An 18.3 MJ charging and discharging pulsed power supply system for the space plasma environment research facility (SPERF): the subsystem for the magnetic mirror coil.

The magnetic reconnection process relevant to that at the magnetotail is one of the research contents of the Space Plasma Environment Research Facility, which is under construction at the Harbin Institute of Technology in China. Two magnetic mirror sub-coils placed symmetrically in the vertical direction and connected in series cooperate with a dipole coil to generate a magnetic field environment similar to the Earth's magnetotail. A capacitor-based pulsed power supply (PPS) system with a modular design is developed to excite two magnetic mirror sub-coils to generate a magnetic field with a magnetic flux density of not less than 200 G at the center of the two sub-coils. The PPS should deliver a pulsed current with a peak of more than 8 kA, and the duration of the current not be less than 95% of the peak over 5 ms to two magnetic mirror sub-coils when the charging voltage is not less than 20 kV. In addition, the duration from the peak to 10% of the peak is not more than 130 ms. The detailed design of the PPS is discussed in this paper, and a test method is designed to reduce the risk of damage to the wires and the connection between the wires and the coaxial cables of the PPS when the PPS discharges at a higher charging voltage. Finally, the discharge test of the PPS is carried out to verify the design of the PPS.

Plasma Nitriding of Inner Surface of Slender Tubes using Small Diameter Helicon Plasma.

A steady-state, high-flux N2/Ar helicon wave plasma (HWP) with a small diameter (10 mm) was used to nitride the interior of a slender austenitic stainless steel (ASS) 316L tube at a temperature of 450 °C. N2 and Ar were fed to a 500 mm long slender tube with 10 mm inner diameter and were ionized inside the tube using a helicon wave in the magnetic field of 2000 G. The microstructure and depth of the nitrided layers, in addition to the morphology and hardness of the nitrided surfaces, were intensively characterized by employing scanning electron microscopy (SEM), optical microscopy (OM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), as well as microhardness tests. The results confirmed that the nitrided layer consisted primarily of the expanded austenite phase γN, and neither CrN nor iron nitride precipitates. An increasing trend in microhardness was observed in inductively coupled plasma (ICP) and HWP modes; however, the increase in HWP nitriding (up to HV 1820 with a thickness of 14 µm) was approximately 1.5 times greater than that achieved through ICP plasma nitriding. This was owing to the higher N+ ion density in the HWP mode. Considering the successful control of N2 plasma discharge in a slender tube with a small diameter, this study opens up a new avenue for achieving high-yield nitride layers inside slender tubes.

The magnet system of the Space Plasma Environment Research Facility (SPERF): Parameter design and electromagnetic analysis.

A magnet system is used in the SPERF to create the magnetic field configuration for simulating the space plasma environment. In this paper, the parameters of the system are designed to achieve the target fields needed by the scaling laws, and the electromagnetic analysis has been performed to validate the results. A procedure to obtain the parameters is proposed based on the investigation into the physical and technological constraints. The vacuum magnetic fields for studying the 3D magnetic reconnection at the magnetopause, Earth's magnetosphere, and 3D magnetic reconnection driven by a plasma gun are computed. In addition, the engineering complexity is reviewed in brief. This research is crucial to the construction of the SPERF, and it is valuable to designing the magnets applied in other fields.

An 18.3 MJ charging and discharging pulsed power supply system for the Space Plasma Environment Research Facility (SPERF): Modular design method and component selection.

The capacitor-based pulsed power supply (PPS) system is an important subsystem of the Space Plasma Environment Research Facility being built as a user facility at Harbin Institute of Technology in China. It has been developed with a modular design to drive magnetic coils to generate magnetic fields and plasma for the physical experiments. In this paper, the modular design and component selection are proposed based on a calculation of parameter ranges of components and the number of modules followed by a simulation and an engineering test. Both the simulation and test results show the feasibility of the selected components and the number of modules to meet the designing requirements of the PPS.

An 18.3 MJ charging and discharging pulsed power supply system for the Space Plasma Environment Research Facility (SPERF). I. The overall design.

The Space Plasma Environment Research Facility (SPERF) is a new ground-based experimental device for fundamental research studies on space plasma currently under construction at Harbin Institute of Technology in China. Scientific objectives of the SPERF include studying the asymmetric reconnection dynamics relevant to the interaction between the interplanetary and magnetospheric plasmas, reproducing the inner magnetosphere to simulate the processes of trapping, acceleration, and transport of energetic charged particles restrained in a dipole magnetic field configuration, and revealing the physical mechanism of the dipolarization front in the magnetotail. The device comprises a vacuum chamber, 11 coils consisting of 18 groups of sub-coils that are independently programmablely energized, and the plasma source system to provide the magnetic field and the plasma required by the physical experiments. Thus, each of these 18 groups of sub-coils requires a separate pulsed power supply; furthermore, the 18 pulsed power supplies constitute the pulsed power supply system of the SPERF of which the total storage energy is up to 18.3 MJ, and the technical challenges have to be overcome. The power supply energizing a dipole field coil (labeled OJC coil) wired by the copper wire to provide a dipole magnetic field is the most energetic power supply (labeled OJC power supply) with a 2.42 MJ, 16.8 mF capacitor bank charged to 20 kV. The OJC power supply delivers a current with a peak of 18 kA for a rise time of ∼26.69 ms, and the duration of the current is not less than 95% of the peak over 10 ms to the OJC coil. Meanwhile, the most challenging power supply is the power supply labeled poloidal field power supply with a 5.04 mF capacitor bank charged to 20 kV, which provides the excitation current for the load coil set with the current not less than 360 kA at the typical time of 0.11 ms to produce the sufficient growth of the magnetic field that the experiments need. In this paper, the overall design of the pulsed power supply system, the design concept of the modularization, and the principle selection basis of the key components are presented. The technical details of each power supply will be demonstrated in the future.