Passive and active control of the field errors at the poloidal gaps of the RFX shell

An analog feedback control system was designed and implemented to control the magnetic configuration in RFX and in particular to minimize the field errors at the gaps. The correction during the plasma current rise phase, when the control system is not active yet, is accomplished by means of passive elements connected in series to the field shaping windings. A description of the system and the experimental results are presented.