Pattern Formation in Plasmas: On Why Staircases are Inevitable in Drift-Rossby Turbulence
Patrick H. Diamond
CMTFO and CASS, U.C. San Diego
In this talk, I will review the problem of pattern formation in drift wave turbulence in magnetized, confined plasmas. A brief introduction to the key physics of confined plasmas will be given. Then, I will focus on the two fundamental pattern formation trends in drift wave turbulence. There are:
A. Zonal Flow Formation: which occurs as a consequence of inhomogeneous mixing of potential vorticity (or, alternatively, polarization charge). Zonal flows are azimuthally symmetric shear layers, which necessarily limit E×B mixing and radial transport.
B. Avalanching, which occurs as a consequence of sequential overturning on instability events. Avalanching is scale independent, and results in the formation of radially extended, intermittent bursts.
The key problem, of course, is that zonal flows and avalanches are mutually exclusive.
Staircases solve the pattern formation problem by concentrating the zonal shear into thin layers or steps – while avalanches propagate in between. Staircases form naturally as a consequence of a time delay between the local heat flux and the local gradient, which allows over-shooting and jam formation. This talk will discuss E×B staircases, scenarios for their formation, and will review staircase physics in light of related phenomena in pure QG fluids and thermosolutal convection.