Power Deposition Research Articles

Ozone production by an He+O2 radio-frequency atmospheric pressure plasma jet driven by tailored voltage waveforms

Atmospheric pressure plasma jets are efficient sources of reactive oxygen and nitrogen species with potential applications in medicine, materials processing, green industry and agriculture. However, selective control over the production of reactive species presents an ongoing challenge and a barrier to the widespread uptake of these devices in applications. This study therefore investigates the production of ozone by a radio-frequency plasma jet driven with tailored voltage waveforms composed of up to five consecutive harmonics, with a fundamental frequency of 13.56 MHz. The plasma is supplied with helium with small admixtures (0.1%–1.0%) of oxygen gas. The ozone density in the far effluent is measured with Fourier transform infrared spectroscopy and the gas temperature in the plasma channel is determined with optical emission spectroscopy. Voltage waveform tailoring is found to enhance the ozone density in the far effluent of the plasma jet in comparison to operation with single-frequency voltage waveforms. Increasing the number of applied harmonics in the driving voltage waveform for a fixed peak-to-peak voltage enhances the ozone density but significantly increases the gas temperature within the plasma channel. Meanwhile, increasing the number of applied harmonics while maintaining a constant RF power deposition allows the density of ozone in the effluent to be increased by up to a factor of 4 relative to single-frequency operation, up to a maximum density of 5.7 ×1014 cm−3, without any significant change to the gas temperature. This work highlights that tailored voltage waveforms can be used to control the density of ozone delivered through the plasma effluent, marking an important step towards realising the potential of these plasmas for applications.

Characterization of water propellant in an electron cyclotron resonance thruster

A coaxial electron cyclotron resonance thruster operating on water vapor propellant is investigated to determine the influence of molecular propellant chemistry on thruster performance. The performance is characterized at different mass flow rates (0.1–0.4 mg/s) and powers (20–200 W) using a thrust stand, ion energy analyzer, and spectrometer. Experimental data are compared to the results from a theoretical model that includes non-equilibrium chemical kinetics. The thruster is observed to transition from a state where power deposition favors propellant dissociation and ionization into a state where it favors electron heating and ion acceleration. The results suggest that the majority of plasma heating occurs in a core region that surrounds the thruster antenna and that propellant flow outside this region is not efficiently utilized for propulsion.

Suppression of the m/n = 2/1 tearing mode by electron cyclotron resonance heating on J-TEXT

Stabilization of tearing modes and neoclassical tearing modes is of great importance for tokamak operation. Electron cyclotron waves (ECWs) have been extensively used to stabilize the tearing modes with the virtue of highly localized power deposition. Complete suppression of the m/n = 2/1 tearing mode (TM) by electron cyclotron resonance heating (ECRH) has been achieved successfully on the J-TEXT tokamak. The effects of ECW deposition location and power amplitude on the 2/1 TM suppression have been investigated. It is found that the suppression is more effective when the ECW power is deposited closer to the rational surface. As the ECW power increases to approximately 230 kW, the 2/1 TM can be completely suppressed. The island rotation frequency is increased when the island width is reduced. The experimental results show that the local heating inside the magnetic island and the resulting temperature perturbation increase at the O-point of the island play dominant roles in TM suppression. As the ECW power increases, the 2/1 island is suppressed to smaller island width, and the flow shear also plays a stabilizing effect on small magnetic islands. With the stabilizing contribution of heating and flow shear, the 2/1 TM can be completely suppressed.

