SUPERSONIC JETS WITH PERIODIC STRUCTURE DUE TO ARC PLASMA EXPANSION INTO A LOW-PRESSURE AMBIENT

A supersonic plasma jet was produced by a d.c. are plasma generator op erated at normal pressure and connected to a low-pressure (p(infinity) =0.2-50 kPa) chamber via cylindrical nozzle with diameter of 2.5 mm. T he argon gas flow rate was G=0.025 to 0.35 g . s(-1). In some experime nts current I-E less than or equal to 30 A passed coaxially through th e initial part of the jet. Photographic records of the jet and pressur e measurements are in agreement with theoretical predictions by a simp le one-dimensional, gasdynamical model capable of self-consistent calc ulations throughout the plasma source/jet system. Periodic jet structu re is observed over a wide range of experimental conditions, incl. in highly under-expanded flow. The jet expansion angle and Mach disc posi tion vary with p(infinity), G and I-E, but are nearly constant at diff erent arcing currents.