Preliminary investigation of the use of visible images to validate the magnetic reconstruction of the boundary on JET

The reconstruction of the magnetic fields, which produce the confinement of the plasma, is an essential ingredient of tokamaks, since they affect both the operation of the devices and the interpretation of the physics results. This work reports a preliminary investigation to determinate whether the position of last magnetic flux surface can be evaluated from the images collected by JET visible cameras. To this end, the frames of some JET visible cameras have been analyzed with the phase congruency method to extract the position of the emission at the boundary on the high field side. The results of the comparison between the optical reconstruction of the plasma boundary obtained from the cameras and the separatrix position derived from the equilibrium code EFIT has been performed. Depending on the measurements used as inputs to EFIT, the difference between the two estimates of the separatrix position is below 10 cm.