Electron Cyclotron Resonance Ion Thruster Research Articles

Numerical simulation of magnetic field influence on plasma and electron extraction of electron cyclotron resonance neutralizer

Electron cyclotron resonance (ECR) neutralizer is a key component of electron cyclotron resonance ion thruster (ECRIT) with a diameter of 10 cm, which plays an important role in maintaining the spacecraft potential balance and neutralizing the ions in the plume region. Optimizing magnetic field distribution is an important way to improve the performance of neutralizer. At the same time, the uniformity of the magnetic field and the position of the magnetic trap can affect the magnetic field characteristics, plasma performance, electron extraction process, and beam current. Previous experimental researches showed that the beam current extraction performances of the two ECR neutralizers with different magnetic field uniformity and different magnetic trap locations are significantly different. However, it is difficult to reveal the physical phenomena and causes only through experiments, so numerical simulation is needed. Therefore PIC/MCC codes for the ECR neutralizers with different uniformity of magnetic field and different positions of magnetic trap are established. Under the given electron extraction potential, numerical simulations are accomplished to study electron extraction procedure and analyze its influence on the performance of the neutralizer. The simulation results show that when the magnetic field uniformity is low and the magnetic trap is located upstream of extraction orifice, the migration of electrons from the magnetic trap to the outlet is limited by the magnetic field and the electric field, thus a higher potential energy is needed to extract the electrons. Otherwise, when the magnetic field uniformity is high and the magnetic trap is located at the downstream of extraction orifice, electrons will be more likely to migrate towards the magnet trap. After the electrons reach the magnetic trap, under the action of the anode potential, the external potential is higher, and the external weak magnetic field almost fails to hold these electrons, Therefore a large number of electrons can be extracted at low extraction potential. This research will lay an important foundation for the development of high-performance ECR neutralizer.

Wall material effects in a minimized electron cyclotron resonance ion thruster

Wall material effects in micro-ion thrusters attracts significant research attention with respect to weakening plasma wall loss, and increasing propellant utilization to obtain high-precision and low-thrust of micro-Newton propulsion, as required in new generation space observation missions. In this study, we compare the performance and discharge characteristics of different wall materials, namely, Mo and Al2O3 in a minimized electron cyclotron resonance ion thruster. The results show that the propellant utilization and specific impulse of the ceramic are about three times higher than those of the Mo at a low mass flow rate of 0.03 sccm. In addition, a planar Langmuir probe is used in the discharge chambers, and the results show that the secondary electron emission of Al2O3 effectively reduces the electron temperature, increases the electron density, and results in high efficiency. These results are helpful for improving the performance of micro-ion propulsion devices for microsatellites and space-borne gravitational wave detection missions.

Influences of coupling magnetic field of 2 cm electron cyclotron resonance ion thruster on plume neutralization

An electron cyclotron resonance ion thruster (ECRIT) has advantages of long service life and simple structure. The external coupling magnetic field of the ECRIT is one of factors that influences the plume neutralization process and coupling voltage of the neutralizer. The coupling magnetic field varies with the installation direction of the ion source and neutralizer as well as the direction of the internal magnetic pole. Calculating the distribution law of the coupling magnetic field and experimentally studying the influence of the coupling magnetic field on plume neutralization are very important. This paper focuses on two power rates and two flow rates of the ion source and conducts experiments on neutralization within the acceleration voltage range of 350 to 1 450 V to study the influence of changes in the direction and position of the ion source and the influence of the neutralizer′s magnetic pole on the ion beam extraction and maximum coupling voltage. The results indicate that the ion beam extraction is not influenced by the direction of the magnetic pole and the installation direction of the ion source and neutralizer. When the ion source is installed relatively perpendicular to the neutralizer, its coupling voltage is reduced. At the same time, changing the direction of the magnetic pole of the neutralizer into the opposite of the direction of the magnetic pole of the ion source also reduces the coupling voltage of the neutralizer. When the ion source is installed perpendicular to the magnetic pole of the neutralizer in the opposite direction, the coupling voltage is the lowest.

