Clean and limitless energy supply can be provided by creating the process
powering the sun called nuclear fusion. Recreating the sun on Earth has been
proven to be immensely complex and challenging. Ray Chandra investigated the
physics behind different ways to protect the surface of the walls of fusion
reactors from the extremely hot plasma inside.
One crucial problem in recreating the sun on Earth is the survival of the
structure housing the fusion reaction. Nuclear fusion requires heating the
gaseous fuel to extreme temperatures, changing its state into a cloud of
charged particles known as plasma. The structure must be able to withstand
contact with plasma for years.
Plasma detachment
One possible way to solve this problem is to maintain a state where the
plasma is extinguished before it touches the vessel. This state, known as
plasma detachment, was investigated experimentally in the Netherlands using
Magnum-PSI, a device capable of producing the plasma conditions expected to
occur near the walls of fusion reactors.
Plasma detachment was achieved by injecting cold gas which greatly reduced
the heat flow. Understanding how the cold gas can be so effective is crucial
in developing the same method for future fusion reactors.
Ray Chandra investigated the physics governing the reduction of heat by the
cold gas using computer simulations to replicate the experimental
observations in Magnum-PSI. His Ph.D. thesis describes the simulation work
and results using a specific code named B2.5-Eunomia, as well as the
analysis of detailed processes that causes plasma detachment.
He revealed that interaction of the plasma and the gas is predominantly
governed by friction between the main plasma particles and gas molecules.
This interaction contributes the most in lowering the plasma temperature,
and in turn triggering plasma recombination, a process where the plasma
neutralizes into neutral gas.
In addition, the plasma flow is slowed down by the same friction and
consequently enhances plasma recombination further. This insight may lead to
better reactor designs with easier access to detachment and improvements in
future simulation studies.
Liquid metal
In his thesis, Chandra also investigated an alternative way to protect
surfaces from the hot plasma, by covering them with liquid metal. They have
self-regenerating properties and are excellent candidates as plasma facing
materials.
The most promising candidates are liquid lithium and tin. However, the
evaporation of these metals can pollute the plasma and greatly reduce or
even disrupt the fusion performance of the reactor. Hence, it is of great
importance to understand particle transport from the liquid into the plasma.
Using the same B2.5-Eunomia code, lithium particles are simulated coming
from a liquid lithium target material in a Magnum-PSI environment. Varying
strengths of lithium erosion are simulated to observe its effects to the
plasma and to the amount of lithium transported away to the walls.
Chandra revealed that the transport of lithium particles is impeded by the
plasma flow and high plasma temperatures. This work is the first step in
simulating liquid metal transport that will be used to understand liquid
metal experiments in Magnum-PSI, and in the future, the application of
liquid metals in fusion reactors.
Ray Chandra defended his Ph.D.-thesis, titled "Plasma exhaust for fusion
reactors: numerical simulation and comparison with plasma beam experiments,"
on February 17.
Source: Link
Tags:
Physics