14th Space X launch—Space Thrusters. Image Credit: Impedans.
What are Fusion Devices?
The development of fusion devices is one area of plasma application that is growing of late. Since the technology is a nuclear process and not a chemical process, these devices are thermal plasma because the ions and electrons are both extremely hot. The sun is a fusion plasma and harnesses its power from fusion reactions.
Earthbound plasma has to be relatively hotter than the sun due to the fusion reaction scales as the product of the density, temperature, and confinement time of the particles. The sun’s size makes the confinement and density greater. In fusion devices, magnetic fields are employed to confine the plasma and sustain its high temperature.
Significance of Negative Ions, Passing the Magnetic Field
To heat a fusion plasma and boost fusion power, a particle beam can be directed into the plasma. However, because of the magnetic fields, the particles need to be neutral to pass via the confinement fields. The beam begins life in an ion source and is fast-tracked to high energies and then changed from charged particles to neutral particles.
Converting negative ions, rather than positive ions, to neutral particles is relatively easier, particularly at high energies. So a source of negative ions is a significant technology for a majority of the fusion devices.
Interpreting negative ion sources will become very crucial if negative ions are needed to heat upcoming plasma fusion devices on a large scale. To produce and separate negative ions in a plasma is very complicated, and it necessitates a thorough understanding of the interaction of charged particles in the plasma with the electrical and magnetic fields inside the ion source.
In general, any technology can usually lead to new applications. Ion sources are also employed in thrusters for space applications. A huge challenge with ion thrusters is that the beam is charged and a current flows; this current charges up the satellite or spacecraft, which can result in many problems. To prevent these problems, a plasma beam containing both positive ions and negative ions can be used. This beam has a net current of zero and eliminates the need for charging up the beam.
Image Credit: Impedans
Space Travel Solution
Plasma thrusters provide the ideal technology solution for space travel, but then this information is already known from listening to Scotty. The customers under review have been using a Langmuir probe to measure and interpret the plasma within a negative ion source.
The Langmuir probe quantifies ion density, electron density, electron temperature, and also plasma potential. These measurements assist the customers to resolve what is taking place inside the ion source and allow them to understand the main processes and propose enhancements to make the technology more applicable.
How is Plasma Produced?
Plasma is produced by using a radio frequency source that is inductively coupled into the plasma. A shield is used to eliminate the electrical field and just couple the magnetic field. This is analogous to the technology used in wireless battery charges being developed. The coupling of only the magnetic field decreases the so-called capacitive coupling.
Due to the presence of RF fields in the plasma, problems arise that make the measurement and analysis of Langmuir more complex. In addition to an RF magnetic field, the ion source also has a continuous magnetic field used to filter the electrons and ions. This is a main component of the ion source.
Is RF Magnetic Field Doing its Job?
The customers demonstrated that when the shield is located in the coupling circuit, the RF plasma potential reduces from 181 V to just 45 V. This demonstrates that the shield is performing its job as anticipated. The customers measured plasma density and temperature along the magnetic filter, which allows them to obtain a theory of operation. This can be used to describe the operation of the source and comprehend what is taking place. It also enables them to design improved solutions and expand the source.
The customers were able to determine that the bright plasma strip positioned at the magnetic field starts in the transverse drift of the electron fluid intercepted by the dielectric walls of the discharge tube. This means the drift does not form a closed loop in this condition, in contrast to what is achieved in Hall Effect thrusters. Therefore, past learning in positive ion thrusters does not apply to this new kind of plasma density plasma thruster.
Plasma without shield (a) and with shield (b). The magnets in brown/orange are placed around the tube. The plasma cools and does not glow inside the magnetic field (strip) with the shield in position. The shield is located to the right of the glow and is positioned in front of the spiral inductive coil. Image Credit: Impedans.
In conclusion, due to their plasma measurements and the comprehensive theory developed and tested, scientists can now comprehend the effect of the filter magnetic field on ion formation efficiency and plasma beam uniformity. They were able to clearly predict the performance in other geometries, which would permit them to design larger scale and more efficient systems in the days to come, so that mankind can go where no one has ventured before.
This information has been sourced, reviewed and adapted from materials provided by Impedans Ltd.
For more information on this source, please visit Impedans Ltd.