Design Considerations of Flywheel for Future Perspective Power Deposition

Design Considerations of Flywheel for Future Perspective Power Deposition

Experimental investigation of PDI bifurcation of lower hybrid waves during electron density ramp-up in EAST

The effect of parametric decay instability (PDI) on the current drive efficiency of 4.6 GHz lower hybrid (LH) waves in EAST is investigated experimentally, showing the PDI channel bifurcation of LH waves for the first time in EAST. First, experiments with three platforms of LH power were performed, achieving the LH power required for the PDI occurrence. Second, PDI bifurcation experiments were further carried out by ramping up the plasma electron density. The loop voltage increases with an increase in density, implying a decrease in the current driven by the LH wave. PDI bifurcation during electron density ramp-up was studied by analyzing the parallel refractive index ( n∥ ) and the frequency spectrum broadening, which is measured with a radio frequency magnetic probe array recently installed close to the LH antenna. It is observed for the first time that they both first increase with density, then there is not much variation and a clear sideband in the frequency spectrum is also observed when the density is up to 4×1019 m−3 , suggesting a change in the PDI channel. Calculation of the mode growth rate driven by PDI shows that when the edge electron density is up to 1.9×1018 m−3 , the growth rate of the ion cyclotron quasi-mode (ICQM) will exceed that of the ion sound quasi-mode (ISQM), quantitively explaining that with an increase in density, the PDI channel partly transits from the ISQM to the ICQM channel. Studies provide a possible way to reduce the power deposition in the edge region and improve drive capability by means of mitigating PDI behavior.

Repeatability of image quality in very low-field MRI.

Very low-field MR has emerged as a promising complementary device to high-field MRI scanners, offering several advantages. One of the key benefits is that very low-field scanners are generally more portable and affordable to purchase and maintain, making them an attractive option for medical facilities looking to reduce costs. Very low-field MRI systems also have lower RF power deposition, making them safer and less likely to cause tissue heating or other safety concerns. They are also simpler to maintain, as they do not require cooling agents such as liquid helium. However, these portable MR scanners are impacted by temperature, lower magnetic field strength, and inhomogeneity, resulting in images with lower signal-to-noise ratio (SNR) and higher geometric distortions. It is essential to investigate and tabulate the variations in these parameters to establish bounds so that subsequent in vivo studies and deployment of these portable systems can be well informed. The aim of this work is to investigate the repeatability of image quality metrics such as SNR and geometrical distortion at 0.05 T over 10 days and three sessions per day. We acquired repeatability data over 10 days with three sessions per day. The measurements included temperature, humidity, transmit frequency, off-resonance maps, and 3D turbo spin echo (TSE) images of an in vitro phantom. This resulted in a protocol with 11 sequences. We also acquired a 3 T data set for reference. The image quality metrics included computing SNR and eccentricity (to assess geometrical distortion) to investigate the repeatability of 0.05 T image quality. The image reconstruction included drift correction, k-space filtering, and off-resonance correction. We computed the experimental parameters' coefficient of variation (CV) and the resulting image quality metrics to assess repeatability. We have explored the impact of electromagnetic interference (EMI) on image quality in very low-field MRI. The investigation involved varying both the distance and amplitude of the EMI-producing coil from the signal generator to analyze their effects on image quality. The range of temperature measured during the study was within 1.5 °C. The off-resonance maps acquired before and after the 3D TSE showed similar hotspots and were changed mainly by a global constant. The SNR measurements were highly repeatable across sessions and over the 10 days, quantified by a CV of 6.7%. The magnetic field inhomogeneity effects quantified by eccentricity showed a CV of 13.7%, but less than 5.1% in two of the three sessions over 10 days. The use of conjugate phase reconstruction mitigated geometrical distortion artifacts. Temperature and humidity did not significantly affect SNR or mean frequency drift within the ranges of these environmental factors investigated. The EMI experiment showed that as the amplitude increased the SNR decreased, and concurrently the root mean square of the background increased with a rise in EMI amplitude or a reduction in distance. We found that humidity and temperature in the range investigated did not impact SNR or frequency. Based on the CV values computed session-wise and for the overall study, our findings indicate high repeatability for SNR and magnetic field homogeneity.

Modeling and measurement of lead tip heating and resonant length for implanted, insulated wires.

