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A phenomenology-based virtual metrology (VM) for monitoring SiO2 etching depth was proposed by Park (2015). It achieved high prediction accuracy by introducing newly developed plasma information (PI) variables as designated inputs, called PI-VM. The PI variables represent the state of the plasma, the sheath, and the target during the process. We investigate how a PI variable can help to improve prediction accuracy of VM and how it plays a special role in the statistical selection. We choose only PIEEDF among the three PI variables to focus on the investigation. The PIEEDF is determined from the ratio of line-intensities of optical emission spectroscopy. We apply Pearson's correlation filter (PCF), principal component analysis (PCA), and stepwise variable selection (SVS) as statistical selection methods on the variables set including PIEEDF or not. Multilinear regression is used to model the VM. This study reveals that PIEEDF variable is a good variable in terms of independence from other input variables and explanatory power for an output variable. Especially, VM using SVS method applied to variable sets including PIEEDF achieves the highest accuracy, comparable to Park's PI-VM. This study shows that PIEEDF variable is particularly useful for monitoring of the fine variations in semiconductor manufacturing process and it also extends the utilization of OES sensor data.

The effects of ion collisions on plasma–sheath formation are investigated experimentally for a low-density and low-pressure discharge. The space potential and ion velocity distribution measurements at high spatial resolution show that the ion collision properties observed in the presheath are maintained in the plasma–sheath transition region. The potential drop in the transition region indicates the existence of ionization as an effect of ion collisions in the transition region owing to the non-negligible density of the electrons penetrating the sheath. Based on comparisons between the space potential measurements and Riemann’s presheath–sheath transition solution, the ion collision length λ i was determined as a key parameter in the presheath and transition region. And it represents that the thermal properties of ions and neutral gases affects space potential by the charge exchange and ionization collisions. The existence of the ion collision effect in the transition region suggests possible influence on the incident conditions of ions and electrons near the sheath edge. Consequently, the energy distributions of ions and electrons incident on the material surface facing the sheath are sensitive to the collisionality and operating conditions.

Purpose The atmospheric pressure plasma jet (APPJ) has been introduced as an effective disinfection method for titanium surfaces due to their massive radical generation at low temperatures. Helium (He) has been widely applied as a discharge gas in APPJ due to its bactericidal effects and was proven to be effective in our previous study. This study aimed to evaluate the safety and effects of He-APPJ application at both the cell and tissue levels. Methods Cellular-level responses were examined using human gingival fibroblasts and osteoblasts (MC3T3-E1 cells). He-APPJ was administered to the cells in the experimental group, while the control group received only He-gas treatment. Immediate cell responses and recovery after He-APPJ treatment were examined in both cell groups. The effect of He-APPJ on osteogenic differentiation was evaluated via an alkaline phosphatase activity assay. In vivo, He-APPJ treatment was administered to rat calvarial bone and the adjacent periosteum, and samples were harvested for histological examination. Results He-APPJ treatment for 5 minutes induced irreversible effects in both human gingival fibroblasts and osteoblasts in vitro. Immediate cell detachment of human gingival fibroblasts and osteoblasts was shown regardless of treatment time. However, the detached areas in the groups treated for 1 or 3 minutes were completely repopulated within 7 days. Alkaline phosphatase activity was not influenced by 1 or 3 minutes of plasma treatment, but was significantly lower in the 5 minute-treated group (P=0.002). In vivo, He-APPJ treatment was administered to rat calvaria and periosteum for 1 or 3 minutes. No pathogenic changes occurred at 7 days after He-APPJ treatment in the He-APPJ-treated group compared to the control group (He gas only). Conclusions Direct He-APPJ treatment for up to 3 minutes showed no harmful effects at either the cell or tissue level., Graphical Abstract

