Impact of TF Magnet Mass Flow on Conductor Margin and on Cryogenic System of JT-60SA

In the framework of the JT-60SA project, a para- metric study was performed on the He mass flow rate cooling the Toroidal Field (TF) system. This mass flow is a crucial design parameter, since a high value is favorable regarding the temperature margin criterion, but requires more circulation power thus generating one of the main cryogenic loads. The study was led with the Tacos/Texto tool, based on Ansys (thermal) and Gandalf (thermohydraulics) codes. The impact of the TF conductor mass flow was analyzed, regarding on the one hand the temperature margin criterion, and on the other hand cryogenic aspects such as the TF magnet heat loads smoothing and the impact on the overall cryogenic system loads. Concerning the temperature margin criterion, the analysis showed that the foreseen nominal value of 4 g/s per conductor is appropriate for the studied reference scenario, while proposing a lower mass flow value in case of less demanding operation conditions, notably without or with low neutron heating. In such conditions, a TF mass flow limitation could bring an appreciable reduction of cryogenic loads, but shouldn´t involve significant benefit regarding heat load smoothing.