Weiwei Xu

Concept design of hybrid superconducting magnet for CFETR Tokamak reactor

CFETR which stands for “China Fusion Engineering Test Reactor” is a new tokamak device. The mission and goal of CFETR are as follows: (1) ITER-like; complementary with ITER; (2) Fusion power 50-200 MW; (3) Duty cycle time (or burning time)~(30-50%); (4) Tritium must be self-sufficiency by blanket. The main parameters of low temperature superconducting magnet system are as follows: (1) The central magnetic field in plasma area is designed as 5.0 T. (2) The major and minor radius of plasma is 5.7 m and 1.6m. The main parameters of CFETRs were optimized several times within past year according to the further physical target and engineering. Due to the restrictions of the critical magnetic field strength, low temperature superconducting conductor may difficulty applied in low aspect ratio tokamak device in a limited space. In order to achieve a much higher central magnetic field in plasma area and much higher maximum capacity of the volt seconds provided by center solenoid winding, it is possible to apply hybrid superconducting magnet to the TF coil and CS coil in a low aspect ratio design condition. In this paper, the hybrid magnet winding by using of Nb3Sn and Bi2212 are designed and detailed analyzed which can be selected as a reference for CFETRs magnet system design. The high temperature magnet part is Bi2212 conductor, its dimension is 30 mm×35 mm/turn and current density is 117.46 A/mm2. The low temperature magnet part is Nb3Sn conductor which can good work under 11T, its current density is about 80A/mm2. In addition, the hybrid superconducting magnet system will be expected to save space for sufficient tritium blanket due to reduced conductor size.

In-vessel Components

Why we need various in-vessel components in a tokamak? Firstly it is necessary to know the goal and characteristics of a tokamak experimental device or fusion reactor. The device is used for the study of high temperature (tens of millions centigrade degrees) plasma and controllable nuclear fusion or to generate some Gigawatt net fusion energy. So, obviously two critical issues would come up. One is how the components facing the plasma can survive or how to protect the permanent components installed in the vacuum vessel (VV) from so high temperature plasma and the other is how to extract the nuclear heat from the hot plasma in the VV and transfer it to the outside of the device. These are what plasma facing components (PFCs) basically do. In addition to the PFCs, there are also many other components installed in the VV for the purpose of measuring the parameters of the plasma and magnetic field, of diagnosing the behavior of the plasma and the PFCs, etc. All these components installed in the tokamak VV are the so-called in-vessel components.

Electromagnetic, Structural and Thermal Analyses of the Vacuum Vessel

This chapter deals with the electromagnetic (EM), structural, and thermal analyses of the vacuum vessel (VV) of Tokamaks. First, the structure, the basic functions, and operation circumstance of VV are introduced. The VV, which is one of the key components, will have to withstand not only the EM force due to the plasma disruption and the Halo current, but also the pressure of shielding fluid and the thermal stress due to baking. In this chapter, as a typical EM load, the induced current, and resulting EM forces on the VV during a major disruption are studied in detail by analytical and numerical methods. According to the principle of EM induction, by simplifying the VV double-shell structure to several dozens of circular coils, distribution of the induced current and its effects on the background magnetic field are analyzed, and the resulting EM forces are simulated with Fortran software codes. Finite element methods are used to analyze the eddy current, the EM force, and the stress on VV during MD more accurately. Prior to operation, the VV is to be baked out and discharge cleaned at a higher temperature in order to get an ultra-high vacuum and a clean environment for plasma operation. During baking out the nonuniformity of temperature distribution on the VV will also bring about serious thermal stress that may damage the vessel. The temperature field and thermal stress of the VV during baking is analyzed detailed.