Increase In Plasma Density Research Articles

Statistical Analysis of Pc1 Wave Ducting Deduced From Swarm Satellites

AbstractTransverse Pc1 waves propagating from magnetospheric source regions undergo mode conversion to the compressional mode in the ionosphere due to the induced Hall current. Mode converted Pc1 waves propagate across the magnetic field through the ionospheric waveguide. This process is called Pc1 wave ducting (PWD). PWDs have been observed by magnetometers on both ground and low Earth orbit satellites over a wide latitudinal and longitudinal range. In this work, we present the statistical analysis results of PWD exploiting Swarm satellites from 2015 to 2019. Spatial distributions show that the PWDs are mainly observed over the South Atlantic Anomaly longitudes, possibly due to the high Hall conductivity and F‐region density, and at subauroral/auroral latitudes ( MLAT). The occurrence rate of PWD increases with increasing AE and SYM‐H indices. Seasonal dependence shows that PWD exhibits a high occurrence rate during equinox and local summer while local winter hosts only a low occurrence. The asymmetry between summer and winter can be explained by the ionospheric plasma density. The high occurrence rate in equinox may result from intense geomagnetic activity during the equinox, probably due to the Russell‐McPherron effect. From our statistical analysis, we conclude that the occurrence of PWD is controlled by both ionospheric plasma conditions and geomagnetic activity, and that the mode conversion and PWD occur more efficiently as plasma density increases.

INFLUENCE OF METAL HYDRIDE HOLLOW CATHODE ON PENNING ION SOURCE OPERATION

The influence of metal hydride hollow cathode on a Penning ion source operation has been carried out. The feature of investigation is hydrogen injection only due to its desorption from metal hydride under ion-stimulated processes. The regimes of optimal discharge operation in the hollow cathode mode are determined. It has been revealed that the transition to the hollow cathode mode occurs at lower voltages, the discharge works without external gas supply, and the working pressure in the cell is set at the level determined by the discharge current. The supply of a negative bias to the metal hydride hollow cathode weakly affects the features of the emission of axial particles, although it allows the increase of plasma density near the metal hydride hollow cathode.

Surface Morphology and Sputtering Mechanism of Etched Areas of a Metallic Target by Magnetron Sputtering

As an important functional thin-film material in the field of electronic information, high-purity titanium (Ti) is widely used in different industries, such as integrated circuits, flat-panel displays and solar energy, indicating the importance of further research on Ti targets. Herein, a titanium target is placed in a UDP-650 closed-field nonequilibrium magnetron sputtering ion coating machine for deep etching to form racetrack grooves, and different positions of etching grooves are analyzed to understand the target etched behavior. The sputtering-induced etching of the Ti target, from shallow to deep regions, changes from the preferential sputtering of scratches and other defects in the edge area to the surface sputtering pits, with discontinuous distribution and uneven size, to grain boundary sputtering and, finally, to closely packed grain surface sputtering. The etching behavior of different regions exhibits different characteristics, mainly showing selective sputtering. The surface roughness of the sputtered area initially increases with the increase of sputtering depth and plasma density, followed by a slight decrease. Moreover, different degrees of incomplete recrystallization occur in different sputtering areas due to the uneven distribution of plasma on the target surface. The grain size increased from the transition area between sputtering and non-sputtering (112 μm) to the deepest sputtering area (139 μm). Moreover, the relationship between the cross-sectional grain size and sputter surface roughness renders a correlation coefficient of 0.802, indicating a strong influence of grain size on surface roughness. Therefore, it is of utmost importance to refine grains and increase the sputtering yield of the target as well as reduce the surface roughness of the target after etching to obtain a high-quality thin film.

