text: A consequence of the toroidal geometry to the guiding-center orbits is that some particles can be reflected on the trajectory from the outboard side to the inboard side due to the presence of magnetic field gradients, similar to a magnetic mirror. The reflected particles cannot do a full turn in the poloidal plane and are trapped which follow the banana orbits.
  This can be demonstrated by considering tokamak equilibria for low- and large aspect ratio which have nearly circular cross sections, where polar coordinates  centered at the magnetic axis can be used with  approximately describing the flux surfaces. The magnitude of the total magnetic field can be approximated by the following expression: indicates value at the magnetic axis ,  is the major radius,  is the inverse aspect ratio, and  is the magnetic field. The parallel component of the drift-ordered guiding-center orbits in this magnetic field, assuming no electric field, is given by:
  where  is the particle mass,  is the velocity, and  is the magnetic moment (first adiabatic invariant). The direction in the subscript indicates parallel or perpendicular to the magnetic filed.  is the effective potential reflecting the conservation of kinetic energy .
  The parallel trajectory experiences a mirror force where the particle moving into a magnetic field of increasing magnitude can be reflected by this force. If a magnetic field has a minimum along a field line, the particles in this region of weaker field can be trapped. This is indeed true given the form of  we use. The particles are reflected (trapped particles) for sufficiently large  or complete their poloidal turn (passing particles) otherwise.
  To see this in detail, the maximum and minimum of the effective potential can be identified as  and . The passing particles have  and the trapped particles have . Recognising this and define a constant of motion , we have
  * Passing: 
  * Trapped: