High Voltage Probe Research Articles

Ferroelectric Domain Wall p-n Junctions.

We have used high-voltage Kelvin probe force microscopy to map the spatial distribution of electrical potential, dropped along curved current-carrying conducting domain walls, in x-cut single-crystal ferroelectric lithium niobate thin films. We find that in-operando potential profiles and extracted electric fields, associated with p-n junctions contained within the walls, can be fully rationalized through expected variations in wall resistivity alone. There is no need to invoke additional physics (carrier depletion zones and space-charge fields) normally associated with extrinsically doped semiconductor p-n junctions. Indeed, we argue that this should not even be expected, as inherent Fermi level differences between p and n regions, at the core of conventional p-n junction behavior, cannot occur in domain walls that are surrounded by a common matrix. This is important for domain-wall nanoelectronics, as such in-wall junctions will neither act as diodes nor facilitate transistors in the same way as extrinsic semiconducting systems do.

Electron transfer induced contact-electrification at oil and oleophobic dielectric interface

The oil dielectric has been used for enhancing the performance and durability of triboelectric nanogenerators (TENGs), but little is known about the contact-electrification (CE) (or triboelectrification) characteristics of the oil. Here, the CE behavior of different oil droplets with oleophobic surfaces is systematically investigated by dropping oil on a single-electrode TENG. The electrification trace is clearly imaged using a high-voltage scanning probe approach. Thermally stimulated discharge techniques are adopted for studying the detailed trapping characteristics of contact-generated charges with a homemade instrument, and the results are consistent with the thermionic emission model. The research provides systematic understandings on oil CE with oleophobic surfaces, together with general investigation paradigms and characterization methods for electrification phenomena on surfaces. Meanwhile, because typical oils are regarded as free of ions, their CE is attributed to electron transfer, which may contribute to the understanding of fundamental CE mechanisms.

Study on Characteristics of Special ICP-Heated Wind Tunnel by Improved HCN Laser Interferometer

The results of the experimental investigation of a plasma jet created by a large-volume, high-enthalpy plasma wind tunnel are presented. The plasma wind tunnel generates an electric field by applying a time-varying power with a frequency of 440 kHz, which excites the plasma and ejects it from the nozzle due to the pressure difference. This article uses high-voltage probes, cameras, and laser interferometers to understand the properties of plasma wind tunnels. In order to diagnose the electron density at different positions of the plasma jet, a laser interferometer is improved in this article. The waveform of the power supply, the length of the plasma jet, and the brightness and electron density of the plasma jet were obtained during the experiment. The results show that the electron density increases by about an order of magnitude when the supply voltage rises from 8 to 12 kV. As the distance increases by 150 mm, the plasma electron density decreases by a factor of 1.5 or 2, but the electron density increases with the increase of pressure. Finally, the electron density distribution characteristics can be explained by the simulation results.

Helium plasma jet interaction with different target materials and the plasma characteristics on the irradiation area

The experimental study on the dynamic behavior of helium atmospheric pressure plasma jet exposed on the surface of different conductivity is reported in this article. Electrical, optical, and gas dynamics characteristics are monitored using a high voltage probe, current probe, and imaging technique. The turbulence-free plasma jet length is estimated from the image of the plasma jet and correlated with the length estimated through the Electrohydrodynamic number (Ehd number). It has been shown that plasma species strongly modify the gas dynamics on the contact surface. The irradiation area on agar gel, metal, and Teflon is observed and the different flow regimes (free jet, stagnant region, and accelerating region) are identified. The irradiation area is significantly broadened for the polymer-like substrate and intensity is higher close to the stagnant region. The excited nitrogen and OH intensity is higher than the other observed chemical species on the target surface. The turbulence is higher near the outer radius of the irradiated surface, and it increases with operating voltage. The chemistry of the water changes with the presence of the metal probe inside the water.

