PLASMA-DENSITY EVOLUTION IN COMPACT POLYACETAL CAPILLARY DISCHARGES

We have measured the temporal evolution of the electron density of plasmas 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 determined from Stark-broadened line profiles of the 4f-3d O VI transition taking into account opacity effects. The electron density was found to increase continuously during the rise of the current pulse, and to decrease near the end of the current pulse, when a drop in plasma temperature 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 measured 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 discharge to 5 X 10(19) cm-3 for a 30-J discharge in a 1.5-mm-diam. capillary.