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To study the characteristics of radio frequency (RF) power coupling, RF plasma diagnostics, actively cooled tube, and negative ion production, a plasma source was designed as a small-scale test facility. The matching network was carefully designed and successfully applied to the 2-MHz RF plasma source. In this article, the design method of the matching unit will be presented; with the assistance of this matching unit, the RF plasma source was successfully lit and the reflected power was reduced to a very low level. A $V\!\!-\!\!I$ probe was installed in front of or in the rear of the matching network, respectively, to in situ measure the RF voltage, current, and phase angle. The equivalent resistance of the RF plasma source was analyzed in detail. The RF power coupling efficiency was derived in two different methods, and the relationship between the coupling efficiency and the equivalent resistance of the plasma source is verified. At the same time, the equivalent resistance of the plasma source was also collected to optimize the matching unit. [ABSTRACT FROM AUTHOR]

In order to study the generation and extraction of negative ions for neutral beam injection application, a prototype radio frequency driven negative ion source and the corresponding test bench are under construction at the Institute of Plasma Physics, Chinese Academy of Sciences. A new design of infrared radiation diagnostic calorimeter for testing beam characteristics is put forward. Compared with the conventional calorimeter, the calorimeter adopts the block structure (8 × 28 tungsten hexahedron blocks) and modularization design (4 modules), so it has higher precision and good scalability. The thermal performance of the calorimeter is assessed using a finite element method. Simulation results show that the design can be achieved to operate in the stable-state mode at the maximum thermal flux 6.45 MW/m2 and meet the full requirement of beam diagnosis. [ABSTRACT FROM AUTHOR]

Negative ion source is a core part of the neutral beam injection system for magnetic confinement fusion devices. The density of produced hydrogen negative ions is a critical parameter of the negative ion source. Cavity ring-down spectroscopy (CRDS) is an ultrasensitive absorption diagnostic technique for density measurement. Based on the photodetachment process, CRDS can measure the integrated line-of-sight hydrogen negative ion density in a high power ion source. The CRDS diagnostic system has been applied to Hefei utility negative ion test equipment with the radio frequency (RF) source, which is now one of the references for the China Fusion Engineering Test Reactor neutral beam injection system. Typical ring-down signals are obtained to calculate the density of hydrogen negative ions. The time evolution of hydrogen negative ion density is successfully measured. Preliminary experiments show the accurate relationship between RF power and measured hydrogen negative ion density. [ABSTRACT FROM AUTHOR]

Neutral beam injection (NBI) is one of the most effective tools of four auxiliary plasma heating methods for fusion plasma heating and current drive. Now, a next generation fusion device, China Fusion Engineering Test Reactor, is under design, and a large negative NBI is foreseen. In order to demonstrate the key technology and performance of a negative ion source, a negative radio frequency (RF) ion source test facility has been developed since 2017 in the Institute of Plasma Physics, Chinese Academy of Science. A prototype RF ion source with double drivers (having the same structure with an inner diameter of 200 mm) was developed and tested on the test facility to preresearch the key technology of the RF plasma generator. The driver is equipped with a water-cooled Faraday shield to protect the alumina cylinder from the plasma, and the plasma expands into the rectangular expansion chamber. The RF power of 100 kW with a frequency of 1 MHz is transferred to the RF driver by a matching unit. The characteristics of plasma discharge were studied with classical diagnostic tools, such as the Langmuir probe and water flow calorimeter. Based on the plasma performance tests, a high power of 82 kW plasma discharge for a long pulse of 1000 s was achieved. In this paper, the details of the ion source design, characteristics of plasma, and future research plan will be presented. [ABSTRACT FROM AUTHOR]

A negative ion source acts as a critical part in a neutral beam injector (NBI). A high current ion source is required for the high-power NBI. In this paper, a prototype radio frequency (RF) ion source and its test facility are developed in the Institute of Plasma Physics, Chinese Academy of Sciences, to demonstrate the key technology of the high power negative ion source. The structure design of the RF negative ion source is presented, involving the designs of the ion source plasma generator and accelerator. The detailed structure design and analysis of the key parts of the ion source are also presented, such as the Faraday shield (FS) and accelerator grids. The fluid-thermal-structural coupling characteristics of the FS and grid are explored with different mechanisms of fluid pressure, RF power, and the structure type on the thermal stress. Then, the processing and manufacturing scheme of the FS and grids are also given. Finally, the results were presented with a manufactured three cooling channel FS. The experimental results prove that the developed structure design of the RF ion source is effective and reliable, and the correctness of finite element analysis is also verified by experimental data comparison. [ABSTRACT FROM AUTHOR]

