The consortium of Russian researchers is discussing further works on new fusion devices. One of the goals is the development of superconducting magnets of the demonstration hybrid facility - Fusion Neutron Source (DEMO FNS) based on the tokamak concept with the conventional aspect ratio ~3 [1, 2]. This device should have 5 T on the plasma axis and ~12 T on the toroidal coils. Because of high neutron flow and thick shielding necessity, a tight space remains for TF magnet inner legs that leads to a high current density in windings and high operating current. Several magnet designs have been addressed up to now. In all proposals the toroidal winding should be made of Nb3Sn based CICC with critical current density of Nb3Sn wires ~1300 A/mm2. That is at least twice higher than in the ITER and could be achieved by use of internal tin technology development. Electrical and mechanical parameters of SC strands should survive in high neutron fluency and will be explored using fast particles irradiation. The new design of conductor prototypes and basic strands should be developed for such conditions. The high mechanical stresses of DEMO-FNS magnet system should be taken into account along with desirable minimization of AC losses. In this review, we discuss possible designs of TF magnet system; requirements for parameters of strands; actual progress and prospective in Nb3Sn wires fabrication (including activities in collaboration with CERN); different designs of conductors for DEMO-FNS. The developments of HTS current leads with low heat leak and bus burs for fusion machine are discussed as well.
1. D.P. Ivanov, et.al, "Superconducting Magnet for Russian Fusion Neutron Source DEMO FNS", Proceedings of 25 IAEA Fusion Energy Conference FEC 2014, , Poster FIP/P 7-10,
2. D. P. Ivanov, et.al, “Superconducting Magnet for Thermonuclear Neutron Source", available at: http://snf.ieeecsc.org/sites/ieeecsc.org/files/documents/snf/abstracts/HP103_Magnet%20TNS_final_012216.pdf