Measured Exit Plane Properties of a Low-Power Simulated-Hydrazine Arcjet

Abstract

Introduction I N two previouspaperson the 1-kWhydrazinearcjet, two types of electrostatic probe diagnostics were used at the nozzle exit plane to measure electron density ne , electron temperature Te, ion Mach number, plasma velocity u i , gas temperature Tg , and related quantities. All measurements were performed at 10 A and 50 mg/s propellantmass  ow on a NASA Lewis Research Center design,3 at a speciŽ c power of P= P mD 22:4 MJ/kg. These measurements were then compared to the two-temperaturechemicalnonequilibriumnumerical arcjet model of Megli et al. The quantitiesne , Te, and ion Mach numberwere determinedwith a novel quadrupleelectrostatic probe swept across the exit plane,with the probe axis parallel to the  ow velocity.1;6 The plasma velocity was measured with a double electrostatic probe using a technique similar to current modulation velocimetry (CMV).2;6 Both radial and axial variations of plasma propertieswere measured and compared to the numerical results. This Note presents further results for P= P mD 19:8 MJ/kg and P= P mD 26:0 MJ/kg (Ref. 6). The arcjet operating conditions are given in Table 1. This range of P= P m is representative of the stable operating range of this arcjet on simulated hydrazine (1 mole N2, 2 moles H2). The speciŽ c impulse is interpolatedfromdata acquired elsewhere on a comparable thruster. The quadruple probe combines the triple probe method of Chen and Sekiguchi, Ž rst applied to electric thruster plumes by Tilley et al.,8;9 with the crossed probe theory of Kanal,10 Ž rst applied to a single-speciesplasma by Johnson andMurphree and to a two-species plasma by Burton and Bufton.1 The quadrupleprobe was Ž rst appled to an electric thruster plume by DelMedico and Burton et al.13 The plasma velocity, assumed to equal the ion velocity u i , is determined by a modiŽ cation of a technique Ž rst developed by Pobst et al., in which the arc current is brie y interruptedand the resulting deŽ cit in electron density is convected at the plasma velocity and either detected optically or by a double time-of- ight (TOF) electrostaticprobe. Radial velocity proŽ les generatedby this technique are accurate to §500 m/s and provide excellent agreement with those generated by numericalmodeling.