A tunable narrow-band plasma photonic crystal filter based on bound state

Photonic crystals are widely used in a class of narrow-band frequency selective filter due to their excellent ability to control electromagnetic waves, in which the working frequency depends on the structural parameters of the point defect resonant cavity of the photonic crystal, and the introduction of some dispersive media into the cavity makes the filter adjustable. In general, this kind of cavity-filter is very sensitive to the parameter disturbance of the cavity, and the quality factor of the filter can be reduced significantly by material loss. On the other hand, some studies have shown that there may be bound states at the interface between two different photonic crystals, and the bound state is often accompanied by narrow band and high transmittance, which implies that a narrow-band filter based on bound states is feasible. Importantly, filters based on bound states may be resistant to material loss to some degree. In this paper, a bound state related tunable narrow-band filter composed of a one-dimensional photonic crystal and a two-dimensional plasma photonic crystal is proposed, and the working frequency of the filter is located in the common band gap of the two photonic crystals. The COMSOL Multiphysics finite element simulation software is used to study the influences of geometric parameters of the one-dimensional photonic crystal and plasma parameters on the performance of the filter. It is found that the closer to each other the center frequencies and depths of the two different forbidden bands are, the greater the peak transmittance of the filter, in which the center frequency dominates, will be. On the other hand, the working frequency of the filter is directly proportional to plasma density and inversely proportional to collision frequency. The quality factor of the filter first increases and then decreases with the increase of plasma density, and decreases with the increase of collision frequency. The peak transmittance of the filter first increases and then decreases with the increase of plasma density, and decreases with the increase of plasma collision frequency. Finally, with the increase of collision frequency, both the peak transmittance and the quality factor decrease slightly, which indicates that the filter has a certain resistance to plasma loss. We believe that this work is helpful in investigating some new plasmonic photonic crystal filters.

Formation of the bow shock indentation: MHD simulation results

Simulation results from a global magnetohydrodynamic (MHD) model are used to examine whether the bow shock has an indentation and characterize its formation conditions, as well as its physical mechanism. The bow shock is identified by an increase in plasma density of the solar wind, and the indentation of the bow shock is determined by the shock flaring angle. It is shown that when the interplanetary magnetic field (IMF) is southward and the Alfven Mach number (Mα) of solar wind is high (> 5), the bow shock indentation can be clearly determined. The reason is that the outflow region of magnetic reconnection (MR) that occurs in the low latitude area under southward IMF blocks the original flow in the magnetosheath around the magnetopause, forming a high-speed zone and a low-speed zone that are upstream and downstream of each other. This structure hinders the surrounding flow in the magnetosheath, and the bow shock behind the structure widens and forms an indentation. When Mα is low, the magnetosheath is thicker and the disturbing effect of the MR outflow region is less obvious. Under northward IMF, MR occurs at high latitudes, and the outflow region formed by reconnection does not block the flow inside the magnetosheath, thus the indentation is harder to form. The study of the conditions and formation process of the bow shock indentation will help to improve the accuracy of bow shock models.

Gap length effect on discharge mode and etching profiles in asymmetric dual frequency capacitive CF<sub>4</sub>/Ar discharges

The capacitive CF<sub>4</sub>/Ar discharges driven by a dual frequency source based on the electrical asymmetry effect (EAE) are studied by using a one-dimensional fluid coupled with Monte-Carlo (MC) model and a two-dimensional trench model. The effects, induced by varying the relative gap distance, on self-bias voltage, electronegativity, ion flux, neutral flux and other plasma characteristics are systematically discussed. In this asymmetric discharge, as the gap distance increases, the absolute value of the self-bias voltage and electronegativity decrease. Meanwhile, the plasma density and absorption power increase accordingly because the effective discharge area expands but the boundary loss is still limited. In addition, both <inline-formula><tex-math id="M72">\begin{document}$ \mathrm{\alpha } $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20210546_M72.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20210546_M72.png"/></alternatives></inline-formula> mode and drift-ambipolar (DA) mode can play their important roles in the discharges with different gap distances, though DA mode is weakened in large gap discharge. Owing to the fact that the self-bias is larger and electronegativity is stronger for the case of smaller gap distance, the sheath expansion electric field at the powered electrode and the bulk electric field heat the electrons, leading the ionization rate to greatly increase near the collapse of the sheath at the grounded electrode. Besides, at the larger gap distance, the maximum value of the ionization rate decreases due to the reduction of electrons with relatively high-energy, and the ionization rate near the grounded electrode is reduced evidently. Moreover, with the increase of the gap distance, the maximum ion energy decreases and the ion energy distribution width becomes smaller due to the reduction of the self-bias voltage. Meanwhile, the etching rate increases a lot since the neutral flux increases significantly near the powered electrode. However, as the gap distance increases to 5 cm, the etching rate stops increasing and the trench width at the bottom becomes narrow because the neutral flux increases greatly compared with ion flux, forming a thick layer of polymer. So, besides separately controlling the ion energy and flux, optimizing the synergistic effect of ion flux and neutral group flux to adjust the etching rate and improve the etching morphology is also an interesting topic in the asymmetric CF<sub>4</sub>/Ar discharges.

