Phase-space structures in plasma turbulence

[maxime.lesur]

Here is a glimpse of my current research. This is a kinetic simulation of electrostatic waves in a bump-on-tail plasma, with multiple resonances and some dissipation. Quasi-linear theory predicts a flattening of the velocity distribution over the range of resonant velocities of linearly unstable modes. However, self-coherent phase-spaces structures known as holes and clumps change this picture significantly.

This physics is relevant to tokamaks (magnetically confined fusion devices), where the frequencies of several co-existing Alfvén eigenmodes, which are driven by energetic ions, have been observed to sweep in time (chirping). Chirping is a signature of evolving holes and clumps.
What I am wondering is whether there are implications in space plasma. Do you know of any experimental observation or theoretical work on the nonlinear effect of phase-space structures on turbulence?

More on this simulation:
Nonlinear growth, evolution and interaction of self-coherent phase-space structures in a dissipative bump-on-tail plasma simulation with multiple resonances, using the kinetic code COBBLES. Up: perturbed distribution function. Down: spatially-averaged velocity distribution. Dashed vertical lines at the beginning of the video show the resonances that are linearly unstable. Holes are in blue and clumps are in yellow.
Quasi-linear theory predicts a flattening of the velocity distribution over the range of resonant velocities of linearly unstable modes. However, self-coherent phase-spaces structures known as holes and clumps change this picture significantly. During this simulation, several hole/clump pairs spontaneously emerge at different resonance velocities and subsequently merge with each others, until there remains mainly one single hole. Note that phase-space structures survive for a collisional diffusion time, which is much longer than the quasi-linear diffusion time. Final time in this video, normalized to the plasma frequency: 2400.

More on the code: M. Lesur, Y. Idomura, and X. Garbet, Fully nonlinear features of the energy beam-driven instability, Phys. Plasmas 16, 092305 (2009).

More on the model: M. Lesur, The Berk-Breizman model as a paradigm for energetic particle-driven Alfvén eigenmodes, PhD Thesis (2011).

Thanks!

 

[Astronuc]

Interesting thesis.

One might find this book of interest.
http://www.physics.ucsd.edu/~tmurphy/phys239/BookFINAL.pdf

With respect to:

What I am wondering is whether there are implications in space plasma. Do you know of any experimental observation or theoretical work on the nonlinear effect of phase-space structures on turbulence?

I believe that CMEs (and flares and prominences) and solar helioseismology (turbulence) involved investigation of nonlinear effects of phase-space structures.

 

[maxime.lesur]

Thank you!

Actually it is this very book that inspired my current work. Very insightful indeed. On the theory side at least. The first author of this book is also a co-author of a paper I'm writing on a related topic. I'll post the paper here when it's published.

However, in this book I didn't find any example of experimental study of the effect of phase-space structures (granulations) on turbulent astrophysical systems.

One example, which shows striking similarities with phase-space structures in turbulent plasmas, is zonal flow in quasi-geostrophic systems, such as Jupiter. However, the structures live in real space, not in phase-space. The equations of conservation of potential vorticity and phase-space density (the QG equation and the Vlasov equation) are similar, but there's an important qualitative difference in the Hamiltonian, which makes me doubt we can expect similar physics.