Plasma Resistance Research Articles

Optimization of Ion Beam-Assisted Deposition Process for Y<sub>2</sub>O<sub>3</sub> Film to Enhance Plasma Resistance

A ceramic-based plasma etcher window (Lid) requires robust resistance to plasma, especially when exposed to harsh fluorine-based plasma conditions. In this study, a Y<sub>2</sub>O<sub>4</sub> film was deposited using e-beam evaporation with ion beam-assisted deposition (IBAD), and the physical properties of the IBAD-based Y<sub>2</sub>O<sub>4</sub> coating film were thoroughly examined to enhance the mechanical and chemical resistance of the ceramic part, including the Y<sub>2</sub>O<sub>4</sub> film, against etching plasma. The hardness and surface morphology of the IBADbased Y<sub>2</sub>O<sub>4</sub> could be precisely controlled by various deposition processing parameters, such as beam voltage, beam current, and Ar/O2 gas ratio. Following the IBAD deposition of the Y<sub>2</sub>O<sub>4</sub> film, a plasma etching process (Ar/CF<sub>4</sub> mixture gases with 150 W RF power for 60 minutes) was applied to evaluate the plasma resistance of the deposited Y<sub>2</sub>O<sub>4</sub> coating film. The surface morphology characteristics of the Y<sub>2</sub>O<sub>4</sub> films were compared using atomic force microscopy, and their grain size was studied through scanning electron microscopy image analysis. Furthermore, a nanoindenter was used to determine the hardness of the Y<sub>2</sub>O<sub>4</sub> film. These results suggest that optimizing the IBAD coating process requires an in-depth study that fully considers the correlation between deposition processing parameters and physical properties. This optimization can be instrumental for enhancing the durability of the ceramic part.

Power transfer efficiency in an air-breathing radio frequency ion thruster

Abstract Due to a series of challenges such as low-orbit maintenance of satellites, the air-breathing electric propulsion has got widespread attention. Commonly, the radio frequency ion thruster is favored by low-orbit missions due to its high specific impulse and efficiency. In this paper, the power transfer efficiency of the radio frequency ion thruster with different gas composition is studied experimentally, which is obtained by measuring the radio frequency power and current of the antenna coil with and without discharge operation. The results show that increasing the turns of antenna coils can effectively improve the radio frequency power transfer efficiency, which is due to the improvement of Q factor. In pure N2 discharge, with the increase of radio frequency power, the radio frequency power transfer efficiency first rises rapidly and then exhibits a less steep increasing trend. The radio frequency power transfer efficiency increases with the increase of gas pressure at relatively high power, while declines rapidly at relatively low power. In N2/O2 discharge, increasing the N2 content at high power can improve the radio frequency power transfer efficiency, but the opposite was observed at low power. In order to give a better understanding of these trends, an analytic solution in limit cases is utilized, and a Langmuir probe was employed to measure the electron density. It is found that the evolution of radio frequency power transfer efficiency can be well explained by the variation of plasma resistance, which is related to the electron density and the effective electron collision frequency.

Effects of plasma resistivity in FELTOR simulations of three-dimensional full-F gyro-fluid turbulence

A full-F, isothermal, electromagnetic, gyro-fluid model is used to simulate plasma turbulence in a COMPASS-sized, diverted tokamak. A parameter scan covering three orders of magnitude of plasma resistivity and two values for the ion to electron temperature ratio with otherwise fixed parameters is setup and analysed. Two transport regimes for high and low plasma resistivities are revealed. Beyond a critical resistivity the mass and energy confinement reduces with increasing resistivity. Further, for high plasma resistivity the direction of parallel acceleration is swapped compared to low resistivity.Three-dimensional visualisations using ray tracing techniques are displayed and discussed. The field-alignment of turbulent fluctuations in density and parallel current becomes evident. Relative density fluctuation amplitudes increase from below 1% in the core to 15% in the edge and up to 40% in the scrape-off layer.Finally, the integration of exact conservation laws over the closed field line region allows for an identification of numerical errors within the simulations. The electron force balance and energy conservation show relative errors on the order of 10−3 while the particle conservation and ion momentum balance show errors on the order of 10−2.All simulations are performed with a new version of the FELTOR code, which is fully parallelized on GPUs. Each simulation covers a couple of milliseconds of turbulence.

