Insulator Rings Research Articles

Design Optimization and Flashover Probability Evaluation of a 3 MV, 3.4-m-Diameter Four-Level Axial Vacuum Insulator Stacks for a 15 MA Z-Pinch Accelerator

A four-level axial insulator stack is designed for a 15 MA Z-pinch accelerator. The height and diameter are 1.5 m and 3.4 m. The two upper levels operate at 2.5 MV, while the two bottom levels operate at 3.0 MV. The insulator ring stages in series, the vacuum flares, and water flares are optimized in details. By reiterative optimizations, the two upper levels consist of five 5-cm-thick insulator rings and four 0.8-cm-thick grading rings. While the two bottom levels consist of six insulator rings and five grading rings with the same individual insulator and grading ring. The inductance of each level is 14.02 nH, 15.48 nH, 18.71 nH, and 20.88 nH, respectively. The equivalent inductance is 4.21nH with the four levels in parallel. The voltage variations from average for the four levels are within ±4.9%, ±4.9%, ±2.1%, and ±2.2%, respectively. At the average operating electric field of 100 kV/cm, the predicted flashover probability for the two upper level and the two bottom level insulator stacks are about 0.29% and 0.53%, respectively.

Aharonov-Bohm Interference and Phase-Coherent Surface-State Transport in Topological Insulator Rings.

We present low-temperature magnetotransport measurements on selectively grown Sb2Te3-based topological insulator ring structures. These devices display clear Aharonov-Bohm oscillations in the conductance originating from phase-coherent transport around the ring. The temperature dependence of the oscillation amplitude indicates that the Aharonov-Bohm oscillations originate from ballistic transport along the ring arms. We attribute these oscillations to the topological surface states. Further insight into the phase coherence is gained by comparing with similar Aharonov-Bohm-type oscillations in topological insulator nanoribbons exposed to an axial magnetic field. Here, quasi-ballistic phase-coherent transport is confirmed for closed-loop topological surface states in the transverse direction enclosing the nanoribbon. In contrast, the appearance of universal conductance fluctuations indicates phase-coherent transport in the diffusive regime, which is attributed to bulk carrier transport. Thus, it appears that even in the presence of diffusive p-type charge carriers in Aharonov-Bohm ring structures, phase-coherent quasi-ballistic transport of topological surface states is maintained over long distances.

Design and Development of 0.3-T Toroidal Field Coil System for Small-Sized MT-II Spherical Tokamak

The achievement of a high toroidal magnetic field in a small spherical tokamak is challenging because of the small bore area in the central cylinder of the vacuum vessel. In this paper, we present a toroidal field coil of 0.3 T at the center of the MT-II tokamak. It has been designed, developed, and tested for installation at Pakistan Tokamak Plasma Research Institute (PTPRI). The coil is made of highly pure oxygen-free copper. It has a cross-sectional area of 10 × 15 mm2 (150 mm2) for the flow of an approximately 20-kA current to produce a 0.33 T toroidal magnetic field at the center of the tokamak. Mechanical support for the central stack of the inner legs is provided by a twisted grooved nylon cylinder to control the torque and attractive forces. The repulsive force density between the joints of the outer and inner legs is balanced by nuts and bolts along with an insulated ring of Teflon and an isolated metallic clamp from both ends. This compressive force also reduces connection resistance. The simulated currents and magnetic field are confirmed from the experimental results as well.

Development of simple drift tube design for ion mobility spectrometry based on flexible printed circuit board material

A study on the use of flexible printed circuit board material for the construction of drift tubes for ion mobility spectrometry is reported. This is significantly less complicated than the conventional approach based on stacked electrode and insulator rings, as the material can simply be rolled up to obtain a string of circular electrodes. The size and spacing of the electrodes was found to have a strong effect on the resolving power. For an optimized geometry with electrodes of 1.5 mm width at a pitch of 3.5 mm resolving powers of up to 80 were achieved for quaternary amines introduced by electrospray ionization into a drift tube of 10 cm length and an applied voltage of 4200 V. This performance was found to be comparable to that of a conventional drift tube based on stacked rings with otherwise identical geometry and operating conditions. The entire instrument was constructed in-house. Its utility was demonstrated with the determination of the C12, C14 and C16 benzalkonium ions in several commercial cleaning products with limits of detection of 20, 25, and 38 μg L−1, respectively.

