ECR Ion Thruster Research Articles

Magnetic confinement less microwave discharge gridded ion thruster

A watt-level microwave discharge is induced without magnetic confinement for a high-precision gridded ion thruster, making use of a coaxial transmission line resonator. The thruster is characterized by performance measurements and plasma diagnosis, and a description of the operating mechanism of this thruster is given in this paper. A Faraday probe and a retarding potential analyzer are employed for the diagnosis. The results show that the plume divergence increases due to the electric field formed between the plume and the ion-induced electron emission cathode. A discharge mode transition is found during the increase of the microwave power, in which the bulk heating mode is converted to the surface heating mode. The magnetic-less microwave discharge gridded ion thruster performs a continuously adjustable thrust range of 5–115 μN and a highest total efficiency of 17.2%. Compared to the common ECR ion thruster, this thruster is free from magneto-static interference on the instruments and the additional magnetic momentum on the spacecraft.

A minimized electron cyclotron resonance ion thruster for China’s space-borne gravitational wave detection missions

Space-borne gravitational wave (GW) detection spacecraft works in the state of drag free for which a disturbance reduction system is utilized to offset the non-conservative force. The key actuator of drag-free control loop is a micro-thruster with the performance of a high precision thrust and wide-range operations. Ion thruster, such as electron cyclotron resonance ion thruster (ECRIT), is one of the options because its thrust can be controlled precisely by the method of beam current feedback. However, there is still a barrier for the conventional ECRIT to achieve the low thrust of 1 μN as required in space-borne GWs detection missions due to its radial structure. In this work, a minimized ECR ion thruster (mini-ECRIT) is designed by a new idea that it employs an axial ring-cusped field to exploit the low-pressure adaptability of resonance heating. The mini-ECRIT is tested and results in a dynamic thrust range of 1–100 μN, a resolution of 0.1 μN, a thrust noise of 0.1 μN/Hz1/2, and a response time of about 10 ms. In addition, the specific impulse of this thruster can reach as high as 510 s at low thrust 5 μN, being higher than that of previous ion thrusters by a factor of about 5, which may significantly reduce the propellant consumption. This minimized ECR ion thruster may support China’s space-borne GW detection missions such as TianQin.

Size Optimization of Disk Antenna for 5-cm ECR Ion Thruster

Size Optimization of Disk Antenna for 5-cm ECR Ion Thruster

Investigation on the radial distribution of electron density in a miniaturized ECR ion thruster of wide-range operations

A miniaturized thruster with a wide tuning range of thrust plays an important role for the drag-free control in the task of space-borne gravitational wave detection. For the design of a high-precision miniaturized thruster, it is necessary to study the spatial distribution of the electron density in its discharge chamber. This work investigates the electron density distribution in an ECR ion thruster of 2-cm diameter, with the input microwave power and mass flow rate tuned in a wide range. At relatively low power and flow rate, there is a peak of electron density at the radial position r = 4 mm, which is around the region of resonant power absorption. However, the density distribution in the center region becomes flat with the increase of power and flow rate; at high power and flow rate, it tends to be a Bessel function with a peak in the center (r = 0 mm). In the view of tuning of thrust, it is found that the above variation of electron density distribution can be as important as (or even more important than) the variation of peak value of electron density. A further discussion on the influence of the evolution of electron density distribution is given by considering the thruster design, operation, and control for the task of space-borne gravitational wave detection.

Characteristics of microwave ECR ion thruster powered with plate antenna in cross-magnetic field: Standing wave, skin effect, and mode transition

In a 2.45 GHz electron cyclotron resonance xenon ion source powered with circular plate-antenna, a rapid evolution of radial plasma-profile with discharge power in a region below 35 W and the abrupt jump of ion beam current accompanied by sudden radial-expansion of discharge glow were observed. Based on analyses about quantified glow images captured from the end-view of the discharge chamber and the ion beam current against the discharge power, the fast evolution of the radial plasma-profile is attributed to the counteraction of standing wave and the skin effect, the coincidence of enhanced microwave absorption in the electron plasma resonance layer, and the transverse magnetic confinement of electrons. The jump of ion beam current and the sudden radial-expansion of discharge glow are confirmed to be originated from the extraordinary-wave discharge at the electron cyclotron resonance layer beyond the plate antenna when the skin effect is dominant.

