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Abstract A 95W–3.5Ni–1.0Fe–0.5Co heavy alloy was surface modified by pack carburization. A new carburized layer consisting of outside surface layer and inner surface layer was formed. The double layered microstructure showed porous WC aggregates in the outside surface layer and W grains coated by shell-like (Ni, Co, Fe) 6 W 6 C carbides in the inner surface layer. There were two paths for C atoms diffusion and reaction through W grains and matrix phase. Co changed the formation orders of carbides and acted as a medium for promoting C atoms reaction with Ni, Fe, Co and W in the matrix to form shell-like (Ni, Co, Fe) 6 W 6 C carbides in the inner surface layer. Meanwhile, C atoms diffused in the W grains and reacted with W in an order of W→W 2 C→WC. WC nucleated and grew in carburized W grains and micropores produced in the growing WC crystals due to the lattice expansion from W→W 2 C→WC. As the carburization process continued, the shell-like (Ni, Co, Fe) 6 W 6 C carbide was also carburized to WC, and finally the whole W grain was carburized into porous WC aggregates in the outside surface layer. Graphical abstract Image 1 Highlights • A pack carburized 95W–3.5Ni–1.0Fe–0.5Co heavy alloy was characterized using XRD, SEM, EPMA and TEM. • A new carburized layer consisting of outside surface layer and inner surface layer was formed. • Porous WC aggregates formed in the outside surface layer. • W grains coated by shell-like (Ni, Co, Fe) 6 W 6 C carbides were obtained in the inner surface layer. • The new carburized microstructure was found to be related to the Co addition. [ABSTRACT FROM AUTHOR]

• Occurrence of flying off of tappet caused impact forces between tappet and cam. • Weak adhesion and brittleness of CL were responsible for the early delamination. • The nitrided tappet inserts with its CL removed was an effective countermeasure. • CL of nitrieded parts should be grinded off under a heavy load with impact forces. Early delamination of the nitrided tappet inserts in the valve train of a high speed and heavy duty diesel engine occurred and thus the failure mechanism of early delamination was investigated with the method of numerical simulation and experiment at first. Additionally, the countermeasure was put forward and identified using a valve train bench test rig. Flying off of the tappet in valve train took place, causing repeated impact forces between the interfaces of the tappet and cam. Early delamination of the compound layer (CL) was formed once the surface crack connected with the subsurface crack. Removal of the CL of the nitrided tappet inserts was verified as an effective countermeasure for avoiding the early delamination as well as protecting the matching part, which suggests the hard and brittle CL of the nitrided part should be removed under a heavy load condition especially accompanying with repeated impact forces. [ABSTRACT FROM AUTHOR]

• Due to the uncertainty of the field experimental conditions, the fast discharge unit may be unable to open and the magnet power supply may have a ground fault. Therefore, it is necessary to systematically analyze the above possible faults. • The breaking current and breaking voltage of quench protection system in normal operation are analyzed. The inductance and resistance of TF coil are calculated. • The TF coil fault simulation model is built, and the fault state of the magnet power supply is systematically and comprehensively analyzed. • The research in this paper has certain guiding significance for the design of fast discharge unit and TF magnet coil grounding system, and plays an important role in the performance and safety of fusion device operation. The magnet power supply system is one of the important subsystems of nuclear fusion devices. Although it has undergone strict safety and stability verification before design and operation, the experimental conditions at the work site still have uncertainty. The fast discharge unit may not be able to open and the magnet power supply may have a ground fault. Therefore, it is necessary to systematically analyze the above possible fault conditions, in order to better protect the superconducting magnet. In this paper, the quench protection system and grounding protection system of TF coil magnet power supply are theoretically analyzed and calculated. According to the calculation results, the TF coil fault simulation model is built in MATLAB/Simulink, and the influence of the fault state of the power supply on the magnet is systematically analyzed. The results show that the maximum voltage at fault is much higher than the rated voltage during operation, so a larger margin should be considered in the design process to protect the superconducting magnet. The research in this paper has certain guiding significance for the design of fast discharge unit and TF magnet coil grounding system, and plays an important role in the performance and safety of fusion device operation. [ABSTRACT FROM AUTHOR]