Quantitative Analysis of Insulator Degradation in a Single Layer Solenoid by Renormalization of the Transmission Parameter

In this paper, a novel method to quantitatively analyze insulator degradation in a single layer solenoid is proposed. The suggested method employs renormalization of scattering parameters to efficiently detect changes of permittivity in a degraded solenoid. Firstly, a transmission line model, including a locally degraded part in the insulator, was developed, and it was determined that the phase information of the transmission parameter was very informative to check the permittivity change in the transmission line. To check the workability of this idea in a solenoid, a 30-turn single-layer solenoid was designed and fabricated, and 51 degraded states for mimicking insulation deterioration in each turn were introduced by installing additional insulator rings, which increased local relative permittivity. The phase data of the measured transmission parameter turned out to be useful for quantifying changes of the insulator in the solenoid. To maximize the detectability, the measured scattering parameters were renormalized with different reference impedances, which was very useful for detecting degradation in the transmission parameter. In this paper, detailed procedures for quantitatively analyzing degradation of an insulator are proposed and we verify that the suggested renormalization technique is very promising for effectively evaluating the degradation of a solenoid.

Performance and plume evolutions during the lifetime test of a Hall-effect thruster

To demonstrate the qualifications of the thruster lifetime, performance and reliability design, an 8000-h ground test of a Hall-effect thruster was conducted. Except for the ignition stage, the thruster operated at the nominal condition with a gas flow rate of 53.7 sccm and a discharge current of 4.2 A. In this paper, the research focuses on the evolutions of the thruster performance parameters and plume plasma properties during the long-duration (about 8240 h) test. An optical imaging system was developed to observe the erosion configuration of the insulator rings. The far-field diagnostic instruments consisted of a Langmuir probe, a Faraday probe and a Retarding Potential Analyzer. These probes were configured to measure the local plasma potential, plasma density, ion current density and ion energy. The results show that the thrust value first increases and then decreases during the first 2000 h. At the stage ranging from 2000 to 8240 h, the thrust value shows a slowly rising trend on the whole and stabilizes at the end. The thruster plume exhibits the phenomena of beam expansion and beam contraction at the early-to-mid lifetime stage and the mid-to-late lifetime stage, respectively. During these two periods, the relevant variations of the plume plasma parameters are related to the erosion configuration of the insulator ceramic walls. It also suggests that the evolutions of the thruster performance are largely determined by the properties of the plume plasma, especially the behaviours of the beam ions.

Research on the Key Technology of Medium Voltage Environmental Protection Metal-enclosed Switchgear

This article introduces environmentally-friendly metal-enclosed switchgear, and comprehensively summarizes the development status, technical characteristics, technical difficulties and development trends of solid-insulated ring network cabinets and environmentally-friendly gas-insulated switch cabinets. The development status of solid insulated ring network cabinets and environmentallyfriendly gas insulated switch cabinets are reviewed, and their technical characteristics are summarized in terms of volume, structure, maintainability, safety and environmental adaptability. Focus on the analysis and study of the technical difficulties of solid insulated ring network cabinets and environmentally friendly gas insulated switch cabinets, and pointed out the partial discharge control of the surface of the insulating parts, the strengthening of the sealing, the cost control, the recycling and utilization of epoxy resin, the optimization of insulation, and the breaking capacity. The guarantee of the quality, the selection and recovery of mixed gas are their future development trends. It provides a useful reference for the development and improvement of environmentally-friendly metal-enclosed switchgear.

