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Broadband UV-assisted thermal annealing of low- <i>k</i> silicon carbonitride films using a C-rich silazane precursor
摘要： Low-k dielectric silicon carbonitride (SiCxNy) films are deposited by plasma-enhanced chemical vapor deposition using a carbon-rich silazane precursor, N-methyl-aza-2,2,4-trimethylsilacyclopentane (SiC7NH17), at 100 °C. The post-treatments of SiCxNy films are carried out by thermal annealing and a broadband UV-assisted thermal annealing (UV-annealing) at 400 °C for 5 min. Compared to the thermal annealing treatment, UV-annealing can improve both dielectric and mechanical properties of low-k SiCxNy films. Under thermal annealing, SiCxNy films show great thermal stability, but little structural change. In contrast, upon UV-annealing, most of the Si–H and N–H bonds are broken up, which induces more Si–N cross-linking and converts Si–C matrix into Si–N matrix. The ethylene bridges in Si–(CH2)2–Si also remain intact, but the unbridged hydrocarbons in Si–(CH2)2–N and Si–CH2–CH3 bonds decompose completely during the UV-annealing process. These account for the reduced dielectric constant to k = 3.2 from 3.6 and a 21% enhancement of Young’s modulus to 7.4 GPa in the SiCxNy films after UV-annealing. Broadband UV-annealing shows promise as a post-treatment method for enhancing the properties of low-k dielectric barrier, SiCxNy films.
关键词： low-k dielectric,silicon carbonitride,UV-assisted thermal annealing,plasma-enhanced chemical vapor deposition,mechanical properties
更新于2025-09-10 09:29:36
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Electron Cyclotron interaction in the early stage of EC-assisted plasma breakdown
摘要： Electron Cyclotron (EC) wave interaction with very low temperature electrons in conditions like those occurring for EC-assisted plasma breakdown is investigated via the Hamiltonian adiabatic formalism. Estimates of interest for applications to present tokamak experiments are derived. The analysis allows ultimately to derive analytically the particle energy gain per single beam crossing and to characterize the dependency of the maximum possible energy variation as a function of the wave frequency, harmonics and polarization and EC power and beam width. The investigation confirms that electrons can easily gain energies well above the ionization energy in most conditions, as observed in experiments.
关键词： tokamak experiments,beam width,Hamiltonian adiabatic formalism,harmonics,polarization,Electron Cyclotron,wave frequency,EC power,plasma breakdown
更新于2025-09-10 09:29:36
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Sequential modelling of ICRF wave near RF fields and asymptotic RF sheaths description for AUG ICRF antennas
摘要： A sequence of simulations is performed with RAPLICASOL and SSWICH to compare two AUG ICRF antennas. RAPLICASOL outputs have been used as input to SSWICH-SW for the AUG ICRF antennas. Using parallel electric field maps and the scattering matrix produced by RAPLICASOL, SSWICH-SW, reduced to its asymptotic part, is able to produce a 2D radial/poloidal map of the DC plasma potential accounting for the antenna input settings (total power, power balance, phasing). Two models of antennas are compared: 2-strap antenna vs 3-strap antenna. The 2D DC potential structures are correlated to structures of the parallel electric field map for different phasing and power balance. The overall DC plasma potential on the 3-strap antenna is lower due to better global RF currents compensation. Spatial proximity between regions of high RF electric field and regions where high DC plasma potentials are observed is an important factor for sheath rectification.
关键词： plasma heating,SSWICH,ICRF antennas,RAPLICASOL,RF-sheath rectification
更新于2025-09-10 09:29:36
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Numerical simulation on the surface charge accumulation process of epoxy insulator under needle-plane corona discharge in air
摘要： Most of the HV power equipment with gas–solid insulation suffers a lot from the surface charge accumulation due to corona discharge. The existence of surface charge distorts the local electric field and leads to surface flashover faults in extreme situations. As a result, it is important to figure out the mechanism of surface charge accumulation process. In this study, a simulation model combining both the plasma hydrodynamics and charge trapping–detrapping process was built. The simulation results have a good agreement with the experimental data, the main summary is as follows: in the surface charge accumulation process, the corona discharge intensity increases first and then decreases with time. The curves of the surface potential distributions have different shapes at different times, the central value goes up rapidly with time in the beginning and finally reaches saturation. Surface charges exist in the skin layer of epoxy insulator, some of them may be captured by traps while transporting away under built-in electric field.
关键词： corona discharge,charge trapping–detrapping process,plasma hydrodynamics,epoxy insulator,surface charge accumulation
更新于2025-09-10 09:29:36
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Measurement of Argon emission spectral of ICP plasma using a diagnostic system based on photomultiplier tubes array
摘要： Optical emission spectroscopy (OES) is one of the most important diagnostic tools in plasma physics. A self-built spectroscopic diagnostic system, owning temporal and spatial resolution, has been constructed using photo multiplier tubes (PMTs) array, spectrometer and other parts. The problem of superposition between inlet plane of bundle fiber and the focal plane of the spectrometer is analyzed and solved. In addition, the synchronization regulation of output of PMTs has been completed. This system is installed on an inductively coupled (ICP) plasma chamber in order to study the Argon (Ar) emission spectrum generated from typical radio frequency (RF) and pulse discharges. The test results show that the intensity of Ar emission spectrum increases with the power and pressure, but increase less with the flow and current ratio. Under pulse discharge condition, the intensity of spectrum does not change with the frequency, neither does the broadening of spectrum with time.
