INTERFEROMETRY OF FLASHBOARD AND CABLE-GUN PLASMA OPENING SWITCHES ONHAWK

Interferometry of plasma opening switch (POS) plasmas on the Hawk gene rator has shown many important features of the plasma evolution during conduction and opening. Opening occurs when a low-density region form s at a radial location determined by plasma redistribution during the conduction phase, consistent with J x B forces and the measured plasma distributions produced by the sources alone. High neutral densities h ave been detected in the POS region during conduction. Low-density pla sma appears between the POS and the load at the time current appears i n the load, and high-density plasmas appear there later in time. There are two important differences between the density evolution of POS's utilizing flashboard and cable-gun plasma sources. 1) There is a subst antial (two-three times) increase in the electron inventory during con duction using cable guns that is not detected using flashboards. This is attributed, primarily, to ionization of ions and neutrals for the c able-gun case. 2) The conduction scaling with plasma density implies t hat the cable-gun POS has an effective ion mass/charge ratio about dou ble that for the flashboard POS.