EXIT-PLANE ELECTROSTATIC-PROBE MEASUREMENTS OF A LOW-POWER ARCJET

Improved understanding of the flow processes in a 1-kW hydrazine const ricted arcjet is achieved with multiple electrostatic probe surveys in the exit-plane region of the plume. Quadruple, triple, and single ele ctrostatic probe techniques are utilized for measurements of the elect ron temperature T-e, density n(e), and ratio of ion axial velocity to most probable thermal speed u(i)/c(m,H+). Centerline axial profiles of T-e and n(e) are presented for 2.2-6.2 mm downstream of the exit-plan e, yielding T-e = 6600 K +/- 15% and n(e) = 3.6 x 10(12) cm(-3) +/- 60 % close to the thruster exit. Quadruple probe theory is modified to ac count for radial gradients in T-e and n(e) over the probe radial dimen sion, and is used to extract exit-plane radial T-e and n(e) profiles. Floating probe measurements yield estimates of the radial electric-fie ld profile at the thruster exit, implying a small amount of current an d ohmic heating downstream of the exit-plane.