To study implant lead tip heating because of the RF power deposition by developing mathematical models and comparing them with measurements acquired at 1.5 T and 3 T, especially to predict resonant length. A simple exponential model and an adapted transmission line model for the electric field transfer function were developed. A set of wavenumbers, including that calculated from insulated antenna theory (King wavenumber) and that of the embedding medium were considered. Experiments on insulated, capped wires of varying lengths were performed to determine maximum temperature rise under RF exposure. The results are compared with model predictions from analytical expressions derived under the assumption of a constant electric field, and with those numerically calculated from spatially varying, simulated electric fields from body coil transmission. Simple expressions for the resonant length bounded between one-quarter and one-half wavelength are developed based on the roots of transcendental equations. The King wavenumber for both models more closely matched the experimental data with a maximum root mean square error of 9.81°C at 1.5 T and 5.71°C at 3 T compared to other wavenumbers with a maximum root mean square error of 27.52°C at 1.5 T and 22.01°C for 3 T. Resonant length was more accurately predicted compared to values solely based on the embedding medium. Analytical expressions were developed for implanted lead heating and resonant lengths under specific assumptions. The value of the wavenumber has a strong effect on the model predictions. Our work could be used to better manage implanted device lead tip heating.

Power deposition in the He bath induced by the Z gradient coil in the 11.7 T Iseult magnet: theory versus measurements

Gradient-magnet interactions increase with higher field magnets and stronger gradient coils. Perhaps the most sensitive aspect is magnet quench, which can be induced by a loss of superconductivity of the main coil caused by a rise of the temperature of the He bath with gradient activity. Predicting power depositions thereby can be a very valuable tool to avoid dangerous frequency zones but also eventually correct design flaws. In this work, we report model predictions compared to measurements of power deposition in the He bath of the Iseult 11.7 T magnet for the Z gradient coil axis.

Point-of-Care Bedside Brain Magnetic Resonance Imaging Is Safe in Extracorporeal Membrane Oxygenation Patients With Swan Ganz Catheters: A Phantom Experiment and Single Center Experience

IntroductionMore than 1.2 million pulmonary artery catheters (PACs) are used in cardiac patients per annum within the United States. However, it is contraindicated in traditional 1.5 and 3T magnetic resonance imaging (MRI) scans. We aimed to test preclinical and clinical safety of using this imaging modality given the potential utility of needing it in the clinical setting. MethodsWe conducted two phantom experiments to ensure that the electromagnetic field power deposition associated with bare and jacketed PACs was safe and within the acceptable limit established by the Food and Drug Administration. The primary end points were the safety and feasibility of performing Point-of-Care (POC) MRI without imaging-related adverse events. We performed a preclinical computational electromagnetic simulation and evaluated these findings in nine patients with PACs on veno-arterial extracorporeal membrane oxygenation. ResultsThe phantom experiments showed that the baseline point specific absorption rate through the head averaged 0.4 W/kg. In both the bare and jacketed catheters, the highest net specific absorption rates were at the neck entry point and tip but were negligible and unlikely to cause any heat-related tissue or catheter damage. In nine patients (median age 66, interquartile range 42-72 y) with veno-arterial extracorporeal membrane oxygenation due to cardiogenic shock and PACs placed for close hemodynamic monitoring, POC MRI was safe and feasible with good diagnostic imaging quality. ConclusionsAdult ECMO patients with PACs can safely undergo point-of-care low-field (64 mT) brain MRI within a reasonable timeframe in an intensive care unit setting to assess for acute brain injury that might otherwise be missed with conventional head computed tomography.

Investigating the impact of applied magnetic field and current on anode power deposition in AF-MPDT

The high temperature superconductors enhanced magnetoplasmadynamic thruster is a promising device for various space mission scenarios. However, a critical issue hindering the enhancement of the thruster’s performance is the problem of anode power deposition. Previous studies have identified the anode fall voltage as a major contributor to this power deposition. This paper introduces an approximate analytical formula for calculating anode power deposition resulting from anode fall voltage. The paper further analyzes and calculates the variation of anode fall voltage with an applied magnetic field and discharge current. The findings reveal a direct correlation between applied magnetic field and both anode fall voltage and power, indicating an increase with higher magnetic field values. In contrast, while the anode fall voltage experiences a slight decline with increased discharge current, the anode power deposition remains elevated due to the transition from field ionization to thermal ionization. To gain a comprehensive understanding of anode power deposition, an experiment was conducted to obtain measurements under different operating conditions, involving varying levels of applied magnetic field and discharge current. The experimental results align with the theoretical predictions. These insights have the potential to serve as a valuable reference for enhancing the efficiency of magnetoplasmadynamic thrusters, bringing us closer to unlocking the full potential of these remarkable propulsion systems in the realm of space exploration.