• Based on the mechanism of shock wave generation from electrical wire explosion, a novel driving method utilizing electrical wire explosion technology is proposed as an alternative to traditional high-energy explosive-driven pyro-breaker. This is a crucial issue of the reliability of quench protection system in large fusion device. • Through experiments, the arc contact breaking process of the pyro-breaker was observed, and the pressure required for breaking was measured. • A microsecond experimental platform for underwater wire electric explosion was established, and the discharge parameters and shock wave intensity were measured and analyzed. The experimental results indicate that the shock wave intensity generated by the electrical wire explosion meets the design requirements for breaking arc contact. • In this paper, this study provides a theoretical foundation and technical support for the optimization of the driving source in pyro-breaker within quench protection system, which will significantly reduce the cost of pyro-breaker. Quench protection system (QPS) is critical for ensuring the safety operation of superconducting magnets in nuclear fusion devices, while the pyro-breaker is wildly used in QPS for backup protection. This paper discusses the feasibility of using Underwater Electrical Wire Explosion (UEWE) to drive pyro-breaker. Firstly, the overall structure and the driving mechanism of arc contact of pyro-breaker are analyzed. Secondly, the detonation pressure required for contact breaking is measured by experiment. Then a microsecond-level UEWE experimental platform was established to test the discharge characteristics and shock wave intensity during the electrical explosion process. Finally, the detonation pressure generated by UEWE is measured and compared with contact driving mechanism of pyro-breaker. The experiment demonstrates that the UEWE has sufficient potential for replacing the explosive and driving the pyro-breaker. This study provides a new pathway for the design of the pyro-breaker. [ABSTRACT FROM AUTHOR]

• The reliability of high-power switches in Fast Discharge Unit (FDU) is very important for the safety operation of superconducting magnets. In this paper, the reliability and test number of FDU switches are discussed. • The FDU configuration characteristics of different types of superconducting magnets are introduced, and some explanation and calculation on reliability are provided. • The reliability interval estimation after a certain test number is discussed by using the binomial distribution theory. • The reliability conformance test based on the claimed reliability is discussed to derive the test number. High-power switches, as the important active part of Fast Discharge Unit (FDU) in Tokamak, are designed to interrupt the circuit current and transfer the quench energy for protecting expensive superconducting magnets. Hence, their reliability has always been highly underlined. In this paper, the reliability and test number of FDU switches are discussed, mainly including three issues. First, the FDU configuration characteristics of different types of superconducting magnets are introduced, and explanations and calculations on reliability are provided. Second, the reliability interval estimation after a certain test number is discussed by using the binomial distribution theory. Three, the compliance test based on the claimed reliability is studied, and two types of test plans are discussed and compared to derive the test number. The discussion in this paper focuses on the FDU switches and provides valuable guidance for their reliability test and assessment. [ABSTRACT FROM AUTHOR]

• The control system for the quench protection unit is crucial for ensuring the safety of superconducting magnet coils. • The control system for the quench protection unit is used to control high-power DC switch action to protect the safety of magnet coils. This paper introduces a control system design method for the quench protection unit with soft and hard separation. • The software design and hardware selection of the control system for the quench protection unit are analyzed in detail. • A cross-core scheduling algorithm is proposed for fast task prioritization to meet the hundred-microsecond action requirement of high-power DC switches. Quench Protection Unit (QPU) is required to immediately control the high-power DC switch when the quench event occurs in the superconducting magnet. The energy in the magnet coil is quickly transferred to the Fast Discharge Resistor (FDR), which dissipates a large amount of stored energy and protects the magnet coil from damage. To ensure reliable protection of magnet coils, this paper proposes a design scheme of a soft-hard separation control system based on The Windows Control and Automation Technology (TwinCAT3). According to the high-power DC switch requirement for hundred-microsecond operation in QPU, this paper proposes a fast task priority cross-core scheduling algorithm. Tasks with short cycle times are prioritized and allocated to different cores. The experiment results demonstrate that the control system has excellent accuracy, speed, and reliability. Therefore, it can meet the high-power DC switch action requirements in QPU. [ABSTRACT FROM AUTHOR]

