Accurate modelling of laser propagation and energy deposition in direct-drive Inertial Confinement Fusion (ICF) is crucial to performing predictive simulations. Cross-Beam Energy Transfer (CBET) is an interaction of laser light and the plasma state of matter, which can halve the deposited power in direct-drive implosions and amplify deposition asymmetries by an order of magnitude. Computational models which do not account for CBET, can therefore not be truly predictive. This thesis presents the development, validation and use of SOLAS: a 3-D, ray-based CBET model, which has been integrated into the CHIMERA code.

The development of SOLAS and its integration into the CHIMERA code are described. Test problems were conducted which validated the ray-trace, energy deposition, electric field reconstruction and CBET solver. CHIMERA-SOLAS simulations of direct-drive targets on the OMEGA laser facility are presented, which are in excellent agreement with existing codes.

A study is presented, which investigated the role of CBET with respect to the beam radius initial condition for direct-drive implosions. The results demonstrate that in the absence of CBET, increasing the beam radius improves the stagnation state symmetry of implosions. However, a larger beam radius leads to more CBET and a subsequent symmetry degradation. These results could help to explain observed trends in statistical modelling of OMEGA implosions.

A final study is presented, which aimed to understand how the role of CBET changes when a target is magnetised prior to the laser drive. Magnetised direct-drive experiments have demonstrated that anisotropic thermal conduction in the coronal plasma can lead to asymmetry of the implosion. Simulations of magnetised direct-drive targets were conducted, to understand if coronal magnetisation affected CBET scattering. Although CBET was observed to be dynamically significant to the implosions, the interplay of CBET with the magnetic field was found to be minimal.