Microwave Energy Deposition in Supersonic Flows on Laser-Initiated Dipole Structures

Abstract

The results of feasibility study of organization axially-elongated MW discharges in high density supersonic flow (up to atmospheric static pressure) are reported. The laser-ignited structures in test flow are creating with using of double pulse laser. The test flow has Mach number 1,35, static pressure 173 Torr., static temperature 215 K and stagnation temperature300 K. Experimental setup contains the double – pulse YAG laser (2×145 mJ, 10 ns, 532 nm) and microwave system. The last based on impulse high-power magnetron, (3,125 sm, 1.5 mks, peak power 250 KW) and quasi-optical focusing system with axial orientation of electric field. The maximal MW electric field strength on the focus area of focusing system (quasi – optical cylindrical paraboloid) is about 4,6-4,7 kV/sm. This level allows to realize MW discharge in gas flows with static pressure diapason less than 110 Torr. The focusing laser lens has a focus length 23,3 mm and permits to achieve in the focus area the electric field strength (optical diapason) about 7,3*10 6 V/sm. This level is sufficient for laser spark creation in gas with static pressure diapason 760-70 Torr. The first and the second laser pulses could have the tuning time shift. Results of our experiments clearly show that laser initiation technique permits to realize the stable MW energy deposition in high-density supersonic flows (up to atmospheric static pressure) under comparatively weak electrical MW field (substantially less than threshold level for tested flow). This kind of Laser-MW discharge could be realized as to single laser initiation, as for double (dipole, or multipoint) laser initiation. At the last case, the elongation of plasmoid in tested flow could be essentially increased.