| The nuclear fusion experimental device is an all-superconducting Tokamak experimental device with well-defined plasma confinement,high aspect ratio and non-circular cross-section,which was independent designed and built by Hefei Institute of Physics,Chinese Academy of Sciences Institute of Plasma Physics.The EAST cryogenic system was designed from 1999 and debugged successfully in 2005.The EAST full superconducting Tokamak device started its first cooling experiment in February 2006 and took a total of 16 days to drop superconducting magnet and other components from room temperature to below 4.5 K liquid helium temperature,and at the same time the coil power test,the successful completion of the first commissioning of the EAST device.EAST helium cryogenic system is currently the largest domestic cooling capacity and the longest running helium cryogenic refrigeration system.Helium refrigerators provide the required cooling capacity for Tokamak and their subsystems as one of the key subsystems of EAST devices.The helium turbine expander is the core component of helium refrigerator or helium liquefier.In this paper,related issues of new eddy current brake technology of high-speed,low-power helium turbine expander was explored for the experimental study of the object based on helium cryogenic system of Institute of Plasma Physics Chinese Academy of Sciences and helium turbine expander research platform,that had important theoretical significance and application value.Currently,common brake methods of helium turbine expander include fan brake,oil brake and eddy current brake.Compared with other brake methods,eddy current brake has the advantages of fast response,timely brake,simple structure,stable brake,improving the rotor structure and easy to realize automatic control as one of the most effective brake way of turbine expander.In this paper,the characteristics of helium turbine expander were studied from the aspects of thermodynamic performance and mechanical performance.The advantages of eddy current brake technology on the helium turbine expander were analyzed and the key problems in the structural design of eddy current brake were proposed.Then the mathematical models of two eddy current brake structures were respectively established and the physical mechanism of brake was studied by COMSOL Multiphysics.The feasibility of the second brake structure was confirmed through thermodynamic analysis of the rotor.Afterwards,the influence of each parameter on brake power was analyzed separately with the help of control variable method.In order to achieve the required brake power,the optimal parameter combination was obtained through parameter optimization.Finally,the internal cooling passage of eddy current brake was determined,and the structure design of entire eddy current brake was completed. |