A phenomenological-based virtual metrology (VM) technique is developed for predicting the silicon nitride film thickness in multi-layer plasma-enhanced chemical vapor deposition (PECVD). Particularly, the analysis of optical emission spectroscopy based on the excitation kinetics in nitrogen plasma is used to develop novel variables, named plasma-information (PI) variables. One variable, PIWall, is determined by analyzing the light transmittances of the nitrogen emissions at the contaminated window, representing the drift of reactor-wall condition. The other variable, PIVolume, is determined by analyzing vibrational distribution of N2( $\text{C}^{3} {\Pi }_{\text u}$ , $\nu =0-4$ ) states, representing the drift of plasma density and temperature. These PI variables are applied as part of input variables of VM to improve the prediction accuracy. The partial least squares regression is adopted as the statistical method and the contribution of PI variables on the VM are evaluated through the variable influence evaluation on projection. It demonstrates the necessity of PI variables in VM for PECVD and the reactor-wall condition is a major cause of drift in PECVD.

Numerical analysis on the electrical and thermal flow characteristics of Ar-N2 inductively coupled plasma (ICP) were carried out for N2 content from 0 to 50 mol% at plasma power level of 50 kW. Firstly, the computational results of thermal flow fields revealed that the addition of N2 could reduce the radiation heat loss, together with increasing the exit enthalpy. For example, the radiation heat loss of Ar-N2 ICP with N2 content of 20 mol% is reduced by ∼ 33%, compared with that of Ar-only ICP, which are essential for the safe operation of an ICP system at the high power level of 50 kW. In addition, the increase of N2 content was also found to increase the load resistance of a tank circuit for a vacuum tube oscillator. Equivalent circuit analysis using the numerical results shows that this increase of the load resistance comes from the increasing equivalent resistance and the decreasing equivalent inductance of Ar-N2 ICP, corresponding to the changes of thermal flow fields with the increase of N2 content. For a tank circuit consisting of a capacitor and an inductor with a capacitance of 6,500 pF, and an equivalent inductance of 0.84 μH, the load resistance was calculated to be increased from 81 Ω for Ar only ICP to 130 Ω for Ar-N2 ICP with N2 content of 20 mol%. Considering the internal resistances of high power vacuum tubes higher than 130 Ω, this increase of load resistance clearly shows that N2 addition can improve the impedance mismatching of an ICP torch system with a vacuum tube oscillator having no variable part to tune the load resistance. By providing these basic data for the calculation of load resistance and thermal flow characteristics, the numerical analysis combined with equivalent circuit analysis used in this work can help in designing and operating a high-powered ICP torch system with a vacuum tube oscillator.

The high-value process strategy in the organic light emitting diode display manufacturing requires strict etching profile control to obtain the normal performance of the display pixels because of the correlation between the etched structure of the processed pattern and the current–voltage characteristics of the pixels. The critical dimension, etch depth, and sidewall angle area are important management points of the etching profile. Because of two-dimensional continuous characteristics of the display as the numerous arrays of the thin film transistors, the etching profiles should be controlled in the analog way rather than only the fact of spec-in or -out. Therefore, the sheath properties which govern the ion flux-driven etching effect and the polymer passivation characteristics of the sidewall of the etching hole are needed to be tailored spatially even in the micro-range. The embossing structured electrode surface applied for the large area display manufacturing dry etching process causes micro-scale non-uniformity of the sheath and passivation properties, and introduces the process faults. To control this micro-range non-uniformity of the etching profiles, a PI-VM (Plasma Information based Virtual Metrology) model was developed by applying the PI parameters. PI parameters include the information on the sheath potential for electronegative plasmas and the heat transfer properties in the chamber. PI parameterization utilized a big data pool of the optical emission spectroscopy and equipment engineering system data accumulated during the mass production. The developed PI-VM model could predict the fault with 80% accuracy, and analysis of the highly contributing PI parameters to the events could give the way to control the manufacturing.

