New cooling system with dielectric fluid for magnetizing winding in RFX-mod experiment

In order to improve the number of pulses per day in RFX-mod, in view of a plasma current up to 2.0 MA, a new cooling system of the magnetizing winding has been studied, designed and implemented. The former magnetizing winding cooling system was built up in 1991 with ultra pure water used as coolant fluid. In order to avoid the problems due to the use of water as coolant in high voltages components, and in particular in maintaining the water ultrapure characteristics, an assessment of alternative coolant fluids has been carried out. Dielectric fluids have been considered as the more suitable solution for this application. Perfluorinated fluid MITENI-RM101 has been chosen as coolant. With respect to water, RM101has good insulation properties and it is much more chemically stable, but it has poor heat transfer efficiency. The paper describes the modifications to the former cooling system, highlighting the adaptation of existing components, designed for the use with water, to the new fluid, considering the reduction of cooling performance of dielectric fluid in comparison to ultrapure water and the different compatibility with materials. The working conditions of the circuit have been set to limit pressure drops and to enhance heat transfer, taking into account the high density and the low specific heat of the new fluid. The new plant performances and the results obtained using the RM101 as coolant, are presented.