Error Estimation for Plasma Power Deposition in Tokamak First Wall Designs

Error Estimation for Plasma Power Deposition in Tokamak First Wall Designs

Combined ns pulsed-RF excitation and impedance matching considerations for the production of moderate E/n atmospheric pressure discharges for gas conversion

Sub-breakdown radiofrequency (RF) discharges enabled by a nanosecond (ns) pulse ignition source are studied at atmospheric pressure in a range of gas mixtures from completely inert (in Ar) to completely reactive (in CO2). An electrical characterisation of the continuous wave (CW) RF discharge (13.56 MHz) is performed to determine plasma impedance and plasma power dissipation. Two different measurement methods to electrically characterize the system are described and compared. One method uses in-situ measurements of discharge parameters (voltage, current and the phase angle), and the other method performs ex-situ measurements of the load circuit using a vector network analyser. It was found that RF plasma power deposition depended on the applied RF power as well as the gas mixture composition. Using the in-situ voltage, current and phase angle measurements, plasma power deposition was calculated to be as much as 85% and 76% of the applied RF power for the pure Ar and pure CO2 cases, respectively. A preliminary qualitative assessment of the plasma composition was performed by optical emission spectroscopy, and CO2 conversion by mass spectrometry. CO2 to CO conversions of 11.2% and 5.5% in a 20:80 (CO2:Ar) mixture and in 100% CO2, respectively, were observed. This study demonstrates a RF plasma source for gas conversion applications at atmospheric pressure in a completely reactive gas.

Broadening of electron cyclotron power deposition and driven current profiles caused by dissipative diffractive propagation

Improvements in electron cyclotron resonance heating (ECRH) and current drive (ECCD) predictions are important issues for the design and control of high-performance fusion plasmas in future devices, where these should play a more important role as actuators than in devices to date. A newly developed EC-prediction package based on the quasioptical ray tracing code PARADE revealed in JT-60SA that (i) the radial profiles of both EC power deposition and driven current are broadened and (ii) the net driven current is increased by a few kA/MW, in comparison with conventional predictions due to dissipative diffractive propagation (DDP). The mechanism of DDP is as follows: EC wave beam obliquely passing through the resonant surface is dissipated non-uniformly on its beam cross section, so that the beam trajectory shifts gradually and thus the resonant position also shifts, resulting in the broadened power deposition profile. This novel ECCD and ECRH prediction package based on PARADE is applicable not only to JT-60SA but other existing devices and even, future devices.

Effect of a negative DC bias on a capacitively coupled Ar plasma operated at different radiofrequency voltages and gas pressures

The effect of a negative DC bias, |V dc|, on the electrical parameters and discharge mode is investigated experimentally in a radiofrequency (RF) capacitively coupled Ar plasma operated at different RF voltage amplitudes and gas pressures. The electron density is measured using a hairpin probe and the spatio-temporal distribution of the electron-impact excitation rate is determined by phase-resolved optical emission spectroscopy. The electrical parameters are obtained based on the waveforms of the electrode voltage and plasma current measured by a voltage probe and a current probe. It was found that at a low |V dc|, i.e. in α-mode, the electron density and RF current decline with increasing |V dc|; meanwhile, the plasma impedance becomes more capacitive due to a widened sheath. Therefore, RF power deposition is suppressed. When |V dc| exceeds a certain value, the plasma changes to α–γ hybrid mode (or the discharge becomes dominated by the γ-mode), manifesting a drastically growing electron density and a moderately increasing RF current. Meanwhile, the plasma impedance becomes more resistive, so RF power deposition is enhanced with |V dc|. We also found that the electrical parameters show similar dependence on |V dc| at different RF voltages, and α–γ mode transition occurs at a lower |V dc| at a higher RF voltage. By increasing the pressure, plasma impedance becomes more resistive, so RF power deposition and electron density are enhanced. In particular, the α–γ mode transition tends to occur at a lower |V dc| with increase in pressure.

