An f/1 Streak Camera for Spark Studies in Both Ultraviolet and Visible

A rotating-mirror streak camera with 0.015 in./μsec writing speed, f/1 aperture and spherical reflection optics (save for a fused-quartz window) has been constructed. The camera, which is equally useful in the ultraviolet and visible light ranges, has a rotating mirror driven by a 1500-rps electric motor. A technique for molding film to the required spherical focal surface has been developed. — The camera is used to study the electrical breakdown development rate and structure of 2-m air gaps by high-voltage discharges, particularly the very high-speed low-luminosity processes which precede the final brilliant arc phase. This last arc phase must be suppressed in order to avoid severe fogging of the record. Techniques are described for superimposing reference points on the image to define time axis, gap axis, spark position in space and writing speed. Photographs show the appearance of the filamentary corona, the growth of the glow discharge at velocities exceeding 108cm/sec and the discontinuous stepped progress of the spark leade