Fast gas injection system for plasma physics experiments

A system has been developed for fast, feedback controlled injection of hydrogen and various other gases into a vacuum system. Gas flow is through short (about 30-mm length), submillimeter diameter tubing at pressures in the fluid flow regime. The flow is controlled by a piezoelectric valve and measured by a miniature pressure sensor mounted in the body of the valve. Flow rates from a single valve of up to 500 Torr liter/s for hydrogen have been obtained. Response time of the flow is a rise time of 0.5 ms (with a 3-ms ringing decay time) and a fall time of 0.3 ms. The flow rate is basically a linear function of the measured pressure. A model has been developed to explain the observed functional dependence of flow rate on pressure, gas type, and tube radius