Applied-field Magnetoplasmadynamic Research Articles

Observation of fast Alfvén wave in KAERI plasma beam irradiation facility using an applied-field MPD thruster

Electromagnetic fluctuations between 300 and 500 kHz were observed in both ion saturation current and magnetic field measurements in the KAERI plasma beam irradiation facility where the applied-field magnetoplasmadynamic (MPD) thruster is used as a plasma source. In this study, the plasmas were ignited with deuterium gas and the plasma current (input power) was varied from 55 A (2 kW) to 155 A (6 kW). The electron temperature and density measured downstream of the MPD thruster plasma were ∼5 eV and (2–4) × 1012 cm−3, respectively. To identify the fluctuations, the dispersion relation and the phase velocity were experimentally obtained using the Beall method and were compared to the theoretical values under warm plasma conditions. It was revealed that the observed fluctuations were fast Alfvén waves with a circularly polarized magnetic field. In addition to the fast Alfvén waves, we also observed electrostatic fluctuations at a higher frequency that was similar to the lower-hybrid frequency.

Modelling the Quench Behavior of an NI HTS Applied-Field Module for a Magnetoplasmadynamic Thruster Undergoing a 1kW Discharge

Recent advances in commercial miniaturised cryocoolers and high-temperature superconductors (HTS) have revived the discussion of using HTS electromagnets to enhance the thrust and efficiency of electric thrusters for space applications. <p xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">An HTS applied-field magnetoplasmadynamic (AF-MPD) thruster is currently being developed. While the thruster is operating, there will be a large time-variable heat load on the cryogenic environment. The operation of a low-power cryocooler and energised HTS coils (operating at 70 K) adjacent to streams of hot plasma and large electrical discharges (on the order of 1 kW) represents a significant thermal management problem. The electromagnetic and thermal behaviour of non-insulated (NI) coils under these conditions, and how resilient they are to quenching during thruster operation, is not well understood. <p xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">In this paper, a model is formulated to study the transient electromagnetic and thermal behaviour of an HTS-AF-MPD thruster with NI coils. The thruster and a conduction cooled cryogenic design are coupled via surface-to-surface radiation heat transfer. The model predicts current flow within the HTS, copper stabiliser and between turns, with the contact resistivity being a key input variable. Critical current is determined locally using temperature, magnetic field, and field angle in combination with a measured data set for a specific conductor. <p xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">This model reveals conditions where the cryocooler can passively compensate for large instantaneous heat loads on the coils, demonstrating quench resistance.

High-temperature superconductor-based power and propulsion system architectures as enablers for high power missions

The increasing competitiveness of electric propulsion systems (EPS) for primary spacecraft propulsion has paved the way for higher payload mass fractions by offering significantly higher specific impulses than chemical systems. Concurrently, High-Temperature Superconductors (HTS) have reached an unprecedented level of industrial maturity in recent years, and considering their low masses, compactness, and high current densities, they offer the potential to act as a disruptive technology in several spaceflight applications such as power management systems, re-entry and radiation shielding as investigated in the EU-funded MEESST project, as well as EPS. In the latter case, efforts are already ongoing to develop an HTS-enhanced Applied-Field Magnetoplasmadynamic (AF-MPD) thrusters for high power mission applications. The Tsiolkovsky equation infers that the payload mass fraction increases indefinitely with increased Specific Impulse (Isp), however, in the case of electric propulsion, the dependence of thrust on the available power complicates this issue when transfer time is a primary driver. Here, the Tsiolkovsky equation becomes inadequate and considering a non-dimensional version of the Tsiolkovsky equation in terms of the mission ΔV and transfer time, the EPS thrust efficiency, and the specific mass of the power system becomes necessary. This paper first discusses the recent advances in HTS and their suitability for spaceflight, before reviewing The development of power system technologies is reviewed and a conceptual power system architecture incorporating HTS is presented. These technologies are analysed using a non-dimensional Tsiolkovsky approach and their impacts on the overall payload mass fraction are assessed. For high-power missions (>100 kW), the use of HTS is shown to have a highly beneficial impact on the mass of the power system. Correspondingly, this enables higher payload mass fractions achievable at increased specific impulse operation, thus strengthening the case for high-power, high-Isp EPS technologies such as AF-MPDT.

