  Direct numerical simulations of the time dependent parallel heat transport
equation modeling heat pulses driven by power modulation in 3-dimensional
chaotic magnetic fields are presented. The numerical method is based on the
Fourier formulation of a Lagrangian-Green's function method that provides an
accurate and efficient technique for the solution of the parallel heat
transport equation in the presence of harmonic power modulation. The numerical
results presented provide conclusive evidence that even in the absence of
magnetic flux surfaces, chaotic magnetic field configurations with intermediate
levels of stochasticity exhibit transport barriers to modulated heat pulse
propagation. In particular, high-order islands and remnants of destroyed flux
surfaces (Cantori) act as partial barriers that slow down or even stop the
propagation of heat waves at places where the magnetic field connection length
exhibits a strong gradient. Results on modulated heat pulse propagation in
fully stochastic fields and across magnetic islands are also presented. In
qualitative agreement with recent experiments in LHD and DIII-D, it is shown
that the elliptic (O) and hyperbolic (X) points of magnetic islands have a
direct impact on the spatio-temporal dependence of the amplitude of modulated
heat pulses.