Plasmonic multi channel filter based on split ring resonators: Application to photothermal therapy

In this study, we developed and analyzed a multichannel filter based on multiple plasmonic split ring resonators. In the proposed structure, split ring resonators were coupled to T-shaped and straight waveguides. The field distribution and transmission characteristics were investigated using the finite-difference time-domain method. In the proposed filter, the split ring resonators, and straight and T-shaped waveguides were made of air situated in a silver background. The proposed structure can confine light to sub-wavelength dimensions and it can be utilized in photonic integrated circuits. The results showed that the proposed structure functioned as a typical filter and the electromagnetic wave energy at different wavelengths could be trapped in different insulator rings. The sensitivity factors and dependence of the multichannel filter on the coupling lengths (Li) and ring widths (Ci) were also investigated. Based on the linear relationships with the refractive indices and resonance wavelengths in the ring resonators, sensitivity factors could be obtained for different rings. By increasing the refractive index, the resonance wavelengths exhibited considerable red shifts. The proposed structure with high transmission efficiencies and resonance wavelength ranges (near infrared) will be useful in highly integrated optical circuits, photothermal therapy, and cancer treatment.

Topological insulator ring with magnetic impurities

Topological insulators exhibit gapless edge or surface states that are topologically protected by time-reversal symmetry. However, several promising candidates for topologically insulating materials (such as Bi$_2$Se$_3$ and HgTe) contain spinful nuclei or other types of magnetic impurities that break time-reversal symmetry. We investigate the consequences of such impurities coupled to electronic edge states in a topological insulator quantum ring threaded by a magnetic flux. We use spin conservation and additional symmetry arguments to derive a universal formula for the spectrum of propagating edge modes in terms of the amplitude of transmission through the impurity. Our results apply for impurities of arbitrary spin. We show that there exists an energy regime in which the spectrum becomes nearly independent of the flux and significant spectral gaps form. We further analyze the electron-impurity entanglement entropy, finding that maximal entanglement occurs near the gaps in the spectrum. Our predictions can be investigated with quantum ring transport interference experiments or through spin-resolved STM measurements, providing a new approach to understand the role of impurities in topological insulator edge transport.

Thermo‐physical and kinetics parameters determination and gases emissions of self‐ignition of sieved rice husk of different sizes on a hot plate

AbstractHot plate self‐ignition standard tests at constant temperature have been performed on a paddle rice husk of size 75 to 1500 μm and a sieved rice husk of sizes 75 : 106, 106 : 120, and 120 : 150 μm. Modified tests using insulated metal ring have been investigated and compared with the standard test. Gases emissions showed that CO is the main component, and its maximum percentage occurs at the maximum temperature and depends on the dust layer thickness. It was found that as the thickness of dust layer increases, the maximum temperature and its corresponding time increase. Ring with insulation showed lower maximum and ignition temperature and ignition time compared with that without insulation. The flue gases temperature and CO% and CO2% emissions were higher in case of insulated ring. Thermal and physical properties as density, thermal conductivity, heat transfer coefficient, and kinetic parameters as activation energy and frequency factor have been determined. The activation energy of the sieved husk (75 : 106, 106 : 120, 120 : 150 μm) and paddle husk was 174.76, 183.37, 189.1, and 206.1 kJ/mol, respectively. Also, (QA0) factors were 2.696 × 1014, 6.211 × 1016, 6.105 × 1019 and 3.0461 × 1016 (J/kg s), respectively. It has been noted that as the dust particle size increases, the (E) and (QA0) values increase. © 2017 Curtin University of Technology and John Wiley & Sons, Ltd.