Experimental observation of heat flux mitigation during divertor detachment in the DIII-D small angle slot divertor

Abstract Employing an array of surface eroding thermocouples (SETCs), the heat flux measured at the outer strike point of the DIII-D Small Angle Slot (SAS) divertor was found to be reduced by ~50% when the plasma reached the detachment regime compared to the attached state. Reduction in heat flux of similar magnitude has been found in both toroidal field directions (obtained by ramping up the plasma density) but with different characteristics: With the ion B × ∇B drift direction toward the SAS divertor, the heat flux measured by the SETCs first increased as plasma density increased, which may due to reduction in energy losses in the upstream and hence increase in the power flow into the divertor, and then began to roll over concurrent with a reduction in ion saturation current density on nearby Langmuir probes. In contrast, with the ion B × ∇B drift directed away from the SAS, the heat flux began at a higher value but decreases monotonically with increasing plasma density. This leads to lower heat flux in this BT direction at up to 20% lower line-averaged density. These significant differences in the onset of detachment in opposing BT directions are believed to be largely determined by the impacts of E × B drifts. Because ITER’s divertor must be operated with some degree of plasma detachment to radiate most of the power arriving in the scrape-off-layer, it is crucial to further understand the impact of magnetic drifts on plasma detachment behavior in a tight divertor geometry.

Statistical analysis of short-wave fadeout for extreme space weather event estimation

Solar flares trigger an increase in plasma density in the ionosphere including the D region, and cause the absorption of radio waves, especially in high-frequency (HF) ranges, called short-wave fadeout (SWF). To evaluate the SWF duration and absorption statistically, we analyze long-term (36 years) ionosonde data observed by the National Institute of Information and Communications Technology (NICT). The minimum reflection frequency, fmin, is used to detect SWFs from 15-min-resolution ionosonde observations at Kokubunji, Tokyo, from 1981 to 2016. Since fmin varies with local time (LT) and season, we refer to dfmin, which is defined as fmin subtracted by its 27-day running median at the same LT. We find that the occurrence of SWFs detected by three criteria, (i) dfmin ≥ 2.5 MHz, (ii) dfmin ≥ 3.5 MHz, and (iii) blackout, during daytime associated with any flare(s) greater than the C1 class is maximized at local noon and decreases with increasing solar zenith angle. We confirm that the dfmin and duration of SWFs increase with the solar flare class. We estimate the absorption intensity from observations, which is comparable to an empirical relationship obtained from sudden cosmic noise absorption. A generalized empirical relationship for absorption from long-distance circuits shows quantitatively different dependences on solar flare flux, solar zenith angle, and frequency caused by different signal passes compared with that obtained from cosmic noise absorption. From our analysis and the empirical relationships, we estimate the duration of extreme events with occurrence probabilities of once per 10, 100, and 1000 years to be 1.8–3.6, 4.0–6.8, and 7.4–11.9 h, respectively. The longest duration of SWFs of about 12 h is comparable to the solar flare duration derived from an empirical relationship between the solar flare duration and the solar active area for the largest solar active region observed so far.

Neutral flow interaction with a magnetic dipole plasma II. Global model

A simulation study is presented for a collisional, low-temperature dipole plasma encountered by rarefied, hypersonic neutral gas flow. A global model is developed and averaged over a toroidal control volume to describe the mass and energy exchange between the neutral stream and plasma. Simulations over a large range of magnet and freestream parameters reveal three distinct physical regimes that have significant bearing on the magnitude of plasma/flow interaction. The transitions between these regimes exhibit characteristics of resistive critical ionization, whereby the relative kinetic energy between plasma and neutral gas collisionally heats electrons, driving rapid and complete ionization of the gas. Two regime transitions are observed here with sudden exponential increases in plasma density occurring at velocity thresholds that depend on several energy loss mechanisms. The higher-velocity transition is a classical presentation of critical ionization where flow neutrals are ionized directly by plasma electrons. The other is a unique case in which charge exchange between ions and flow neutrals supplies both the particles and energy required to initiate critical ionization. This transition is distinct from any critical ionization effect reported in literature and indicates the existence of a lower critical velocity governed by collisional and diffusive effects as opposed to ionization energy losses only. Drag force on the magnetic field is considered by examining absorption and deflection of ionized flow by the dipole. The critical ionization thresholds increase the force on the magnet by up to two orders of magnitude compared to aerodynamic drag on an equivalently sized flow impediment.

