The pellet rocket effect in magnetic confinement fusion plasmas
Typ
Examensarbete för masterexamen
Master's Thesis
Master's Thesis
Program
Physics (MPPHS), MSc
Publicerad
2024
Författare
Guth, Nico J.
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Nuclear fusion power generation is widely regarded as a promising technology for
a clean and sustainable future. To achieve positive energy gain from fusion, the
fuel (deuterium and tritium) has to be sustained at temperatures around ten times
hotter than the core of the sun. Most of the power plant designs are currently based
on magnetic confinement fusion (MCF), where this fusion plasma is isolated and
compressed by strong magnetic fields. Refuelling, control of the plasma density
profile and mitigation of off-normal events (disruptions) are done by injecting fast
tiny pellets of dense frozen material, which quickly disintegrate from the extreme heat
in the fusion plasma. While the efficiency of this material deposition in the plasma
depends on the pellet trajectory, the dynamics involved are poorly understood. This
thesis develops a semi-analytical model for the so-called pellet rocket effect, which
accelerates and deflects pellets in a fusion plasma. Asymmetries in the heat flux
onto the pellet surface enhance the ablation on one side of the pellet. Consequently,
the pellet is pushed in the opposite direction to the ejected material, similarly to
a rocket. This effect was shown in experiments to significantly modify the pellet
trajectory. Projections for reactor scale devices indicate that it may even stop the
pellet before it reaches the plasma core, which would severely limit the effectiveness
of pellet injection methods. Our model predicts magnitudes of the pellet rocket
acceleration (10^5 to 10^6 m/s^2) similar to the results of more sophisticated simulations
and experimental observations. Thus, the essential physics of the pellet rocket
effect are successfully captured in our model. With further validation and potential
improvements, we expect that this approach can be used to inform the planning and
operation of pellet injection in future power plants.
Beskrivning
Ämne/nyckelord
fusion plasma , magnetic confinement , pellet injection , ablation , pellet rocket , acceleration , asymmetric heating , NGS model