Tokamak Toroidal Coils Research Articles

Mechanical pre-dimensioning and pre-optimization of the tokamaks’ toroidal coils featuring the winding pack layout

The structural integrity of superconducting magnets that are key elements of a fusion reactor must be ensured. At an early design stage relatively simple calculation tools can greatly facilitate design optimization. The main objective of this paper is the mechanical pre-dimensioning of the tokamak toroidal field coils by simple means prior to the global 3D numerical modeling. A semi-analytical calculation tool that reasonably estimates the static strength of the toroidal field coil under the electromagnetic forces at the critical location (inner leg equatorial plane) is described. The novelty of the approach is that it treats not only the massive coil casing but also the winding pack conductor jacket under an essentially 3D stress state. The calculation tool features pre-optimization of the coil winding for graded layered winding layouts. The minimum space (radial built) required for the coil inboard portion that is a key design parameter is defined after possible winding pre-optimization. The procedure has been successfully benchmarked against numerical solutions and has been used for pre-dimensioning the toroidal coils in the frame of the current 2015 DEMO activity.

Test results and perspectives of the cluster test program

The Cluster Test Facility has been constructed and successfully tested at the Japan Atomic Energy Research Institute (JAERI) for the development of superconducting tokamak toroidal coils. The Cluster Test Coils, constructed in 1980, are 20MJ, NbTi, pool-cooled coils. During the first test operation, the two coils were charged successfully to the rated current value of 2,145A without quenching. The detailed data obtained during the cool down was significant. This information pertains mainly to the efficiency of the cooling surface and thermal properties of the coil legs composed of stainless steel and glass epoxy. Results of strain measurements during the charging tests indicated a serious problem of analytical calculations. This problem arises primarily from the difficulty of defining the mechanical properties of winding-structure interface. The first test module coil is a 10T, Nb 3 Sn coil. This coil is now under construction and will be tested in the Cluster Test Facility in 1982.