Development of preionisation systems for RFX

The initiation of the plasma discharge in RFX can become a critical issue under certain experimental set-up conditions. Several specific experiments have been tried to overcome these difficulties using two different preionisation systems: the first makes use of microwaves to excite the electron cyclotron resonance in the gas, the second increases the initial ionisation in the gas by injecting charged particles with a suitable electron gun. In this paper the engineering aspects of the preionisation experiments in RFX are presented together with the results obtained. A physical model which allows their interpretation is also described.