In this paper we present time-discretized spectra of spark discharges in air, N2 and O2. In previous work, a system for temporally resolved spectral analysis of extreme ultraviolet (EUV) and vacuum ...ultraviolet (VUV) emission from spark discharges was presented, along with some initial results. As was noted in this paper, statistical variances and the lacking of an apparatus sensitivity profile limited the usability of the data obtained. We have investigated the cause of these variances and improved the setup to reduce their effect. We also investigated the apparatus sensitivity profile to correct the intensity of measured lines. Newly obtained spectra in dry air, N2 and O2 are presented. Air and N2 show high emission in the vicinity of 100 nm, where direct photoionization of molecular oxygen is possible, in the first 250 ns of the discharge. We conclude this emission originates from nitrogen, which has several intense molecular transitions in this region. This finding is confirmed by our experimental results which show the emission in this region is much lower in oxygen.
Water-vapor fed electrolysis, a simplified single-phase electrolyzer using a proton-exchange membrane electrode assembly, achieved >100 mA cm−2 performance at <1.7 V, the best for water-vapor ...electrolysis to date, and was tested under various operating conditions (temperature and inlet relative humidity (RH)). To further probe the limitations of the electrolyzer, a mathematical model was used to identify the overpotentials, local water activity, water content values, and temperature within the cell at these various conditions. The major limitations within the water-vapor electrolyzer are caused by a decreased water content within the membrane phase, indicated by increased Ohmic and mass transport losses seen in applied voltage breakdowns. Further investigations show the water content (λ, mole of water/mole of sulfonic acid) can decrease from 13 at low current densities down to 6 at high current densities. Increasing the temperature or decreasing RH exacerbates this dry-out effect. Using our mathematical model, we show how these mass transport limitations can be alleviated by considering the role of water as both a reactant and a hydrating agent. We show that low cathode RH can be tolerated as long as the anode RH remains high, showing equivalent performance as symmetric RH feeds.
Abstract
Direct-current ionization breakdown in argon at very high voltage on the low-pressure branch of the Paschen curve is studied by means of kinetic simulation. The employed ...particle-in-cell/Monte Carlo collision model tracks the motion of electrons, ions and fast neutral atoms, as well as their collisions with the background gas. Secondary electron emission due to the bombardment by ions and fast atoms, as well as backscattering of different species on the electrode surfaces are also consistently accounted for. To validate the model, we compare the Paschen curve predicted by kinetic simulations against published experimental results as well against the prediction of a reduced (fluid) model. The model is then applied to predict, for the first time, the low-pressure branch of the Paschen curve for argon gas in the 10–300 kiloVolt range of applied voltage. One of the findings is the existence of a turning point on the Paschen curve at
V
b
r
≈
20
k
V
and
p
d
≈
0.08
T
o
r
r
⋅
c
m
, where
V
b
r
is the breakdown voltage and the reduced pressure
p
d
is the product of the gas pressure with the inter-electrode distance. According to our analysis, the presence of the turning point is due to the phenomena of electron and ion runaway in high electric field. We further investigate the role of the heavy species (i.e. ions and fast neutral atoms) in sustaining the Townsend discharge at high voltage and thus setting the breakdown threshold. Specifically, the role of fast atoms is significant over the entire low-pressure branch of the Paschen curve due to their contribution to both ionization and secondary electron emission. Also, the ions, as the precursor for the fast atoms, show an important influence on the latter process. The newly predicted low-pressure branch of the Paschen curve for argon at high voltage should provide an essential reference for the design of high-voltage devices, e.g. circuit breakers in electrical power transmission.
Abstract
According to the abnormal curve of opening characteristics in the process of double pulse test, the failure of 6.5kV/100A SiC module is judged, and it is preliminarily concluded that the ...gate of the module is damaged; The failure of the module is located by means of module anatomy, static characteristics test and chip screening test. It is concluded that the failure of the module is caused by the abnormality of two SiC MOSFET chips in the module; The damage of the chip was located by using stereomicroscope, OBIRCH, SEM and other equipment, and the root cause of MOSFET failure was studied by stripping anatomy. The preparation process of the gate and passivation strip on the MOSFET was poor, and the introduction of defects led to the breakdown of the gate unable to withstand high voltage.
Coherent optical links improve spectral efficiency over their intensity-modulation direct-detect (IM-DD) counterparts using advanced modulation schemes such as quadrature phase shift keying (QPSK) ...and quadrature amplitude modulation (QAM), and by utilizing dual polarization (DP) of light. This increase in spectral efficiency also leads to stringent requirements for the link components. The transmitter (TX) must simultaneously achieve high bandwidth (BW), linearity, output swing, and reliability. In this article, we present a silicon-photonic Mach-Zehnder modulator-based optical TX on an Silicon-on-Insulator (SOI) process, and linear, high-swing SiGe drivers on 130-nm BiCMOS process. The output stage of the driver uses a voltage breakdown enhancement technique to ensure the reliability of the TX. A resistor-based capacitor splitting technique is introduced, and aided by other methods such as zero-peaking and degeneration, the targeted gain, BW, swing, and linearity for the driver are realized. The driver achieves a differential swing of 6 V peak-to-peak, a total harmonic distortion (THD) of 3.6%, and more than 40 GHz of electrical BW. Co-designed and co-packaged with the silicon-photonic modulators, the TX achieves 272 Gb/s/wavelength with DP-16 QAM at 6-V peak-to-peak driver swing and exceeds 0.5 Tb/s/wavelength data rates with DP-16 QAM at 2.4-V peak-to-peak driver swing. The low-cost, compact, and all-Si/SiGe design matches the required optical SNR performance of LiNbO 3 modulators with III-V drivers at 34 Gbaud.