Analysis of vacuum insulator stack flashover probability with statistical model

The statistical model is used as a typical method for vacuum insulator stack flashover probability calculation. We have calculated the stack flashover probability and the g factors by which a flashover will change the voltages on the each of the insulator rings with different conditions. The calculated results show that the real performance of insulator stack characteristics with the multi-stage and large circumferential transit time. The matrix a in the statistical model was predigested to reduce the g calculation time and make the probability calculation accurate. Finally, analysis based on fixed distance between insulation rings showed that there were some optimized ring numbers with maximum voltage amplitude and electrical field amplitude. This conclusion could be used for evaluation of insulation ring number in insulator stack design.

Mechanically flexible nanoscale silicon integrated circuits powered by photovoltaic energy harvesters

In this work, we demonstrate mechanically flexible extremely thin silicon on insulator (ETSOI) ring oscillators with a stage delay of ∼16ps at a power supply voltage of 0.9V. Extensive electrical analyses of the flexible ETSOI devices reveal the unchanged properties of the devices during the layer transfer process. Furthermore, we discuss the use of flexible silicon and gallium arsenide photovoltaic energy harvesters for powering flexible ETSOI ring oscillators under different illumination conditions. Our results illustrate innovative pathways for the implementation of optically powered flexible ETSOI technology in future flexible hybrid electronics.

Research transmission characteristics of a plasmonic multiple-ring shaped metal-insulator-metal waveguide

A multiple-ring shaped metal-insulator-metal (MIM) plasmonic waveguide is proposed and the transmission characteristic is investigated using the finite-difference time-domain (FDTD) method. The results show that the proposed structure has typical filtering function and the electromagnetic wave energy of different wavelengths can be trapped in different insulator rings. The resonance theory is employed to analyze the trapping phenomenon successfully. This kind of multiple-ring shaped MIM waveguide may useful for plasmonic designs.

Optimization of the vacuum insulator stack of the MIG pulsed power generator

The MIG multi-purpose pulsed power machine is intended to generate voltage pulses of amplitude up to 6 MV with electron-beam loads and current pulses of amplitude up to 2.5 MA and rise time '00 ns with inductive loads like Z pinches. The MIG generator is capable of producing a peak power of 2.5 TW. Its water transmission line is separated from the vacuum line by an insulator stack. In the existing design of the insulator, some malfunctions have been detected. The most serious problems revealed are the vacuum surface flashover occurring before the current peaks and the deep discharge traces on the water-polyethylene interface of the two rings placed closer to the ground. A comprehensive numerical simulation of the electric field distribution in the insulator of the MIG generator has been performed. It has been found that the chief drawbacks are nonuniform voltage grading across the insulator rings and significant enhancement of the electric field at anode triple junctions. An improved design of the insulator stack has been developed. It is expected that the proposed modification that requires no rearrangement of either the water line or the load-containing vacuum chamber will provide higher electric strength of the insulator.

Design of a 10MPa Nanosecond Gas Switch with Adjustable Gap

This paper introduces a method to adjust the gap distance of nanosecond gas switch from outside when it is filled with high pressure gas. By using a two-stage planetary gear train and a pinion-and-rack device the gap between the electrodes can be linearly adjusted. The adjusting precision is 0.05 mm and adjustment range is 0 to 10 mm. The sealing of the insulator ring, rotation axle and outside conductors is designed. The performance of the rotation axle is pretty well under 12MPa gas pressure, air leakage not found. Experimental study on switch discharging is carried out by using a high voltage nanosecond pulse generator. The results show the output voltage of the pulse can reach 600kV by adjusting the switch gap. The rise-time of the pulse can be shortened form 3.5ns to 1ns.