This paper clearly demonstrates the structure of Experimental Advanced Superconducting Tokamak (EAST) power supply system and analyzes principles of the finite-state machine (FSM) elaborately. Depending on the characteristics of EAST power supply system and the requirements of it, this paper chooses the real-time Linux as system platform and experimental physics and industrial control system (EPICS) as development tool to design a control system of the EAST poloidal field power system supply. This paper utilizes a temporal logic control based on the FSM in order to regulate the operation process of real-time sequence logic control of 12 sets of power controllers. This design is evaluated and tested, and it completely meets the real-time requirement of the poloidal field power supply (PFPS) control system. Several experiments have proved that this design definitely meets the real-time sequence logic control requirement of the PFPS control system in the complex situations under magnetic fields. [ABSTRACT FROM AUTHOR]

This paper clearly demonstrates the architecture of time synchronization network of experimental advanced superconducting tokamak (EAST) poloidal field (PF) power supply control system and analyzes characteristics of the IEEE 1588 in detail at the same time. IEEE 1588 has unique advantages for this paper to utilize as protocol in order to improve the accuracy of the time synchronization network (TSN). Consequently, we design a time synchronization system based on PCI eXtensions for Instrumentation-6683H. This paper utilizes one master node to synchronize all slave nodes on the time network in each second. The result shows that the synchronization accuracy can be achieved within 50 ns. According to results of experiments, this system can perfectly meet the requirements of EAST PF power supply control system. [ABSTRACT FROM AUTHOR]

This paper presents the architecture and the implementation of the upgraded Experimental Advanced Superconducting Tokamak (EAST) Poloidal Field Power Supply (PFPS) monitoring system. To meet the requirements of EAST long pulse discharge, the monitoring system has been upgraded based on experimental physics and industrial control system (EPICS) and MDSplus. It provides an integrated management of supervision, data acquisition and real-time control. The program is flexible and portable, which improves the system performance. The I/O interrupt mechanism of the device support module is used to read the updated data, which reduces the network communication load. Asynchronous Driver Support (AsynDriver) is used to develop the device's specific interfacing code for the DAQ card driver, simplify writing of drivers and make the program more reliable. The HMI is developed using Control System Studio (CSS). During the experiment, the collect data is stored in the archiving system from PFPS system and sent to the MDSplus data server at the same time, so that the operator can view and analyze the online data and offline data. The upgraded monitoring system provides a general design scheme, which can be well integrated into the control system. The experimental results show the system realizes the remote operation and monitoring of equipment of PFPS and provides a friendly human-machine interface, supports multiuser operation. [ABSTRACT FROM AUTHOR]

• The architecture of two layers is designed following the guidelines specified by the PCDH issued by IO. • Architecture of field layer designed by redundant ring network topology based on EtherCAT with high real-time communication. • Mini-CML developed by the CODAC system to achieve the real-time monitoring, remote operation, data storage, query, and alarm. • A method to realize cross-platform data transmission of control system based on EPICS is presented. This paper describes ITER PF converter system architecture in details. According to its real-time and reliability characteristics, ITER PF converter system uses an industrial Ethernet fieldbus based on EtherCAT protocol with high real-time communication performance to develop its remote monitoring system. This system follows ITER design specification, it realize the real-time monitoring of thousands of analog and digital signals, and can realize remote operation of the switches in the field layer, real-time data and historical data query, event alarm and authority management functions. The system has achieved continuous and stable operation on the test platform of ITER PF converter system, meeting the requirements of high real-time performance and reliability of the remote monitoring system of ITER PF converter system. [ABSTRACT FROM AUTHOR]

• Three layers of subsystems are constructed for the control system of EAST poloidal field power supply. • Architecture based on real-time system and high speed communication network is proposed to make control loops on power supply controllers running at strict cycle-time. • Handy human-machine interface and sensitive alarming mechanism based on EPICS are achieved to monitor the power system. • Unified external clock and external trigger scheme are developed to enhance the data acquisition management system. This paper introduces the architecture and characteristics of the poloidal field power supply, and describes the architecture of its control system, which is composed of data acquisition management system, operation monitoring system and real-time control system. According to the characteristics of the control system, a data acquisition management system based on Qt, an operation monitoring system based on EPICS and the real-time control system is based on Linux real-time kernel are designed. The control system realizes real-time control of EAST poloidal field power supply system in 1 ms cycle time, and the equipment status detection and monitoring, data acquisition, storage and inspection. Several experiments have proved that the control system definitely meets the requirements of the poloidal field power supply control system in the complex situations under magnetic fields. [ABSTRACT FROM AUTHOR]