Tungsten has been considered as the most promising candidate for plasma-facing materials (PFMs) in a next generation fusion reactor. It is well known that commercialized ITER (International Thermonuclear Experimental Reactor) grade tungsten is manufactured by the mechanical processing at high temperature after sintering to ensure a high density with an improved structural stability. In this study, in order to obtain the high-density sintered tungsten with more enhanced structural stability, spark plasma sintering (SPS) method was employed, where a pulsed direct electric current was applied during heat treatment of powders with a pressure in the specimen. It is well known that by utilizing SPS, high-density sintered materials at a relatively lower temperature for a shorter time could be achieved compared to the other conventional sintering methods. In particular, in this study, reduction in H 2 atmosphere and two-step sintering were introduced to remove the residual oxygen and achieve the full densification with suppressed grain growth at relatively low operating temperature. In an optimized condition, a fully densified sintered tungsten with a relative density of 99.9% and an average grain size of 4.4 μm was fabricated. The thermal stability of tungsten specimens was evaluated by high heat flux (HHF) test, where the surface temperature was set up to 2300 °C by nitrogen plasma. Then, the microstructural changes of the specimen surface have been examined after the HHF test. As a result, it was confirmed that the high-density sintered tungsten samples fabricated by SPS show an excellent microstructural stability for PFMs.

In the semiconductor etch process, as the critical dimension (CD) decreases and the difficulty of the process control increases, in-situ and real-time etch profile monitoring becomes important. It leads to the development of virtual metrology (VM) technology, one of the measurement and inspection (MI) technology that predicts the etch profile during the process. Recently, VM to predict the etch depth using plasma information (PI) variables and the etch process data based on the statistical regression method had been developed and demonstrated high performance. In this study, VM using PI variables, named PI-VM, was extended to monitor the etch profile and investigated the role of PI variables and features of PI-VM. PI variables are obtained through analysis on optical emission spectrum data. The features in PI-VM are investigated in terms of plasma physics and etch kinetics. The PI-VM is developed to monitor the etch depth, bowing CD, etch depth times bowing CD (rectangular model), and etch area model (non-rectangular model). PI-VM for etch depth and bowing CD showed high prediction accuracy of R-square value (R2) 0.8 or higher. The rectangular and non-rectangular etch area model PI-VM showed prediction accuracy R2 of 0.78 and 0.49, respectively. The first trial of virtual metrology to monitor the etch profile will contribute to the development of the etch profile control technology.

With the advent of more than Moore’s law era, control of plasma etch process is expected to become inevitable. Given that highly complex plasma is a medium of etch processes, plasma parameters are key factors to be controlled. In addition, highly interactive plasma characteristics require multivariate control schemes. In this paper, we design a multi-loop controller which controls effective plasma parameters in Ar plasma conditions. The effective plasma parameters obtained by optical emission spectroscopy are paired with plasma reactor instrumental variables through relative gain array and singular value decomposition. Each single input-single output (SISO) system based on the pairing result shows successful disturbance rejection performance but interactions between SISO controllers occur. In order to handle the interactions, 2 × 2 multiple input-multiple output (MIMO) controllers with and without decouplers are simulated to track set point change. Based on the simulations, a MIMO controller with decouplers is implemented in a capacitively coupled plasma reactor and show feasible control performance without interaction. Hopefully, the results introduced in this paper contribute to making progress in plasma parameter control.

The air plasma spraying method has a problem in the formation of many splat boundaries throughout the plasma sprayed layer, which seriously degrades mechanical properties of the metal layer. In order to improve the mechanical properties of air plasma sprayed tungsten (APS-W) by reducing the splat boundaries, a pulsed electric current is applied on as-sprayed specimens. Through microstructure observations and microhardness measurements, it was confirmed that the reduction of splat boundaries and the increase of hardness were obtained. The results are compared with those of APS-W annealed using induction heating under the same temperature, time and pressure.

The blisters formation and destruction induced by the deuterium ions on a polycrystalline tungsten were investigated with varying irradiation deuterium ion fluence from 3.04 × 1023 to 1.84 × 1025 D m−2 s−1 and an fixed irradiated ion energy of 100 eV in an electron cyclotron resonance plasma source, which was similar to the far-scrape off layer region in the nuclear fusion reactors. Target temperature was monitored during the irradiation. Most of blisters formed easily on the grain with (1 1 1) plane orientation which had about 250 nm in diameter. In addition, the areal number density of blisters increased with increasing the ion fluence under the surface temperature reaching to about 900 K. When the fluence exceeded 4.6 × 1024 D m−2, the areal number density of the blister decreased. It could be explained that the destruction of the blister was initiated by erosion at the boundary region where the thickness of blister lid was thin and the sputtering yield was high by oblique incident ions, resulting in remaining the lid open, e.g., un-eroded center dome. It is possible to work as a tungsten dust formation from the plasma facing divertor material at far-SOL region of fusion reactor.

