PLASMA-DENSITY EVOLUTION IN COMPACT POLYACETAL CAPILLARY DISCHARGES

We have measured the temporal evolution of the electron density of pla smas produced in polyacetal capillaries with diameters between 0.5 and 1.5 mm excited by 110-ns full-width-at-half-maximum discharge pulses with currents between 13 and 42 kA. The electron density was determine d from Stark-broadened line profiles of the 4f-3d O VI transition taki ng into account opacity effects. The electron density was found to inc rease continuously during the rise of the current pulse, and to decrea se near the end of the current pulse, when a drop in plasma temperatur e causes the degree of ionization of the plasma to decrease. The peak plasma density in a 1-mm capillary excited by a 24-kA pulse was measur ed to be 5 X 10(19) cm-3. The plasma density was observed to increase linearly with discharge energy from 7.5 X 10(18) cm-3 for a 5-J discha rge to 5 X 10(19) cm-3 for a 30-J discharge in a 1.5-mm-diam. capillar y.