Study of High-Flow Argon Through Cascaded Arc for Use as a Gas Target Isolator

The so-called plasma window is a dc cascaded arc whose function, in this paper, is to greatly restrict gas flow from high pressure (upward of 40 kPa) chamber to a low-pressure side (order of 10 Pa). This is motivated by its potential to contain a gas charge stripper on a beamline of a high-intensity heavy-ion accelerator without the need for solid windows that would obstruct beam passage and not survive the beam's intensity. At the National Superconducting Cyclotron Laboratory (NSCL), a test stand for this plasma window has been developed to study how this flow rate restriction is impacted by plasma physical properties and window geometry. Proposed mechanisms for this flow rate restriction are, first, a significant increase in temperature causing greatly enhanced viscosity in the plasma channel, and second, a choked flow condition being established through gas speed reaching supersonic conditions. The study in this paper is limited to pure Ar gas. Optical emission spectroscopy demonstrates the plasma that has an electron temperature of about 1.7 eV and an electron density of about 10
¹⁶
cm
^-3
.