Electron ITB formation in EAST high poloidal beta plasmas under dominant electron heating

Plasma confinement and transport in tokamaks play a crucial role in the development of high poloidal beta steady-state operation scenarios. Therefore, it is very important to study the relevant mechanism of internal transport barriers (ITBs), which can help plasmas to obtain better confinement in order to achieve higher fusion gain. This paper mainly introduces the analysis of the characteristics of electron heat transport of discharges with ITB in high βP operation regime in Experimental Advanced Superconducting Tokamak (EAST). Based on the statistical analysis of stable discharges with βP > 1.5, it is found that there is an obvious bifurcation of the normalised electron temperature gradient (ETG) ( R/LTe ) in the range of βP = 2–2.2. Then the discharges of lower βP ( βP < 2, where the value of βP is below the bifurcation threshold) and of higher βP ( βP > 2.2, where the value of βP is above the threshold) were selected for analysis. The diagnostic data provided by Thomson scattering, x-ray crystal spectrometry and charge exchange recombination spectroscopy are used to provide reliable parameter profiles and then combined with the data of external magnetic probe measurements and the polarisation interferometer diagnosis system to fully reconstruct the balance. A relevant plasma current calculation model is used to calculate and analyse the current density profiles and power deposition, and then the transport analysis is carried out. Interestingly, in the higher βP discharges, it is found that the turbulence intensity provided by the CO2 laser collective scattering system gradually decreases and the normalised ETG R/LTe gradually increases. It is also found that the electron heat transport coefficient decreases in the discharge with higher βP and the growth rate of the electron-scale turbulence calculated by transport gyro-Landau fluid (TGLF) is significantly reduced. Meanwhile, similar conclusions are also obtained in the discharges when the βP is further increased.

Power measurement analysis of moderate pressure capacitively coupled discharges

This study examines the transition of 13.56 MHz, capacitively coupled plasmas (CCP) from low to intermediate pressure regimes. Here, we investigate power deposition/plasma production in argon, nitrogen, and oxygen discharges as a function of pressure. These three feed gases were chosen as they provide a set of electropositive and electronegative gases and they are widely discussed in the existing literature. Experiments were conducted for all combinations of pressures: 0.5, 1.5, and 2.5 Torr, and nominal power density between 0.1 and 0.7 W/cm2 for each feed gas at a fixed electrode gap of 24 mm, a commonly employed gap in many industrial processes. Our study shows that increasing pressure results in an increase in current at a given electrode bias in argon and oxygen discharges, while there is no discernible pressure-induced change in nitrogen discharges. We attribute this increase to an increase in plasma density, which might result from a change in power deposition or ionization processes. It is likely that heating via secondary electrons becomes more important at intermediate pressures, resulting in increased plasma density and current. Specifically, based on our measurements, it appears that the mechanisms through which power is deposited into the plasma change with increasing pressure for both argon and oxygen discharges but not for nitrogen discharges. Our experimental results align with the outcomes of our simulations and the simulation results of CCP discharges conducted by other researchers under similar conditions.

Effect of target material on electrical properties of a two-electrode dielectric barrier helium plasma jet

In this paper we present electrical characterization of a dielectric barrier discharge plasma jet operating with He (2 slm and 3 slm) as working gas and interacting with Cu, polyethylene terephthalate and distilled H2O targets. We used a plasma jet with two copper electrodes wrapped around a glass tube. One electrode was powered by a high-voltage sinusoidal signal of 30 kHz, whereas the other electrode and the target holder were grounded. We have performed detailed investigation of the voltage and current waveforms, phase differences, volt–current (V–I) characteristics, calculated impedances and power deposition. The aim was to determine the influence of different target materials and their conductivity on the plasma properties. We calculated the total harmonic distortion factor that showed that the current through grounded electrode depends on the conductivity of the target. We also calculated the power delivered to the plasma core and the plasma plume regions and observed that the change in the target conductance influenced the power in both plasma regions. The experimentally characterized electrical circuit was simulated by a model of equivalent electrical circuit corresponding to the plasma-off and plasma-on regime. Voltage controlled current source was added as model of a streamer formed in plasma-on regime.

