Wei Liu

Radio-frequency (RF) negative ion sources are essential component for neutral beam injection systems in magnetic confinement fusion devices. In this work, the RF power coupling efficiency of the Comprehensive Research Facility for Fusion Technology dual-driver RF negative ion source was experimentally measured on the Hefei Open-facility for Negative-ion Source Research test facility. The effects of selected external configurations were evaluated, including the relative RF coil current direction, the diameter of the electromagnetic shielding (EMS) for the RF driver coil, and the cusp magnet configuration. Under the reference configuration without EMS or cusp magnet systems, the RF power coupling efficiency was approximately 55%. Changing the relative RF coil current direction had only a marginal effect on the coupling efficiency and electron density. The installation of EMS improved the plasma density uniformity in front of the plasma grid (PG), while the EMS diameter affected both network resistance and RF coupling efficiency. The cusp magnet system mounted on the backplate of the RF driver reduced the RF coupling efficiency and electron density near the extraction region, whereas the additional sidewall cusp magnet system increased the electron density in front of the PG despite a further decrease in coupling efficiency. The results show that the evaluated external configurations can increase the RF power coupling efficiency by up to approximately 10% and increase the plasma density in the extraction region by about 6%.

I. As one of the most effective auxiliary heating methods, neutral beam injection (NBI) is widely used for heating and current drive in fusion devices. To support Experimental Advanced Superconduct...

Comprehensive Research Facility for Fusion Technology (CRAFT) is a technology development and validation platform for fusion technology in China. Neutral beam injection is one of the most important auxiliary heating and current drive methods in magnetically confined controlled fusion. Consequently, a negative ion based neutral beam injector (NNBI) testing facility with a beam energy of 400 keV is being developed in CRAFT. The core snubber, which provides an equivalent parallel resistance and inductance, will be used as the main surge suppression method for the CRAFT NNBI power supply system. In this paper, a core snubber for CRAFT NNBI based on Fe-based amorphous alloy is designed. The transmission line resistance, inductance, and capacitance of the high-voltage circuit have been considered during the design process. The snubber is made thin and long for even weight distribution while ensuring choke capacity. One of the snubber units was tested on the test bench. The test results indicate that the choke capacity of the snubber meets the requirement and can achieve significant suppression of peak ignition current and oscillation.

Radio frequency negative ion source is the best choice for neutral beam injection (NBI) in future nuclear fusion. Cs injection is an important means to increase the yield of negative hydrogen ions. In addition, the stability of the ion source is influenced by the distribution of Cs inside the source in the vacuum phase and plasma phase. Liquid Cs is heated into Cs vapor and then diffused into the source through a nozzle, the shape of which has a direct effect on the angular distribution of the Cs flux. This article studies the ballistic transport process of simulating three types of nozzles: cylindrical, bent, and edge-cut by developing a Monte Carlo program. The results show that the angular distribution of Cs flux from cylindrical nozzles approximates the cosine square distribution in the case of the same nozzle diameter. In comparison, the peak coverage density increases with a certain shift of the distribution state relative to the cosine square for bent and edge-cut nozzles. By analyzing the flux distribution of different nozzles, this study provides a reference for subsequent simulations of Cs and the design of Cs injection systems.

The fundamental requirements for experimental advanced superconducting tokamak neutral beam injection (EAST-NBI) are high power and long pulse. The electrostatic probe’s inherent properties, which affect the probability of electrode ignition, cause the extraction beam current to decrease with increasing extraction time in the probe feedback mode of arc power. A power feedback technique of arc power supply is suggested to stabilize the beam current and lengthen the extraction time. The output power of the arc power supply is adjusted via feedback to keep the plasma density in the arc chamber largely steady by multiplying the output voltage and current. The beam current decrease in the arc power feedback mode is substantially smaller than that of the probe feedback, which is helpful for extending the extraction time.

Neutral Beam Injection (NBI) is one of the four efficient ways of assistant heating on the Experimental Advanced Superconducting Tokamak (EAST) device. Measures have been taken to ensure more reliable monitoring of NBI components’ thermal data. Infrared thermometers, unlike surface-mounted thermocouples, have the advantage of non-contact and thus will not cause interference and get far less chance of malfunctioning [Childs et al., Rev Sci. Instruments 71, 2959–2978 (2000)]. In this paper, the remote infrared temperature measurement with optical fiber is reported to meet the requirement of the EAST-NBI diagnostic system. Some tests have been conducted on the remote infrared temperature measurement under the working condition, and an atmospheric propagation simulation was performed to estimate the atmosphere absorption. The results indicate that the detector’s response is in line with the theory, and the atmosphere absorption within a certain wavelength should not be ignored. Temperature measurement error is within one percent at temperatures above 200 °C. So, for the temperature range of 200–600 °C, the remote infrared temperature measurement by the optical fiber can fully meet its expectation.

The RF-driven negative ion source has a steady state characteristic and will be a promising ion source for neutral beam injection (NBI) in the future. Cesium (Cs) injection is an efficient method to enhance the yield of negative ions during plasma discharge. In order to support the engineering and physical research in this field, the Cs oven prototype has been developed for negative ion source based neutral beam injector at ASIPP. This article presents the design details of a Cs oven system, including the constant temperature control system, the mechanical structure of Cs oven, and the surface ionization detector (SID). SID is a measurement method for the cesium flux in the nozzle. The experiment results of constant temperature control system show that the control accuracy and function meet the requirements of device operation. Meanwhile, the simulation analysis of Cs vapor concentration has been carried out in this paper. According to the simulation results, the graph of total Cs flux is given in the article, which presents the reference for the subsequent device testing.

To explore the generation and extraction of negative ions for neutral beam injection, a prototype radio-frequency (RF)–driven negative ion source is designed at the test facility, which is under construction at the Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP). The control system provides beam pulse set up, remote supervision, plant control, timing synchronization, data management, and interlock and protection for the RF negative ion source. It plays an important role in negative ion source operation. The negative ion source prototype is currently in the development phase, involving more than 20 plant units. To match the requirements of control, data acquisition, and protection for different plant units, the plant control loop time is designed within the range of 10 μs to 100 ms, timing synchronization accuracy is 1 μs, the maximum sampling interval for data acquisition is 10 ms, the volume of data storage is tens of terabytes/year, and the interlock and protection response time is designed within the range of 10 μs to 100 ms. This paper describes the conceptual design of the control system for the prototype RF-driven negative ion source at the ASIPP, discusses the system requirements and the specifications for the control system, and shows the present status of system integration.