Transport phenomena in plasma – the flow of particles and energy
Transport processes describe how particles, heat and momentum are transported within a medium, such as a liquid, gas, or a plasma. Transport occurs naturally whenever a hot and cold object are in contact with each other, which results in energy flowing from the hot to the cold object. This can be very undesirable, as many processes require that a specific temperature is maintained: for example, maintaining a body temperature of about 37 °C is essential for staying alive; many chemical and nuclear processes will only take place at a reasonable rate above certain temperatures.
The highest temperature requirements in any application today are those for energy extraction from nuclear fusion, where temperatures ten times those in the core of the sun need to be sustained. At these temperatures, matter is ionized, and exists in the form of a plasma, which can be confined by a magnetic field.
Apart from extreme temperatures, these plasmas also display extreme variations in plasma parameters and composition. The edge of these plasmas often feature regions with sharp temperature and density variation, where the temperature goes from being comparable to that in the core of the sun to near zero over a distance of a few centimeters. In addition, highly-charged impurities can enter the fusion plasma from the surrounding walls, and these impurities behave differently from the singly-charged hydrogen that make up the bulk of the plasma.
This thesis is concerned with calculating the transport of particles, heat and momentum in these magnetically confined fusion plasmas, by utilizing new simulation codes and mathematical formulations that allow the treatment of collisional transport in regions with sharp variations of plasma characteristics, and the treatment of highly-charged impurities. With our novel descriptions of these processes, we have been able to investigate how aspects such as plasma composition and magnetic field configuration affect the transport in the plasma.