Real-time plasma controller for SF 6 /O 2 /Ar etching process plasma was developed to reduce first wafer effect caused by cleaning of plasma facing components. After the cleaning of the reactor, the etch rate of silicon decreased 12 % from the etch rate of normal state and increased with repeating etching processes. To reduce the first wafer effect, real-time feedback controller for fluorine density was developed. The controller adjusted O 2 gas flow rate to keep monitored fluorine density constant. With the controller, the etch rate of silicon after the cleaning was kept within 1 % variation.

PURPOSE The atmospheric pressure plasma jet (APPJ) has been introduced as an effective disinfection method for titanium surfaces due to their massive radical generation at low temperatures. Helium (He) has been widely applied as a discharge gas in APPJ due to its bactericidal effects and was proven to be effective in our previous study. This study aimed to evaluate the safety and effects of He-APPJ application at both the cell and tissue levels. METHODS Cellular-level responses were examined using human gingival fibroblasts and osteoblasts (MC3T3-E1 cells). He-APPJ was administered to the cells in the experimental group, while the control group received only He-gas treatment. Immediate cell responses and recovery after He-APPJ treatment were examined in both cell groups. The effect of He-APPJ on osteogenic differentiation was evaluated via an alkaline phosphatase activity assay. In vivo, He-APPJ treatment was administered to rat calvarial bone and the adjacent periosteum, and samples were harvested for histological examination. RESULTS He-APPJ treatment for 5 minutes induced irreversible effects in both human gingival fibroblasts and osteoblasts in vitro. Immediate cell detachment of human gingival fibroblasts and osteoblasts was shown regardless of treatment time. However, the detached areas in the groups treated for 1 or 3 minutes were completely repopulated within 7 days. Alkaline phosphatase activity was not influenced by 1 or 3 minutes of plasma treatment, but was significantly lower in the 5 minute-treated group (P=0.002). In vivo, He-APPJ treatment was administered to rat calvaria and periosteum for 1 or 3 minutes. No pathogenic changes occurred at 7 days after He-APPJ treatment in the He-APPJ-treated group compared to the control group (He gas only). CONCLUSIONS Direct He-APPJ treatment for up to 3 minutes showed no harmful effects at either the cell or tissue level.

Thermal barrier coatings are widely used in aerospace industries to protect exterior surfaces from harsh environments. In this study, functionally graded materials (FGMs) were investigated with the aim to optimize their high temperature resistance and strength characteristics. NiCrAlY bond coats were deposited on Inconel-617 superalloy substrate specimens by the low vacuum plasma spraying technique. Functionally graded Ni-yttria-stabilized zirconia (YSZ) coatings with gradually varying amounts of YSZ (20%-100%) were fabricated from composite powders by vacuum plasma spraying. Heat shield performance tests were conducted using a high- temperature plasma torch. The temperature distributions were measured using thermocouples at the interfaces of the FGM layers during the tests. A model for predicting the temperature at the bond coating–substrate interface was established. The temperature distributions simulated using the finite element method agreed well with the experimental results.

The type of induced material damage in the tungsten irradiated by using deuterium ions was investigated for various value of the fluence at low energy. Experiments were carried out in an electron cyclotron resonance (ECR) plasma source that provided an ion flux of 2.8 × 1021D2+/m2s and a sheath energy of 100 eV/D2+ on the tungsten target. The energy of irradiated ions was much smaller than the threshold energy for generating cascade collisional damage (∼ 250 eV) in tungsten and was similar of the plasma at the first wall of KSTAR. The target temperature was kept as 700 − 800 K by using an active cooling system. Secondary ion mass spectroscopy (SIMS) was employed to observe the depth profiles of deuterium. The peak of the trapped deuterium concentration in the irradiated tungsten was located near 16 − 17 nm for 2.0 − 4.0 × 1025D2/m2, which is far deeper than the 1.6 nm for ion implantation at 100 eV/D2+ ions. Thermal desorption spectroscopy (TDS) data were analyzed to determine the binding energy (Eb = 1.45 eV) of trapped deuterium, which corresponded to an oversaturation-induced vacancy. This observation is very important for understanding the refueling property of the retained deuterium during steady-state fusion plasma operation.