Comparison of high density and nitrogen seeded detachment using SOLPS-ITER simulations of the tokamak á configuration variable

First of a kind SOLPS-ITER simulations on tokamak á configuration variable (TCV) that include nitrogen have been performed to model recent nitrogen seeded detachment experiments. Based on spectroscopic measurements, a nitrogen recycling coefficient 0.3–0.5 on the graphite walls of TCV is estimated. The experimentally observed decrease of core nitrogen density with increasing plasma density is reproduced and linked to a reduction of the ionisation mean free path in the scrape-off layer. Although the influence of sputtered carbon impurities from TCV’s graphite wall cannot be fully eliminated, seeding nitrogen increases control over the total impurity density. This facilitates disentangling the effect of impurities from that of high upstream density on the main characteristics of detachment, namely target power and ion current reductions and the development of a parallel pressure drop. Increasing the density and the seeding rate reduce the power on the divertor targets in a different way: with density, the ion current increases and the target temperature strongly decreases, whereas seeding impurities decreases the ion current and affects less strongly the temperature. The reduction in ion current when seeding nitrogen is due to a lower ionisation source, which is not related to power limitation nor an increased momentum loss, but to a decrease of the ionisation reaction rate. Impurity seeding leads to less volumetric momentum losses (and hence pressure drop) than density ramps, for the same level of energy flux reduction. Additionally, main chamber sputtering of carbon is identified as a possible explanation for the missing target ion current roll-over during density ramps in the simulations.

Complementary Metal-Oxide-Semiconductor Compatible Deposition of Nanoscale Transition-Metal Nitride Thin Films for Plasmonic Applications.

Transition-metal nitrides have received significant interest for use within plasmonic and optoelectronic devices because of their tunability and environmental stability. However, the deposition temperature remains a significant barrier to widespread adoption through the integration of transition-metal nitrides as plasmonic materials within complementary metal-oxide-semiconductor (CMOS) fabrication processes. Binary, ternary, and layered plasmonic transition-metal nitride thin films based on titanium and niobium nitride are deposited using high-power impulse magnetron sputtering (HIPIMS) technology. The increased plasma densities achieved in the HIPIMS process allow thin films with high plasmonic quality to be deposited at CMOS-compatible temperatures of less than 300 °C. Thin films are deposited on a range of industrially relevant substrates and display-tunable plasma frequencies in the ultraviolet to visible spectral ranges. Strain-mediated tunability is discovered in layered films compared to that in ternary films. The thin film quality, combined with the scalability of the deposition process, indicates that HIPIMS deposition of nitride films is an industrially viable technique and can pave the way toward the fabrication of next-generation plasmonic and optoelectronic devices.

Study of ionospheric scintillation during geomagnetic storms at equatorial anomaly region Bhopal

GPS L-band signals get affected by ionospheric scintillation; as a result, satellite navigation too gets affected. The most extreme scintillation activity is expected to occur near the equatorial region during geomagnetic storms. The behavior and morphology of low-latitude ionosphere are different from the other latitudes. The space weather conditions in low latitude show different nature because of the geomagnetic field. Due to penetration of soft, high energetic particles, the plasma density increases, which is the main source of generation of ionospheric irregularities scintillation. GPS scintillation at low latitudes is primarily associated with equatorial spread F. Equatorial spread F is caused by ionospheric irregularities with a spatial spectrum extending from 100 km to less than 1 m. When GPS signals encounter the ionospheric irregularities of various sizes produced during high geomagnetic and solar activity, they undergo drastic changes in their phase and amplitude scintillation indices. The accuracy and reliability of GPS system get affected by scintillation. Also the atmosphere air molecule’s content and deviation of electrons, protons, neutrons according to flow rate are observed. In the present paper, we have studied the scintillation activity at low-latitude station Bhopal.

