Design Study Of High Current HTS Conductors For Central Solenoids In Fusion Reactors

The Central Solenoid(CS)magnet of future magnetic confinement fusion reactor asks for higher magnetic field and compact space,which provides a perfect opportunity for high temperature superconducting(HTS)materials.From wires that are in millimeter,to a magnet in meter,a cabled and jacketed conductor that could carry tens of kilo-ampere current must work as a bridge.Therefore,the design of such a conductor is a necessary step.At present,REBCO and Bi-2212 are the two most promising HTS materials.Although the superconductivity in these two materials were found almost at the same period,their conductor designs are now in quite different situation,and different challenges are faced.There are already few different conductor designs for REBCO,almost all of which showed good performance during the preliminary tests.One of the most important following issue is quench protection,which is regarded as one of the biggest challenges for HTS applications.In this dissertation,quench performance of the REBCO conductor designed by EPFL-SPC for the CS magnet of Euro-DEMO is studied by numerical simulations with THEA code,which are supplemented by experiments.In the developed multi-monolithic-strand model,the anisotropic critical current of REBCO tapes and the multi-stage thermal-electrical processes in a REBCO conductor are considered.The optimization of the conductor is also studied according to the quench performance with respect to different parameters.Besides,in this dissertation,the thermal-hydraulic-quench-back effect is studied for possibly accelerating the normal zone propagation in a quenched REBCO conductor.Both a quasi-quantitative analysis and a numerical study show its feasibility.In addition,the concept "twisted stacked tape conductor",which is widely used in REBCO conductor design,is discussed for its influence on current balance among tapes in a charging process.Results show that twist is not really necessary for twisted stacked tape conductors,as least for current balance,Comparing with the blooming REBCO conductors,Bi-2212 conductor is still struggling to survive.A key issue is its non-compatible with copper or stainless steel during the heat treatment in an O2 atmosphere,but its brittleness after heat treatment makes it is not able to withstand high stress or strain.In this dissertation,based on the published data of Bi-2212 wires,the feasibility of a Bi-2212 React and Wind flat cable conductor(BRead conductor)is preliminarily verified with quantitative analysis.