Feasibility study of RFX-mod2 performance improvement by additional magnetic energy storage

RFX-mod is an experimental fusion device built to explore and study plasma physics, especially in Reversed Field Pinch (RFP) configuration. RFX-mod allowed performing experiments with a plasma current up to 2 MA and obtaining stationary self-organized helical plasmas. Considering the results achieved so far, a significant upgrade of the device (RFX-mod2) is presently being implemented. This paper presents the feasibility study of a significant increase of the plasma current and flat-top duration via a limited upgrade of the RFX power supply system, without overstressing the poloidal windings or overcoming the power limits of the main step-down transformers (300 MVA) and maintaining the present set of thyristor converters units. The application of this concept to RFX-mod2 will be studied starting from the RFX-mod configuration, focusing on the needed modification of the present circuits and the desired improved performance. The increase of the maximum plasma current and flat-top duration, under the current and mechanical limits of the coils, can be reached using additional magnetic energy storage and a complete revision of the configuration and operating principle of the power supply system of the poloidal field coils. With this new operational concept, during the charging phase, the magnetizing winding is charged along with an additional inductor, which acts as an energy storage reservoir. The stored energy, in the order of 100 MJ, is transferred to the magnetizing winding, and thus to the plasma, via transfer resistors in the last phase of the plasma current ramp-up, to reach values of plasma current up to 2.6 MA.