Noble liquid radiation detectors have long been afflicted by spurious electron emission from their cathodic electrodes. This phenomenon must be understood and mitigated in the next generation of ...liquid xenon (LXe) experiments searching for WIMP dark matter or neutrinoless double beta decay, and in the large liquid argon (LAr) detectors for the long-baseline neutrino programmes. We present a systematic study of this spurious emission involving a series of slow voltage-ramping tests on fine metal wires immersed in a two-phase xenon time projection chamber with single electron sensitivity. Emission currents as low as 10−18 A can thus be detected by electron counting, a vast improvement over previous dedicated measurements. Emission episodes were recorded at surface fields as low as ∼ 10 kV/cm in some wires and observed to have complex emission patterns, with average rates of 10–200 counts per second (c/s) and outbreaks as high as ∼ 106 c/s. A fainter, less variable type of emission was also present in all untreated samples. There is evidence of a partial conditioning effect, with subsequent tests yielding on average fewer emitters occurring at different fields for the same wire. We find no evidence for an intrinsic threshold particular to the metal-LXe interface which might have limited previous experiments up to fields of at least 160 kV/cm. The general phenomenology is not consistent with enhanced field emission from microscopic filaments, but it appears instead to be related to the quality of the wire surface in terms of corrosion and the nature of its oxide layer. This study concludes that some surface treatments, in particular nitric acid cleaning applied to stainless steel wires, can bring about at least order-of-magnitude improvements in overall electron emission rates, and this should help the next generation of detectors achieve the required electrostatic performance.
Research is devoted to investigation of properties of pulsed explosive emission cathodes for X-ray tubes. Three types of annular explosive emission cathodes were studied: metal ceramic with slits (of ...a comb-shaped kind), ring metal ceramic, and carbon ceramic. A pulsed high-voltage generator used in experiments is characterized with the following parameters: voltage pulse full-width at half-maximum is about 20 ns, pulse voltage amplitude is up to 150 kV, and pulse repetition rate is up to 200 Hz. The installation makes it possible to study demountable models of pulsed X-ray tubes of different designs. Current and voltage waveforms corresponding to different operation modes and rates of rise of X-ray tube anode voltage were analyzed. The obtained characteristics of explosive cathodes depend on the cathode's material, the shape, and the supply voltage of the primary energy storage. The current pulse duration for the ring carbon-ceramic cathode is considerably lower than that for the other cathodes, although it generates a higher radiation dose rate.
The phenomena during recovery of voltage after current interruption of vacuum interrupters are reviewed. Metal vapor, post-arc plasma, droplets and the effects of a molten contact surface may be ...involved in breakdown after current-zero. Sintered CuCr contact material has proven to be the one and only choice for vacuum circuit breakers. What justifies the better performance compared to other materials and in particular pure copper? Many investigators have tried to get more clarity on the process of breakdown initiation after current-zero, however, hardly succeeded in the past 50 years. This paper gives a description of the main findings. It summarizes the condition of vacuum interrupter contacts after high-current interruption for CuCr and Cu contacts. Measured breakdown probabilities and breakdown rates are evaluated and discussed. Small metal droplets ejected during arcing and after current-zero seem to play only a minor role as well as solid protrusions. The largest impact originates from the contact surfaces melted by the arc remaining liquid for a considerable time after current-zero. Large hot droplets and protrusions drawn out of the liquid are suspected to initiate breakdown at gross electric field strengths exceeding 8 kV/mm. Key parameter is the surface temperature and the properties of the liquid contact material. If the metal vapor density exceeds 10^{22}/{\mathrm {m}}^{3} at higher surface temperatures-equivalent to a line integral of the density across the contact gap of 4 x 10^{19}/{\mathrm {m}}^{2}, a Townsend discharge in metal vapor is feasible.
This study sought to apply nanotechnology to develop the electrical characteristics of palm oil. Experiments were conducted using three types of nanoparticles: zinc oxide (ZnO), titanium dioxide ...(TiO2), and barium titanate (BaTiO3). The nanofluid samples were prepared by mixing the nanoparticles with palm oil using various processes. In the first scenario, a combination of palm oil with nanoparticles at 0.01 vol% was created, while the next sample had 0.03 vol% of nanoparticles. The samples were then fully dispersed using a magnetic stirrer, followed by ultrasonic dispersal in order to ensure homogeneity of the nanofluid. The electrodes were set 2.5 mm apart and the test was performed six times on each test sample in compliance with the IEC 60156 standard. The voltage breakdown characteristics were recorded for each of the liquids at temperatures varying from 35 °C to 90 °C. The results showed that for the palm oil samples containing nanoparticles, the voltage breakdown was greater than for the samples containing unmodified palm oil.
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