Non-local transport effects on hohlraum radiation drive
File(s)
Author(s)
Antony, Abetharan
Type
Thesis
Abstract
Hohlraum X-ray radiation drive deficit is one of the critical problems in modern indirect-drive inertial confinement fusion. The multiple physical time and length scales cause the modelling of the hohlraum to be highly complex, and numerous approximations are made. The prime simplification is using the fluid approximation to model electrons in regions not necessarily in this regime.
One of the critical consequences of the fluid approximation is that the heat flow is local and obeys classical transport theory. However, in practice, this assumption is not valid in many areas of the hohlraum. In particular, the hohlraum wall is often in a regime where kinetic models are required to describe it. Approximate kinetic models or \textit{ad hoc.} corrections to classical transport used at present are usually inaccurate. As a result, the redistribution of energy through transport may be modelled inaccurately in the hohlraum and explain part of the radiation drive deficit problem.
This thesis applies a novel electron transport modelling approach to the hohlraum radiation problem. Utilising direct coupling between Vlasov-Fokker-Planck and Radiation-Hydrodynamics codes allows for high fidelity electron thermal conduction whilst modelling the majority of the system as a fluid.
This novel method is applied to a selection of hohlraum problems to discern whether higher fidelity calculations explain the radiation deficit. It was first applied to the National Ignition Campaign. It was found that higher accuracy transport did not change the radiation behaviour significantly nor explained the radiation drive deficit due to the radiation and laser heating being fully co-located, albeit producing different thermodynamic profiles. The observed behaviour was possibly due to the lack of high-Z opacity data. As a result, the modelled problem was a lower-Z surrogate hohlraum which was in a different regime than a high-Z hohlraum.
However, applying the method to variations on the hohlraum problem found that either transport dependent ablation or low laser heating efficiency provided the environment for transport to cause significant changes in the radiation drive behaviour.
One of the critical consequences of the fluid approximation is that the heat flow is local and obeys classical transport theory. However, in practice, this assumption is not valid in many areas of the hohlraum. In particular, the hohlraum wall is often in a regime where kinetic models are required to describe it. Approximate kinetic models or \textit{ad hoc.} corrections to classical transport used at present are usually inaccurate. As a result, the redistribution of energy through transport may be modelled inaccurately in the hohlraum and explain part of the radiation drive deficit problem.
This thesis applies a novel electron transport modelling approach to the hohlraum radiation problem. Utilising direct coupling between Vlasov-Fokker-Planck and Radiation-Hydrodynamics codes allows for high fidelity electron thermal conduction whilst modelling the majority of the system as a fluid.
This novel method is applied to a selection of hohlraum problems to discern whether higher fidelity calculations explain the radiation deficit. It was first applied to the National Ignition Campaign. It was found that higher accuracy transport did not change the radiation behaviour significantly nor explained the radiation drive deficit due to the radiation and laser heating being fully co-located, albeit producing different thermodynamic profiles. The observed behaviour was possibly due to the lack of high-Z opacity data. As a result, the modelled problem was a lower-Z surrogate hohlraum which was in a different regime than a high-Z hohlraum.
However, applying the method to variations on the hohlraum problem found that either transport dependent ablation or low laser heating efficiency provided the environment for transport to cause significant changes in the radiation drive behaviour.
Version
Open Access
Date Issued
2022-07
Date Awarded
2023-06
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
Kingham, Robert
Publisher Department
Physics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)