Transmission and multiple reflection mechanisms of guided streamers propagating through grounded annular electrode and interacting with grounded surface electrode

The repeatable dynamics and the reversal propagation of guided streamers remains a major question of fundamental physics. In this article, trains of positive guided streamers are generated within an atmospheric pressure plasma jet supplied in helium and polarized by a high-voltage nanosecond pulse generator. The device is completed by two distant targets: a grounded annular electrode (GAEL) coaxially centered around the capillary through which guided streamers can propagate, and a grounded surface electrode (GSEL) on which they can interact. The resulting transmitted and multiple reflected guided streamers are measured combining optical characterization (fast intensified charge-coupled device (ICCD) imaging) and electrical characterization (high voltage probe and current monitors). While the electrical approach provides information on the capacitive/conductive nature of the current peaks as well as on their positive/negative value, fast ICCD imaging distinguishes whether the guided streamers are incident, reflected or transmitted. Combining these two techniques allow us to demonstrate experimentally that the reflected streamers are negative contrarily to the others. Besides, four types of reflections have been highlighted: a reflection (r) at the outlet of the capillary, a reflection on the GSEL (R) and two reflections (r′ and r″) observed when an incident guided streamer passes through the GAEL. The two techniques agree that the characteristic propagation times are always shorter for reflected negative streamers than for the positive ones propagating forward. Hence, for a GAEL placed 3 cm away from the high voltage electrode, propagation time is 80 ns for reflection versus 250 ns for transmission. These characteristic propagation times are even shorter when the annular electrode is brought closer to the surface electrode with velocities typically higher than 300 km s−1. In addition, the intensity ratios of reflected/incident guided currents drop sharply, typically losing one decade over a counter-propagation length of only 3–5 cm. Finally, all these experimental data are utilized to build an equivalent electrical model that allow to better understand the dynamics of the guided streamers and explain their transmission and reflection modes upon their interaction with the two distant grounded electrodes.

Resistive High-Voltage Probe with Frequency Compensation by Planar Compensation Electrode Integrated in Printed Circuit Board Design

Resistive voltage dividers tend to have a highly non-linear transfer function as parasitic and stray capacitances exert an increasing influence with increasing frequency. The non-linear transfer function depends on the topology and resistors used and consists of a low-pass filter with an additional high-pass component in the GHz range. Due to the non-linear transfer function the measured signal differs from the original input signal. Here, we present an improved resistive voltage divider with additional compensation capacities to extend the linear bandwidth. With this new concept, the linear bandwidth is improved from 115 kHz to 88 MHz, while maintaining a DC input impedance of 10 MΩ. For high-voltage insulation and easy manufacturing, surface mounted resistors on a printed circuit board with a compensation electrode on the adjacent side are used. The performance of this resistive voltage divider is demonstrated by measuring a series of high-voltage pulses with an amplitude of 2.5 kVpeak-peak. The measured pulse rise time is about 16 ns, corresponding to an average slew-rate of 150 V/ns. Finally, the developed resistive voltage divider is successfully used to measure fast high-voltage transients required for advanced ion mobility spectrometers with integrated collision induced fragmentation.

Development of a High-Linearity Voltage and Current Probe with a Floating Toroidal Coil: Principle, Demonstration, Design Optimization, and Evaluation.

As the conventional voltage and current (VI) probes widely used in plasma diagnostics have separate voltage and current sensors, crosstalk between the sensors leads to degradation of measurement linearity, which is related to practical accuracy. Here, we propose a VI probe with a floating toroidal coil that plays both roles of a voltage and current sensor and is thus free from crosstalk. The operation principle and optimization conditions of the VI probe are demonstrated and established via three-dimensional electromagnetic wave simulation. Based on the optimization results, the proposed VI probe is fabricated and calibrated for the root-mean-square (RMS) voltage and current with a high-voltage probe and a vector network analyzer. Then, it is evaluated through a comparison with a commercial VI probe, with the results demonstrating that the fabricated VI probe achieved a slightly higher linearity than the commercial probe: of 0.9967 and 0.9938 for RMS voltage and current, respectively. The proposed VI probe is believed to be applicable to plasma diagnostics as well as process monitoring with higher accuracy.

