Plasma beam characterization along the magnetic nozzle of an ECR thruster

Abstract

Experimental characterization of plasma properties along the magnetic nozzle of an Electron Cyclotron Resonance thruster is presented here. A permanent magnet prototype and a solenoid prototype are tested, whose main difference relies on the magnetic field strength and topology. A cylindrical Langmuir probe is used to measure plasma potential, plasma density and electron temperature. In the permanent magnet thruster setup , a Laser Induced Fluorescence diagnostics is performed simultaneously with the Langmuir probe to measure the mean ion kinetic energy, and a Faraday gridded probe to characterize the angular plasma beam. An effective electron cooling rate has been identified, as well as the dependence of the total plasma potential drop with the mass flow rate. Results are compared with a supersonic collisionless fluid-kinetic 1D model where electron dynamics account for magnetic mirror effects and potential barriers, while ions are treated as a fluid cold species. The comparison allows to estimate the sonic transition of the plasma flow.

The curling probe: A numerical and experimental study. Application to the electron density measurements in an ECR plasma thruster

“…Hairpin and curling probe measurements are always in good agreement, as can be seen in Figure 14, where the electron density is plotted against the thruster absorbed power. The longitudinal profiles along the thruster axis presented in Figure 15 are consistent with previous LP measurements [38]. The curling probe that is the most adapted to the characterization of the ECR plume in this range of flowrate is the CP1400, as it allows density measurements both in the near field and in the far field plume.…”

Macroscopic and parametric study of a kinetic plasma expansion in a paraxial magnetic nozzle

“…The adiabatic caseᾱ = 0 corresponds toγ = 5/3 and, as the relative heat flux increases,γ decreases. For instance, the intermediate value α = 7/2, extracted from figure 10(c), o yieldsγ ≈ 1.2, a value close to some experimental evidence [26][27][28][29]39]. Implementing the crude closure (37) in the energy equation (33) yields the known law between the electric potential fall and the polytropic coefficient, [34] e|φ…”

“…Commonly-claimed isothermal or polytropic closures for collisionless electrons lack proper physical justification: the first case is just an ad hoc simplification while the second one must be understood as a phenomenological closure based on fitting experimental data. This data fitting shows electron cooling in a divergent MN with a polytropic coefficient in the range 1.1-1.3 [26][27][28][29]. Paraxial (i.e.…”

“…However, the main point to stand out is that both of them are crude phenomenological closures of a collisionless fluid model and do not reproduce the real electron energy balance, mainly in the divergent MN, which generally is the region of most practical interest. This would partially explain that some experimental data requires to be matched with piecewise polytropic laws [27,28].…”

Magnetic nozzle radiofrequency plasma thruster approaching twenty percent thruster efficiency

“…Various types of the electrodeless plasma thrusters have been proposed and investigated so far, e.g., a variable specific impulse plasma rocket (VASIMR) 10 , a helicon double layer thruster (HDLT) 11,12 , a magnetic nozzle rf plasma thruster (often called a helicon thruster: HPT) [13][14][15] , and an electron cyclotron resonance plasma thruster (ECRT) 16 . These utilize an expanding magnetic field (called a magnetic nozzle) downstream of the plasma source, where various plasma acceleration and momentum conversion processes occur as vigorously investigated so far.…”