Development of plasma beam irradiation facility using applied-field MPD thruster to study plasma-surface interactions

A plasma beam irradiation facility was developed based on the applied-field magnetoplasmadynamic (AF-MPD) thruster concept for studying plasma-surface interactions. The AF-MPD thruster was chosen because it can produce a plasma beam with high plasma density in continuous-wave mode. Two types of AF-MPD thruster were developed and used in this study: a type I source with a wide thruster channel was used for a heat flux test with Ar or Xe gas, while a type II source with a narrow thruster channel was used for an ion flux test with H2 or He gas. The plasma initially showed the characteristics of abnormal glow discharges and then a transition to arc occurred when the plasma current exceeded a threshold value. It was found that a cathode made of thoriated tungsten significantly lowered the threshold current for the transition from abnormal glow to arc. The maximum heat flux provided by our facility was measured to be 7 MW m−2 using a custom-made heat flux sensor, while the maximum hydrogen ion flux was measured to be 1 × 1023 m−2 s−1 using a Langmuir probe. The electron temperature ranged between (4–5) eV, while the electron density at the plasma plume (downstream) ranged between (1–4) × 1018 m−3.

Heat and particle load test facility using an applied-field MPD thruster for studying fusion divertor technology

A test facility for high heat and particle loads relevant to a fusion divertor has been developed using an applied-field magnetoplasmadynamic (AF-MPD) thruster. The AF-MPD thruster can provide high heat and particle fluxes to a target at a relatively low pressure with a relatively strong magnetic field. Several diagnostics for heat and particle fluxes such as a calorimeter and Langmuir probe were utilized to confirm that a heat flux of 4.0 MW m−2 and particle flux of 4.2 × 1022 m−2 s−1 were achieved using a 0.17 T permanent magnet. The electron temperature and electron density were estimated to be 4 eV and 1013 cm3, respectively, using optical emission spectroscopy based on the collisional-radiative model.

Theoretical and experimental investigation of low-power AF-MPDT performance in the high mass flow rate low discharge current regime

We performed a test campaign in order to fill the gaps in the experimental data and understanding of the performance of the Applied Field Magnetoplasmadynamic Thruster in low current, high mass flow rate regime. Thrust and discharge voltage were measured for two anode geometry configurations with different mass flow rate distribution, discharge current and external magnetic field strength. The general trends in thruster behavior using argon as propellant are analyzed in this paper and an approach for thruster optimization is investigated. We find an unexpectedly weak dependence of thrust efficiency on discharge current in low current, high mass flow rate regimes. Using a cylindrical anode configuration, we managed to achieve thrust efficiency of 21%, which is significantly higher than that reported in literature for AF-MPDTs operating in this regime.

2-D Extended Fluid Model of Applied-Field Magnetoplasmadynamic Thruster With Solid and Hollow Cathodes

In this paper, a 2-D model for simulation of an applied-field magnetoplasmadynamic (AF-MPD) thruster with solid and hollow cathodes was built using COMSOL Multiphysics. Extended fluid model was used for self-consistent simulation of discharge processes in the thruster. Ion energy balance equation was developed and added to extended fluid model. A viscously dominated steady-state fully formed gas flow was considered with argon gas used as a propellant. Electron transport properties as well as rates of electron-impact reactions were calculated using electron energy distribution function. Plasmachemical reactions taken into account included direct and stepwise ionization of argon atoms, excitation of metastable levels, three-body and radiation recombination, and so on. Coupling fluid equations with Poisson equation for electric potential allowed for self-consistent description of plasma and sheaths. Distribution of such discharge parameters as charged and excited particle densities and fluxes, charged particles’ mean energies and temperatures, and gas temperature and electric potential were obtained. Comparison of simulation results allowed for concluding that using hollow cathode in an AF-MPD thruster can contribute to power efficiency and lifetime of the device.