Current Sheet Evolution in a Planar Inductive Pulsed Plasma Thruster

Abstract The evolution of the current sheet is fundamental to the understanding and operation of planar inductive pulsed plasma thrusters. Methods for experimentally determining the time-varying mutual inductance and plasma resistance associated with the current sheet are presented. From these, time-histories of the resistive heating in and electromagnetic acceleration of the sheet are found. Analysis of experimental data obtained from a compact, low discharge energy inductive pulsed plasma thruster shows that current sheet evolution is well described by three phases: ionization, formation, and acceleration. Evidence is provided for the plasma current and resistive heating becoming localized near the upstream edge of the current sheet as the sheet forms. The influence of initial propellant density and pre-ionization on the characteristics of the sheet are examined. Both higher propellant densities and increased pre-ionization are found to produce current sheets which exhibit greater magnetic impermeability. Higher densities cause the sheet to form closer to the coil face, improving coupling, while stronger pre-ionization leads to more rapid resistive heating, causing the sheet to form earlier in time.

Optimization of Al-excess nonstoichiometry on the densification and plasma resistance of YAG ceramics

The effects of Al-excess nonstoichiometry on the densification and plasma etching behavior of yttrium aluminum garnet (Y3Al5O12, YAG) were investigated. Al-excess composition driven by Al2O3 debris introduced during Al2O3 ball milling can promote the densification of YAG ceramics. This hypothesis was proved by using Al2O3 powder as an additive to YAG powder. It was verified that Al-excess nonstoichiometry designed by the addition of excess Al2O3 powder resulted in increased densification of YAG ceramics. At 1450 °C for sintering, the relative density of YAG ceramics increases from 98.58 % to 99.88 % with the addition of Al2O3 from 0 to 0.512 wt%. However, above 0.342 wt% concentration, Al2O3 was prepcipated in the YAG matrix, degrading the etching resistance. The optimum balance between the density and plasma etching resistance of YAG ceramics for application in a plasma environment was realized by adding 0.171 wt% of excess Al2O3. The density and surface roughness (Ra) of YAG ceramic after etching are 99.61 % and 17.6 nm, respectively.

Different effects of the companion antiretroviral drugs on dolutegravir trough concentrations.

Dolutegravir is widely used in different dual and triple antiretroviral regimens. Here, we sought to investigate the effect of the companion antiretroviral drug(s) on dolutegravir plasma trough concentrations in persons with HIV, with a focus on dual regimens. Dolutegravir concentrations collected from October 2015 to March 2023 ( n = 900) were stratified according to the main antiretroviral classes (NRTIs, NNRTIs, protease inhibitors) and according to single drugs. Dolutegravir concentrations measured in persons with HIV concomitantly treated with lamivudine were considered as the reference group. Dolutegravir trough concentrations were significantly higher in persons with HIV given protease inhibitors compared with the reference [1886 (1036-2940) versus 1575 (1026-2226) ng/ml; P = 0.004]. The highest dolutegravir concentrations were measured in persons with HIV concomitantly treated with unboosted atazanavir [2908 (2130-4135) ng/ml]. Conversely, co-administration of darunavir/ritonavir resulted in significantly lower dolutegravir exposure [909 (496-1397) ng/ml; P = 0.002 versus reference]. Among NNRTIs, the higher dolutegravir concentrations were measured in presence of rilpivirine [2252 (1489-2686); P < 0.001 versus reference]. Dolutegravir trough concentrations are differently affected by individual antiretroviral drugs, with some drug combinations (i.e. dolutegravir/darunavir/cobicistat, or dolutegravir/rilpivirine) providing significantly higher than expected dolutegravir exposure. Such combinations might be advantageous when there are concerns about dolutegravir plasma exposure or resistance.

