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CFETR TF and Testing

6. CFETR TF and testing

Objective

TheTF magnet system of CFETR consists of 16 TF coils that generates a 6.5Tmagnetic field at the plasma center (at 7.2m position) to confine the plasma.CRAFT TF coil project's overall goal is to develop a full scale prototype of TFcoil which can meet the physical and engineering requirements of CFETR, developand validate of fusion reactor large-scale superconducting coil manufacturingtechnologies, containing superconducting wire, coil, structure componentsdesign & analysis, R&D, manufacturing technologies and QA/QC,meanwhile, to set up corresponding standards to guide future reactorsuperconducting magnets.

MainTechnology Parameters

TheTF coil is wound by CICC conductors with a maximum magnetic field of 14.5T. Inorder to optimize manufacturing cost utilization, the method of 3 gradesconductors has been adopted, that is, the NbTi wire, ITER Nb3Sn andhigh-performance Nb3Sn wire (Jc>1000A/ mm2@14.5T, 4.2K) is used in the low field, the middle field andhigh-performance respectively. TF coil is composed of 9 windings, a total of154 turn, and the internal windings of the high filed and middle field areconnected by internal joints, of which joint resistance is less than 0.2nΩ. Thecoil case is made of two materials based on stress distribution of the coilcase, of which the straight section is made of high-strength austeniticstainless steel (yield strength > 950 MPa@4.5K) and the rest is made of316LN austenitic stainless steel (yield strength > 800 MPa@4.5K). The coilsand cases are cooled by supercritical helium at a cooling pressure of 0.6Mpaand a temperature of 4.5K.The inductance of the 16 TF coil is 26.3H, the operatingcurrent of the conductor is 95.6kA, the energy storage is 120GJ, and themaximum operating voltage is 10kV. The single coil (including the supportingparts on the coil case for other coils) is 21.7m high, 12.3m wide and 743theavy.

SystemDescription

The TF coil is mainly composed ofthe winding package (WP), the coil case (AP, BP, AU and BU), the gravitysupport and the PF coils support, outer inter-coil structure, coil terminal.The structure of the TF coils is shown in Fig.


Fig. 1 TF Coil Structure

KeyTechnologies

Greatchallenges in the material development and the coil manufacture techniques havebeen faced due to the high operating parameters and large scale of CFETR TFcoil. The following key technologies are needed to be developed:

Ÿ   High-Jc Nb3Snstrand and high performance Nb3SnCICC development and industrialization

The performance of theITER Nb3Sn strand cannot meet the requirement of CFETR-TF coil,High-Jc Nb3Sn strand has to be developed. WST has made abreakthrough in improving the performance of high-Jc Nb3Snstrand (Jc>2500 A/mm2@4.2K,12T,RRR~270), which canmeet the requirement of CFETR TF coil. Meanwhile, WST also has progress inindustrial of high-Jc Nb3Sn strand (piecelength>1000m).

Ÿ   High-strength,high-precision and large-size coil case

Analysis results showthat the peak stress of the inboard straight leg of CFETR-TF coil case islarger than 800 MPa. The development of the high-strength austeniticstainless-steel material, components machining, welding and inspection areongoing by cooperation with two domestic companies.

Ÿ   Assembly and testingof large-size windings and coil cases.

The technical schemeof winding horizontal insertion has been basically determined. Heavy-load andhigh-precision winding insertion system, winding case sealing welding and VPIin the winding case have been started.