The helium and argon have been widely used as discharge gases in atmospheric pressure plasma jets (APPJs) for bacteria inactivation. The APPJs show apparent different in bullet propagation speed and bacteria inactivation rate apparently vary with discharge gas species. This work shows that these two distinctive features of APPJs can be linked through one factor, the metastable energy level. The effects of helium and argon metastable species on APPJ discharge mechanism for reactive oxygen nitrogen species (RONS) generation in APPJs are investigated by experiments and numerical estimation. The discharge mechanism is investigated by using the bullet velocity from the electric field which is obtained with laser induced fluorescence (LIF) measurement. The measured electric field also applied on the estimation of RONS generation, as electron energy source term in numerical particle reaction. The estimated RONS number is verified by comparing NO and OH densities to the inactivation rate of periodontitis bacteria. The characteristic time for bacteria inactivation of the helium-APPJ was found to be 1.63 min., which is significantly less than that of the argon-APPJ, 12.1 min. In argon-APPJ, the argon metastable preserve the energy due to the lack of the Penning ionization. Thus the surface temperature increase is significantly higher than helium-APPJ case. It implies that the metastable energy plays important role in both of APPJ bullet propagation and bacteria inactivation mechanism.

Vacuum pumps of different ages were used to prepare Cl 2 based plasmas for use in Cr etching. The effects of the vacuum pump age on the etching results were investigated using optical emission spectroscopy analysis. The composition of gas at the base pressure was mainly nitrogen and oxygen, although the ratio depended on the vacuum pump age and therefore, modulated the etch rate in a manner that was difficult to monitor. The effects of the pump age on the etch rate were clearly observed in the Cl 2 plasma-assisted chromium film etching process, in which oxygen and chlorine radicals were responsible for the etching process. The electron energy distribution function (EEDF), which provided a proxy for the thermal equilibrium properties of the etching plasmas, was monitored. The shape of EEDF was derived from an analysis of the optical emission spectral data using an analysis model described previously. Because molecular nitrogen has a higher threshold energy and a larger cross-section of inelastic collisional processes than oxygen, the tail of the EEDF depends on the mixing ratio between nitrogen and oxygen. The various mechanisms that contribute to the chromium etch rate varied with subtle differences in the vacuum conditions, which were determined by age of the turbo molecular pump. The rates at which oxygen and chlorine radicals were generated were estimated using the measured EEDF, and the estimated oxygen radical and etching product contents were verified by comparing the residual gas analyzer data. The results revealed that the residual nitrogen partial pressures in two etchers equipped with either a new or an aged pump differed by 0.18%, and the EEDF tail areas differed by 10 − 4 . Importantly, the chromium etch rates in these two instruments differed by 30%. These results suggest that the chamber-to-chamber mismatch should be monitored during plasma-assisted device fabrication processes.

Acceptable data for electron energy probability function (EEPF) measurement in low-pressure plasmas require a small depletion in near-zero electron energy and a large dynamic range in the high-energy regime. The voltage drop across internal resistance and noise from the data acquisition system cause a rounding of the EEPF near the zero electron energy and a reduction in the dynamic range due to a low signal-to-noise ratio of the high-energy regime, respectively, leading to erroneous interpretation in the EEPF measurement. A digital smoothing filter can be employed to reduce the noise signal, but it can also cause additional depletion near the zero energy. In order to obtain reliable EEPF data, a novel technique is proposed using two Langmuir probes with differing collecting areas and the Savitzky–Golay and Blackman window methods. The technique enables the internal resistance effect to be removed using a slope of the current – voltage characteristic taken from the probes. In addition, the Savitzky–Golay and Blackman window methods in the technique apply separately to two regimes of the EEPF, i.e., the near-zero energy regime and the inelastic energy regime, because appropriate smoothing methods that minimize loss and distortion of information differ for the two regimes. This allows one to decrease the noise signal, minimizing the additional depletion near the zero energy. This technique improves the dynamic range of the EEPF from 30 to 55 dB to 65–105 dB and provides more accurate electron density and effective electron temperature from the EEPF, compared to those of the conventional technique.