Enhancing the fretting damage resistance of suspension plasma sprayed hydroxyapatite coating with Titania addition

The damage of the bioactive HAp ceramic coatings on titanium implants and debris generated at the implant stem-bone interface is a major concern as it causes osteolysis, metallosis, and loosening of implants. Attempts are made to develop strong and wear-resistant biocompatible HAp coatings through the addition of different ceramics and with better coating processes. The addition of titania to HAp was found to strengthen the coating, and this paper reports the fretting wear resistance of titania-added HAp suspension plasma spray coating. Expected micro motion between the stem–bone interface in the implants due to applied loads is estimated using numerical simulations. The fretting wear resistance of the titania-added coating was evaluated using the simulated ball-on-flat contacts. The titania-added HAp suspension plasma spray-coated samples exhibited reduced fretting friction coefficient and increased wear resistance. High hardness and modulus of the 50 % titania added HAp contribute to the reduced fretting damage and wear debris generation at the interface.

Interplay of plasma resistivity and rotation on β limits in free boundary diverted tokamaks

A plasma resistivity-β driving mechanism aimed at explaining the appearance of long wavelength global instabilities in free boundary high-β tokamak plasmas with a divertor is presented. These perturbations resemble very closely the resistive wall mode phenomenon. Performing a proper toroidal analysis, we show that the magnetohydrodynamic stability is worsened by the interplay of plasma β and resistivity. By modelling the effect of a magnetic separatrix through a careful positioning of the resonant surfaces, we find that in an ideal plasma wall effects are effectively screened, so that the ideal β limit becomes independent of the wall position/physics. A lower wall dependent critical β is found if plasma resistivity is allowed. We find that global stability can be improved with a toroidal flow, small enough not to induce equilibrium modification. The rotation stabilisation effectiveness depends upon the proximity of the plasma equilibrium parameters to the resistive marginal boundary.

Effect of aluminum content on plasma resistance and contamination particle generation in yttrium aluminum oxide coatings

Yttrium aluminum oxide (YAO) has garnered interest due to its ability to protect the interior parts of process chambers from the corrosive effects of fluorine-based plasma. This ability is attributed to its low melting point, which enhances the internal bonding capabilities of the atmospheric plasma spray (APS) method. We explored the resistance of YAO coatings, with varying yttrium-to-aluminum content ratios, to fluorine-based plasma. These coatings were applied using the APS method and subsequently subjected to NF3/O2 gas. Our results revealed that a higher Al content ratio resulted in a decreased number of defects within the coating, which also led to selective etching at the initial Al2O3-rich sites, primarily creating relatively weak Al-F bonds and smaller particles. In particular, selecting an appropriate yttrium-to-aluminum content ratio significantly reduced the coating defects and enhanced the etch rate compared to coatings with a higher yttrium content ratio. This improvement was attributed to the balanced presence of Al-F and Y-F bonds. Furthermore, for coatings rich with the yttrium aluminum garnet (YAG) phase, the resistance to fluorine-based plasma was primarily influenced by the thickness of the APS-Y2O3 layer. This layer, used to augment adhesion to parts, relies on the low-temperature crystallization features of YAG. The findings of this study offer valuable insights for optimizing YAG coating in dry-etching processes requiring high-density APS coatings.

Abstract 18931: A PCSK9 and APOB Double Heterozygote Presenting Phenotypically Similar to Homozygous Familial Hypercholesterolemia

Introduction: Familial hypercholesterolemia (FH) is an inherited disorder associated with mutations in APOB, PCSK9 and LDLR genes. Heterozygous FH (HeFH) generally has one gene mutation. Homozygous FH (HoFH) has two mutations in the same gene and is characterized by vastly elevated plasma LDL-C, accelerated ASCVD and resistance to standard lipid-lowering therapy. Combinations of mutations can present with a phenotype similar to HoFH. We present a double heterozygous patient with unreported mutations in PCSK9 and APOB genes, exhibiting clinical features of HoFH. Hypothesis: Patients with multiple gene mutations for FH can present clinically similar to HoFH and would benefit from novel lipid lowering therapies Methods: 73-year-old female with a history of diabetes and hyperlipidemia presented in 2018 with dyspnea on exertion. Cholesterol (TC) and triglycerides (TG) were 430 and 715 mg/dl respectively, on rosuvastatin 40 mg and omega 3 fatty acids. Physical exam showed arcus senilis. A nuclear stress test showed ST depressions in inferolateral leads but normal scintigraphy. Genetic testing revealed APOB and PCSK9 mutations. She was then treated with rosuvastatin, icosapentyl ethyl, ezetimibe and fenofibrate. TC, LDL, TG and ApoB levels were 463, 236, 747 and &gt;240 mg/dl respectively. Evolocumab was added, with reduction of TC, TG and ApoB levels to 326, 432 and 182mg/dl, despite maximal available therapy. Results: Genetic testing revealed APOB variant NP_000375.2:p.Gln3378His and PCSK9 variant NP_777596.2:pAla544Thr, which were unreported mutations with unknown clinical significance. Genetically, this patient is a double heterozygote but expresses a phenotype similar to HoFH due to a poor response to maximum therapy. Conclusions: Although usually genetically defined, the phenotype of HoFH can present with different genetic variations. Chaudhry et al established genetic diagnosis of HoFH in 0.9% of patients initially diagnosed as HeFH, of which 3 were true homozygotes and 3 were compound heterozygotes. These findings support the idea that various heterozygous combinations of mutations in the genes for LDLR, APOB and PCSK9, may present clinically similar to HoFH. Patients with these mutations could benefit from novel agents such as evinacumab.

