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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. [ABSTRACT FROM AUTHOR]

A global model was developed to investigate the densities of negative ions and the other species in a low-pressure inductively coupled hydrogen plasma with a bi-Maxwellian electron energy distribution. Compared to a Maxwellian plasma, bi-Maxwellian plasmas have higher populations of low-energy electrons and highly vibrationally excited hydrogen molecules that are generated efficiently by high-energy electrons. This leads to a higher reaction rate of the dissociative electron attachment responsible for negative ion production. The model indicated that the bi-Maxwellian electron energy distribution at low pressures is favorable for the creation of negative ions. In addition, the electron temperature, electron density, and negative ion density calculated using the model were compared with the experimental data. In the low-pressure regime, the model results of the bi-Maxwellian electron energy distributions agreed well quantitatively with the experimental measurements, unlike those of the assumed Maxwellian electron energy distributions that had discrepancies. [ABSTRACT FROM AUTHOR]

An institutional, prospective clinical data analysis. To evaluate the safety and efficacy of a new navigable percutaneous disc decompression device (L'DISQ) in patients with lumbar disc herniation with radicular pain. We performed disc decompressions using L'DISQ on 27 patients with persistent disabling back and leg pain for 1 month or longer (average 6.48 months) due to a herniated lumbar intervertebral disc. Baseline data were prospectively gathered before the index procedure and at 1, 4, 12, and 24 weeks post-procedure. Data included pain intensity (visual analog scale [VAS]), measure of disability (Oswestry Disability Index [ODI] and Rolando-Morris Questionnaire [RM]), health-related quality of life (Bodily Pain Scale of Short Form-36 version 2 [SF-36 BP]), and passive straight leg raising test (SLR). The VAS fell from 7.08 ± 1.22 to 1.84 ± 0.99 scores at 24 weeks post-procedure. At 24 weeks, the ODI had fallen from 41.88 ± 10.61 to 16.66 ± 8.55% and the RM from 11.52 ± 3.91 to 2.68 ± 1.97 points. The SF-36 BP dropped significant improvement from 32.89 ± 5.83 to 49.57 ± 4.96 scales. In the SLR test, the angular change of 24 weeks showed considerable improvement from 60.20 ± 20.02 to 83.00 ± 14.29 degrees. No major complication occurred, although two cases developed a disc reherniation 1 month post-procedure. The L'DISQ device is specifically designed to remove herniated disc using a wand that can be navigated into a disc protrusion or extrusion. Following decompression, we measured clinically significant pain improvement and decreased disability for patients with both radicular and axial pain caused by protruded and extruded discs. [ABSTRACT FROM AUTHOR]

A numerical simulation on the spray-type dielectric barrier discharge (DBD) is carried out for a mixture gas of nitrogen (N2) and sulfur hexafluoride (SF6) at atmospheric pressure to understand the electrical characteristics and the plasma flow dynamics that depend on design parameters and operating conditions. A 2-D axiymmetric nonuniform grid is employed in the simulation code consisting of the following three numerical modules: 1) discharge module; 2) flow module; and 3) reaction calculation module. Through the coupling of these modules, the discharge and plasma flow characteristics are interactively calculated for discharge properties and behaviors of charged and neutral particles in the N2/SF6 plasma, including 26 species interacting among them by 59 reactions. As a result of numerical simulations, the effects of the spray hole and the gas flow on the plasma flow characteristics are discussed in the spray-type DBD reactor. The existence of a spray hole in the grounded barrier/electrode plate induces strong electric fields along the spray hole barrier wall, and these high fields trigger a localized discharge similar to the surface discharge. The localized discharge spreads out in the discharge region toward the powered electrode barrier and gives the discharge current a pulsed shape according to the group behavior of a high-density electron to eventually produce a high-density fluorine atom in both the spray hole and spray regions. When the spray hole radius decreases, the fluctuations of hole-induced electric field also decreases, accompanied by the reduced production of average densities of the electron and the fluorine atom. However, the reduced spray hole size enhances the advective velocity along the hole axis, and therefore, the overall fluorine atom density over the substrate surface is increased. With increasing inlet gas flow velocity, the localized discharges occur more frequently because of electric potential formation by interacting among meta-stable species and ions to enhance the fluorine atom production. The fast advective velocity also enlarges the radial distributions of effluent rate and fluorine atom density in the spray region and on the substrate surface due to the transport of neutral particles. [ABSTRACT FROM AUTHOR]

The influence of the phase shift between rf voltages applied to the powered electrodes on plasma parameters and etch characteristics was studied in a very high-frequency (VHF) capacitively coupled plasma (CCP) triode reactor. rf voltages at 100 MHz were simultaneously applied to the top and bottom electrodes having a controlled phase shift between them, which could be varied between 0° and 360°. Several plasma and process characteristics were measured as a function of the phase shift: (i) radial profiles of plasma-emission intensity, (ii) line-of-sight averaged plasma-emission intensity, and (iii) radial profiles of blanket SiO2 etching rate over a 300 mm wafer. Radial profiles of plasma emission were obtained using the scanning optical probe. It has been shown that all the measured characteristics strongly depend on the phase shift: (i) plasma-emission intensity is minimal at phase shift equal to 0° and maximal at 180° for all radial positions, while the emission radial profile changes from bell-shaped distribution with considerable nonuniformity at 0° to a much more flattened distribution at 180°; (ii) line-of-sight averaged plasma-emission intensity shows a similar dependence on the phase shift with minimum and maximum at 0° and 180°, respectively; and (iii) the etch-rate radial profile at 180° shows a much better uniformity as compared to that at 0°. Some of these results can be qualitatively explained by the redistribution of plasma currents that flow between the electrodes and also from the electrodes to the grounded wall with the phase shift. We suggest that the phase-shift effect can be used to improve the plasma and etch-rate spatial uniformity in VHF-CCP triode reactors. [ABSTRACT FROM AUTHOR]