Investigation of the Load Current Tail Phenomenon on the Qiangguang Generator

The phenomenon of load currents with long decaying tails can be found on many pulsed-power generators, such as the Z accelerator at Sandia National Laboratories in the U.S. and the Angara-5-1 facility in Russia. In this paper, the reasons that cause the load current tail on the Qiangguang generator are investigated. The experiments were carried out using two insulator stacks with different diameters and insulator ring numbers. The results show that the current tail on the Qiangguang generator is not caused by measurement error but rather by electrical flashover across the surface of the insulator stack and by leakage current through the water between the stack and the outer wall of the water-filled transmission line that feeds the vacuum section on the Qiangguang generator. Also, an equivalent circuit for the Qiangguang generator was constructed and used in PSpice simulations. By adding a time-dependent resistance in parallel with the load, the simulations were able to produce current waveforms that closely match those recorded during experiments. In additional experiments, an optical fiber was used with a photoelectric cell to collect the flashover light emitted from the surface of the vacuum-insulator rings. The data collected show that the fiber signal and the beginning of the load current tail are time correlated. More recently, a new insulator stack made of Rexolite was acquired and used in yet more experiments. The results of these experiments show that, by using the new insulator stack, the onset of the load current tail phenomenon is significantly delayed. The data from all of the experiments show that stack flashover is the main cause of the load current tail on the Qiangguang generator.

Bound states and persistent currents in topological insulator rings

We analyze theoretically the bound state spectrum of an Aharonov Bohm (AB) ring in a two-dimensional topological insulator using the four-band model of HgTe-quantum wells as a concrete example. We calculate analytically the circular helical edge states and their spectrum as well as the bound states evolving out of the bulk spectrum as a function of the applied magnetic flux and dimension of the ring. We also analyze the spin-dependent persistent currents, which can be used to measure the spin of single electrons. We further take into account the Rashba spin-orbit interaction which mixes the spin states and derive its effect on the ring spectrum. The flux tunability of the ring states allows for coherent mixing of the edge- and the spin degrees of freedom of bound electrons which could be exploited for quantum information processing in topological insulator rings.

Vacuum Surface Flashover Characteristics and Secondary Electron Emission Characteristics of Epoxy Resin and FRP Insulator

Neutral beam injectors (NBI) used for JT-60 are required to generate negative ions of 500 keV energies. To produce such high-energy ions, the electrostatic accelerators consisting of 3-stage of electrodes and three insulator rings are applied. The insulators are made of Fiberglass Reinforced Plastic (FRP) which is composed of epoxy resin and glass fibers. The surface discharges along the insulators are one of the most serious problems in the development of NBI. To increase the hold-off voltage against surface flashover events, it is necessary to investigate the FRP and epoxy resin insulator properties related to surface discharges in vacuum. This paper describes surface flashover characteristics for epoxy resin, FRP and Alumina samples under vacuum condition. In addition, the measurements of secondary electron emission (SEE) characteristics are also reported. These are important parameters to analyze surface discharge characteristics of insulators in vacuum.

Tunable polymer/silicon over insulator ring resonators

A tunable ring resonator RR formed from Si/SiO2 waveguides with an electro-optic polymer cladding is proposed with em- phasis on the trade-off between the tuning voltage and ring radius. The ring resonator circuit combines the advantages of Si/SiO2 and polymer technologies. The advantages of this hybrid ring design over previously proposed tunable silicon rings include an increased switching speed, from 5 GHz to 20 to 100 GHz, single-polarity instead of dual-polarity voltage tuning and a voltage-independent quality factor. The hybrid de- sign also displays a greater free spectral range 1.85 nm instead of 0.1 nm and a wider tuning range 0.925 nm instead of 0.05 nm and is further compatible with silicon devices. Moreover, the device has a high quality factor of 3.410 4 . © 2008 Society of Photo-Optical Instrumentation

High-speed polymer/silicon on insulator ring resonator switch

We design a high-speed tunable electro-optical (EO) polymer-clad silicon over insulator (SOI) racetrack resonator with a 80-µm length and 5-µm radius that exhibits a switching speed of 100 GHz, a tuning voltage of 6.81 V, and an extinction ratio of 109.55 dB. This work employs high electro-optical coefficient polymers (r33=1000 pm/V), which are currently under development, to implement very high speed switches.