An RF-driven negative-ion source development program has been started at ASIPP-Hefei with a small test equipment, Hefei utility negative ion test equipment with RF source (HUNTER). It is devoted to some crucial issues of the RF-driven negative-ion source, such as the improvement of RF efficiency, the enhancement of the extracted negative-ion current density, and the promotion of the beam qualities. In the initial stage, the HUNTER negative-ion source conservatively adopted a similar structure of the ITER prototype source developed at IPP, Garching. It consists of single or double RF driver on the back side of a plasma expansion chamber, and a negative ion accelerator which is able to extract 120 beamlets up to 60 kV for 10 s. In the first phase operation of the HUNTER-ion source, a low-pressure (0.3 Pa) plasma has been successfully achieved by coupling 46-kW RF input power and different plasma parameters have been measured by using Langmuir probes and optical emission spectroscopy. Besides the negative-ion source, the HUNTER comprises the vacuum vessel, the special cooling system, the power supply system, and the source plasma and beam diagnostic system are also ready for the next phase operation of hydrogen negative ion beam extraction. [ABSTRACT FROM AUTHOR]

• Influence of magnetic field in RF plasma source of CRAFT was investigated. • Checkboard and symmetric arrangement of magnets were simulated and tested. • Symmetric arrangement with three rows of magnets gave the best performance in term of plasma parameters. • The results are helpful to optimize the performance of high power ion sources. Radio Frequency (RF) driven negative ion source is the preferred ion source for negative ion based Neutral Beam Injection system (NNBI). The plasma generator, which consists of RF driver(s) and an expansion chamber, is one of the key parts for NNBI. The distribution of cusp magnetic field which is generated by permanent magnets installed at the lateral wall of the expansion chamber is a common issue, due to the great influence on electron density, electron temperature and spatial uniformity of plasma density in the extraction area. Two kinds of configuration of cusp magnetic field (checkerboard type and symmetric type) and three types of arrangement of permanent magnets (with three, four and five rows of magnets) have been carried out with the approach of finite element and the experimental performance. On the RF negative ion source testbed, a moveable Langmuir probe has been adopted to investigate the characteristic of electron density and temperature near the extraction area. Since the symmetric type with three rows of permanent magnets generates the distribution of cusp magnetic field that contribute to extract the plasma from RF driver and improve the probability of particle collision easily, the higher electron density and the lower electron temperature was obtained via simulation. The experimental conclusion is that the symmetric type with three rows of permanent magnets leads to a higher electron density and lower electron temperature, showing a great agreement with simulation results. The results are helpful to optimize the structure and performance of high power ion source, and provide support for the development of large area RF negative ion sources with multi-driver. [ABSTRACT FROM AUTHOR]

In order to study the generation and extraction of negative ions for neutral beam injection application, a prototype RF-driven negative ion source and the corresponding test bed are under construction at Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP). The target of the negative ion source is extracting a negation ion beam of 350 A/m 2 for 3600 s plasma duration and 100 s beam duration. According to the required parameters of test bed, the design of power supply system is put forward for earlier study. In this paper, the performance requirements and design schemes of RF power supply for plasma generation, impedance matching network, bias voltage power supply, and extraction voltage power supply for negative beam extraction are introduced in details. The schemes provide a reference for the construction of power supply system and lay a foundation for the next phase of experimental operation. [ABSTRACT FROM AUTHOR]

A radio frequency (RF) ion source was designed and developed for neutral beam injector in Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP). Recently, the RF ion source was upgraded with new RF power generator (50 kW with frequency of 1 MHz), a new matching unit and the faraday shield with water cooling. Two new methods were used for the ion source tests on the test bed. The high pressure was used for the ignition of plasma and change to low pressure of 0.3 Pa to maintain the plasma. The RF plasma can be generated without the start filament successfully. In order to avoid the plasma oscillation with high power, the RF power was set to increase with two stages without change the matching unit. High power of 46 kW with pulse length of 22 s was achieved on the test bed and the plasma duration can be extended too. [ABSTRACT FROM AUTHOR]

• The design details of quarter size of RF based negative beam source for CRAFT NNBI was presented. • The structure design of RF negative beam source and the manufacturing process of key components, such as Faraday Shield and accelerator grids are presented. • The insulator for accelerator was designed and several the manufacturing techniques were tested and the results are presented. A high-power radio frequency (RF) beam source is a key component for Negative Neutral Beam Injector (NNBI) in ASIPP. According to the technical route planning of CRAFT-NNBI beam source project, ASIPP started the development of quarter-size RF negative source and corresponding test facility. The inner diameter of the faraday shield (FS) of RF driver is 240 mm, the outer diameter of the accelerator is 1 m, with three-layer grids extraction system, which comprises the plasma grid (PG), extraction grid (EG) and ground grid (GG). The size of PG is 512 mm × 396 mm × 9 mm, with two rows of 16 × 6 apertures made of pure molybdenum. The structure design of RF negative beam source and the manufacturing process of key components are presented, with emphasis on the manufacturing process of FS as well as grids. Furthermore, the fluid-thermal-structural analysis of PG, the mechanical analysis and material bonding strength test of the main insulation structure of beam source, as well as the preliminary layout of the latest test facility are presented. [ABSTRACT FROM AUTHOR]