Electromechanical behaviour of REBCO coated conductor toroidal field coils for ultra-high-field magnetic-confinement plasma devices

Abstract

The development of rare-earth barium copper oxide (REBCO) coated conductors with an extremely high critical current density under ultra-high fields opens up a high-field path towards large-scale fusion. The latest technology has inspired cable-in-conduit conductors (CICC) such as conductor on round core (CORC) wires, twisted stacked tape conductor (TSTC) cables and Rutherford cables with outstanding current-carrying capacities. In order to realise an inductance balance and decrease magnetic diffusion, these cables have been twisted or folded to a certain extent, thus breaking the mechanical behaviour of the ceramic superconductor and limiting their potential for ultra-high-field applications. One possible solution is to employ a non-twisted cable, which offers maximum protection of its mechanical properties and enables a parallel orientation of the toroidal field vector to the surface of REBCO coated conductors. However, the applied physics community’s attitude towards using non-twisted, parallel REBCO stacked-tape cables is one of scepticism, the main argument being that the nonlinear E-J behaviour associated with screening current in the parallel stack might lead to a field distortion and reduce the performance of superconductivity. Recent analyses have demonstrated that the effect of screening current decreases significantly owing to a wavelike magnetic field distribution along the cable. The authors obtained similar results using H-formulation and T-A formulation based finite element methods and demonstrated that the non-twisted cable may be feasible for DC current transmission toroidal field coils in magnetic-confinement devices. Furthermore, the electromechanical behaviour of toroidal field coils has been evaluated via the Maxwell stress, solved by using an A-V formulation. It was discovered that the stress generated by the toroidal field coils is within the stress tolerance of the REBCO coated conductor, something which is of great significance in promoting the application of REBCO coated conductors for ultra-high-field magnetic-confinement plasma devices.

AC Loss Reduction in REBCO Coated Conductors Using the Hexagonal Arrangement Cabling Method

“…A comparison of the total losses which contain AC losses in REBCO stacks and eddy-current losses in the copper former in the hexagonal arrangement cabling configuration, the regular non-twisted REBCO cabling configuration [10], and the twisted-stacked tape-conductor (TSTC) cabling configuration [11] has been carried out. In the condition that these cables have a similar packing density with REBCO coated conductors, and the number of REBCO coated conductors in a REBCO stack, the number of REBCO stacks in a cable, and the AC currents transmitted in these cables are the same, the total losses produced in a cycle by the hexagonal arrangement cable are around three-quarters of the TSTC cable and threefifths of the regular non-twisted REBCO cable as shown in Fig.…”

“…In this article, a hexagonal arrangement REBCO cabling method with the function of achieving inductance balance and reducing AC losses is proposed. The inspiration of this cabling method is from the twisted stacked tape conductor (TSTC) cable and the non-twisted REBCO cable that were developed in our previous studies [10] [11]. AC losses in the REBCO coated conductors and eddy-current losses of the copper formers in the cable are specifically analyzed using finite element methods.…”

Numerical study on the electromagnetic characteristics of multi-layer CORC cables

“…The conductor on round core (CORC) cable [9][10][11][12][13] wound by HTS tapes is considered as a good candidate for the central solenoid magnet of the tokamak device due to its isotropic infield performance [14], and low AC losses [15][16][17][18][19][20][21]. Tokamak systems that confine a plasma using magnetic fields is a promising way to achieve controllable nuclear fusion [22][23][24][25][26]. * Author to whom any correspondence should be addressed.…”

Synthesis Studies of Radiation Dense Reactive Sintered Borides (Rsb) Nuclear Shielding Materials

“…In the past decade, nuclear fusion is transitioning from a physics problem to an engineering problem, particularly following on from the recent record breaking D-T campaign with JET in 2022 [1]. The recent development of high-field, high-temperature superconducting magnets [2,3] make compact spherical tokamaks (cSTs) a feasible option for rapid testing and deployment of fusion reactors but a major difficulty is shielding the magnets from the neutron and gamma radiation, particularly the central column [4]. cSTs require compact radiation shielding to be practical devices and candidate materials are currently under consideration include W and W-metal alloys [5], mixed borides including reactive sintered borides (RSBs) [6,7] tungsten borides [8][9][10] and cemented tungsten carbide (cWCs) [4,11,12].…”