A plasma source has been developed for use in cylindrical plasma opening switches (POS). The "inverse pinch" (IP) produces a radially expanding plasma ring formed from a gas puff and is designed to be mounted inside the center conductor of a POS. Interferometric measurements and magnetic probes were used to study the expansion dynamics of the plasma that behaves similar to an ideal snowplow. Plasma density measurements were also made with the source in a POS configuration. These measurements have shown that the IP injects a discrete quantity of plasma into the POS gap over time scales of interest. This results in a number of different plasma density distributions depending on the source delay. Furthermore, the quantity of plasma can be controlled by adjusting the size of the gas puff. This fact, coupled with the ability to vary the type of gas, enables the inverse pinch to supply to the POS a wide range of mass densities.