How does the HDLT work?

HDLT testing

Our laboratory is internationally recognised as the inventor and prime developer of the helicon source, arguably the most efficient plasma source available. Krypton (but eventually Xenon) gas is injected into a tube, called the source, that is open at one end and terminated at the other and is energised by a radio frequency antenna. Solenoids create an expanding magnetic field that is roughly uniform in the source tube but that expands very rapidly out into space until it is only a few gauss 20cm away from the source. The high density plasma formed in this way is restricted from exiting the source by a non-linear plasma effect known as a current free electric double layer that is located near the exit of the source tube.

This double layer can be thought of as a thin standing shock wave across which there exists a strong electric field gradient. It is this electric field that accelerates ions from the source plasma to very high exhaust velocities creating thrust. Because the double layer is purely the result of plasma density, system and magnetic field geometry, no accelerating grids are required. Also, because there is equal flux of electrons and positive ions from the thruster there is no need for a neutraliser. It is in this sense that the HDLT is a "true" plasma thruster as it ejects equal numbers of both positive ions and negative electrons.

Power is required only for the maintenance of plasma and the creation of the magnetic field. In our current bench top prototype, 250W is sufficient to create several milli-Newtons of thrust. In space the solenoids that generate the 250 Gauss of magnetic field this requires we estimate could be cooled to 200K, reducing the resistance in the coils by a factor of 5 and representing a power consumption of a few 10s of Watts. Relative to other existing systems this constitutes quite a power saving and is well with-in the capabilities of solar panels. The 0.5sccm of feed gas represents a mass consumption of 160 mg/hr, so that a typical 5 hour burn would use 0.8g of propellant.

Updated:  17 August 2017/ Responsible Officer:  Head of Department/ Page Contact:  Physics Webmaster