Metal target dry etching process applied for the organic light emitting diode display manufacturing is hard to control without the generation of the defect particles. A large amount of the metal-halide by-prodcucts with the non-volatile physical nature are produced in the large area plasma-assisted process chamber. To achieve high-density plasma-based throughput, the inductively coupled plasma type dry etchers were adopted for large-area display manufacturing processes. However, this type of plasma source causes the ion flux-driven damages on the chamber inner walls near the RF power supplied antenna. Sputtered Al atoms from the ceramic parts or etching targets were redeposited onto the chamber inner walls after they form the metal-halide compounds. Redeposited by-prodcucts have very high binding energies to decompose. Undecomposed layers were stuck on the chamber inner wall and flaked off later to form the defect particles. To control this undesired phenomenon, decomposition reaction activated—and plasma locality controlled—two types of ISDs (In Situ Dry cleanings) were designed. A more appropriate type of ISD had selected referring to the developed PI-VM (Plasma Information based Virtual Metrology) model, which qualifies the start of mass production after the discontinuities of the process. The big data set of equipment engineering system and optical emission spectroscopy, accumulated during the mass production, were parameterized to the PI parameters and were applied to the PI-VM modeling. Management of the mass production with the designed ISD and PI-VM model could reduce the 25% of defect particle driven yield loss.

Objective A minimally invasive procedure for intervertebral disk resection using plasma beams has been developed. Conventional parameters for the plasma procedure such as voltage and tip speed mainly rely on the surgeon's personal experience, without adequate evidence from experiments. Our objective was to determine the optimal parameters for plasma disk resection. Methods Rate of ablation was measured at different procedural tip speeds and voltages using porcine nucleus pulposi. The amount of heat formation during experimental conditions was also measured to evaluate the thermal safety of the plasma procedure. Results The ablation rate increased at slower procedural speeds and higher voltages. However, for thermal safety, the optimal parameters for plasma procedures with minimal tissue damage were an electrical output of 280 volts root-mean-square (Vrms) and a procedural tip speed of 2.5 mm/s. Conclusion Our findings provide useful information for an effective and safe plasma procedure for disk resection in a clinical setting.

In recent years, plasma etching process has been considered important because it is one of the most critical processes in semiconductor manufacturing. Numerous research results have been presented in relation to the plasma etch processes, especially plasma parameters control. Although the above results are expected to bring about positive effects in various fields, they do not consider the variability of the system. In this paper, we performed the recursive model estimation of which the model structure is ARX considering the time delay. The recursive algorithm contains the Kalman filter interpretation to the model parameters. we have confirmed that the system model updated in real-time by our recursive model estimation algorithm continuously calculates the model parameters that predict the output variable precisely. Through these results, we expect the better performance of MPC control using the recursive model estimation

In recent years, the development of AI has been accelerated so that the semiconductor manufacturing process has also been regarded as a very important issue. Many research results related to the plasma etch process which is one of the most important processes in the semiconductor manufacturing process have been presented in various forms. Recently, our research group has also presented a case of successful real-time multivariable control of plasma parameters based on optical emission spectroscopy. Although the above results are expected to bring about positive effects in various fields, they do not consider the variability of the system. Plasma related systems are so sensitive that online system identification is inevitable. In this paper, we performed the online system identification of the system composed of the plasma parameter through recursive parameter estimation method. Through the recursive algorithm using forgetting factor and input and output information which was gathered in real-time, we detected that the system was changing in real-time and updated the model parameters. We expect the results introduced in this paper contributes not only to the semiconductor manufacturing process but also to all the processes using plasma.

