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MagnetIc NOzzle thruster with elecTron cyclOtron Resonance

Periodic Reporting for period 2 - MINOTOR (MagnetIc NOzzle thruster with elecTron cyclOtron Resonance)

Reporting period: 2018-01-01 to 2020-07-31

The MINOTOR project’s (MagnetIc NOzzle elecTron cyclOtron Resonance thruster) main objective is to demonstrate the feasibility of the ECRA technology (Electron Cyclotron Resonance Accelerator) as a disruptive technology for electric propulsion, and to prepare roadmaps for the potential future developments of the technology. The project is focused on the understanding of the physics and the demonstration of the technology, rather than on the production of a fully operational prototype.

Based on electron cyclotron resonance (ECR) as the sole ionization and acceleration process, ECRA is a cathodeless thruster with magnetic nozzle, allowing thrust vectoring. It has significant potential advantages in terms of global system cost and reliability compared to mature technologies. It is also scalable and can potentially be considered for all electric propulsion applications.

The plasma is created by ECR inside the thruster cavity by injecting and ionizing neutral gas, resulting in a high-density plasma. The topology of the external magnetic field is purely diverging and acts as a magnetic nozzle, where the magnetized electrons are accelerated by the conservation of the electron energy and magnetic moment µ. This leads to an ambipolar electric field that directly accelerates ions to high velocities. Electrons with high energy escape the potential barrier to conserve the quasi-neutrality of the exhaust plasma beam, which is ensured since the thruster is floating. Thus, neither grids nor hollow cathode neutralizers is not needed. The plasma then detaches from the magnetic lines and produces a net thrust force.

The first results obtained with ECRA have been encouraging, but the complexity of the physics at play has been an obstacle for the understanding and development of the technology. Indeed, the ionization chamber involves absorption of microwave energy in a magnetized, flowing plasma, which is challenging to model, and the understanding of the physics in the magnetic nozzle is still a subject of research. Thus, an in-depth numerical and experimental investigation plan has been devised for the project, in order to bring the ECRA technology from TRL3 to TRL4.

In order to demonstrate the potential of this technology in comparison to other technologies in a large range of thrust levels, it is planned to have achieved the following objectives by the end of the project:
• Get a full understanding of the physics, by in-depth numerical modelling studies in parallel to an extensive experimental investigation, leading to optimised designs, performance maps and scaling laws for the thruster;
• demonstrate ECRA performances with tests at three thrust levels (30W, 200W and 1 kW) and erosion tests;
• demonstrate features such as compatibility with alternative propellants and magnetic beam steering;
• demonstrate the feasibility of an efficient PPU;
• determine quantitatively the impact of the ECRA technology on the EP system and satellite platform at systems level, and establish the future industrial roadmaps for development. These roadmaps shall aim at realising a high TRL in the timeframe of 2023-2024.
In the second period of the project, the following main achievements are reported:

For the WP1, Ethics issue in the project have been monitored and none have been identified. The Deliverable D1.1 has been submitted.

WP2, is conducting management, dissemination and exploitation activities according to initial planned.

Regarding WP3 activities, the modelling codes SURFET and ROSEPIC have been successfully developed. SURFET was used to perform extended parametric analyses of the physics and operation of the ECRT in terms of the input power, mass flow rate, neutral gas injector location and geometry, ECR surface location and applied magnetic field strength. The actual geometry, field, and data of the 30W prototype at ONERA were used for the simulations. SURFET results were presented in deliverable D3.3 D3.4. ROSEPIC was developed first for 1D and 3D (D3.2) but major effort was spent to develop 2D capabilities, and first simulations were achieved. A preliminary kinetic-analytical model was also developed to better understand the physics of the source (D3.1).

The work performed in WP4 allowed studying different configurations and materials for the thruster. A new thruster version (waveguide coupled) was also tested. It also developed the proper hardware and protocols to make accurate performance measurements. It comprised the backbone of the experimental efforts in the project. The achievements and results are detailed in D4.1 and D4.2.

WP5 has been devoted to the tests of different gases as propellant, as alternative to Xenon, although in vacuum conditions not completely representative. Krypton, Argon, Air and Carbon Dioxide were tested. Also within WP5, the SURFET code of WP3 was used to simulate the performance of the device with three different propellants (Xe, Ar, Kr). Results are presented in deliverable D5.1.

The WP6 conducted successfully the testing and thrust measurements of the 50 W and 200 W ECR thruster in the JUMBO test facility and dealt with the analysis of the results in terms of performance, endurance and erosion of the thruster. A major achievement was to reach 50% efficiency on the thrusters, with an extrapolated lifetime of several thousand hours for the 200W thruster. Within WP6, the SURFET code of WP3 was used to perform scale-up studies, to compare numerically the performance of the 30W and 200W prototypes. Results were presented in deliverable D6.1 and D6.2.

WP7 has achieved the demonstration of a 25W SSPA with 70% efficiency, and of a combiner structure for several amplifier.

In WP8, a system Impact assessment was performed. A first evaluation led to D8.1. Mission and performance estimates by Safran then allowed TAS-B to assess the ECR technology in a complete mission in D8.2.Thanks to this tool TAS-B was able to highlight critical elements which are only visible in a point of view of global comparison. One example is the consequences of an extension of the mission duration due to lower thrust. The RF generator is also a critical element in the system's power supply chains, in particular for the power "scalability" of the system.

Work performed in WP9 consisted in gathering the performances and compare it to other thruster technologies (D9.1 and D9.2) and prepare the future work (D9.3).
All the achievements presented in the previous section represent an advancement with respect to the state of the art on ECR thruster.

The main outcomes to be derived from MINOTOR are the following:
• Provide a cost effective alternative to current technologies.
• Leverage effect and benefit for EU partners.
• Mass adoption of the technologies.
• Market penetration.