Thermionic arc cathodes are the cathodes where thermionic emission is the main electron emission mechanism. They are used in welding (Tungsten pure or doped with rare earth oxides) and plasma arc cutting (Tungsten for cutting with inert gas or Hafnium for cutting with Oxygen plasma). There are two different sources of erosion: constant current (CC) erosion and erosion during arc initiation and termination (cycling erosion). Available experimental data for both types of cathode and both types of erosion (CC and cycling) are presented and discussed. For quite some time, it has been clear that CC erosion is due to cathode evaporation. It has been shown that as almost all the evaporated atoms return back to the cathode, the net erosion rate is much lower than the evaporation rate. The existing model allows one to calculate the ratio of these two (escape factor). It is in the range 10-2-10-3. The important role of cathode geometry and plasma flow pattern in the cathode proximity is discussed. The nature of cathode erosion during arc start and arc termination is much less understood in spite the fact that the corresponding erosion could be very important and even dominate for multiple cycles. Different processes that lead to this type of erosion are considered.

background

A study of cathode erosion in high power arcjets

Erosion of Thermionic Cathodes in Welding and Plasma Arc Cutting Systems

A hybrid nozzle for use in a plasma spray gun, especially for plasma spraying silicon to form semiconductor devices such as solar cell The outlet of the gun includes a two-piece annular electrode against which the plasma is ignited and through which the plasma plume exits the gun together with entrained silicon In one embodiment, the upstream part is composed of graphite to allow ignition of the plasma and the downstream part is composed of pure silicon In another aspect, the silicon feedstock is injected into the plasma plume through ports formed through the silicon part

Hybrid nozzle for plasma spraying silicon

The Roe–Harten-Lax-van Leer and Einfeldt hybrid flux method has been used to model the phenomena occurring in the Princeton benchmark Self-field MagnetoPlasmaDynamic thruster. The eigensystem has been computed by Powell’s technique, and an optimized monotonic upstream-centered scheme for conservation laws has been applied to achieve a high-resolution method. Also, a one-dimensional description of a collisionless sheath has been taken into account to predict the anode fall voltage. In this study, the argon plasma propellant, with mass flow rate of 4  g/s, has been considered to be in thermal and chemical nonequilibrium states. For the discharge current of 16 kA, the values of fall voltage, electric field, and Hall parameter have been respectively predicted about 3.75 V, 5.5  MV/m, and 1 at the anode midlip. The simulated hot spots near the anode and cathode, the inner flow of ions around the cathode, and the exhaust plume structure have been captured in good agreement with the other corresponding experimen...

Numerical Investigation of Plasma Behavior and Anode Sheath in a Magnetoplasmadynamic Thruster

Arc root behavior affects the energy transfer and nozzle erosion in an arcjet thruster.
To investigate the development of arc root attachment in 1 kW class N2 and H2-N2 arcjet
thrusters from the time of ignition to the stably working condition, a kinetic series of end-on
view images of the nozzle obtained by a high-speed video camera was analyzed. The addition
of hydrogen leads to higher arc voltage levels and the determining factor for the mode of arc
root attachment was found to be the nozzle temperature. At lower nozzle temperatures, constricted
type attachment with unstable motions of the arc root was observed, while a fully diffused
and stable arc root was observed at elevated nozzle temperatures.

Development of arc root attachment in the nozzle of 1 kW N2 and H2-N2 arcjet thrusters

Arc-heated facilties play an important role in ground tests, such as appraisal of thermal protection systems(TPS) of various hypersonic vehicles and simulation of a high Mach scramjet's thermal structure and combustion chamber performance. This paper analyzes the requirements for developing a high power arc heater. Key technologies for developing it include high power, high voltage, high enthalpy and electrode erosion in high currents. Finally, the paper proposes the related ideas and methods for these key technologies, providing theoretical references for China's development of a super-high power arc heater.

/pdf/overview-of-key-technologies-of-high-power-arc-heater-2c7hm3tnyl.pdf

A study of cathode erosion in high power arcjets

Citations

Erosion of Thermionic Cathodes in Welding and Plasma Arc Cutting Systems

Hybrid nozzle for plasma spraying silicon

Numerical Investigation of Plasma Behavior and Anode Sheath in a Magnetoplasmadynamic Thruster

Development of arc root attachment in the nozzle of 1 kW N2 and H2-N2 arcjet thrusters

Overview of key technologies of high power arc heater

Related Papers (5)

Experimental investigation of an applied field low power arcjet

Computational Investigation on the Characteristics of a Low Power DC Arcjet Thruster

Pulsed operation of a low power arcjet

Arcjet Thruster Operated With Different Propellants

Numerical Studies of the Flow Field in a DC Arcjet Thruster