Dynamic Electrical Characteristics of 4H-SiC Drift Step Recovery Diodes of High Voltage

In order to evaluate the prospects of high-voltage (HV) silicon carbide (SiC) drift step recovery diode (DSRD) on pulsed power field and feasibility of outputting pulse with fast rise rate, a parallel trigger circuit is adopted and the circuit parameters affecting pulse characteristics are discussed. The simulation model of the circuit based on Sentaurus TCAD is established, in which the effects of various circuit parameters on the peak voltage and the prepulse voltage of output pulse are discussed, including the forward pumping time, the input voltage, and the inductance of reverse loop. The suitable forward pumping time and reverse loop inductance value are determined as 80 ns and 200 nH in this circuit, respectively. Experiments show that the 2.302-kV output pulse with the rise time of 1.236 ns can be obtained by HV SiC DSRD developed in our laboratory. Excluding the influence of HV probe, the actual rise time is 1.011 ns. To reduce prepulse voltage, it is effective to increase the input voltage or the inductance value of reverse loop, while the forward pumping time has little influence on it. Along with the increase of input voltage, the peak value and the rise rate of output pulse increase. Consequently, in order to improve the quality of output pulse, the input voltage should not be too low (≥200 V), while the forward pumping time and the inductance value of reverse loop should be moderate.

Reconfiguration of an Electrothermal-Arc Plasma Source for In Situ PMI Studies

An electrothermal-arc plasma source (ET-Arc) has been developed to produce transient plasma heat and particle fluxes similar to those produced by edge localized modes onto divertor plasma-facing components in tokamaks. The ET-Arc utilizes a capacitive discharge to send current through a 4-mm-diameter, 9-cm-long capillary source liner. The liner material is ablated to form a high-velocity plasma jet that impacts the target downstream. With the current discharge circuit configuration, pulse lengths are 1 to 2 ms in duration and deliver heat fluxes of 0.25 to 2.1 GW m−2. The plasma was previously characterized with optical emission spectroscopy (OES) on helium emission lines. The He I line ratios were interpreted with collisional radiative analysis to calculate ne and Te. The electron temperature and electron density ranged from Te = 1 to 5 eV and ne = 1022 to 1028 electrons/m3, respectively. Recently, the vacuum configuration and target of the ET-Arc device were modified to allow greater diagnostic access for plasma-material interaction (PMI) studies and diagnostic development. The diagnostic suite included two Tektronix high-voltage probes to measure the capacitor and discharge potentials, a discharge current monitor, Edgertronic SC1 high-speed cameras to image the discharge, and a FLIR SC4000 infrared camera to estimate heat flux on the target. The system used OES for plasma characterization, but a new Thomson scattering (TS) diagnostic has been implemented. This system is an Advanced Research Projects Agency - Energy (ARPA-E)-funded, portable diagnostic package for spectroscopic measurements of ne, Te, ni, Ti,, and vi, which includes both TS and OES. Additionally, a novel digital holography (DH) surface-imaging diagnostic was implemented to measure erosion rates in situ. Results from ex situ DH characterization of stainless steel targets exposed to the ET-Arc source indicated that surface erosion of ~150 nm per shot occurred and an in situ DH characterization of similar targets was planned. The arc-triggering system will be revised and optimized to better synchronize with the laser diagnostics. Details of the reconfigured ET-Arc source are reported here.

