TRANSPORT TO THERMAL EQUILIBRIUM
(Rigid Rotation)
Research Activity on Transport
This group does research on both bulk particle transport and test particle transport.
On this page we will discuss the work on bulk particle transport done on the EV apparatus.
The work on test particle transport is done on the IV apparatus.
Jason Kriesel,
current curator and chief researcher on the EV machine, has
begun work on measuring bulk particle transport toward thermal equilibrium in a pure-electron
plasma. Thermal equilibrium in such a plasma is characterized by a state of rigid
rotation, i.e. w(r)=constant, where w is the TOTAL fluid rotation frequency
(ExB part + diamagnetic part).
When external torques (due to neutrals and field errors)
are made negligible, the transport
is found to conserve
total angular momentum and depend
upon the shear in the TOTAL fluid velocity,
indicating a viscous-like internal transport mechanism.
The measured coefficient of viscosity is 100 to 10,000 times larger
than classical theory predicts and scales as B¹
for similar plasma parameters (such as shear, density, and radial position).
When plasmas with differing parameters are considered,
the viscosity is found to go as the inverse of the
ExB shear (which scales as B¹ ).
The same viscous-like mechanism appears to be responsible for transport in plasmas with
either a
monontonic or non-monotonic ("hollow") rotation profile.
A new 2-D (bounce-averaged over the z-motion along the magnetic field)
theory of "ExB drift
collisions" is currently being examined by Profs. Dubin & O'Neil, which
may provide an explanation for the above experimental observations.
In this theory a larger ExB shear means particles interact for
a shorter amount of time, leading to a smaller coefficient of viscosity.
Click here for Collisional Transport Theory
Click here for Collisional Thermalization Theory
Goto EV page