Generation of the defect particles during the plasma-assisted metal dry etching process is induced by the various mechanisms. Most of these mechanisms are caused by the non-volatility of metal-halide compounds generated during the etching process. Degeneration of the metal etching process chamber condition is observed as the frequent process fault caused by the defects, but the worse condition is not recovered by itself. Because of this property of the metal etching process, proper work of the preventive maintenance (PM) to restore the process chamber or the addition of a discharge cleaning step is required periodically. However, inadequate PM or discharge cleaning by the uncertain cause analysis of the defect generation should be a just temporary remedy, and might lead the repetition of similar problems. To solve this problem, the virtual metrology (VM) model based on the plasma information (PI) parameters, known as PI-VM, was developed and applied for the defect control of the metal layer dry etching processes in organic light emitting diode (OLED) display manufacturing. To obtain the information about the generation rates of non-volatile compounds and their removal rates by the exhaustion system, PI parameters are designed with the consideration of the reaction kinetics in the metal etching plasma volume, sheath, and reacting surface using the big data of equipment engineering system (EES) and optical emission spectroscopy (OES) accumulated during the mass production process. The developed PI-VM index could be applied to a 2–3 h earlier alarm system for the defect occurrence, and had succeeded over 90% of alarm rate. This PI-VM alarm was applied to predictive control of the process by the early substitution of the discharge cleaning step or by the repair of the proper parts in the process chamber. By the control of processes based on the predicted results of the PI-VM, management of the mass production line with about 30% decreased defect was possible in OLED display manufacturing. [ABSTRACT FROM AUTHOR]

The enhancement of deuterium retention was investigated for tungsten in the presence of both 2.8 MeV self-ion induced cascade damage and fuel hydrogen isotope plasma. Vacancy clustering in cascade damaged polycrystalline tungsten occurred due to deuterium irradiation and was observed near the grain boundary by using all-step transmission electron microscopy analysis. Analysis of the highest desorption temperature peak using thermal desorption spectroscopy supports reasonable evidence of defect clustering in the damaged polycrystalline tungsten. The defect clustering was neither observed on the damaged polycrystalline tungsten without deuterium irradiation nor on the damaged single-crystalline tungsten with deuterium irradiation. This result implies the synergetic role of deuterium and grain boundary on defect clustering. This study proposes a path for the defect transform from point defect to defect cluster, by the agglomeration between irradiated deuterium and cascade damage-induced defect. This agglomeration may induce more severe damage on the tungsten divertor at which the high fuel hydrogen ions, fast neutrons, and self-ions are irradiated simultaneously and it would increase the in-vessel tritium inventory. [ABSTRACT FROM AUTHOR]

A novel method is proposed to determine an electron energy distribution function (EEDF) that includes the highly populated tail originated by energetic beam-like electrons (>20 eV), which often occur in narrow gap, very-high-frequency capacitively coupled plasma (VHF-CCP). This method combines conventional Langmuir probe analysis to represent the EEDF in the low-energy regime and the line-ratio method taken from the optical emission spectrum to represent the highly populated tail of the EEDF. Here the emission lines are chosen with consideration of the excitation rates, which are a function of the shape of the cross-section of the spin- and dipole-forbidden states of an argon atom and the EEDF at corresponding energy. In this method, the analytical EEDF model is chosen for the composition of the Maxwellian for low-energy (bulk) electrons, and Schulze’s time-averaged form of the shifted Maxwellian (Schulze et al 2008 J. Phys. D: Appl. Phys. 41 042003) is chosen for the highly populated tail of the EEDF. The variables of the time-averaged form of the shifted Maxwellian, the fraction and mean energy of the beam-like electrons, are determined using an emission model of line-intensity ratios, which describes the line-intensities as a function of the EEDF. This method is advantageous for the diagnostics of a time-averaged EEDF with a highly populated tail, especially where this is due to beam-like electrons that originate from stochastic heating, compared to a two-temperature EEDF. [ABSTRACT FROM AUTHOR]

Recent studies have demonstrated that the two-ion-stream-instability occurs near the plasma boundary and makes the ions reach the ‘modified Bohm velocity’ at the sheath edge. In most low-temperature plasmas, however, the ion-neutral collisions can disturb the growth of instability to occur frequently, and the ions exit the plasma boundary with their own Bohm velocities. We report some experimental observations regarding this issue. The spatial variations of the ion drift velocities and the space potential near the sheath edge were measured in Ar/Xe mixture plasmas by increasing the total pressure in the range of 0.5–2.1 mTorr. The results show that the instability cannot occur above a certain pressure condition and that is consistent with the theoretically driven pressure criteria for the onset of the instability. [ABSTRACT FROM AUTHOR]

This paper introduces how to determine concentrations of ion species in a mixed gas plasma that are not linearly proportional to their neutral partial pressures. A particle balance model was developed to predict the relative ion concentrations in multiple-ion-species plasmas, considering their ionization rates and loss fluxes to the wall. Analysis is carried out especially with Ar/Xe and Ar/He multi-dipole plasmas in which the neutral gases are directly ionized by the mono-energetic primary electrons. The experimental data of ion concentrations were obtained using the ion acoustic wave measurement method of the concentration of two ion species. The comparison reveals that the ion concentration ratio is linearly proportional to the ratio of the ionization cross sections and the ion loss velocity between two gas species. Especially, the model prediction is improved with using the two-ion-species sheath model (recently reported by Baalrud and Hegna) for obtaining the ion loss velocity at the sheath boundary. [ABSTRACT FROM AUTHOR]