Effects of magnetic field configurations on the minimized ECR ion thrusters for micro-Newton and wide-range operations

Space-based gravitational wave detection missions require precise thrusts over a wide-range of 1–100 μN. In this study, the axial ring-cusp magnetic field configuration is used to design a miniature electron cyclotron resonance ion thruster with a radius of 5 mm. Two typical configurations, i.e., open-type and closed-type, are compared in terms of electron density, electron temperature, and thrust for micro-Newton and wide-range operations. The results show that the open-type achieves high performances owing to the high efficiency of absorption of input microwave power. The lower limit of the mass flow rate in the electron cyclotron resonance (ECR) discharge is expanded to a very low value of 3 × 10−2 sccm to achieve 1 μN in the open-type. The thrust in the open-type could be tuned in a wide-range of 1–119 μN, meeting the requirement.

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.

Computational and experimental research on the performance of ECRIT ion source with nitrogen propellant

Electron cyclotron resonance ion thruster (ECRIT) with a diameter of 2 cm has the characteristics of no hot cathode and high specific impulse, which is suitable for the air-breathing electric propulsion system. In order to adapt to the atmospheric composition characteristics of nitrogen and oxygen in low orbit, the computational and experimental research on the performance of the ECRIT ion sourse with nitrogen propellant is an important basis for analyzing the feasibility of applying ECRIT to the air-breathing electric propulsion system. In this paper, the global model of the nitrogen ECRIT ion source with a diameter of 2 cm is established to calculate its performance. Then, the computational results are compared with the experimental results to analyze the difference. The research results show that when the input power of the ion source is 8 W and the gas flow rate is 2 ml/min, the computational and experimental results of the extracted ion beam current and thrust reach the maximum with the extracted beam current of 16.2 and 12.5 mA and the thrust of 476.6 and 368 μN, respectively. When the input power is 8 W and the gas flow rate is 0.6 ml/min, the computational and experimental results of the specific impulse are 2 095.8 and 1 855.6 s, both reaching the maximum value. The relative errors between the computational and experimental results of the extracted ion beam current, thrust and specific impulse all range from 2% to 32%. When the input power and gas flow rate used are 8 W and 1 ml/min in calculation, and 8 W and 0.8 ml/min in experiment, the ion source is on the optimal operating state. At this situation, the computational and experimental propellant utilization efficiencies with 17.8% and 16.2% respectively are high, and the ion energy loss with 443.9 and 596.2 W/A respectively is low.

Study on the effect of discharge chamber length on the performance of electron cyclotron resonance ion thruster

Discharge chamber length is one of the factors in optimizing the electron cyclotron resonance ion thruster performance. It adjusts the distance between bulk plasma and grid system to change the plasma density upstream of the screen grid, which will affect the ion beam current and focusing state to achieve optimization purpose. However, new evidence shows the discharge chamber length plays an important role in ionization during ion beam extraction, which means that the effect of discharge chamber length on the performance of electron cyclotron resonance ion thruster should be reexamined. After applying grid voltages, another high electron temperature region located upstream of the screen grid is observed in the integrated simulation using particle-in-cell with Monte Carlo collision method, but it is not observed in the traditional discharge chamber simulation. It is believed in the paper that the high electron temperature region exists objectively, because the Child-Langmuir sheath will repel electrons moving towards screen grid back to magnetic mirrors again. Those electrons will gain energy from microwave, and finally form a high electron temperature region along the Child-Langmuir sheath. This phenomenon implies that discharge chamber length can adjust the high electron temperature distribution upstream of screen grid to affect the plasma generation. Therefore, in this work, the effect of discharge chamber length on discharge and ion beam performance is systematically studied by adopting the integrated simulation. In this paper, three ion thrusters with different discharge chamber lengths are simulated. Under the conditions of same magnetic field and operation parameters, the comparisons of electron energy gain, plasma parameter distributions and ion beam current among the three ion thrusters are conducted. The results show that shorter discharge chamber length has higher electron energy gain, plasma density and voltage, but smaller ion beam current. This abnormal phenomenon can also be seen experimentally. By analyzing the ionization rate inside the chamber, it can be seen that high-temperature electrons upstream of the screen grid have a significant contribution to ionization. And thus, a little bit longer discharge chamber length with lower plasma density inside the chamber has bigger ion beam current for having higher plasma density upstream of the screen grid. According to this phenomenon, an electron heating mode is proposed: electrons gain energy by reciprocating through the electron cyclotron resonance layer between the Child-Langmuir sheath and magnetic mirrors. This heating mode can be used as a supplement to the electronic constraints outside the magnetic mirrors to improve the energy utilization efficiency of the thruster, which can provide a new insight into the electron cyclotron resonance ion thruster design in the future.