CHANGES IN THE PARAMETERS OF THROMBODYNAMICS AND BLOOD CLOT CONTRACTION IN PATIENTS WITH RHEUMATOID ARTHRITIS

Autoimmune diseases, including rheumatoid arthritis (RA), are risk factors for thrombotic events. Understanding the pathogenetic role of hemostatic changes in RA can assist in developing measures for prevention, prognosis, early diagnosis, and treatment of immune thromboses. Objective: to investigate the state of platelet and plasma hemostasis in patients with RA, as compared to other laboratory parameters and clinical manifestations of the disease. Subjects and methods. Hemostasis was investigated using two relatively new laboratory tests: thrombodynamics and kinetics of blood clot contraction (BCC). Examinations were made in 60 patients with RA and in 50 apparently healthy individuals of the control group. Results and discussion. In patients with RA, the parameters of thrombodynamics and BCC were found to be significantly different from the normal values. According to thrombodynamics, there was an increase in plasma clot growth rate, size, and density, which indicates chronic hypercoagulation. The rate and completeness of BCC were substantially reduced due to platelet dysfunction in patients with RA compared to healthy individuals. The changes in the parameters of thrombodynamics and BCC correlated with the laboratory signs of systemic inflammation and depended on the radiographic stage of the disease. Conclusion. The results of this investigation confirm that hemostatic disorders are present in RA and indicate the informative value of thrombodynamics and BCC tests as indicators of a pre-thrombotic state, including autoimmune pathology.

Influence of Electrode Interval and Barrier Thickness in the Segmented Electrode Micro-plasma DBD Reactor on CO2 Decomposition

In this paper, the decomposition of pure CO2 into CO and O2 were carried out in a segmented electrode DBD micro-plasma reactor at ambient pressure. With the assistance of gas chromatography, the influence of key factors like electrode interval and barrier thickness on the DBD filamentary behavior and CO2 decomposition process were investigated systematically. Meanwhile, the detailed electrical characterization during discharge process was also performed. The results indicated that a relatively higher CO2 conversion and energy efficiency could be obtained at the propitious condition of longer interval between adjacent electrodes and smaller barrier thickness, and the highest CO2 conversion and corresponding energy efficiency are 16.9% and 3.6%, respectively, at the condition of an applied voltage of 18 kV and 1.0 mm barrier thickness. Longer electrode interval can result in an increase in plasma density as well as enhance fringe effect. While the smaller barrier thickness, the smaller corresponding gas breakdown voltage, which meant that more electrical power was used for gas excitation. Accordingly, more energetic electrons were generated and more collisions between the electrons and CO2 molecules occurred. These were considered to be main reasons for enhanced CO2 decomposition process.

Impacts of sawtooth crashes on tokamak plasmas in DEMOs

Self-consistent simulations of sawtooth oscillations on four DEMO (demonstration fusion power plant) designs, proposed by European, Indian, Chinese, and Korean teams, are carried out using the Porcelli sawtooth triggering model and the modified version of the Kadomtsev magnetic reconnection model coupled with the BALDUR integrated code. The simulation results suggest that all sawtooth crashes are triggered by the driving force for the internal kink instability overcoming the fast ion stabilization found in all DEMOs. Conversely, different expansions of the pre-crash helical flux are found, causing different mixing radii on each design. The mixing radius of the European DEMO is found to be the largest, resulting in the largest reduction of the core plasma temperature after the sawtooth crash. It is also observed that for all DEMOs except the Chinese DEMO, regular sawtooth crashes lead to an increase in the core plasma density and radiative power density in different levels, which are due to the steepness of the pre-crash hollow density profile. Furthermore, while helium is found to be outwardly transported by sawtooth crashes for all DEMOs, the sawteeth yield a penetration of the seeded impurities, remarkably found in the European design. Interestingly, based on the European design, a decrease in the atomic mass of the plasma fuels and seeded impurities are found to yield greater flatness of the pre-crash density profile and thus a smaller impact of sawtooth oscillations on central density. Additionally, the sawteeth degrade the plasma performance in the Chinese DEMO, but demonstrate positive impacts on the performance in the European, Indian, and Korean DEMOs, which results from the increase of the central ion density caused by the sawteeth. Furthermore, variation in neutral beam injection power exhibits both positive and negative correlations of sawtooth oscillation impacts on central ion density. The sensitivity of the mixing region of DEMOs is also investigated for scans where the main plasma parameters are varied.

Synthesis and characterization of super-hard AlCrTiVZr high-entropy alloy nitride films deposited by HiPIMS

Super-hard AlCrTiVZr high-entropy alloy (HEA) nitride films were synthesized by high power impulse magnetron sputtering (HiPIMS) without external heating. The effect of N2 gas low rate (FN), ranging from 0 sccm to 20 sccm, on the HiPIMS plasma discharge characterization, element concentration, deposition rate, microstructure, cross-sectional morphology, residual stress, and mechanical properties of films were explored. Results show that increasing FN increases the HiPIMS discharge current, accompanying with the decreased deposition rate. The saturated nitride (AlCrTiVZr)N films were obtained at FN = 8 sccm and higher, which exhibit a simple NaCl-type FCC structure. A continuous variation in the microstructure, from amorphous to columnar crystal structure, has been observed for these nitride films. It is discovered that the moderate FN of 0 sccm to 12 sccm leads to an enhanced bombardment with high-energy particles due to the increased plasma density, while the bombardment effect is weakened because of the decreased plasma energy as the FN is increased further. The nitride films deposited at FN = 12 sccm have super-hardness of 41.8 GPa and low wear rate of 2.3 × 10−7 mm3/Nm. Meanwhile, a change of preferred orientation from (2 0 0) to (1 1 1) is presented as the FN increases from 12 sccm to 20 sccm.

