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Investigation on laser plasma instability of the outer ring beams on SGIII laser facility
摘要： In order to study the laser plasma instabilities (LPIs) in the context of some novel six-side laser-driven indirect designs like the six-cylinder-port hohlraum and the three-axis cylindrical hohlraum, where the laser beams inject in hohlraum with a large angle. LPI experiments in cylindrical hohlraum with only outer beams were designed and performed based on the current laser arrangement condition of SGIII laser facility for the first time. Stimulated Brillouin backscatter (SBS) was found to be the dominant instability with high instantaneous reflectivity in experiments. A typical feature was obtained in the time-resolved spectra of SBS, which maintained similar for different laser intensities of the interaction beam. The experimental data are analyzed by the hydrodynamic simulations combined with HLIP code, which is based on the ray-tracing model. By analysis of experimental data, it is argued that the mixture of gas and Au in the region of their interface is important to SBS, which indicates the need for the mixture model between the filled gas and the high Z plasma from hohlraum wall in the hydrodynamic simulations. Nonlinear saturation of SBS as well as the smoothed beam are also discussed here. Our effective considerations of the ions pervasion effect and the smoothed beam provide utilitarian ways for improvement of the current ray-tracing method.
关键词： laser plasma instabilities,hydrodynamic simulations,stimulated Brillouin backscatter,ray-tracing model,SGIII laser facility
更新于2025-09-09 09:28:46
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Experimental investigation on the optical emission spectroscopy of dielectric barrier discharge plasma actuators at different atmospheric pressures
摘要： The experiment of dielectric barrier discharge (DBD) plasma actuator using an asymmetrical electrodes configuration is conducted to investigate optical emission spectroscopy of the plasma discharge at pressures from 0.02 to 0.1 Mpa in air mixed with various concentrations of Ar (0%, 20%, 50%, and 80%). The measurements were performed with a sinusoidal driven DBD having an amplitude of 12 kV and a frequency of 1 kHz. The diffuse DBD discharge images and the optical emission spectra are recorded successfully, and the effects of pressure and concentration of Ar are investigated, respectively. It is found that the emission intensities of air discharge increase with decreasing the pressure but increasing the concentration of Ar to some extent. Especially, when the pressure is lower than 0.04 Mpa or the concentration of Ar is over 50%, the emission intensities increase obviously rapidly. The experimental results indicate that the low pressure environment and the high concentration of Ar are beneficial to improve the performance of the DBD plasma discharge actuators.
关键词： atmospheric pressure,plasma actuator,optical emission spectroscopy,dielectric barrier discharge,Ar concentration
更新于2025-09-09 09:28:46
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Optical emission spectroscopy investigation of the current sheet in a small-bore parallel-plate electromagnetic plasma accelerator
摘要： The optical emission spectrum of the propagating current sheet in a small-bore parallel-plate electromagnetic plasma accelerator has been studied. The accelerator is powered by a fourteen stage pulse forming network, which yields a damped oscillation square wave of current with a pulse width of 20.5 ls. The movement of the first current sheet and the second current sheet is identified using three single magnetic probes placed at various axial positions. Current sheet canting is measured by two double magnetic probes. The spectrum of the current sheet is measured using a spectroscopic system. The electron density of the current sheet plasma is determined via Stark broadening of the hydrogen Ha line. The current sheet is almost perpendicular to the electrode. The current sheet electron density increases as the current sheet propagates. The current sheet electron density is mainly determined by the prefill pressure rather than the discharge current. The impurity charged particles caused by ablation of the back wall insulator exists in the current sheet. Residual particles are generally left behind the first current sheet and are swept and ionized by the second current sheet. The estimated current sheet sweeping efficiency is greater than 80%. The parallel-plate electromagnetic plasma accelerator developed in this paper shows great potential in generating high electron density plasma jets.
关键词： Stark broadening,optical emission spectroscopy,parallel-plate electromagnetic plasma accelerator,current sheet,electron density
更新于2025-09-09 09:28:46
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[IEEE 2018 43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz2018) - Nagoya, Japan (2018.9.9-2018.9.14)] 2018 43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Far Infrared and THz Detectors: Principles of Operation and Figures of Merit
摘要： In this paper we discuss characteristics of detectors and their experimental applications in the Far Infared (FIR) and lower THz spectral range: 50-3000 GHz (6mm-100 μm), with special attention to Plasma Diagnostics, THz-TDS and Free Electron Lasers (FEL). The International System of Units (SI) will be used throughout.