Method for determining the reliability of the ion current sensor with eight high-voltage probes

Method for determining the reliability of the ion current sensor with eight high-voltage probes

Effect of pressure on discharge mode transition in radio-frequency capacitively coupled micro-beam plasmas

Micro-beam radio-frequency (RF) capacitive discharges have been widely used in the plasma enhanced chemical vapor deposition of nanocrystalline particles such as nano silicon crystal. However, the plasma column shrinks radially at a sufficiently high gas pressures as manifested by their glow not entirely filling the radial cross-section of the discharge tube. This greatly limits the dissociation rate of gas in plasma. In order to obtain the information about the plasma column varying with gas pressure, the formation of different gas discharge mode under different pressure is discussed. In this paper the spatial characteristics of micro-beam RF capacitive discharges are investigated by using an intensified charged-coupled device (ICCD) and a single lens reflex camera (SLR camera). Furthermore, high voltage probe and current probe are used to record the electrical characteristics of the high voltage electrode. The results indicate that in a pure argon discharge, the discharge mode evolves from a glow discharge into a filament discharge with the increase of pressure. As the pressure continues to increase, the filament is split: a single channel of plasma is split into two or more filaments at a certain gas pressure. However, the glow discharge in a mixture of 99% argon and 1% hydrogen at a low pressure is observed: the plasma spreads throughout the tube. As the pressure increases, the filament disappears, and the plasma column still can be observed in the center of quartz tube. The glow shrinks in the radial center at a moderate pressure. At a high pressure, the "annulus" glow discharge is achieved as manifested by a glow ring on the surface of the discharge tube. In addition, in pure hydrogen discharges, the discharge mode evolves from the full-space glow discharge into an "annulus" glow discharge with pressure increasing. Finally, through the interaction between the electron heating by the radio frequency electric field and heat conduction of gas, the filament discharge in a low thermal conduction gas is explained. In addition, special attention is paid to the pure argon filamentation, which is the splitting of a single channel of plasma into two or more smaller filaments as a result of the skin effect.

A Practical Circuit Design for Measuring Output Voltage of High Voltage Frequency-modulated Power Supply

At present, the measurement of output high voltage at intermediate frequency or high frequency of AC power supply relies too much on expensive experimental equipment such as oscilloscope and high-voltage probe. In response to this problem, a design of measuring circuit of the output high voltage at intermediate frequency or high frequency of AC power supply is proposed. In this design, the output high voltage is sampled by setting tap on the high voltage side of the power transformer and using compensation capacitance. The AC voltage obtained by sampling is then converted into DC voltage and measured on gauge outfit. At the end of the article, the experiment shows that the design scheme in this paper has very small error in measurement and can meet the requirements of high voltage experiment for measurement accuracy. High-voltage AC power supply with this circuit can display the measurement of its output high voltage independent of expensive experimental equipment such as oscilloscope and high-voltage probe. Consequently, high-voltage AC power supply with this circuit can help save the cost of experiments and becomes more intelligent and more portable in the experimental situation where researchers are desired for the value of high voltage at intermediate frequency or high frequency output by high-voltage AC power supply.

A reliable data-driven model for Ablative Pulsed Plasma Thruster

Ablative Pulsed Plasma Thrusters (APPTs) are high specific impulse electric space propulsion system, but a reliable model equivalent of the experimental model is still unavailable. In this paper, a reliable model is developed based on APPT experimental data by using Machine Learning (ML) ecosystem. The goals of this study are to justify the accuracy and reliability of the newly built APPT model with the existing experimental and simulation model. For four sets of operating conditions, 600 experimental and simulation test operations are done. The experimental voltages and currents are measured with a high-voltage probe and a Rogowski coil, respectively. The simulation voltages and currents are gathered by running the respective simulation program. Comparison results show that the newly built APPT model has better accuracy and reliability than the simulated APPT model as compared to real APPT used in the experiment. This data-driven approach provides a novel way of designing a reliable alternative model of physical APPTs.

A multiple-approximation method to calibrate switch capacitive voltage dividers without standard probe in Tesla-type generators

When a capacitive voltage divider (CVD) in a component is calibrated, the introduction of a standard high-voltage (HV) probe usually affects the original field distribution of this component. Therefore, the voltage ratio of the CVD is affected, especially when the distance between the HV probe and the CVD is close. A multiple-approximation method to calibrate the CVD of gas switches in Tesla-type generator without a standard HV probe is being put forward. The basic idea is to calculate the theoretical switch voltage uth based on the equivalent circuit of this type of generators and to use uth to substitute the real voltage ur acquired by the standard HV probe to calculate the voltage ratio β for the CVD of a gas switch. Since the gas-gap resistance Rs of the switch is not zero, uth is not equal to ur, and β therefore deviates from the real value β0. To solve this question, two steps are implemented: first, β(d) at different gas-gap distances d is obtained; second, the true voltage ratio β(0) when d = 0 is extrapolated. The theoretical basis of this method was analyzed first. Then, it is verified by experiments. In the end, the uncertainty of this method is evaluated.

