A cold thermionically emitting dusty air plasma formed by radiative heating of graphite particulates

Formation of an atmospheric pressure dusty air plasma is explored experimentally in this paper. The plasma is created by seeding an air flow with graphite particles and irradiating the particulates with a focused CO/sub 2/ laser beam. The graphite particles are, thus, heated to thermionically emitting temperatures, and average particle temperatures and average particle number densities are measured. The presence of charges is inferred both from these measured quantities using a simple theoretical transient model, and experimentally by applying a dc bias across the irradiated region. It is found that an electron density of /spl sim/6.7 /spl times/ 10/sup 5/ cm/sup -3/ (6.7 /spl times/ 10/sup 11/ m/sup -3/) can be produced at steady state in the presence of O/sub 2/. This value can be increased to 3.6 /spl times/ 10/sup 7/ cm/sup -3/ (3.6 /spl times/ 10/sup 13/ m/sup -1/) in the ideal case where an electron attachment to O/sub 2/ is suppressed and where a lower work function particulate is used.