Water and xenon ECR ion thruster—comparison in global model and experiment

Gridded ion thrusters are one of the most commonly used types of electric propulsion, and alternative propellants have been studied for miniature ion thrusters to meet the demand of propulsion systems for micro-/nano-satellites. Water is a candidate as an alternative non-pressurized propellant for a CubeSat thruster. It is consistent with the CubeSat concept of short-term and low-cost development. In this paper, the characteristics of a miniature water ion thruster were compared with those of a xenon one using a global model and experiments. The dependence of the performance on the mass flow rate and the input microwave power was examined, and the effects of dissociation and doubly charged ions were directly measured by a quadrupole mass spectrometer. The estimates on the model were compared against experimental results for both propellants, and the performance of the thruster operating on xenon propellant was compared to the performance operating on water propellant. In the comparison between the estimates and the experimental results, the two differences were discussed: the one between water and xenon and the other from the experimental result in both cases. A performance decrease in the propellant utilization efficiency and the specific impulse cannot be avoided when using water as a propellant in an ion thruster. However, the ion production cost did not increase, and it showed the capability of water ion thruster for CubeSat application taking advantage of safety, low cost, non-pressurized system, and human-friendliness of water when used as a propellant.

Microwave power absorption to high energy electrons in the ECR ion thruster

The microwave power absorption efficiency of the μ10 ECR ion thruster, utilized in the Japanese asteroid explorers Hayabusa and Hayabusa2, is investigated in order to allow performance measurement and provide information for its improvement. A model detailing the local electron behavior in a real ECR plasma discharge, based the magnetic field characteristics, is presented. Three methods to evaluate the microwave power absorption efficiency are proposed: an estimation based on the chamber geometry and magnetic field characteristics, a measuremen based on performance parameters and a measurement performed with Langmuir probes. The equations used for each method are analytically derived. The local electron behavior model is confirmed with a Langmuir probe experiment. Measurement of the microwave power absorption efficiency is performed with the two independent methods proposed. Results from the two experiments show good agreement with each other and with the theory. Finally, a diffusion model explaining the different electron temperature distributions observed in the chamber is proposed. The model and experiments clarify the physics behind previously observed performance variations and give valuable hints for future chamber improvement.

Analysis of the primary experimental results on a 5 cm diameter ECR ion thruster

An ECR ion thruster with a diameter of 5 cm has been developed and tested. Four different antenna positions were experimentally and numerically investigated, and the results suggest that the optimal location for the antenna is where it is perfectly surrounded by the electron cyclotron resonance layer. We also evaluated two different antenna configurations, and found that the star configuration is preferable to the circular configuration, and also that the circular antenna is only 40% as efficient as the star antenna. The experimental curve of the ion beam current and voltage agrees with the fitting results from the analytic solution. The simulation of the magnetic topology in the discharging chamber with different back yoke heights indicates that it needs to be further verified.

Microwave Frequency Tuning of an ECR Ion Thruster for Impedance Matching

Microwave Frequency Tuning of an ECR Ion Thruster for Impedance Matching

Particle Simulation of Three-Grid ECR Ion Thruster Optics and Erosion Prediction

Ion optics is a critical component of ion thrusters. A two-dimensional axisymmetric model is developed to study the characteristics of three-grid electron cyclotron resonance ion thruster optics. The code is based on a particle-in-cell combined with the Monte Carlo collision method to simulate ion dynamics and charge-exchange processes in the grid region. The simulation results show that the mode can give a reasonable estimate of the physics characteristics of the ion optics. The design of the ion optics satisfies the requirement of preventing electron backstreaming. Charge-exchange ions can cause damage to the grids, especially to the accelerator grid. ‘Barrel’ erosion can increase the accelerator grid aperture radius at a rate of 1.91×10−11 m/s, while the decelerator grid plays an important role in reducing ‘pits-and-grooves’ erosion.

Improvement of the Thrust Force of the ECR Ion Thruster μ10

Based on the success of the Japanese asteroid explorer Hayabusa, the ECR ion thruster μ10 will be installed in Hayabusa's successor, Hayabusa-2, and is scheduled to be commercialized for use in geostationary satellites within the next three years. To increase the thrust force of the μ10 as much as possible without major design changes, luminescence measurements were conducted using an optical fiber probe. The probe gave an internal view of the μ10, and it was discovered that there was plasma in the waveguide. As the plasma, the density of which is higher than the cut-off density, interferes with the transmittance of microwaves, the propellant injection location was changed. In addition to the change in propellant injection location, the grid system was also refined. These improvements increased the thrust force from 8.0 mN to 10.1 mN with a decrease in specific impulse by 40 sec from 3200 sec to 3160 sec.