Virtual metrology (VM) model based on plasma information (PI) parameter for C 4 F 8 plasma-assisted oxide etching processes is developed to predict and monitor the process results such as an etching rate with improved performance. To apply fault detection and classification or advanced process control models on to the real-mass production lines efficiently, high-performance VM model is certainly required and principal component regression (PCR) is preferred technique for VM modeling despite this method requires many number of data set to obtain statistically guaranteed accuracy. In this paper, as an effective method to include the “good information” representing parameter into the VM model, PI parameters are introduced and applied for the etch rate prediction. By the adoption of PI parameters of b- and q-factor and surface passivation parameters as PCs into the PCR-based VM model, information about the reactions in the plasma volume, surface, and sheath regions can be efficiently included into the VM model; thus, the performance of VM is secured even for insufficient dataset provided cases. For mass production data of 350 wafers, developed PI-based VM model was satisfied required prediction accuracy of industry in C 4 F 8 plasma-assisted oxide etching process.

Morphological changes of graphite plasma facing component (PFC) were investigated with various ion irradiation conditions which may change the sputtering yield and the scrape-off layer (SOL) plasma property. The experiments were carried out by using electron cyclotron resonance deuterium plasma with the conditions of electron density range of 2.5–3.5 × 10 11 cm −3 , electron temperature range of 3.3–4.1 eV, and ion energy range of 17–100 eV. The graphite morphology was changed from plane to conical tip with increasing ion energy and dose. In addition, morphological changes increase the sputtering yield due to the increase of local angle of ion incidence. The inflow of hydrocarbon causes the increase of electron density and the decrease of electron temperature due to its higher dissociation and ionization rates than those of deuterium. This result suggests that the morphological changes of graphite should be considered in the SOL plasma interaction with graphite PFC.

The characteristics of a two–radio-frequency (RF)–driven dual antenna inductively coupled hydrogen plasma is investigated for the development of a high efficient RF negative hydrogen ion source dri...

A novel laser-assisted Hμ spectroscopy is proposed to measure negative ion density in a hydrogen plasma. The laser-induced photodetachment of negative ions leads to a decrease in Hμ intensity due to blocking of the mutual neutralization channel associated with generation of H (n=3) atoms. The relationship between the reduced Hμ intensity and the negative ion density is investigated experimentally and analytically. It is observed that the reduced Hμ intensity follows the trend in the negative ion density as a function of pressure, indicating that this spectroscopy holds promise for determining the negative ion density. In addition, a departure from linearity between the reduced Hμ intensity and the negative ion density is also analyzed because it can affect the quantitative determination of the negative ion density in the laser-assisted Hμ spectroscopy. The departure is found to be attributed to the change in the mutual neutralization reaction rates depending on plasma conditions.

The effect of interface diffusion between tungsten and graphite on embrittlement has not been examined over the tungsten ductile-brittle transition temperature. To analyze interface embrittlement w...

Spatial bullet velocity distribution of an atmospheric-pressure plasma jet (APPJ) in the N 2 and O 2 mixture gas were investigated by varying the gas mixing ratio. The bullet propagation from the discharge tube exit was observed by an ICCD and the bullet velocity had three phases as the acceleration, the constant velocity, and the deceleration phases. These velocity phases were analyzed using the simple and analytical fluid model. The density of neutrals and the transport parameters of electron were obtained from CFD-ACE+ and BOLSIG+. It can be envisaged that each of three propagation phases are influenced closely by the Penning ionization effect of helium metastable on N 2 and O 2 ionization, the induced electric field in an APPJ discharge tube, and the formation of negative oxygen molecules, respectively. It is expected that this paper explains the effects of grounded or floated target under the jet on bullet and vice versa.

A non-invasive method for ion energy distribution measurement at a RF biased surface is proposed for monitoring the property of ion bombardments in capacitively coupled plasma sources. To obtain the ion energy distribution, the measured electrode voltage is analyzed based on the circuit model which is developed with the linearized sheath capacitance on the assumption that the RF driven sheath behaves like a simple diode for a bias power whose frequency is much lower than the ion plasma frequency. The method is verified by comparing the ion energy distribution function obtained from the proposed model with the experimental result taken from the ion energy analyzer in a dual cathode capacitively coupled plasma source driven by a 100 MHz source power and a 400 kHz bias power.

