  The use of magnetic fields to improve the performance of hohlraum-driven
implosions on the National Ignition Facility (NIF) is discussed. The focus is
on magnetically insulated inertial confinement fusion (ICF), where the primary
field effect is to reduce electron-thermal and alpha-particle loss from the
compressed hotspot (magnetic pressure is of secondary importance). We summarize
the requirements to achieve this state. The design of recent NIF magnetized
hohlraum experiments is presented. These are close to earlier shots in the
three-shock, high-adiabat (BigFoot) campaign, subject to the constraints that
magnetized NIF targets must be fielded at room-temperature, and use < 1 MJ of
laser energy to avoid risk of optics damage from stimulated Brillouin
scattering. We present results from the original magnetized hohlraum platform,
as well as a later variant which gives higher hotspot temperature. In both
platforms, imposed fields (at the capsule center) of up to 28 T increase the
fusion yield and hotspot temperature. Integrated radiation-magneto-hydrodynamic
(rad-MHD) modeling with the Lasnex code of these shots is shown, where laser
power multipliers and a saturation clamp on cross-beam energy transfer (CBET)
are developed to match the time of peak capsule emission and the P2 Legendre
moment of the hotspot x-ray image. The resulting fusion yield and ion
temperature agree decently with the measured relative effects of the field,
although the absolute simulated yields are higher than the data by 2.0-2.7X.
The tuned parameters and yield discrepancy are comparable for experiments with
and without an imposed field, indicating the model adequately captures the
field effects. Self-generated and imposed fields are added sequentially to
simulations of one BigFoot NIF shot to understand how they alter target
dynamics.