关键词： THz-TDS,Far Infrared,THz Detectors,Plasma Diagnostics,Free Electron Lasers
更新于2025-09-09 09:28:46
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Poly(vinylidene fluoride)/Plasma-Treated BaTiO3 Nanocomposites with Enhanced Electroactive Phase
摘要： Functional C=O and C-O groups are successfully fixated onto the surface of a high dielectric constant material barium titanate (BaTiO3) via non-thermal plasma. The strong dipole interaction exists between these functional groups and CH2 or CF2 groups of poly(vinylidene fluoride) (PVDF), resulting in the enhancement of the electroactive γ-phase of PVDF/BaTiO3 nanocomposites on one hand; on the other hand the dispersion of BaTiO3 is enhanced in the PVDF matrix, where the smaller spherulite size and better hydrophilic property are observed in the PVDF/plasma-treated BaTiO3 nanocomposite, comparing with the untreated ones. Therefore, the PVDF/plasma-treated BaTiO3 nanoparticles exhibited higher dielectric constant and lower dielectric loss than the PVDF/BaTiO3 nanoparticles.
关键词： plasma-treated barium titanate nanocomposites,dielectric constant,electroactive γ-phase,dielectric loss,poly(vinylidene fluoride) (PVDF)
更新于2025-09-09 09:28:46
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Plasma Etching Processes for CMOS Devices Realization || Plasma Etch Challenges for Gate Patterning
摘要： The patterning of the gate electrode is a critical step for transistor fabrication. For years, doped polysilicon (pSi) has been used as a gate metal while silicon dioxide has been used as a gate dielectric. After SiO2 and pSi deposition, the gate was patterned by conventional lithography and plasma etching (described in Chapters 3 and 2, respectively). At each technological generation, the length of the gate and the thickness of the gate dielectric were reduced. However, when the thickness of the gate oxide was reduced below a few nanometers, the tunneling current increased. In addition, high-performance CMOS circuits take advantage of different work functions for the gate metals between P and N transistors. For all these reasons, the standard doped pSi/SiO2 structures shifted towards dual metal (different metal for N and P transistors) high-k dielectric structures. Initially, the dual metal was obtained with different dopings of pSi, and, today, it is obtained by integrating different metal materials between the N and P transistors. The high-k dielectrics were initially based on SiON/SiO2 layers and then shifted to hafnium-based dielectrics (HfO2, HfSiON, etc.).
关键词： high-k dielectric,transistor fabrication,plasma etching,gate patterning,metal gate
更新于2025-09-09 09:28:46
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[IEEE 2017 IEEE International Conference on Plasma Science (ICOPS) - Atlantic City, NJ, USA (2017.5.21-2017.5.25)] 2017 IEEE International Conference on Plasma Science (ICOPS) - Transition Of Thermodynamic Property Of Electron In A Magnetically Expanding Plasma
摘要： Transition of thermodynamic behavior for the electrons in a magnetically expanding plasma is experimentally observed by local measurement using an axially movable cylindrical Langmuir probe. The polytropic indexes which are deduced from the correlations among the plasma potential, effective electron temperature, and electron density seem to have a quite different value of 3 ± 0.2 and 1.17 ± 0.03 near the nozzle throat and far from the nozzle, respectively. The transition of polytropic index can be explained by a theoretical calculation of effective polytropic index depending on the double-adiabatic laws and the thermal energies for magnetized anisotropic plasmas. The results show that the significant electron cooling near the nozzle throat is caused by nearly one-dimensional adiabatic expansion along almost parallel strong magnetic field. With increasing the distance from the nozzle throat, the magnetic field strength decreases and the electron cooling rate is also decreased. The present study demonstrates that a sufficiently high and nearly longitudinal magnetic field configuration can enhance the electron cooling near the nozzle throat significantly. It also means that the ion acceleration can be enhanced through high potential drop generated by high electron cooling rate. Ion demagnetization is correlated with the change in the thermodynamic property of electrons along the distance from the magnetic nozzle.
