The first Vlasov-Fokker-Planck simulations of nanosecond laser-plasma interactions
– including the effects of self-consistent magnetic fields and hydrodynamic
plasma expansion – will be presented. The coupling between non-locality and magnetic
field advection is elucidated. For the largest (initially uniform) magnetic fields
externally imposed in recent long-pulse laser gas-jet plasma experiments (12T) a significant
degree of cavitation of the B-field will be shown to occur (> 40%) in under
500ps. This is due to the Nernst effect and leads to the re-emergence of non-locality
even if the initial value of the magnetic field strength is sufficient to localize transport.
Classical transport theory may also break down in such interactions as a result of
inverse bremsstrahlung heating. Although non-locality may be suppressed by a large
B-field, inverse bremsstrahlung still leads to a highly distorted distribution. Indeed
the best fit for a 12T applied field (after 440ps of laser heating) is found to be a super-
Gaussian distribution – f0 α e−vm – with m = 3.4. The effects of such a distribution
on the transport properties under the influence of magnetic fields are elucidated in
the context of laser-plasmas for the first time.
In long pulse laser-plasma interactions magnetic fields generated by the thermoelectric
(‘∇ne × ∇Te’) mechanism are generally considered dominant. The strength
of B-fields generated by this mechanism are affected, and new generation mechanisms
are expected, when non-locality is important. Non-local B-field generation is found
to be dominant in the interaction of an elliptical laser spot with a nitrogen gas-jet.