Modeling of plasma processes in the slowly diverging magnetic fields at the exit of an applied-field magnetoplasmadynamic thruster

The performance of plasma thrusters with applied electric and magnetic fields can be enhanced by increasing the magnetic field strength, which is applied in the thrust chamber and the exit region propulsive plume. The ejected plasma which passes through a slowly diverging magnetic field will expand but can be restricted within the magnetic nozzle fields. To examine in detail the processes that occur, a new method with Particle-in-cell calculations is applied here. A two-dimensional axisymmetric particle dynamic code is used to model an AF-MPDT (Applied-field Magnetoplasmadynamic Thruster) for which extensive experimental data are available; it used Ar propellant and had applied magnetic coils of 101.5 mm radius and 153 mm length. From the results of the simulation study, it is found that total thrust increases linearly with magnetic field strength in the range of 0–0.1 T, but it decreases with increasing applied magnetic field up to 0.6 T. Thrust efficiency is found to increase to a maximum of 8.4% when B = 0.1 T; further, the peak value of nozzle efficiency reaches 91% at a moderate magnetic field (0.3 T). In detail, it is found that distributions of plasma density (1014–1015 m−3) that form in the magnetic nozzle demonstrate a significant pattern of concentration up to fields of B = 0.3 T where ions begin to be magnetized. However, azimuthal velocities of ions behave differently with different degrees of magnetization, i.e., weakly magnetized ions follow rotating electrons in a right-handed direction, while fully magnetized ions revolve in left-handed direction due to electromagnetic forces. Notably, a feedback effect on total magnetic field due to plasma motion identified in other studies is not found to be present in the working conditions of the AF-MPDT examined here.

Numerical Simulations and Accompanying Experimental Investigations of Magnetoplasmadynamic Thrusters with Coaxial Applied Magnetic Field

An overview is given on a numerical simulation program for applied field magnetoplasmadynamic (AF-MPD) thrusters, which is currently under development at the Institute of Space Systems (IRS). The program allows the simulation of argon plasma flows in thermal and chemical non-equilibrium. The code is based on an axisymmetric finite volume method on unstructured, adaptive meshes. An externally applied magnetic field can be taken into account employing the vector potential formulation. Azimuthal velocity and magnetic field are handled by a quasi three-dimensional approach with vanishing azimuthal derivatives. Additionally, a laboratory AF-MPD thruster for the power range of 10-20 kW has been built up at IRS. The goal of the experimental investigations is the characterization of the operation and performance parameters of the thruster.

Technology and Application Aspects of Applied Field Magnetoplasmadynamic Propulsion

Currently available or realizable applied e eld magnetoplasmadynamic (AF‐MPD) thrusters operating in the power range 5‐100 kW appear to be excellently suited for orbit change and stationkeeping (drag compensation) of large satellites because of their high specie c impulse, sufe cient thrust, and compact geometry. They were developed to considerable maturity almost 20 years ago, but have not yet been used in space because of the lack of missions, appropriate power, and qualie cation. There is evidence that these engines cannot be operated realistically in the laboratory, mainly because of the high vacuum needed to exclude unknown environmental interaction with the plume, even at very low vacua. A space experiment is needed to provide proof of Isp and efe ciency. The International Space Station now provides the opportunity to qualify the engine in space. This paper describes the application potential, performance characteristics, and technological status of the AF‐MPD thruster, remaining application issues to be resolved, and a space experiment proposed to operate and investigate the engine under space-e ight conditions.

Thrust Formula for Applied-Field Magnetoplasmadynamic Thrusters Derived from Energy Conservation Equation

A thrust formula for applied-field magnetoplasmadynamic (MPD) thrusters has been derived from the energy conservation equation for the propellant plasma flow by assuming that the work done by electromagnetic forces is converted into kinetic energy of the exhaust plasma. Three acceleration mechanisms, 1) generalized Hall acceleration, 2) swirl acceleration, and 3) self-magnetic acceleration are taken into account. This formula enables theoretical calculation of thrust of an applied-field MPD thruster from controllable thruster operation parameters, and estimation of the contributions of the respective acceleration mechanisms.