Experimental study on 10-cm ECRIT neutralizer with nitrogen gas

Electron cyclotron resonance ion thruster (ECRIT) with a diameter of 10 cm can be operated in multiple types of gases and it is feasible to be applied to air-breathing electric propulsion systems. The study on the neutralizer of the ECRIT running in nitrogen gas is the basis for the study on the ECRIT running in nitrogen-oxygen mixed gas. When the ECR neutralizer of typical 10-cm ECRIT running in xenon gas runs in nitrogen gas, the extracted electron current is reduced, because ions tend to drift out of the neutralizer, due to the lower molecular weight of nitrogen. The typical neutralizer is no longer suitable for running in nitrogen gas. In this work, based on the 10-cm typical ECR neutralizer, in order to inhibit ions drifting out of the neutralizer and improve the performance of electron extraction, a bipolar ECR neutralizer suitable for running in nitrogen gas is experimentally studied. The results show that under the conditions of gas mass flow rate of 0.04 mg/s and input power of 10 W, the anode voltage required by the typical ECR neutralizer running in nitrogen gas is 150 V when the extracted electron current is 134 mA. However, the bipolar ECR neutralizer requires only 50-V anode voltage, which decreases by about 67%. When the anode voltage is 40V, the power loss of the typical ECR neutralizer is 1204.82 W/A, while the power loss of the bipolar ECR neutralizer is 95.23 W/A, which is about 8.3% of the former. The ion shielding effect of the bipolar ECR neutralizer running on nitrogen gas is remarkable and the electron extraction performance is improved.

Integrative simulation of a 2 cm electron cyclotron resonance ion source with full particle-in-cell method

A two-dimensional full particle-in-cell model is developed to simulate the operation process of a 2 cm electron cyclotron resonance ion thruster. The simulation regions include the discharge chamber, grid system, and plume, and the processes of neutral gas injection, plasma discharge, and ion beam extraction are simulated continuously. Neutrals are treated as particles and managed through an adaptive particle management algorithm. The collisions between charged and neutral particles are approached by the method of combining the Monte Carlo and directly simulation Monte Carlo collisions. The integrative simulation provides a global perspective to learn the gridded ion thruster, such as the Child-Langmuir sheath, acceleration grid erosion, plasma bridge, and so on. In this paper, the response of the plasma system to the accelerating voltage is analyzed, which is related to the bulk plasma, antenna floating voltage, and Child-Langmuir sheath. Besides, an ion density wave is observed in plume, which will increase the current of acceleration grid and cause ion backflow.

Interaction between plasma and electromagnetic field in ion source of 10 cm ECR ion thruster

Through diagnosing the plasma density and calculating the intensity of microwave electric field, four 10 cm electron cyclotron resonance (ECR) ion sources with different magnetic field structures are studied to reveal the inside interaction between the plasma, magnetic field and microwave electric field. From the diagnosing result it can be found that the plasma density distribution is controlled by the plasma generation and electron loss volumes associated with the magnetic field and microwave power level. Based on the cold plasma hypothesis and diagnosing result, the microwave electric field intensity distribution in the plasma is calculated. The result shows that the plasma will significantly change the distribution of the microwave electric field intensity to form a bow shape. From the boundary region of the shape to the center, the electric field intensity varies from higher to lower and the diagnosed density inversely changes. If the bow and its inside lower electric field intensity region are close to the screen grid, the performance of ion beam extracting will be better. The study can provide useful information for the creating of 10 cm ECR ion source and understanding its mechanism.

