RF (Radio Frequency) Plasma Thruster

Electrode-Less Plasma Thruster

Lifetime limitation of spacecraft due to wear of electrodes has been known for tasks in electric thrusters. Therefore, we suggest the electrode-less RF (Radio Frequency) plasma thruster since the electrodes do not directly contact with a plasma. The RF thruster consists of static magnetic coil and RF power system. Plasma is generated by RF discharge and accelerated by magnetic nozzle. However, the thrust efficiency is still less than 20% which is much lower than that of the other practical thrusters (~60 % in typical).

In this laboratory, we investigate how the magnetic field physically affect the thruster's performance by the experiment and simulation. Also, the additional approach to improve the performance is focused and proposed with analyzing and discussing the accleration of plasma.

(A simulation result for the electrode-less plasma thruster)

Traveling Magnetic Field Approach

Some previous researches proposed and researched additional acceleration methods for the performance improvement. As one of the methods, we focused on electrodeless Travelling Magnetic Field (TMF) plasma acceleration method. Previous researches reported 22.5 % of the thrust efficiency.

However, high magnitude of the magnetic flux density is needed for plasma confinement in the presence of axially uniform DC magnetic field lines. In addition, pulse operation is inevitable because this type has a deceleration phase to be removed.

Based on the defects, we are proposing a new additional TMF acceleration method. In this method, the TMF can give electrons momentum and axially accelerate them. To propose this approach, we investigated the operational conditions to optimize the effect. In addition, we spatially measured ion Mach number, electron temperature, electron number density for clarification of a relation between the conditions and spatial acceleration characteristics.

(Left: a schematic image of the TMF, right: experimental setup)

Plasma Actuator

DBDPA (Dielectric Barrier Discharge Plasma Actuator)

DBDPA is an active flow control device using dielectric barrier discharge. It has two electrodes divided by an insulator: one electrode is insulated, and the other is exposed to the air. DBDPA induces a wall-surface jet when an AC high voltage is applied between the electrodes.

We aim to enhance the induced flow by the DBDPA for promoting its practrical use.

　 (Left: a schematic image、right: a hand-made actuator)

Tri-Electrode Plasma Actuator

Tri-electrode plasma actuator (TED-PA), which has an additional electrode with a DC high voltage, is attractive solution because it can induce stronger jet. There, the jet from the DC electrode becomes stronger than the jet from the AC one. Therefore, it is expected that the jet from the DC electrode contributes to the performance improvement.

We conduct both the experiment (PIV;Particle Image Velocimetry and the analysis with stable discharge photos) and a 2D plasma discharge simulation to propose methods to enhance the jet expecially from the DC electrode.

Voltage Waveform Approach

The optimization of the AC waveform is one of the attractive approaches because it does not need any changes in its mechanical structures and any additional power sources. However, the recommended waveforms in the previous reseraches are configured with the basic waveforms such as the square, the sinusoidal and the triangular waveforms in try-and-error process. In addition, the improvement mechanisms remain unclear from the viewpoint of the discharge characteristics.

We propose new AC voltage waveforms with the investigation about the physics of the discharge and flow. Mainly, the thrust measurement, power measurement, PIV and 2D plasma discharge simulation are conducted for this topic.

Numerical and experimental results showing the improvments by the proposed voltage waveforms.

Flow Visualization with BOS (Background Oriented Schlieren) technique

It is generally considered that DBDPA has two kinds of flow control mechanisms; one is the body force generation, and the other is the density disturbance caused from the Joule heating.

Understanding of not only the body force generation but also the density disturbance is important. However, almost of all studies on the density field around DBDPA conducted qualitative discussions using the Schlieren method, and much less work has been done on quantitative measurement of the density field. We focus on the Background Oriented Schlieren (BOS) technique to measure the density field of the flow produced by DBDPA.

The setup for BOS, left: BOS system, right: background image

Flow Control for Aerodynamic Body

Flow around the Heavy Trucks

We aim the drag reduction of the heavy truck vehicles. There, we consider the plasma actuator for the active flow control device for its flow control.

Simulation & Experiment

About the numerical approach, we consider a rectangular cylinder using the plasma actuator by means of two-dimensional numerical simulation. There, we numerically investigate the effect by the plasma actuator to the flow around the rectangular cylinder with a two-dimensional incompressible flow simulation. It is clarified that the drag can be reduced due to the reattachment of the separated flow on the side of the cylinder.

The experimental approach is also carried out in our laboratory. The wind tunnel experiments are conducted to verify the proposed method. We have successfully demonstrated that the plasma actuator promotion of the drag reduction effect by the plasma actuator with the model scale.

A schematic image of the negative drag force to the heavy trucks.