In this study, the effects of various annealing conditions on tungsten film fabricated by atmospheric plasma spraying (APS) were studied to analyze the APS tungsten film and an adequate strategy for the improvement of the mechanical properties of the tungsten film. In general, the use of the APS method to create tungsten films results in splat boundaries in an oxidized state not unlike semi-cracks. We therefore conducted vacuum annealing of the tungsten film at 800 °C and 950 °C under less than 0.1 Torr pressure to strengthen the binding force between splats. Additionally, we conducted press annealing in order to achieve a more dramatic improvement. The micro-hardness of the as-sprayed tungsten film, the vacuum-annealed tungsten film, and the press-annealed tungsten film were 1.55, 1.52, and 2.19 GPa respectively. By utilizing analysis methods such as electron back-scatter diffraction, scanning electron microscopy, Raman spectroscopy, and nano-indentation, we found that filling the gap between the splats, while eliminating the oxides, played a critical role in enhancing the mechanical properties of the tungsten film fabricated by means of the APS method.

A bulk tungsten tile with conventional and shaped castellation structures was exposed to various plasmas in KSTAR during 2012 campaign, in order to verify the functions of the shaped castellation designed for ITER divertor. The thermal response of the tile during the campaign was measured by thermocouples. The tungsten tile was collected after the campaign and the castellation structures were examined. The deposition inside the gap was studied to identify the contributions of ions and charge exchange neutrals. The shaped castellation shows a penetration depth of ions smaller than that of conventional one by a factor of ∼2, thus less deposition inside the gap which is consistent with the prediction made by SPICE2 code. It seems that blister formation and cracking have occurred during plasma shots.

The generality of the non-Maxwellian electron energy distribution function (EEDF) is demonstrated by using optical emission spectroscopy (OES) and Langmuir probe measurements in inductively- and capacitively-coupled low-pressure argon plasmas to analyze the shape factor of the EEDF. To measure the shape factor of the EEDF, we propose a corona — equilibrium (CE) — based analysis model operating at low density, which uses the line intensity ratio of the Ar I to the Ar II emission lines. The Ar I line is chosen to represent the relatively low-energy state, and the Ar II line is chosen to represent the high-energy state. Thus, an analysis of the shape factor is equivalent to monitoring the variation in the high-energy electron fraction represented in the tail of the EEDF. Results show a depleted tail for the Maxwellian distribution in most of the low-density argon plasmas. The analysis reveals that the generation and the stepwise ionization of metastable argon atoms by inelastic collisions with high-energy (∼ 10 eV) electrons are dominant processes of argon plasma generation and cause serious high-energy electron loss in a low-density system compared to the loss in an ideal Maxwellian plasma. The existence of argon metastable states is inevitable; thus, the general shape of the electron energy distribution in low-pressure argon plasmas is non-Maxwellian.

Purpose Direct application of atmospheric-pressure plasma jets (APPJs) has been established as an effective method of microbial decontamination. This study aimed to investigate the bactericidal effect of direct application of an APPJ using helium gas (He-APPJ) on Porphyromonas gingivalis biofilms on sandblasted and acid-etched (SLA) titanium discs. Methods On the SLA discs covered by P. gingivalis biofilms, an APPJ with helium (He) as a discharge gas was applied at 3 different time intervals (0, 3, and 5 minutes). To evaluate the effect of the plasma itself, the He gas–only group was used as the control group. The bactericidal effect of the He-APPJ was determined by the number of colony-forming units. Bacterial viability was observed by confocal laser scanning microscopy (CLSM), and bacterial morphology was examined by scanning electron microscopy (SEM). Results As the plasma treatment time increased, the amount of P. gingivalis decreased, and the difference was statistically significant. In the SEM images, compared to the control group, the bacterial biofilm structure on SLA discs treated by the He-APPJ for more than 3 minutes was destroyed. In addition, the CLSM images showed consistent results. Even in sites distant from the area of direct He-APPJ exposure, decontamination effects were observed in both SEM and CLSM images. Conclusions He-APPJ application was effective in removing P. gingivalis biofilm on SLA titanium discs in an in vitro experiment., Graphical Abstract