OPTICAL-EMISSION SPECTROSCOPY OF ELECTRICAL FOCII DISCHARGES

The optical emission from a dense magnetized plasma column (the Z pinc h) was studied in experiments with a 1 kJ plasma focus using an optica l multichannel analyser (OMA III). The plasma column (about 10 mm leng th and about 1 mm diameter) generated at the end of the co-axial disch arge had a density of about 10(19) cm(-3), a duration of about 200 ns and a maximum circulating current of about 170 kA. All the most intens e lines from the carrier gases (neutral atoms and ions) were found in the specira in the optical range 340-700 nm, showing that the line int ensity was independent of the pinch intensity. Also, an intense emissi on from other elements such as copper (belonging to the brass electrod es) and silicon (from the glass insulator) was observed with a strong dependence of their line emission intensities on the pinch intensity. By partially covering the electrode surfaces with aluminium sheets, an d studying variation of the aluminium and copper sine emission intensi ties with the pinch intensity, ii was shown that the source of contami nation could be attributed in part to the power energy density deposit ion of the current sheath during the breakdown and run down stages of the discharge, before the formation of the dense plasma column. This m ore energetic electrode (and glass insulator) erasion can be associate d with a thinner current sheath, a condition that is also conducive to more efficient pinch formation. The possibility of covering the last centimetre of the electrode surfaces with materials with higher evapor ation points offers an opportunity to reduce the contamination effect when the plasma focus is used as a surface-treatment apparatus.