Microstructure and properties of molybdenum composite coatings by plasma spraying of Mo–SiC and MoO3–Al–SiC composite powders

To improve the sliding wear resistance of plasma sprayed Mo coating, Mo–SiC and MoO3–Al–SiC composite powders were used to prepare Mo composite coatings by plasma spraying. The results show that the introduction of SiC improved the mechanical properties and sliding wear resistance of plasma sprayed Mo coating. The reactivity of Mo and SiC was low during plasma spraying Mo–SiC composite powder. The thermite reaction for MoO3 and Al was not conducive to the densification of the composite coating prepared by MoO3–Al–SiC composite powder, but improved the reactivity of in-situ generated Mo and SiC, and the Nowotny phase Mo4.8Si3C0.6 was observed in the coating. The coating prepared by Mo–SiC composite powder displayed better mechanical properties and sliding wear resistance than that of the coating prepared by plasma spraying MoO3–Al–SiC composite powder. The coating obtained by Mo–SiC composite powder revealed a combination of adhesive wear, abrasive wear and oxidation wear.

A Cross-sectional Study to Assess Insulin Resistance and Atherogenic Index of Plasma as Predictors of Risk of Cardiometabolic Disease among Undergraduate Medical Students at a Tertiary Care Teaching Hospital, Karnataka

Background: Medical profession is known for stress and challenges due to hectic academic schedules which makes students, high-risk candidates for diabetes mellitus, hypertension and cardiometabolic disease (CMD). Surrogate markers such as homeostatic model assessment insulin resistance (HOMA-IR) and atherogenic index of plasma (AIP) along with routine parameters enable early prediction of the disease. Hence, this study aimed at determining HOMA-IR and AIP along with assessment of their correlation with anthropometric and biochemical parameters associated with CMD risk among undergraduate medical students. Methodology : 460 medical students consented to participate in the study. The data related to socio-demographic profile, anthropometry, blood pressure and biochemical parameters such as fasting plasma glucose (FPG), fasting plasma insulin (FPI) and lipid profile was collected and analyzed. HOMA-IR and AIP were calculated. The strength of association between study variables was determined by relevant statistics. Results: The study showed the prevalence of overweight (17.8%), obesity (20.4%), pre-hypertension (37.82%) and hypertension (3.47%). 98.5% of the participants had normal FPG and FPI, whereas 1.5% had impaired levels. Lipid profile analysis showed hypercholesterolemia (3.7%), hypertriglyceridemia (8.1%), increased LDL-c (33.7%) and reduced HDL-c (55.2%). High HOMA-IR and AIP were contributed by 28.9% and 73.3% respectively. HOMA-IR and AIP showed statistically significant positive correlation with CMD risk factors. Conclusion: HOMA-IR and AIP considered as the better predictors of CMD risk among apparently healthy medical students. Thus, incorporation of these surrogate markers along with routine parameters for regular screening can help in early prediction of the risk of CMD among undergraduate medical students. Keywords: Homeostatic model assessment insulin resistance, Atherogenic index of plasma, Cardiometabolic disease, Medical students

The cold atmospheric pressure plasma-generated species superoxide, singlet oxygen and atomic oxygen activate the molecular chaperone Hsp33.

