buoyancy force acting on the plasma channel of the glide arc while maintaining a constantly low external gas flow. To do so, they relied on the Large Diameter Centrifuge at the European Space Agency's European space research and technology centre (ESTEC) facility in Noordwijk, the Netherlands.
They found that gravity strongly influences the glide arc discharge. These effects stem from thermal buoyancy, which increases with gravity. As such, increasing the centrifugal acceleration of gravity makes the glide arc movement substantially faster. Whereas at 1 G the discharge was stationary, at 6 G it glides with 7 Hz frequency and at 18 G that number rises to 11 Hz.
The authors thus established a simple model for the glide arc movement assuming low gas flow velocities, which they validated with experimental results.