Creation of Wide Edge Transport Barrier (WETB) in Tokamaks by Equatorial Coil (EC)

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.