ECMC, a portable two-dimensional code for plasma equilibrium computation on coaxial-multiple-coil systems Original Research Article

A two-dimensional code ECMC for computing field-reversed configuration equilibria is described. Equilibrium states are found by solving the finite difference form of Grad-Shafranov equation by means of a successive over-relaxation method. Plasma rotation and the existence of a toroidal magnetic field component are not taken into account. Plasma trapped current is used as a constraint parameter to achieve an equilibrium state. The code computes any coaxial-multiple-coil system from the input data of coil positions in laboratory coordinates and their respective currents. It was written assuming neither a particular experimental device geometry nor a specific shape for the magnetic flux function in order to simulate the coils. Plasma pressure dependence as a function of the magnetic flux may be changed by providing a routine to replace that given by default. The code simulation includes the possibility of taking into account the infinite axial and radial coordinates. ECMC allows parameters (coil positions and currents, plasma trapped current, data to be written in output files, convergence criteria) to be changed interactively. Examples of simulated equilibria on different experimental devices are given.