Researchers at the Harbin Institute of Technology in China have developed a new inlet design for cylindrical shaped Hall thrusters that significantly increases thrust for satellites and long-distance robotic spacecraft.
Hall thrusters are used in earth-orbiting satellites, and also have the potential to be applied to robotic spacecraft in order to propel them long distances. Hall thrusters usually use xenon as a propellant. The propellant is accelerated by an electric field which strips electrons from the neutral xenon atoms, creating a plasma.
When the plasma is ejected from the exhaust end of the thruster, it is capable of delivering great speeds, typically around 113,000 km per hour.
A variation of the Hall thruster, cylindrical shaped Hall thrusters, are better suited for miniaturisation, and have a smaller surface-to-volume ratio that prevents erosion of the thruster channel. They are designed for low-power operations, but the low propellant flow density can cause inadequate ionisation, affecting the creation of the plasma and the generation of thrust.
The thruster's performance can be improved by increasing the gas density in the discharge channel while lowering the axial velocity.
"The most practical way to alter the neutral flow dynamics in the discharge channel is by changing the gas injection method or the geometric morphology of the discharge channel," said Liqiu Wei, one of the lead authors of the paper.
The researchers tested a simple design change. When the propellant is injected into the cylindrical chamber of the thruster, the nozzles usually point straight in toward the centre of the cylinder. By changing the angle of the inlet nozzles, the propellant is sent into a rapid circular motion, creating a vortex.
The researchers simulated the motion of the plasma in the channel with the varying nozzle angles using a modelling and analysis software. They found that when the nozzles are tilted, the gas density near the periphery of the channel is higher. Gas density in the "vortex mode" is significantly higher and more uniform, improving thruster performance.
The investigators verified their simulation’s predictions experimentally, and the vortex inlet mode successfully produced higher thrust values, especially when a low discharge voltage was used.
The next step is to study how different parameters, including the nozzle angle, diameter, the ratio of depth to diameter and the length of the discharge affects thrust.
[Image: 6 kW Hall thruster in operation at the NASA Jet Propulsion Laboratory. Courtesy NASA/JPL-Caltech.]