# A Novel Transversal-Feed Electron Cyclotron Resonance Plasma Thruster: Design and Plasma Characteristics Analysis

^{1}

^{2}

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## Abstract

**:**

^{18}m

^{−3}. Experimental discharge tests are conducted under various microwave power conditions, demonstrating that the thruster can initiate and cease operation with an incident power as low as 5 W, significantly lower than that of traditional coaxial feed structures. At a power level of 20 W, the ion current density can attain 3 A/m

^{2}. Moreover, the transversal-feed thruster exhibits exceptional performance when the power exceeds 10 W, and the propellant flow rate ranges from 0.5 SCCM to 5 SCCM. The superior performance characteristics of the proposed thruster configuration make it a promising candidate for applications demanding efficient and low-power plasma propulsion systems.

## 1. Introduction

^{13}–10

^{16}m

^{3}, and the ion velocity reaches 20–30 km/s [7]. The French Aerospace Lab (ONERA) used Xenon as the propulsion gas and studied the effects of mass flow and microwave power on the ion current and ion energy distribution. When the microwave power was 50 W, the mass utilization efficiency reached 45%, and the ion energy reached 350 eV [1]. Kyoto University used a two-dimensional axisymmetric particle model of the Monte Carlo collision algorithm to perform a numerical simulation of ECRPT. The numerical calculation was performed at a microwave frequency of 4 GHz and a magnetic induction intensity of 1430 Gauss. The results show that the magnetic field can effectively confine the electrons, and the ions are expelled using the electrostatic field in space. This also verifies the electron cyclotron resonance effect in the discharge chamber region. Finally, the electron number density can reach the order of 10

^{16}m

^{−3}[8]. Inchingolo [9] developed HYPHEN, a 2D model simulating the circular waveguide ECRT concept, and used it to study the EP2 ECRT prototype. This simulation model can be used to evaluate the extent to which the power deposition profile, the ECR region position, and the operating point affect the thrust and plasma transport variables in the magnetic nozzle. Furthermore, Magarotto [10] presents a numerical suite of cathodeless plasma thrusters and discusses their utilization at low power (50 W range). This numerical suite is well suited as a simulation tool for electrodeless ECRPT to study plasma properties and optimize thruster performance.

## 2. ECRPT with Transversal-Feed Structure

#### 2.1. Thruster System Structure

#### 2.2. Microwave Antenna Simulation

#### 2.2.1. Transversal-Feed Structure

#### 2.2.2. Coaxial-Feed Structure

#### 2.2.3. Electric Field Intensity Distribution

^{3}–10

^{4}V/m in the discharge chamber region, which meets the energy requirements of the antenna for exciting the propellant. At the same time, the transversal-feed structure has a higher electric field intensity in the discharge region than the coaxial-feed structure, which indicates that the transversal-feed structure makes it easier to ionize the propellant according to Equation (4). This is due to the microwave resonance phenomenon in the transversal structure.

#### 2.3. Design of Discharge Chamber

**E**is an electric field, ρ

_{q}is free charge density, ε is permittivity in medium, V is potential. The potential distribution can be obtained by solving (5) through the free charge density source term and boundary conditions, and then the electric field distribution can be obtained from (6). The transport theory was used to estimate the characteristics of the plasma, such as the electron temperature, number density of ions, and electrons.

_{e}is the electron number density, R

_{e}is the electron creation rate,

**u**is the ion velocity,

**Γ**

_{e}is the electron flux vector, n

_{ε}is the electron energy density,

**Γ**

_{ε}is the electron energy flux vector,

**D**

_{e}is the electron diffusivity,

**D**

_{ε}is the electron energy diffusivity, S

_{en}is the energy loss or gain due to inelastic collisions, Q is the external heat source, and Q

_{gen}is the generated heat source.

_{k}is the mass faction,

**u**is the mass averaged fluid velocity,

**j**

_{k}is the diffusive flux vector, R

_{k}is the creation rate expression,

**V**

_{k}is the diffusion velocity, D

_{k}is the diffusion coefficient, M

_{n}is the mean molar mass of the mixture, D

_{k}

^{T}is the thermal diffusion coefficient, T is the gas temperature z

_{k}is the charge number, μ

_{k}is the mixture averaged mobility.

