Classical transport theory predicts strong coupling between thermal transport and magnetic
field dynamics in laser produced plasmas; for example, fields are carried with the
thermal
flux, via the Nernst effect, while simultaneously deflecting it, giving rise to a
Righi-Leduc heat-flow. Coupling between these effects is shown here to drive a new kind
of instability-the magnetothermal instability-which is described in detail for the first
time. A linear perturbation theory is derived in the absence of density gradients and hydrodynamical
effects, and yields unstable solutions which propagate as magnetothermal
waves. The theory is compared with full non-linear simulation in the context of a recent
nanosecond gas-jet experiment and found to be in good agreement; exhibiting typical
growth-rates and characteristic wavelengths of order 10ns-1 and 50µ m respectively.
Further incorporation of density gradients and hydrodynamics into the magnetothermal
stability analysis is shown to introduce the well-known field generating thermal instability
source term, which can either complement or counteract the magnetothermal mechanism.
Inequalities for predicting the dominance of each process are given: of the two, the
magnetothermal mechanism is found to represent the main-and sometimes only-source
of unstable feedback for the conditions considered here.
Using super-Gaussian transport theory, the implications of inverse-bremmstrahlung heating
for transport in laser-plasmas are also explored. Super-Gaussian modifications are
shown to suppress a number of classical processes, by up to ~90% in some cases, while
simultaneously introducing new effects, such as advection of magnetic field up density
gradients. The combined consequences of these modifications are considered for the field
generating thermal instability, and super-Gaussian effects are found to reduce growthrates
by [greater than or similar to] 80% compared to predictions from classical transport theory under inertial
confinement fusion conditions. The development of a unique code CTC, written to assist
the exploration of both classical and super-Gaussian transport phenomena, and the new
magnetothermal instability, is also described.