Evaluation of absolute charge density at the bottom of high aspect capillary holes exposed to a pulsed very high frequency plasma

Absolute values of the surface charge densities at the top and bottom of a capillary plate (CP) placed on a powered electrode were evaluated under the influence of pulse-modulated very high frequency (40 MHz) plasma. The peak-to-peak voltage at the top and bottom of the CP was measured using a high-voltage probe; this voltage was carefully calibrated, removing the influence of probe impedance. Based on the peak-to-peak voltage, the capacitances of the sheath and the CP were evaluated. Based on the average voltage, the surface charge density was evaluated for the plasma-on and off phases. A charge density of the order of 10−5 C m−2 was obtained at the bottom of the CP. Furthermore, two important observations were made during the plasma-off phase, namely: conservation of the surface charge density at the bottom of the CP and presence of the residual negative surface charge at the top of the CP.

Development of a prototype radio-frequency system for a radio-frequency quadrupole cooler buncher in the rare isotope science project.

Radioactive ion beams produced using the isotope separation on-line method in the Rare isotope Accelerator complex for ON-line (RAON) experiment are to be delivered with a beam emittance of around 3 π mm mrad, an energy spread of less than 10 eV, and a short beam bunch width of around 10 µs to meet the requirements of an electron beam ion source charge breeder. A radio frequency quadrupole cooler buncher (RFQ-CB) will be used to meet the beam quality requirements mentioned above. Our target bunching capacity of RFQ-CB is 108 ions/bunch for various ion species. Such a high bunching capacity requires an RF amplitude of ∼3 kV and a frequency range of 1.5-4.5 MHz in our RFQ-CB design. We designed and tested the prototype RF system composed of a helical resonator, a high-power RF amplifier, and high-voltage probes. To reduce heat load to the high voltage probes, we employed vacuum capacitors serially connected to the ends of helical resonators. In the experiment, we confirmed that our 4.5-µH helical resonators made of a 12-mm copper tube and variable vacuum capacitor with a capacitance range of 120-1120 pF can produce required voltages and frequencies using a 100-W RF amplifier. As a result, with 2.5-W RF output power, we obtained the maximum voltage amplitude of 1 kV at 4.5 MHz, which is equivalent to 6.4 kV with 100-W RF output power.

Designing and Fabrication of Switching High Voltage Power Supply for Nuclear Medicine Imaging Systems

This paper describes design considerations of the High voltage (HV) module with low ripple and good stability in order to improve the efficiency of nuclear imaging systems consist of Single Photon Emission Computed Tomography (SPECT). In the design of the current HV module, push-pull topology is preferred, due to the fact; it has a better efficiency in comparison with other technologies. The module receives a positive continuous voltage about 5-8 V as input, and provides a programmable positive or negative continuous voltage from 800-2500 V as output for a total load of 200-KΩ. The ripple of the output voltage is 10 mV that it is measured by laboratory equipment’s and safe high voltage (SHV) probe. The measured output power in the designed module is 25 W. Experiment results show that minimum efficiency at full load is around 65%. The proposed HV module shows a good stability, low ripple (noise), fast rise time. So, it can be used in SPECT or gamma camera imaging system to provide the constant voltage for PMTS.

Electromagnetic wave propagation in a fast pulse line ion accelerator.

