Research Of The Loads On Tokamak Electro-magnetic TBM Mock-up During Plasma Disruptions

The breeding blanket with integrated first wall(FW)is the compulsory nuclear component for power extraction,tritium fuel sustainability,and radiation shielding in demonstration power plant reactor(DEMO).Six Test Blanket Modules(TBMs),with their ancillary systems to form six Test Blanket Systems(TBSs),will be integrated in three dedicated equatorial ports of International Thermonuclear Experimental Reactor(ITER)to demonstrate technologies of blankets.Plasma disruptions are fast events in tokamak that lead to the complete loss of the thermal and magnetic energy stored in the plasma.Each disruption event can induce eddy current,excessive thermal and electromagnetic loads onto the in-vessel components,such as blanket.Study on generation mechanisms,distributions and mitigation methods of the disruption loads are major scientific issues of tokamak fusion reactor.Focus on topics above,an Electro-Magnetic(EM)TBM mock-up used reduced activation ferritic/martensitic(RAFM)steel as its structural material was integrated in J-TEXT tokamak.Experimental researches,such as the impacts of the mock-up on the confining magnetic field and the measurements of the disruption loads are presented in this paper.The interaction forms of TBM mock-up with plasma and the generation mechanisms of the loads are analysed and discussed.The assembly methods of J-TEXT TBM mock-up have been designed to meet the radial movement,vacuum-sealing,sensors placement,EMC,security,stability and other demands of experiments.The measurement systems including probe arrays of magnetic field,thermal and electromagnetic disruption loads are also designed and constructed in this paper.The field measurement arrays use coil-type magnetic probes with a poloidal resolution of 4 cm and a toroidal resolution of 1°.The spatial distributions of magnetic flux density could be obtained by scanning measurements.The poloidal distributions of eddy-current in the mock-up FW are measured by flexible printed circuit(FPC)coil-type probes with a resolution of 8 mm and five Rogowski Coils simultaneously.Strain-gage bridges are deployed on the support structure to measure the components of electromagnetic force acting on the mock-up.The distributions of surface temperature during disruptions are acquired using an infrared camera with time resolution of 1 ms.A lot of measurement experiments have been carried out on the J-TEXT tokamak by using systems above,and the comparisons between the experimental results and the simulations of three dimensional finite element analyses have also been performed.The measured results indicate that the ferromagnet material of the TBM mock-up will increase the toroidal and poloidal field ripple to 9.52%and 37%respectively,induce considerable2/1 mode error field,and have some effects on the range of null field region during plasma breakdown.These impacts could be ultimately eliminated by recessing the TBM with 15cm.Radial Maxwell force and radial Lorentz torque are proven to be the primary load forms on the mock-up through measurements of electromagnetic and thermal loads during disruptions.The peak value of the average eddy current density in the mock-up first wall achieves level of 1.5 MA/m~2.The eddy current interacting with the magnetic field generates about 700 N·m of Lorentz torque.Recessing TBM by 10 cm could reduce the electromagnetic torque by 40 percent.Local heat loads on the first wall have been observed during disruptions caused by locked modes and the temperature of the hot spots reaches about 300℃.Disruption experiments have also studied the validity of loads mitigation on the mock-up based on transference of plasma poloidal magnetic energy.The experimental measurement datas of the mock-up accord well with the simulated values,which verifies the essential forms and the generation mechanisms of disruption loads on in-vessel components such as TBM.The results will be guidelines for the structural optimum design of TBM and the rational arrangement of supports.Meanwhile,the measurement experiments will provide valuable data supports for exploring the mitigation methods to reduce impacts on these components and to avoid destroying by electromagnetic and thermal loads during disruptions.