Electrical breakdown of anodized coatings in low-density plasmas

A comprehensive set of investigations has been performed involving arcing o n a negatively biased anodized aluminum plate immersed in a low-density arg on plasma at low pressures (P-0 approximate to 7.5 x 10(-5) torr), These ar cing experiments were designed to simulate electrical breakdown of anodized coatings in a low Earth orbital environment. When electrical breakdown of an anodized layer occurs, an are strikes, and there is a sudden flux of ele ctrons accelerated into the ambient plasma, This event is directly followed by ejection of a quasineutral plasma cloud consisting of ejected material bf own out of the anodized layer. Statistical analysis of plasma cloud expa nsion velocities has yielded a mean propagation velocity, v = 19.4 +/- 3.5 km/s, As the plasma cloud expands into the ambient plasma, energy in the fo rm of electrical noise is generated. The radiated electromagnetic noise is detected by means of an insulated antenna immersed in the ambient plasma. T he purpose of the investigations is 1) to observe and record the electromag netic radiation spectrum resulting from the arcing process, 2) to make esti mates of the travel time of the quasineutral plasma cloud based on fluctuat ions to several Langmuir probes mounted in the ambient plasma, and 3) to st udy induced arcing between two anodized aluminum structures in close proxim ity.