关键词： expanding,plasma,collisionless
更新于2025-09-09 09:28:46
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Titanium coverage for plasma-induced uniform HfSiON film from Hf nanoscale islands on SiO <sub/>2</sub> /Si
摘要： Signi?cant improvement of the in-plane uniformity of an HfSiON ?lm is enabled by a Ti coverage over Hf islands on an SiO2/Si substrate. Surface diffusion of Hf during an HfSiON ?lm growth from Hf (island)/SiO2/Si structure induced by a nitrogen inductively coupled plasma (ICP) exposure is effectively suppressed by the Ti coverage. The nitrogen ICP exposure to the Ti/Hf (island)/SiO2/Si surface forms a TiN layer, which suppresses the surface diffusion of Hf by lowering the surface energy. Even a small Ti coverage of 5% is effective for the uniform Hf concentration in the HfSiON ?lm. The uniformity of the ?lm is monitored by an in vacuo noncontact AFM and a cross-sectional SEM imaging. An ex situ XPS analysis indicates that the TiN layer is sputtered by the ion bombardment and the Ti content in the ?lm decreases less than 1%. The intermixing of Si with Hf and the subsequent nitridation of the ?lm is successfully performed even the surface is covered with TiN. The mercury probe measurement revealed that the improved uniformity by the Ti coverage increases the capacitance and reduces the leakage current of the high-k dielectric ?lm.
关键词： uniform film,capacitance,HfSiON,Ti coverage,leakage current,nitrogen ICP,surface diffusion,plasma-induced,TiN layer
更新于2025-09-09 09:28:46
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Plasma Etching of SiO <sub/>2</sub> Using Heptafluoropropyl Methyl Ether and Perfluoropropyl Vinyl Ether
摘要： As alternative to perfluorocompounds, hydrofluoroether and perfluoroalkyl vinyl ether were used for SiO2 etching. SiO2 was etched in heptafluoropropyl methyl ether (HFE-347mcc3)/Ar and perfluoropropyl vinyl ether (PPVE)/Ar plasmas, separately, and their etch characteristics were compared at bias voltages ranging from ?400 to ?1200 V. The etch rate of SiO2 in a HFE-347mcc3/Ar plasma was approximately 2.5 times higher than that in a PPVE/Ar plasma at a bias voltage of ?400 V. However, the difference in the etch rates decreased with increasing bias voltage, reaching nearly zero at a high bias voltage of ?1200 V. The change in the etch rate of SiO2 was attributed to not only the amount of F radicals but also the characteristics in the steady-state fluorocarbon films formed on the SiO2 substrate. In the low-bias voltage regime (?400 to ?800 V), higher etch rates in a HFE-347mcc3/Ar plasma than those in a PPVE/Ar plasma were obtained because both the thickness and fluorine-to-carbon (F/C) ratio of the steady-state fluorocarbon film controlled the etch rate of SiO2. On the other hand, the F/C ratio of the steady-state fluorocarbon film, rather than its thickness, limited the etch rate of SiO2 in the high-bias voltage regime (?800 to ?1200 V).
关键词： fluorocarbon films,perfluoroalkyl vinyl ether,hydrofluoroether,SiO2 etching,plasma etching
更新于2025-09-09 09:28:46
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Tomographic capabilities of the new GEM based SXR diagnostic of WEST
摘要： The tokamak WEST (Tungsten Environment in Steady-State Tokamak) will start operating by the end of 2016 as a test bed for the ITER divertor components in long pulse operation. In this context, radiative cooling of heavy impurities like tungsten (W) in the Soft X-ray (SXR) range [0.1 keV; 20 keV] is a critical issue for the plasma core performances. Thus reliable tools are required to monitor the local impurity density and avoid W accumulation. The WEST SXR diagnostic will be equipped with two new GEM (Gas Electron Multiplier) based poloidal cameras allowing to perform 2D tomographic reconstructions in tunable energy bands. In this paper tomographic capabilities of the Minimum Fisher Information (MFI) algorithm developed for Tore Supra and upgraded for WEST are investigated, in particular through a set of emissivity phantoms and the standard WEST scenario including reconstruction errors, in?uence of noise as well as computational time.
关键词： Plasma diagnostics - interferometry, spectroscopy and imaging,X-ray detectors,Micropattern gaseous detectors (MSGC, GEM, THGEM, RETHGEM, MHSP, MICROPIC, MICROMEGAS, InGrid, etc),Radiation calculations
更新于2025-09-09 09:28:46