Taisen Zhuang

Electric propulsion for small satellites

Propulsion is required for satellite motion in outer space. The displacement of a satellite in space, orbit transfer and its attitude control are the task of space propulsion, which is carried out by rocket engines. Electric propulsion uses electric energy to energize or accelerate the propellant. The electric propulsion, which uses electrical energy to accelerate propellant in the form of plasma, is known as plasma propulsion. Plasma propulsion utilizes the electric energy to first, ionize the propellant and then, deliver energy to the resulting plasma leading to plasma acceleration. Many types of plasma thrusters have been developed over last 50 years. The variety of these devices can be divided into three main categories dependent on the mechanism of acceleration: (i) electrothermal, (ii) electrostatic and (iii) electromagnetic. Recent trends in space exploration associate with the paradigm shift towards small and efficient satellites, or micro- and nano-satellites. A particular example of microthruster considered in this paper is the micro-cathode arc thruster (µCAT). The µCAT is based on vacuum arc discharge. Thrust is produced when the arc discharge erodes some of the cathode at high velocity and is accelerated out the nozzle by a Lorentz force. The thrust amount is controlled by varying the frequency of pulses with demonstrated range to date of 1‐50Hz producing thrust ranging from 1 µN to 0.05mN.

Ion velocities in a micro-cathode arc thruster

Ion velocities in the plasma jet generated by the micro-cathode arc thruster are studied by means of time-of-flight method using enhanced ion detection system (EIDS). The EIDS triggers perturbations (spikes) on arc current waveform, and the larger current in the spike generates denser plasma bunches propagating along with the mainstream plasma. The EIDS utilizes double electrostatic probes rather than single probes. The average Ti ion velocity is measured to be around 2×104 m/s without a magnetic field. It was found that the application of a magnetic field does not change ion velocities in the interelectrode region while leads to ion acceleration in the free expanding plasma plume by a factor of about 2. Ion velocities of about 3.5×104 m/s were detected for the magnetic field of about 300 mT at distance of about 100–200 mm from the cathode. It is proposed that plasma is accelerated due to Lorentz force. The average thrust is calculated using the ion velocity measurements and the cathode mass consumption r...

Circular periodic motion of plasma produced by a small-scale vacuum arc

A small-scale plasma source based on a low-current vacuum arc is described. Temporal and spatial evolution of the ion current is measured. The plasma plume circular motion follows the cathode spot motion in the retrograde direction and is guided along the magnetic field line. It is observed that the applied magnetic field efficiently guide the plasma leading to an increase in the output ion current by a factor of 50 in comparison with that without the magnetic field.

Application of electrostatic Langmuir probe to atmospheric arc plasmas producing nanostructures

The temporal evolution of a high pressure He arc producing nanotubes was considered and the Langmuir probe technique was applied for plasma parameter measurements. Two modes of arc were observed: cathodic arc where discharge is supported by erosion of cathode material and anodic arc which is supported by ablation of the anode packed with carbon and metallic catalysts in which carbon nanotubes are synthesized. Voltage-current (V-I) characteristics of single probes were measured and unusually low ratio of saturation current on positively biased probe to that on negatively biased of about 1–4 was observed. This effect was explained by increase of measured current at the negatively biased probe above the level of ion saturation current due to secondary electron emission from the probe surface. Since utilization of standard collisionless approach to determine plasma parameters from the measured V-I characteristic is not correct, the electron saturation current was used to estimate the plasma density.

Electric discharge during electrosurgery

Electric discharge utilized for electrosurgery is studied by means of a recently developed method for the diagnostics of small-size atmospheric plasma objects based on Rayleigh scattering of microwaves on the plasma volume. Evolution of the plasma parameters in the near-electrode sheaths and in the positive column is measured and analyzed. It is found that the electrosurgical system produces a glow discharge of alternating current with strongly contracted positive column with current densities reaching 103 A/cm2. The plasma electron density and electrical conductivities in the channel were found be 1016 cm−3 and (1-2) Ohm−1cm−1, respectively. The discharge interrupts every instance when the discharge-driving AC voltage crosses zero and re-ignites again every next half-wave at the moment when the instant voltage exceeds the breakdown threshold.

Laboratory Modeling of the Plasma Layer at Hypersonic Flight

A simple approach to modeling the plasma layer similar to that appearing in the vicinity of a hypersonic vehicle is demonstrated in a laboratory experiment. This approach is based on the use of a hypersonic jet from a cathodic arc plasma. Another critical element of this laboratory experiment is a blunt body made from a fairly thin foil of refractory material. In experiments, this blunt body is heated by the plasma jet to a temperature sufficiently high to ensure evaporation of surface deposits produced by the metallic plasma jet. This process mimics reflection of gas flow from the hypersonic vehicle in a real flight. Two-dimensional distributions of the hypersonic plasma flow around the blunt body were measured using electrostatic Langmuir probes. Measured plasma density was typically 1012  cm−3, which is close to the values measured for real hypersonic flight. The demonstrated laboratory experiment can be used to validate numerical codes for simulating hypersonic flight and to conduct ground-based tests...

Micro-Vacuum Arc Thruster with Extended Lifetime

This paper presents a new configuration of vacuum arc thruster with an aim to extend operational lifetime. Rotation of the cathode spot as a result of an applied magnetic field is demonstrated leading to uniform plasma generation and the possibility of long duration operation. It is shown that a magnetic field leads to an increase in the thruster output by a factor of fifty. Potential applications of this thruster are discussed.

Microcathode Thruster

An experimental observation of microcathode thruster plasma plume is described. An effect of the magnetic field on the plume expansion is considered. Two observation techniques are employed--charge-coupled-device camera and the concentric Langmuir probe. It is found that magnetic field significantly affects the plasma plume, and the strong magnetic field can lead to hollow plume formation.

(\mu\hbox{CT})

Weakly ionized plasma on a blunt body in high speed flows is simulated using magneto– gasdynamic and electrostatic multi–fluid reactive flow models. Small scale laboratory experiments are designed to generate high speed plasma flow over a blunt body and the plasma density on the cone is measured in radial direction using Langmuir probes. The whole experiment is simulated using magneto–gasdynamic multi–fluid reactive flow model and the results are compared. Then weakly ionized plasma on RAMC type blunt body is simulated and the RF wave propagation through the plasma layer is demonstrated using electrostatic multi–fluid reactive flow model.

Plume Characterization

Electrosurgical cutting is a well-known technique for creating incisions often used for the removal of benign and malignant tumors. The proposed mathematical model suggests that incisions are created due to the localized heating of the tissue. The model estimates a volume of tissue heating in the order of 2 10−4 mm3. This relatively small predicted volume explains why the heat generated from the very tip of the scalpel is unable to cause extensive damage to the tissue adjacent to the incision site. The scalpel exposes the target region to an RF field in 60 ms pulses until a temperature of around 100 °C is reached. This process leads to desiccation where the tissue is characterized by a significantly low electrical conductivity, which prevents further heating and charring. Subsequently, the incision is created from the mechanical scraping process that follows.