The pulse line ion accelerator (PLIA) is a low-cost accelerator concept originally designed to accelerate heavy ions. Our group has been investigating the use of PLIA to accelerate light ions and believe a multi-stage PLIA could be useful for short half-life PET isotope production. The goal of this work was to develop a single prototype fast PLIA structure and demonstrate electromagnetic wave propagation using a high-voltage pulser. A 1.6m fast PLIA structure (wave speed>107 m/s) was constructed along with a high-voltage, sinusoidal pulse generator. The latter uses capacitive voltage doubling and spark gap switching. A step-up transformer couples voltage from the pulser to the PLIA coil. Voltage measurements on the coil were made in air using a high-voltage resistive probe, while capacitive probes placed along the length of the PLIA were used to measure wave propagation with the PLIA structure filled with transformer oil. Voltage measurements acquired on the primary and secondary coils of the transformer coupler in air demonstrated a peak-to-peak voltage step-up of 4.2 relative to the pulser DC charging voltage. The maximum voltage time-rate-of-change on the PLIA coil was 0.76×1013 V/s. Capacitive probe measurements indicated voltage oscillations on the PLIA coil with half-period equal to 43±0.9ns and wave speed (with oil) of 1.2×107 m/s. Average and peak accelerating gradients were conservatively estimated to be 0.44 and 0.60MV/m, respectively, with a charging voltage of 55kV. Wave propagation was demonstrated at these gradients without flashover at a vacuum pressure of 9×10-6 Torr. Submerging the pulser in oil would allow for charging voltages up to 150kV and produce accelerating gradients >1.2MV/m. Use of a multi-stage, fast PLIA for light ion acceleration could provide a low-cost complement to cyclotrons for the production of short half-life isotopes used for PET imaging, including carbon-11, nitrogen-13, oxygen-15, and fluorine-18.

Design and experimental study of high-voltage pulsed penning discharge source with grid electrode

A new design of high-voltage pulsed Penning discharge (HVPPD) source with grid electrode was proposed and investigated to provide a plasma channel for high current pulsed electron beam. The grid electrodes of concentric circle structure with different wire width, which were fabricated from stainless steel with thickness of 0.3 mm and shield rate ~10%. The pulsed Penning discharge process was inspected by means of high-voltage probe and digital camera. The results demonstrated that one whole Penning discharge process can be divided into two main stages, i.e. activating and high-current stages with different duration and intensity depending on the working parameters applied. The transport distance of plasma reached several decades of centimeters. With the higher magnetic field strength and working pressure, the HVPPD process operated more quickly and steadily. Comparatively, the grid electrode with 0.3 mm wire width exhibited the better discharge performance. Under the optimum condition of anode voltage 4.8 kV, magnetic field 0.18 T, working pressure 7 × 10−2 Pa and ballast resistor 20 Ω, the activating time was 21 μs and the repetitive accuracy can be controlled under 1 μs.

Experimental investigation of anode arc attachment area in DC arc plasma torch at low pressures

The anode area and anode erosion of a DC arc plasma torch with an external anode are experimentally investigated using different ambient pressures, arc currents, and anode configurations. A high-speed camera, high-voltage probe, electric probes, and a Schlieren system are utilized. The electric field in the anode area is measured using electric probes at arc electric currents lower than 100 A. It is found that a mean value of the arc electric field above the anode can be satisfactorily estimated in a non-intrusive way when the anode attachment is constricted. Anode erosion is proportional to a variable that can be compared in different experimental conditions just by quickly processing high-speed video footage, even while the plasma torch is in operation. Anode erosion decreases along with ambient pressure and it is lower when a diffuse anode arc attachment is present as opposed to a constricted anode attachment. The sources of plasma fluctuations inside and around the plasma jet are mainly the movement of the anode arc attachment and turbulent vortices. The average speed of the anode arc attachment increases with decreases in ambient pressure. On the contrary, the average period of the restrike process, or the distance between the exit nozzle and the average attachment’s position, decreases with reductions in ambient pressure. We report ambient pressure values for the transition between a constricted and diffuse anode arc attachment and for the transition between subsonic and supersonic plasma flow.