Jinxing Zheng

Progress of the Keda Torus eXperiment Project in China: design and mission

The Keda Torus eXperiment (KTX) is a medium-sized reversed field pinch (RFP) device under construction at the University of Science and Technology of China. The KTX has a major radius of 1.4 m and a minor radius of 0.4 m with an Ohmic discharge current up to 1 MA. The expected electron density and temperature are, respectively, 2 × 1019 m−3 and 800 eV. A combination of a stainless steel vacuum chamber and a thin copper shell (with a penetration time of 20 ms) surrounding the plasma provides an opportunity for studying resistive wall mode instabilities. The unique double-C design of the KTX vacuum vessel allows access to the interior of the KTX for easy first-wall modifications and investigations of power and particle handling, a largely unexplored territory in RFP research leading to demonstration of the fusion potential of the RFP concept. An active feedback mode control system is designed and will be implemented in the second phase of the KTX program. The recent progress of this program will be presented, including the design of the vacuum vessel, magnet systems and power supplies.

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.

Conceptual design and analysis of CFETR magnets

CFETR (China Fusion Engineering Test Reactor) is a test reactor which shall be constructed by National Integration Design Group for Magnetic Confinement Fusion Reactor of China. The Reactor has the equivalent scale compared with ITER, but has the complementary function to ITER. CFETR is a demonstration of long pulse or steady-state operation with duty cycle time not less than 0.3~0.5 and the full cycle of tritium self-sustained with TBR not less than 1.2. The magnets design of CFETR is based on the ITER magnet technology. This paper describes a conceptual design and analysis of the CFETR magnets. The constant tension toroidal field coil and three different magnetic equilibrium shapes are present in this paper.

Conceptual Design of the CFETR Toroidal Field Superconducting Coils

The China Fusion Engineering Test Reactor (CFETR) superconducting tokamak is a national scientific research project of China with plasma major and minor radii of 5.7 and 1.6 m, respectively. The magnetic field in the center of plasma at a radius of R = 5.7 m is 5.0 T. The major objective of the project is to build a fusion engineering tokamak reactor with fusion power within the range of 50-200 MW and should be self-sufficient by blanket. Sixteen toroidal field (TF) superconducting coils of CFETR have been arrayed toroidally and are made up of Nb3Sn superconductor. The maximum magnetic field of the TF coil is 10.8 T under the operation current of 67.4 kA. The TF coil should have strong stability margin under the condition of high field and strain. This paper discusses the design parameters, electromagnetic distribution, structure, and thermal and stability analysis of the TF superconducting magnet for CFETR.

Electromagnetic and Stability Study on HTS/LTS Hybrid Superconducting Central Solenoid

Nb3Sn is considered to be one of the best candidate low-temperature superconducting (LTS) materials for the fusion superconducting magnet system. However, in consideration of the optimization design work of the fusion device magnet system, higher volts per second under a presupposition of a much more economical device size needs to be achieved. In our recent work, a type of high-temperature superconducting (HTS) and LTS hybrid magnet has been designed for the central solenoid for the fusion device. It can provide maximum volts per second of 220 V · s with the maximum magnetic field of 19.4 T. The inner HTS part of the magnet is designed with the Bi2212 conductor, whereas the outer LTS part is designed with the Nb3Sn conductor. It can meet the requirements of a high magnetic field and an operation current for fusion device. The structure design of the HTS/LTS hybrid magnet has been carried out. In addition, variation of the electromagnetic properties, according to the flexible structure design of HTS/LTS hybrid magnet and related stability analysis work, are also illustrated in this paper.

Study of Induced Eddy Current Effects on Field Homogeneity for Fast Ramped Bending Magnet

An investigation of induced eddy current effects on the field homogeneity in fast ramped bending magnets was presented in this paper. The transverse field homogeneity and integral field homogeneity were calculated based on two-dimensional/three-dimensional finite-element analysis. The results showed that the transverse field homogeneity and integral field homogeneity were less than 0.05% after the field optimization with static analysis. The fast ramped bending magnet is used to deliver a proton beam for a superconducting proton therapy facility. The energy of the proton beam is adjusted by a fast degrader device and it will require all the magnets in the beam line to follow the energy changes of the degrader as fast as possible. During the energy change stage, induced eddy currents will appear in the beam tube. Then, the transient finite-element analysis is presented at different current ramp rates k and beam tube thicknesses b. The induced eddy currents in the beam tube were analyzed to research the eddy current effects on field quality. It shows that the field quality will be influenced more obviously with increased current ramp rate or beam tube thickness. The maximal field decrease in the midplane caused by eddy currents in the beam tube is the main reason for field quality disturbance. The relationship between the field decrease and current ramp rate k can be expressed simply with a mathematical formula. For different situations, the effects caused by eddy currents on field quality may be different. But the maximal field decrease in the center of the magnet is the same.

High Field Superconducting Magnet Technologies for Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) has become one of the most powerful tools in modern medical diagnosis and interventional therapy. It can achieve very fast scanning due to the synchronization in time and space under the high field with high homogeneity. High field with high stability in time can improve the ratio of signal to noise and the imaging resolution. It has become an important diagnostic tool in the early stages of cancer, and the evaluation of the efficacy of treatment and high-risk surgery, neuroscience, and molecular imaging. On the other hand, in recent years, the development of openness in high field magnets can combine the MRI with positron emission tomography and/or accelerator, which contributes to form more excellent medical diagnosis tools. The high-field superconducting has been widely used in medical imaging. The superconducting magnet technology depends on the development of material and cryogenic technology. In this paper, the superconducting MRI systems applied in the medical diagnosis and interventional therapy in China were reviewed.

Development and verification of mathematical model for halo current in ITER

Confined plasma by magnetic field is appear to be abundant and durable source of energy for future aspects. Tokamak is the most advanced device under controlled condition of magnetic field and current flowing in plasma. The interaction of plasma with vacuum vessel gives halo current following poloidal direction with strong outward magnetic force towards vessel. The vertical disruption events caused by this halo current creates an engineering problem for fusion reactor. Therefore, in this paper, toroidal magnetic field Btor and halo current Ihalo were calculated by mathematical formulation and technique. Since, experimental data has already been got from the EAST experiment, therefore, the aim is to developed and investigate an analytical model and computationally evaluate with theoretical calculations. For this case, vertical disruption events of plasma facing components including the balancing sideways forces due to asymptotic poloidal halo current will be evaluated and examined. The results obtained will be useful for equalizing the simulation and experimental results. The research will be extended to developed new models for other Fusion reactors.