^{18}m

^{−3}. The higher ion number density benefits from the dual excitation effect of microwave resonance and electron cyclotron resonance achieved in the transversal feed.

## 3. Experimental Verification

#### 3.1. Experimental Scheme

^{−1}~10

^{−2}Pa. The vacuum obtaining system consists of 18 L/s RVD-18 rotary vane vacuum pump and 150 L/s ZJP-150 roots vacuum pump.

#### 3.2. Measurement of Ion Current Density under Different Microwave Power Conditions

^{−2}Pa and a mass flow rate of 0.5 SCCM. The ion current densities of the thruster plume region under microwave power conditions of 5 W, 8 W, 10 W, 12 W, 15 W, 18 W, and 20 W were analyzed and compared. Figure 9 shows the thruster discharge under different power conditions.

^{2}, and the voltage at different powers was measured with an oscilloscope. Table 2 shows the ion current and ion current density in the plume region at different powers.

^{2}. In order to observe the changing trend of ion current in the plume region, a fitting curve of ion current density with power was fitted, as shown in Figure 10. It can be intuitively seen from the Figure that in the case of more than 10 W, the ion current density is higher, and the propellant is more fully ionized.

#### 3.3. Measurement of Ion Current Density under Different Mass Flow Conditions

^{−2}Pa, argon gas, and 20 W microwave power. The ion current density of the thruster plume area under different propellant mass flow conditions is analyzed and compared.

^{2}, and the ion current density continuously decreases with the increase in the propellant flow. When the gas flow rate increases, it causes an increase in the number of collisions between the electrons and the gas atoms. As a result, the energy transferred from the electrons to the gas particles increases, causing an increase in the gas temperature by lowering the electron temperature. The lower electron temperature reduces the electron velocity, which results in a lower collected current density.

## 4. Conclusions

^{2}. By changing the flow rate of the propellant gas, it is found that when the gas flow rate is higher than 5 SCCM, the ion current density in the plume area decreases significantly. Therefore, via experimental research, it can be known that the thruster of the transversal-feed structure has a relatively superior working performance when the power exceeds 10 W and the propellant flow is between 0.5 SCCM~5 SCCM.

## Author Contributions

## Funding

## Data Availability Statement

## Conflicts of Interest

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Reaction | Formula | Type | Δε (eV) |
---|---|---|---|

1 | e + Ar => e + Ar | Elastic | 0 |

2 | e + Ar => e + Ars | Excitation | 11.5 |

3 | e + Ars => e + Ar | Superelastic | −11.5 |

4 | e + Ar => 2e + Ar^{+} | Ionization | 15.8 |

5 | e + Ars => 2e + Ar^{+} | Ionization | 4.24 |

6 | Ars + Ars => e + Ar + Ar^{+} | Penning ionization | - |

7 | Ars + Ar => Ar + Ar | Metastable quenching | - |

Microwave Power (W) | Ion Current (mA) | Ion Current Density (A/m^{2}) |
---|---|---|

5 | 0.6232 | 1.50 |

8 | 0.6870 | 1.65 |

10 | 0.7058 | 1.70 |

12 | 0.9348 | 2.25 |

15 | 1.0320 | 2.48 |

18 | 1.1530 | 2.78 |

20 | 1.2600 | 3.03 |

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**MDPI and ACS Style**

Han, Y.; Xia, G.; Sun, B.; Zhang, J.; Chen, L.; Lu, C.
A Novel Transversal-Feed Electron Cyclotron Resonance Plasma Thruster: Design and Plasma Characteristics Analysis. *Aerospace* **2023**, *10*, 865.
https://doi.org/10.3390/aerospace10100865

**AMA Style**

Han Y, Xia G, Sun B, Zhang J, Chen L, Lu C.
A Novel Transversal-Feed Electron Cyclotron Resonance Plasma Thruster: Design and Plasma Characteristics Analysis. *Aerospace*. 2023; 10(10):865.
https://doi.org/10.3390/aerospace10100865

**Chicago/Turabian Style**

Han, Yajie, Guangqing Xia, Bin Sun, Junjun Zhang, Liuwei Chen, and Chang Lu.
2023. "A Novel Transversal-Feed Electron Cyclotron Resonance Plasma Thruster: Design and Plasma Characteristics Analysis" *Aerospace* 10, no. 10: 865.
https://doi.org/10.3390/aerospace10100865