Cold atmospheric pressure plasmas are used for surface decontamination or disinfection, e.g. in clinical settings. Protein aggregation has been shown to significantly contribute to the antibacterial mechanisms of plasma. To investigate the potential role of the redox-activated zinc-binding chaperone Hsp33 in preventing protein aggregation and thus mediating plasma resistance, we compared the plasma sensitivity of wild-type E. coli to that of an hslO deletion mutant lacking Hsp33 as well as an over-producing strain. Over-production of Hsp33 increased plasma survival rates above wild-type levels. Hsp33 was previously shown to be activated by plasma in vitro. For the PlasmaDerm source applied in dermatology, reversible activation of Hsp33 was confirmed. Thiol oxidation and Hsp33 unfolding, both crucial for Hsp33 activation, occurred during plasma treatment. After prolonged plasma exposure, however, unspecific protein oxidation was detected, the ability of Hsp33 to bind zinc ions was decreased without direct modifications of the zinc-binding motif, and the protein was inactivated. To identify chemical species of potential relevance for plasma-induced Hsp33 activation, reactive oxygen species were tested for their ability to activate Hsp33 in vitro. Superoxide, singlet oxygen and potentially atomic oxygen activate Hsp33, while no evidence was found for activation by ozone, peroxynitrite or hydroxyl radicals.

Energetic electron tail production from binary encounters of discrete electrons and ions in a sub-Dreicer electric field

During transient instabilities in a 2 eV, highly collisional MHD-driven plasma jet experiment, evidence of a 6 keV electron tail was observed via x-ray measurements. The cause for this unexpected high energy tail is explored using numerical simulations of the Rutherford scattering of a large number of electrons and ions in the presence of a uniform electric field that is abruptly turned on as in the experiment. When the only active processes are Rutherford scattering and acceleration by the electric field, contrary to the classical Fokker–Planck theory of plasma resistivity, it is found that no steady state develops, and instead, the particle kinetic energy increases continuously. However, when a power loss mechanism is introduced mimicking atomic line radiation, a near steady state can develop and, in this case, an energetic electron tail similar to that observed in the experiment can develop. The reasons underlying this behavior are analyzed, and it is shown that an important consideration is that Rutherford scattering is dominated by the cumulative effect of grazing collisions, whereas atomic line radiation requires an approximately direct rather than a grazing collision.

Effects of HfO2 addition on the plasma resistance of Y2O3 thin films deposited by e-beam PVD

Ceramic Y2O3 thin films are often used to coat the inner walls of etching equipment during semiconductor manufacturing to protect them from bombardment by high-energy plasma ions, which can degrade the equipment and cause semiconductor contamination. In this study, the effects of HfO2 addition to the Y2O3 thin film on the plasma resistance were investigated. Thin films were fabricated using electron beam-physical vapor deposition. The addition of HfO2 maintained the cubic Y2O3 crystalline structure while substantially improving the etch resistance during fluorine-based plasma etching. X-ray photoelectron spectroscopy analysis of the etched surface showed that HfO2 addition resulted in a lower F/(O + F) ratio, thus promoting the formation of more Y–O bonds that are more resistant to physical sputtering. Additionally, the analysis indicated that Hf4+ was more likely to be removed from the etched surface than Hfx+ (x < 4). This novel strategy is expected to aid in the development of improved plasma-resistant ceramic materials.

Penetration properties of applied resonant magnetic perturbation in HL-2A tokamak

Any arbitrary perturbation on a magnetic field separatrix can cause a structure named homoclinic tangle in tokamaks. Both an edge localized mode (ELM) and a resonant magnetic perturbation (RMP) can lead to a perturbation of the magnetic field on the separatrix. Under the appropriate circumstances, RMP could alleviate or even completely suppress a rapid collapse process of an ELM. The simulation results using the CLTx code, the extended version of the three-dimensional toroidal magnetohydrodynamic (MHD) code (CLT (Ci-Liu-Ti, which means MHDs in Chinese)) with a scrape-off layer, show the structure of the homoclinic tangle with a borderline stochastic region resulting from RMP in HL-2A tokamak. Strongly distorted magnetic field lines with the homoclinic tangle could connect to the tokamak divertors. The footprints of these magnetic field lines on the divertors are consistent with the energy deposit spots in the experiment. From Poincaré plots of escaped magnetic field lines, it is found that the depth of the plasma edge region penetrated by these field lines depends on the RMP coil current, the rotation frequency of the RMP field, and the plasma resistivity.

