Tokamaks do have a toroidal
symmetry but do not have a poloidal one, therefore turbulent convection flows
are frozen in the poloidal magnetic field much better than in the toroidal one.
It results in the powerful
and paradoxical particle pinch because plasma expands while moving outward as
n~1/V, where V is the specific volume of plasma tube which can be approximated
by the safety factor V~q. This prediction is well supported by profiles of
L-mode plasmas. The canonical profiles of pressure also follow from that model.
A reversal of specific volume
as a function of radius results in plasma compression as it moves outward and
in natural suppression of convection.
This second prediction is also supported by experiment and is known as
ITBs. Note that the specific volume is more adequate theoretical variable than
q, so experimental profiles of density and pressure as well as positions of ITBs
should be plotted as functions of V to vindicate or disprove the model.
A desirable position of a
transport barrier is at the boundary. For that purpose, an additional poloidal
magnetic field can be created by placing an EC near plasma. Note, that outer
equatorial plane is the location of trapped particles, which feel the poloidal
non-invariance much sharper than transient ones. This new theoretical
prediction of WETB is not very reliable and should be checked first with MHD
and especially gyro-simulations and second with experiments on medium size
tokamaks. I did not found a tokamak with an EC. Perhaps, TVC has enough variability.
The width of WETB is bigger
than the thickness of ion banana and can be regulated; the nature of the WETB
is different from H-mode barrier. In my model, the H-mode is a consequence of
the poloidal rotation resulting in the absence of trapped ions.
