A practical limitation on transport by ripple-trapped ions

Ripple in the toroidal field of tokamaks is predicted to enhance ion transport at low collisionality because ions trapped in the magnetic wells are prevented from moving poloidally along field lines; their grad-B drift then can generate a large radial step for diffusion. However, tokamaks generally have radial electric fields that will drive poloidal motion even for ripple-trapped ions, thereby moderating the transport. For typical parameters, electric field effects enter for collisionalities only somewhat smaller than ripple effects themselves. This suggests that ripple effects will not seriously degrade thermal ion transport. High-energy populations remain subject to strong effects of ripple