关键词： PMTs array,ICP plasma,Argon emission spectrum,Optical emission spectroscopy,RF and pulse discharges
更新于2025-09-10 09:29:36
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Electric field induced Lyman- <i>α</i> emission of a hydrogen beam for electric field measurements
摘要： Electric field induced Lyman-α emission is a new way of measuring weak electric fields in vacuum and in a plasma. It is based on the emission of Lyman-α radiation (121.6 nm) by a low-energy metastable H atom beam due to Stark-quenching of the 2s level induced by the field. In this paper, we describe the technique in detail. Test measurements have been performed in vacuum between two plates polarized at a controlled voltage. The intensity of emitted radiation, proportional to the square of the field modulus, has been recorded by a lock-in technique, which gives an excellent signal to noise ratio. These measurements provide an in situ calibration that can be used to obtain the absolute value of the electric field. A diagnostic of this type can help to address a long standing challenge in plasma physics, namely, the problem of measuring electric fields without disturbing the equilibrium of the system that is being studied.
关键词： Electric field,hydrogen beam,plasma physics,Stark-quenching,Lyman-α emission
更新于2025-09-10 09:29:36
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A computational tool for simulation and design of tangential multi-energy soft x-ray pin-hole cameras for tokamak plasmas
摘要： A new tool has been developed to calculate the spectral, spatial, and temporal responses of multi-energy soft x-ray (ME-SXR) pinhole cameras for arbitrary plasma densities (ne,D), temperature (Te), and impurity densities (nZ). ME-SXR imaging provides a unique opportunity for obtaining important plasma properties (e.g., Te, nZ, and Z eff) by measuring both continuum and line emission in multiple energy ranges. This technique employs a pixelated x-ray detector in which the lower energy threshold for photon detection can be adjusted independently. Simulations assuming a tangential geometry and DIII-D-like plasmas (e.g., ne,0 ≈ 8 × 1019 m?3 and T e,0 ≈ 2.8 keV) for various impurity (e.g., C, O, Ar, Ni, and Mo) density pro?les have been performed. The computed brightnesses range from few 102 counts pixel?1 ms?1 depending on the cut-off energy thresholds, while the maximum allowable count rate is 104 counts pixel?1 ms?1. The typical spatial resolution in the mid-plane is ≈0.5 cm with a photon-energy resolution of 500 eV at a 500 Hz frame rate.
关键词： tokamak plasmas,multi-energy soft x-ray,plasma diagnostics,pinhole cameras,x-ray spectra
更新于2025-09-10 09:29:36
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Two-channel high-resolution quasi-monochromatic X-ray imager for Al and Ti plasma
摘要： High-resolution, high-sensitivity X-ray imaging is a real challenge in high-energy density plasma experiments. We present an improved design of the Fresnel ultra high-resolution imager instrument. Using an Ultra-High-Intensity (UHI) laser to generate hot and dense plasma in a small volume of an Al-Ti mixed target provides simultaneous imaging of both Al and Ti X-ray emission. Specifically, the Al Heβ (or Lyβ) and the Ti Heα lines are imaged with a resolution of (2.7 ± 0.3) μm and (5.5 ± 0.3) μm, respectively. It features two transmission Fresnel phase zone plates fabricated on the same substrate, each associated with a multilayer mirror for spectral selection. Their spatial resolution has been measured on the PTB synchrotron radiation facility laboratory at BESSY II and on the EQUINOX laser facility. Results obtained on an UHI experiment highlight the difference of emission zone sizes between Al and Ti lines and the versatility of this instrument.
关键词： plasma experiments,Fresnel zone plates,multilayer mirrors,high-resolution,X-ray imaging
更新于2025-09-10 09:29:36
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High-power terahertz emission from a plasma penetrated by counterstreaming different-size electron beams
摘要： It is found that multi-cycle pulses of high-power coherent terahertz radiation can be efficiently generated in a plasma by counterstreaming long-pulse electron beams driving potential plasma waves via the two-stream instability. Instead of the well-known three-wave interaction processes between oblique beam-driven modes, we propose to generate electromagnetic radiation near the doubled plasma frequency due to the novel and much more efficient mechanism based on the head-on collision of longitudinal plasma waves with mismatching potential profiles. It is shown that this radiation mechanism can be implemented experimentally either by the collision of low-density electron beams with different transverse sizes or by the counter injection of denser equal-size beams unstable against filamentation perturbations. Particle-in-cell simulations for kiloampere electron beams capable of focusing into millimeter-scale sizes demonstrate the possibility to reach the high efficiency of beams-to-THz power conversion (3%–7%), which opens the path to gigawatt-class THz sources with a narrow spectral line.
关键词： electromagnetic radiation,two-stream instability,plasma,electron beams,terahertz emission
更新于2025-09-10 09:29:36
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Emittance Preservation in an Aberration-Free Active Plasma Lens
摘要： Active plasma lensing is a compact technology for strong focusing of charged particle beams, which has gained considerable interest for use in novel accelerator schemes. While providing kT=m focusing gradients, active plasma lenses can have aberrations caused by a radially nonuniform plasma temperature profile, leading to degradation of the beam quality. We present the first direct measurement of this aberration, consistent with theory, and show that it can be fully suppressed by changing from a light gas species (helium) to a heavier gas species (argon). Based on this result, we demonstrate emittance preservation for an electron beam focused by an argon-filled active plasma lens.
关键词： active plasma lensing,argon,helium,aberration-free,emittance preservation
更新于2025-09-10 09:29:36