The Neptune thruster with plasma expanding into a space simulator. (Source: École Polytechnique)The idea of getting further into outer space will involve new technologies that are able to carry crew and spacecraft faster and more efficiently than current processes allow.

Plasma propulsion is seen as an important step toward this goal because it is an efficient technology for exploration of space, as well as Earth observation. Plasma propulsion systems use electric power to ionize propellant gas to transform it into a state of matter known as plasma. Electricity charged ions and electrons are accelerated in an exhaust beam to generate thrust to propel spacecraft.

Researchers from the University of York and France’s École Polytechnique are investigating a new technology to produce plasma propulsion without the use of a neutralizer.

In established electric propulsion systems, thrusters emit a large number of positively charged particles more so than those with negative charges. To enable the spacecraft to remain charge-neutral, a neutralizer is used to inject electronics to exactly balance the positive ion charge in the exhaust. This comes at a price because additional power from the spacecraft is needed and it adds size and weight to the propulsion system.

The concept plasma system, called Neptune, uses the premise of established gridded-ion thrusters but because there are comparable numbers of positive and negative charged particles present, no neutralizer is needed.

To gear the plasma propulsion system toward spaceflight, researchers wanted to study how plasma behaves in relation to spatial location, time and particle energy.

“The direct observation of how energetic plasma species behave on nanosecond timescales in the Neptune beam will help us to better control the processes that underpin neutralization,” says James Dedrick from the York Plasma Institute at the University of York.

Researchers also studied the dynamics of negatively charged energetic electronics in the exhaust beam of the thruster and its behavior was observed to play a key role in beam neutralization.

“We believe that this arises from a complex interaction between the plasma and acceleration grids, which is highly dependent upon the particle dynamics nearby to the grid surface,” Dedrick says.

The full research report is collected in the journal Physics of Plasmas.