TRANSP can either use magnetic equilibrium input data or
evolve the poloidal current diffusion.

In interpretive mode, TRANSP supports three options for
advancing its representation of the plasma MHD equilibrium
in time, determined by the choice of the LEVGEO variable in
the input namelist. Selecting LEVGEO=8 instructs
TRANSP to read in equilibrium profiles computed by an
external code, performing interpolation in time as
necessary, and not to recompute the equilibrium itself.
LEVGEO=11 invokes the fixed-boundary inverse equilibrium
solver TEQ (originating from LLNL’s Corsica transport code)
to solve for the equilibrium at each geometry timestep given
the pressure and *q* profiles and the value of $R
B_{toroidal}$ at the boundary. The edge *q* is
adjusted iteratively to match the total plasma
current. TEQ requires an existing inverse equilibrium
solution for a given device as an initial guess for its
calculation; nearly 40 devices are currently supported, and
new ones can be added by the TRANSP developers on request.

Finally, setting LEVGEO=12 instructs TRANSP to use the
ISolver free boundary solver to advance the equilibrium.
ISolver maintains a detailed model of the geometry and
material characteristics of the poloidal field coil set for
each device for which it is run, and can either perform a
least-squares fit for the PF coil currents to match a
prescribed plasma boundary; or solve a circuit equation
incorporating coil current data, feedback circuits, and
induced vessel currents, with the shape of the plasma
boundary computed self-consistently. ISolver can also
advance the q profile self-consistently instead of using
TRANSP’s poloidal field diffusion equation, enabling
modeling of the inductive coupling of the coils and vessel
to the plasma.