Investigation of microstructure evolution and electromagnetic shielding mechanism of absorbed MWCNTs-FeCo composites by one-step in situ deposition using high-speed laser cladding

Electromagnetic shielding materials can inhibit or reduce the harm of electromagnetic radiation and have become an important means to protect against electromagnetic pollution. In order to overcome the inconveniences of in situ or conformal manufacturing on the specific equipment, and the resulting assembly errors lead to the reduction of electromagnetic interference shielding effectiveness (EMI SE). As a new technology, high-speed laser cladding can directly design multi-walled carbon nanotubes (MWCNTs)-FeCo alloy composites as absorbents, and it is the first time to realize the rapid manufacturing of electromagnetic shielding materials by one-step in-situ deposition without adding auxiliary materials. According to the temperature field and stress field, it is found that the through-crack defects of electromagnetic shielding coating mainly resulted from the residual stress concentration of microcracks near the bottom fusion line. When the cladding strategy is 1600 W power deposition after preheating at 400 °C, a high-quality cladding layer can be obtained. When the addition of MWCNTs is 1.5 wt%, the material exhibits good electromagnetic shielding performance under the synergistic effect of dielectric loss, conductivity loss, and magnetic loss. And the average EMI SE is 23 dB in the range of 2-18GH. The research shows that high-speed laser cladding can simultaneously meet the requirements of flexible material design and efficient preparation, which realizes the integration of electromagnetic shielding material design and manufacturing.

Spatio-temporal analysis of power deposition and vibrational excitation in pulsed N2 microwave discharges from 1D fluid modelling and experiments

Vibrational excitation of N2 beyond thermodynamic equilibrium enhances the reactivity of this molecule and the production of radicals. Experimentally measured temporal and spatial profiles of gas and vibrational temperature show that strong vibrational non-equilibrium is found in a pulsed microwave discharges at moderate pressure (25 mbar) in pure N2 outside the plasma core and as an effect of power pulsing. A one dimensional radial time-resolved self-consistent fluid model has been developed to study the mechanism of formation of vibrationally excited N2. In addition to the temperature maps, time-resolved measurements of spontaneous optical emission, electron density and electron temperature are used to validate the model and the choice of input power density. The model reveals two regions in the plasma: a core where chemistry is dominated by power deposition and where vibrational excitation starts within the first ∼10 µs and an outer region reliant on radial transport, where vibrational excitation is activated slowly during the whole length of the pulse (200 µs). The two regions are separated by a sharp gradient in the estimated deposited power density, which is revealed to be wider than the emission intensity profile used to estimate the plasma size. The low concentration of excited species outside the core prevents the gas from heating and the reduced quenching rates prevent the destruction of vibrationally excited N2, thereby maintaining the observed high non-equilibrium.

On the Saturation of the Instability of Induced Ordinary Microwave Scattering in the Edge Transport Barrier of a Tokamak during Electron Cyclotron Resonance Heating of a Plasma

The saturation of the low-threshold parametric decay instability of an ordinary wave during electron cyclotron resonance heating in the edge transport barrier of a tokamak due to the stochastic damping of a daughter two-dimensionally localized oblique Langmuir wave has been considered. It has been found that the saturation of instability in modern devices occurs at a relatively low level and does not affect the energy balance during plasma heating. It has been shown that the efficiency of nonlinear pump under expected conditions of microwave power injection in the International Thermonuclear Experimental Reactor will exceed the maximum efficiency of stochastic damping, which will result in the breaking of amplitude-dependent saturation and can significantly modify the power deposition profile.