Numerical simulation of electron extraction from micro electron cyclotron resonance neutralizer under different magnetic circuits

The electron cyclotron resonance (ECR) neutralizer is an important part of the micro ECR ion thruster. The electrons extracted from the neutralizer are used to neutralize the ions extracted from the ECR ion source, thereby avoiding the surface charges accumulating on the spacecraft, and the behaviour of electron extraction affects the overall performance of the thruster. In order to investigate the electron extraction through the orifices of the micro ECR neutralizer, a two-dimensional particle-in-cell with Monte Carlo collision (PIC/MCC) model is established in this work. The effects of different magnetic circuits on the electron extraction of the neutralizer and the influence of different cavity lengths on the wall current loss are studied through numerical simulation. The effects of different magnetic circuit structures on the electron extraction and wall current loss of the neutralizer are studied. The calculation results show that the position of the ECR layer and the magnetic flux lines near the extraction orifices are very important for the electron extraction performance of the neutralizer. When the ECR layer is located upstream of the antenna, electrons are easily lost in migration and diffusion motion, and the energy required for the electrons to cross the potential well before the extraction hole is higher. If more magnetic flux lines pass parallelly through the extraction orifices, the neutralizer requires a small voltage to extract the same electron current. When the ECR layer is cut by the antenna or is located downstream of antenna, more electrons may migrate along the magnetic flux lines to the vicinity of the extraction orifices, thereby reducing the voltage of collector plate. The effects of different cavity lengths on the extraction of electrons under the same magnetic circuit structure are studied. It is found that increasing the length of the cavity allows more parallel-axis magnetic flux lines to pass through the extraction holes to avoid electron loss on the surface of the extraction plate, and thus increasing the extraction electron current. The research results conduce to designing a reasonable neutralizer magnetic circuit and cavity size.

On abnormal behaviors of ion beam extracted from electron cyclotron resonance ion thruster driven by rod antenna in cross magnetic field

In a 2.45 GHz electron cyclotron resonance (ECR) ion thruster powered with rod antenna under a cross magnetic field, abnormal behaviours such as sudden drop of ion beam current (I b) and larger increasing-rate of I b in the high microwave power (P w) discharges at high gas flow rates were observed. A differential method was proposed to reveal the changes in the radial profiles of gray values extracted from the end-view discharge images. The increasing-rate of I b with respect to P w was used to evaluate efficiencies of ion production and transport. Analyses indicate that discharges are dominantly sustained by ordinary wave via electron heating in the electron plasma resonance layer that can shift along the rod-antenna, and extraordinary wave can only ignite a discharge in the ECR layer in the low gas flow rate regime. In terms of the confinement region defined by the magnetic field lines intercepting with the screen grid, the confinement region of the optimized 2.45 GHz cross magnetic field takes the shape of hourglass, enabling the high increasing-rate of I b with respect to P w in high power discharges at high gas flow rates. Correlated with the accompanied bright boundary layer appearing in the differentiated image, the sudden drop of I b in the low gas flow rate regime is attributed to the discharge ignited by the enhanced extraordinary wave in the ECR layer neighbouring the narrowest confinement region, where the produced ions can promptly enter the loss region.

