Plasma expansion in the preshock region

Abstract

The supersonic expansion of an underexpanding argon plasma from a high density arc source with small dimensions into a low-pressure vessel with large dimensions is studied by an extended one-dimensional nonlocal thermal equilibrium fluid model, called SPIRIT. In an expanding plasma the velocity increases and the pressure, the density, and the temperatures decrease severely. In this article the virtual source model is discussed first, which is a model describing the expanding plasma as originating from a virtual source. The virtual source model includes some viscosity and heat transport in simplified form, but most of the viscosity and heat transport contributions are neglected. The SPIRIT code includes the full energy and momentum balances. The inclusion of viscosity and heat sources may lead to deviations from an adiabatic and/or isentropic expansion. The SPIRIT code can analyze the deviations. When deviations are small, the isentropic expressions from gas dynamics can be used to model expanding plasma too. Model outcomes are compared with experimental data.

Spatial evolution of an ion beam created by a geometrically expanding low-pressure argon plasma

“…9, we consider the plasma to originate from a point source and to expand as n͑z͒ = n͑0͒ ϫ͑R 0 2 / R 0 2 + z 2 ͒, where n͑0͒ is the density at the source/ diffusion chamber interface, R 0 is the source tube radius, and z is the axial distance from the interface. 19 The dashed line in Fig. 2 corresponds to a Boltzmann expansion.…”

Supersonic Ion Beam Driven by Permanent-Magnets-Induced Double Layer in an Expanding Plasma

“…Although the details are described later, the existence of the DL near the source exit is implied in this paper. On the other hand, the density profile from the source into the diffusion chamber in the case without the PMs is modeled according to the previously reported geometrically expanding plasma [7], [21] as…”

Ion beam formation in a low-pressure geometrically expanding argon plasma

“…where n͑0͒ is the density at the source diffusion chamber interface, R 0 is the source tube radius, and z is the axial distance from the interface. 14 In Fig. 3͑a͒, the lines show the calculated plasma density.…”