Jianglong Wei

Design of Neutral Beam-Line of EAST

Neutral beam injector for EAST is designed to deliver deuterium beams with a power of 2 MW to 4 MW at an energy of 50 keV to 80 keV into the plasma with a beam dimension of 12 cm × 48 cm. Considering the beam generation and transmission, a columniform beam-line of Φ 250 cm × 400 cm is designed with a neutralizer, ion dump, calorimeter, bending magnet and cryopanels. The arrangement of the internal elements for the beam-line is reported. A rectangular sleeve coupled to the ion source is employed as the neutralizer. At the downstream of the neutralizer, a dipole magnet separates the residual ions from the beam passage with a reflection radius of 42 cm for the full energy particles. The calorimeter and the ion dump serve as high heat flux components, which will work as thermal inertia targets in the first phase of operation.

Monte Carlo Simulation for the Beam Deflection in the EAST Neutralizer Due to Stray Magnetic Field

Abstract Efficient operation of the gas neutralizer is important to the neutral beam injection (NBI) system, which forms part of the auxiliary heating systems for Experimental Advanced Superconducting Tokamak (EAST). The particle transport through the beamline of the EAST NBI system was investigated by the recently developed numerical simulation code based on the Monte Carlo treatment of collisions. This paper reports the simulation results on the ion beam transport through the EAST neutralizer and the beam deflections in the neutralizer due to the EAST stray magnetic field. The results show that the current design of the magnetic shield for the EAST neutralizer is able to meet the requirement. The relations of the optimal neutralizer thickness to the beam energy and the corresponding fractional power carried by each particle species are also given.

Investigation of the adhesive bonding technology for the insulator structure of EAST neutral beam injector

A key issue on the development of EAST ion source was the junction design of insulator structure, which consists of three insulators and four supporting flanges of electrode grid. Because the ion source is installed on the vertical plane, the insulator structure has to withstand large bending and shear stress due to the gravity of whole ion source. Through a mechanical analysis, it was calculated that the maximum bending normal stress was 0.34 MPa and shear stress was 0.23 MPa on the insulator structure. Due to the advantages of simplicity and high strength, the adhesive bonding technology was applied to the junction of insulator structure. A tensile testing campaign of different junction designs between insulator and supporting flange was performed, and a junction design of stainless steel and fiber enhanced epoxy resin with epoxy adhesive was determined. The insulator structure based on the determined design can satisfy both the requirements of high-voltage holding and mechanical strength.

Theoretical discussion for electron-density distribution in multicusp ion source

By introducing some ideas of magnetohydrodynamics (MHD) and kinetic theories, some useful solutions for electron-density distribution in the radial direction in multicusp ion source are obtained. Therefore, some conclusions are made in this perspective: 1, the electron-density distributions in a specific region in the sheath are the same with or without magnetic field; 2, the influence of magnetic field on the electron density obeys exponential law, which should take into account the collision term as well if the magnetic field is strong; 3, the result derived from the Boltzmann equation is qualitatively consistent with some given experimental results.

Feasibility Analysis of 1-D Carbon Material in Application of Negative Particle Beam Diagnostics

Abstract An important feature of the China Fusion Engineering Test Reactor (CFETR) project is the additional heating obtained from the injection of neutral beams based on accelerated negative ions. For the neutral beams based on negative ions, the most important measurements are beam uniformity, beamlet divergence, and stripping losses. According to the CFETR requirement, the maximum allowed beam divergence angle and beam nonuniformity are 6 mrads and ±10%, respectively. As one-dimensional (1-D) carbon tiles have large ratio between perpendicular conductivity and parallel conductivity and high stability, they can be used for beam uniformity and beamlet divergence measurement. This paper investigates the influence on the response of 1-D carbon tile having the thermal characteristics and features of some dedicated diagnostics. Simulations show that it will be possible to verify experimentally whether the beam meets the requirement about the maximum allowed value. This work lays a foundation for design and application of high-precision beam diagnostic targets.

Manufacturing and Testing of Multiaperture and Multichannel Grids for the Prototype Negative Ion Source for CFETR-NBI System

Abstract A prototype negative ion source is in development toward the giant negative ion source for the China Fusion Engineering Test Reactor neutral beam injection system at the Institute of Plasma Physics, Chinese Academy of Sciences. The multiaperture and multichannel grids are the most challengeable during the construction of the prototype negative ion source. The research and development activities for the grid manufacturing method were carried out and divided into detailed design, implementation, and testing phases. Based on a special manufacturing process involving the vacuum brazing technique, some prototype grids were produced. Two prototypes have similar structures to the extraction grid of the prototype negative ion source except for the reduced number of cooling channels. A testing campaign (including dimension inspection, leak tests, thermal imaging tests, and magnetic tests) was carried out. The results demonstrate that the manufacturing process and construction technology can meet the requirements of the extraction grid and can promote the construction of other grids or components having a similar structure.

Ion beam optics analysis and beam transmission simulation in the reflection magnet of the EAST NBI system

Detailed trajectories of the residual ion passing through a reflection magnet, which is installed in the Experimental Advanced Superconducting Tokamak (EAST) neutral beam injector (NBI) system to remove the residual ion from the beam path, are reported. Monte Carlo simulation has been performed to obtain estimations of the beam density on the high heat flux elements of reflection magnet. On magnet pole shielding, there are three high beam power density regions, resulting from beam line focus and corresponding to the full energy, half energy and third energy. These high heat flux regions will bring a serious challenge for steady-state operation. The simulation result indicates that the re-ionization loss is about 2.43% and the magnet pole shielding encounters a problem of beam line focus, which should be taken seriously during the steady-state operation.