Oscillation dynamics of m/n= 3/1 double tearing mode

This study systematically investigates the roles of the plasma viscosity and resistivity in the oscillation dynamics during the decay phase of the m/n = 3/1 double tearing mode using the Ci-Liu-Ti (CLT) code. The primary objectives of this research are to examine the driving and suppressing mechanisms of the oscillation. The oscillation and steady-state are the result of the competition between the external injection and the reconnection annihilation of magnetic flux during the decay phase. In a regime with a higher viscosity (or a lower resistivity), the steady-state arises from the significant damping (weak generation) of plasma flows, resulting in the formation of saturated islands. In a regime with a lower viscosity (or a higher resistivity), the suppression of the oscillation amplitude can be attributed to a strong residual flow that quickly takes the injected magnetic flux away toward to the reconnection region, which caused no enough accumulated magnetic flux to drive oscillations and the system evolves toward a steady-state configuration. The steady-state condition results in the generation of a narrow radial vortex region which promotes formation of internal transport barriers. The upper threshold of the resistivity within the low-resistivity regime to achieve a steady-state decreases as the viscosity increases.

Influence of matching network and frequency on the effective quality factor and performance of a miniature radio frequency ion thruster

The radio frequency ion thruster (RIT) is an electric propulsion device that utilizes radio frequency (RF) power to ionize propellants; thus, its performance is influenced by the frequency and matching network of the RF. In this study, an L&amp;T type wide-range matching network was employed to experimentally investigate the performance of a miniature RIT with 4 cm diameter at different frequencies. The experimental results show that changing the matching parameters of the L&amp;T network at the same frequency leads to changes in the effective quality factor and varying performances of the thruster; under similar effective quality factors, changing the frequency does not significantly affect the performance of the thruster; however, the plasma resistance exhibits frequency dependence. As the frequency increases, the effective collision frequency increases, leading to an increase in plasma resistance, which is beneficial for improving the performance of the thruster at high frequencies. Finally, a set of methods for quickly comparing the performance of RITs was summarized based on the effective quality factor. These research results are also instructive for improving the ionization of induction-coupled discharge devices of other sizes.

Hot corrosion behavior of CYSZ thermal barrier coating with optimized laser surface modification

The current study aims to investigate the influence of laser surface modification on the hot corrosion, fracture toughness, and hardness resistance of atmospheric plasma sprayed Ceria-Yttria Stabilized Zirconia (CYSZ) thermal barrier coating. Throughout the laser surface modification process, a variety of laser processing parameters are used to obtain the finest surface properties and optimum laser parameters. In this study, the whole coating surface is modified using the optimal parameters. The results show that 52.9 W laser power at a 220 mm laser distance and a 60 mm/s scanning speed were found as the optimum laser glazing parameters. A hot corrosion test is performed in a box furnace for 20 h at 1050 °C. Scanning electron microscopy (SEM) images show denser surfaces in laser-glazed coatings when compared to air-spraying coatings. A dense microstructure combined with the top coat is created in the coating cross-section, and a smooth microstructure with a coaxial fracture network is produced on the surface. The laser-glazed layer has superior mechanical characteristics to the as-sprayed coating, including hardness and fracture toughness. This layer also restricts the damaging monoclinic-tetragonal phase change for CYSZ TBC, blocking the infiltration of molten salt. The hot corrosion behavior of TBCs is improved by the inclusion of a dense laser-glazed layer.

Accounting for plasma resistance in the interpretation of probe measurements in gas discharge plasma

The influence of the finite plasma resistance between the Langmuir probe and the reference electrode on the results of measurements of the characteristics of low-temperature plasma: the plasma potential, the average electron energy, the electron concentration, and the electron energy distribution function is analyzed. Specific calculations were made for glow discharge conditions supported by a hollow cathode in helium at a pressure of several millibars.