ECR thrusters and magnetic nozzles

ECR thrusters (ECRT) studied at ONERA are plasma propulsion devices relying on electron cyclotron resonance heating at 2.45 GHz to ionize xenon gas and on a diverging magnetic field, called magnetic nozzle (MN), to produce a plasma jet. In 2020, propulsive performances of 50% have been reached by 30W and 200W prototypes [1].

ECRTs MN are electron-driven. Therefore, plasma expansion has often been approached by modeling thermal electron expansion mechanisms, for example by characterizing the electron cooling and its impact on the ion acceleration [2-3]. We have studied experimentally ion velocity and electron density fields using both a two-axis LIF setup and microwave resonant probes. These quantities can be linked to electron dynamics through  fluid model [4]. A limitation of this approach is the demagnetization of the plasma in the far plume. We have developed a directional faraday cup to measure the angular profile of ion current and provide an experimental determination of the detachment point. Its location is measured for different operating conditions of the thruster, background pressure levels, and magnetic nozzles.

[1] V. Désangles et al., J. Electr. Propuls., vol. 2, p. 10, 2023.

[2] M.Merino and A. Ahedo, IEEE Transactions on Plasma Science, Vol. 43, No. 1, January 2015.

[3] Little and E. Choueri, PRL 117, 225003 (2016).

[4] A. Smolyakov et al., Phys. Plasmas 28, 060701 (2021).