Deuterium experiment with large-scale negative ion source for large helical device

The deuterium experiment with various source plasma diagnostics was conducted at the research and development negative ion source at National Institute for Fusion Science, which is a cesium-seeded large-scale negative hydrogen-ion source with half discharge volume and the same type of ion source for large helical device. A change of filling gas from hydrogen to deuterium increased line-averaged negative ion density by a factor of 1.3 in beam extraction region as a result of flattened profile with keeping central density. Positive ion and electron densities increased threefold. This was influenced by the increase of plasma density in the plasma generation region. The plasma space potential varied as equivalent of the collisionless sheath theory in electro-positive plasma expected by the hydrogen isotope gas species, although the negative ion could affect sheath formation. Higher atomic cesium density was observed because of higher sputtering yield due to higher momentum of deuterium.

Expansion dynamics of atmospheric pressure helium plasma jet in ambient air

In this work, the expansion dynamics of a helium plasma jet in ambient air is examined. By using a fast imaging technique, the expansion of plasma jet from glass nozzle to air is captured which is in the form of plasma bullet propagating into the air. To understand the plasma bullet travel path from glass nozzle to plasma jet tip a drag force model is used. Moreover, the spatial variation of plasma density along the plasma jet length is estimated using drift velocity, plasma jet current and the cross-sectional area of the plasma jet. It is observed that the slight increase in plasma density is due to the combined effect of reduction of drift velocity, plasma jet current, and jet cross-sectional area. The obtained plasma density from glass nozzle to jet tip is in the range of (0.069-5.96) × 1012 cm−3. The above parameters can be of the essence in biological and industrial applications.

Power matching to pulsed inductively coupled plasmas

Matching of power delivery to nonlinear loads in plasma processing is a continuing challenge. Plasma reactors used in microelectronics fabrication are increasingly multi-frequency and/or pulsed, producing a non-linear and, in many cases, non-steady state electrical termination that can complicate efficient power coupling to the plasma. This is particularly the case for pulsed inductively coupled plasmas where the impedance of the plasma can significantly change during the start-up-transient and undergo an E–H (capacitive-to-inductive) transition. In this paper, we discuss the results from a computational investigation of the dynamics of power matching to pulsed inductively coupled plasmas (Ar/Cl2 mixtures of tens of mTorr pressure) using fixed component impedance matching networks and their consequences on plasma properties. In this investigation, we used set-point matching where the components of the matching network provide a best-case impedance match (relative to the characteristic impedance of the power supply) at a chosen time during the pulsed cycle. Matching impedance early during the pulse enables power to feed the E-mode, thereby emphasizing capacitive coupling and large excursions in the plasma potential. This early power coupling enables a more rapid ramp-up in plasma density while being mismatched during the H-mode later in the pulse. The early match also produces more energetic ion bombardment of surfaces. Matching late in the pulse diminishes power dissipated in the E-mode at the cost of also reducing the rate of increase in plasma density.

Simulations of electromagnetic effects in large-area high-frequency capacitively coupled plasmas with symmetric electrodes: Different axial plasma density profiles

In this paper, the electromagnetic effects are investigated in large-area high-frequency symmetric capacitive discharges by solving the Maxwell equations under two different axial plasma density profiles, i.e., the spatially uniform and the axial non-uniform density profiles. Simulation results show that the spatially uniform density profile underestimates the standing wave effect and overestimates the skin effect. Moreover, the electromagnetic effects are significantly affected by the frequency, sheath width, electron-neutral momentum transfer frequency, and plasma density. As the frequency increases, the surface wavelength is significantly reduced, and the standing wave effect becomes pronounced. An opposite result is obtained by increasing the sheath width. As the electron-neutral momentum transfer frequency increases, the radial damping of surface waves when they propagate from the radial edge to the center becomes prominent. As the plasma density increases, the discharge is dominated by the skin effect instead of the standing wave effect, due to the reduced skin depth.