Equilibrium calculations

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.