Numerical simulation of influence of magnetic field on plasma characteristics and surface current of ion source of 2-cm electron cyclotron resonance ion thruster

The cathode-less miniature electron cyclotron resonance ion thruster (ECRIT) has the advantages of long-life and simple-structure. In the ECRIT ion source, the plasma distribution will affect the beam extraction, and the relative position of the ECR layer determined by the magnetic field structure and the flat-ring antenna together affect the plasma distribution. Due to the sheath, the ions or electrons in the plasma will be accelerated to sputter the surface of wall and induce plasma loss. It is important to investigate the wall currents and plasma characteristics. Therefore, particle-in-cell with Monte Carlo collision (PIC/MCC) model is established in this article to study the influence of the magnetic field structure on the plasma and wall current characteristics of 2-cm ECRIT ion source. The calculation results show that the electrons are confined near the ECR layer of antenna by the magnetic mirror, which leads the plasma to be distributed near the ECR layer. When the ECR layer is located on the upstream side of the flat-ring antenna, the plasma is concentrated between the antenna and magnet rings, and the ion density in front of the grid is lowest, which results in a lower ion beam current extracted from ion source and a lower current on the surface of magnetic ring and antenna. When the ECR layer is located on the downstream side of the flat-ring antenna, the plasma density near the upstream side of the antenna and grid is high, which results in higher ion beam current extracted from the ion source and higher current on the surface of antenna and magnetic ring. The plasma distribution and the total wall current of the ion source are affected weakly by the magnetic field structure. In this magnetic field structure, the ion sputtering on the flat-ring antenna is serious. Although such a magnetic field design can increase the extracted ion beam current, it will shorten the working life of the ion source. In the future, when designing a new thruster, it is necessary to weigh the ion current of extraction and lifetime to select the appropriate magnetic field structure.

Calculation on 2 cm ECRIT Thrust Regulation Based on 3D PIC Numerical Simulation Method

Drag-free control is the key technology for space gravitational wave detection, which will be completed by miniature thruster. 2 cm Electron Cyclotron Resonance Ion Thruster (ECRIT) may be used for the drag-free control. Therefore, the 3D PIC method is used to estimate the thrust regulation of 2 cm ECRIT through simulating the property of ion extracting from the double-grid system. Through analyzing the thrust performance and grid focusing property under different grid apertures, the better grid structure is selected for the subsequent calculation. On this basis, the influence of grid voltage and the ion density on the performance of the thruster is analyzed. The result shows that reducing grid aperture can reduce the thrust, but it also affects the focusing property of the grid. Changing the ion density can adjust the thrust in a wide range. At given grid structure and ion density, there is a suitable grid accelerating voltage range to ensure the best ion focus characteristics. Considering the thrust performance and focusing characteristics, the grid structure with screen and accelerating grid aperture in 0.6 mm and 0.34 mm is selected. When the ion density is 1×1 017, 0.7×1 017, 0.4×1 017 and 0.2×1 017 m-3, the thrust can range from 5.05 to 141.44 μN through adjusting the grid accelerating voltage. This study can provide information for analyzing the possibility of the thruster application.

The influence of magnetic circuit and operating parameters on the plasma property of 2 cm ECRIT ion source

The ion source of 2 cm electron cyclotron resonance ion thruster (ECRIT) extracts ion beam to generate thrust. The magnetic circuit of the source has important influence on plasma distribution associated with beam extracting. It is necessary to diagnose the plasma field of the ion source through the straight and bent Langmuir probe. The diagnosing results showed that at the same power and gas flow rate, the magnetic circuits affected the peak values of plasma parameters and their distribution. For different magnetic circuit, the ion density and electron temperature were positively and negatively correlated with the gas flow rate relatively; the ion density and electron temperature were all positively correlated with microwave power. At the high flow rate, microwave power and magnetic circuit affected slightly the plasma distribution. However, at the high power, gas flow rate and magnetic circuit had obviously impact on plasma distribution. In addition, the suitable gas flow rate range of the ion source with different magnetic circuits was different.

