Supersonic Flow of Vacuum Arc Plasma in a Magnetic Field

Abstract

We have investigated the supersonic flow of dense plasma, formed by a pulsed vacuum arc, in a magnetic field of about 1 T using probe and optical diagnostics. Two separate magnetic field configurations were examined—an axial field with either converging or diverging lines of force. We find that for a low-current arc of from 0.4 to 1 kA and pulse duration of 270 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{s}$ </tex-math></inline-formula> , the diverging magnetic field leads to increased plasma flow velocity by about a factor of 2.5, whereas the converging magnetic field reduces the velocity by about the same amount. For a high-current arc of from 5 to 30 kA and pulse duration of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$40~\mu \text{s}$ </tex-math></inline-formula> , the plasma flow velocity increases, although the effect of increased field strength on flow velocity is less significant. Here, we describe these observations and other effects of magnetic field on the parameters of the vacuum arc plasma flow.