Design Optimization and Experiment of 5-cm ECR Ion Thruster

A cross magnetic field configuration (CMFC) was selected to design a microwave electron cyclotron resonance (ECR) ion thruster with a chamber diameter of 5 cm. The design was performed using the COMSOL Multiphysics software. Based on the commercially available arc-shaped samarium-cobalt magnet, the balanced optimization of CMFC was achieved at the frequency of 2.45 GHz. In Xe ion extraction discharge excited with the originally selected rod antenna, arcing on its front end was confirmed. The arcing problem was solved by replacing with a circular plate antenna. In terms of Xe ion extraction, 5-cm CMFC ECR ion thruster was shown to be better than its counterparts. COMSOL plasma simulation was used to reproduce two opposite discharge profiles observed in experiments.

Study on Effect of Structure and Propellant on Beam of ECR Ion Source

To increase the ion current from the ion source is an important way to improve the performance of the electron cyclotron resonance ion thruster(ECRIT). The ion migration distance, magnetic topology and propellant have a close influence on the extracting ion beam. This influence is studied through both magnetic circuit structure calculation and experiments, by using an ion source with different gate mounting positions and magnet lengths. Experimental results show that the distribution of the ECR region will be discontinuous when the length of the magnet is too short. This will greatly reduce the performance of the ion source. To increase the length of the magnet is beneficial to the beam emission at high gas flow rate, but it reduces the beam emission at low gas flow rate. The effect of the ion migration distance on the ion beam is related to the plasma density in the ion source. When the gas flow rate is low, a longer gate mounting ring is beneficial to increase the ion current. When the gas flow rate is high, the different magnetic topology will cause the gate mounting ring which influences on the ion current. At low gas flow conditions, xenon gas can significantly improve the discharge stability of the ion source and increase the ion current. However, at high gas flow rate, the concentration effect of the neutral particles is too strong that affects the energy accumulation process of the free electrons. This would cause the decrease in the ion current.

Equivalent two-dimensional numerical simulation of an ECR neutralizer

The electron cyclotron resonance (ECR) neutralizer is a component of the 10-cm electron cyclotron resonance ion thruster (ECRIT) and its performance has a great effect on the overall performance of the thruster. To clarify the mechanisms of electron extraction of the ECR neutralizer, a particle-in-cell/Monte Carlo collision (PIC/MCC) solver was developed to simulate the plasma in the ECR neutralizer. This paper equivalently simplified the three-dimensional model of the ECR neutralizer into a two-dimensional axisymmetric one according to experimental results and the circumferential electric drift of charged particles. Hence, a two-dimensional three-velocity component full-particle calculation model was used in the solver. Through analyzing ECR heating mechanism, the validity and accuracy of the equivalent ring antenna were discussed. The distribution of plasma parameters and extracted electron current were obtained by tracking the motion of electrons and singly charged xenon ions, simulating the elasticity, excitation, ionization and Coulomb collisions. The results showed that the density of neutral particles can be adjusted to coincide simulation current with experiment. It was also found that due to the magnetic field gradient, plasma will migrate to the magnetic well, where the ion was in dominant position to form a potential well and hinder the extraction of electron.

Experimental study of magnetic circuit and antenna position influence on performance of 2 cm electron cyclotron resonance ion thruster

Experimental study of magnetic circuit and antenna position influence on performance of 2 cm electron cyclotron resonance ion thruster

Experimental Research on the Neutralizer of Micro ECR Ion Thruster

As the key component of micro electron cyclotron resonance (ECR) ion thruster, the initial gas discharge and electron beam extraction performance of ECR neutralizer plays an important role in the whole performance of ECR ion thruster. The experiment on the neutralizer is completed to study the influence of the antenna structure, cavity length and electronic extraction board on the performance. The experimental results show that, within a certain range, as the length of the cavity is longer, the annular segment of antenna is slightly higher than ECR zone and the width of annular segment is smaller, the performance of the neutralizer is better. There is a reasonable structure for the electronic extraction board to make the performance of the neutralizer better. According to the experimental results, the optimal structure of the neutralizer is determined. For Xe gas, when the microwave power is 2.0W and the gas flow rate is 0.2sccm, the best performances of the optimal neutralizer are that extracted electron beam and coupling voltage is 4mA and 31.5V respectively.