Effect of the Electric Field Profile on the Accuracy of E-FISH Measurements in Ionization Waves

Electric field induced second harmonic (E-FISH) generation has emerged as a versatile tool for measuring absolute electric field strengths in time-varying, non-equilibrium plasmas and gas discharges. Yet recent work has demonstrated that the E-FISH signal, when produced with tightly focused laser beams, exhibits a strong dependence on both the length and shape of the applied electric field profile (along the axis of laser beam propagation). In this paper, we examine the effect of this dependence more meaningfully, by predicting what an E-FISH experiment would measure in a plasma, using 2D axisymmetric numerical fluid simulations as the true value. A pin-plane nanosecond discharge at atmospheric pressure is adopted as the test configuration, and the electric field evolution during the propagation of the ionization wave (IW) is specifically analyzed. We find that the various phases of this evolution (before and up to the front arrival, immediately behind the front and after the connection to the grounded plane) are quite accurately described by three unique electric field profile shapes, each of which produces a different response in the E-FISH signal. As a result, the accuracy of an E-FISH measurement is generally predicted to be comparable in the first and third phases of the IW evolution, and significantly poorer in the second (intermediate) phase. Fortunately, even though the absolute error in the field strength at certain time instants could be large, the overall shape of the field evolution curve is relatively well captured by E-FISH. Guided by the simulation results, we propose a procedure for estimating the error in the initial phase of the IW development, based on the presumption that the starting field profile mirrors that of its corresponding Laplacian conditions before evolving further. We expect that this approach may be readily generalized and applicable to other IW problems or phenomena, thus extending the utility of the E-FISH diagnostic.

Formation of the radial electric field profile in the WEST tokamak

Sheared flows are known to reduce turbulent transport by decreasing the correlation length and/or intensity of turbulent structures. The transport barrier that takes place at the edge during improved regimes such as H mode, corresponds to the establishment of a large shear of the radial electric field. In this context, the radial shape of the radial electric field or more exactly of the perpendicular $E\times B$ velocity appears as a key element in accessing improved confinement regimes. In this paper, we present the radial profile of the perpendicular velocity measured using Doppler back-scattering system at the edge of the plasma, dominated by the $E\times B$ velocity, during the first campaigns of the WEST tokamak. It is found that the radial velocity profile is clearly more sheared in LSN than in USN configuration for ohmic and low current plasmas ($B=3.7T$ and $q_{95}=4.7$), consistently with the expectation comparing respectively “favourable” versus “unfavourable” configuration. Interestingly, this tendency is sensitive to the plasma current and to the amount of additional heating power leading to plasma conditions in which the $E\times B$ velocity exhibits a deeper well in USN configuration. For example, while the velocity profile exhibits a clear and deep well just inside the separatrix concomitant with the formation of a density pedestal during L-H transitions observed in LSN configuration, deeper $E_r$ wells are observed in USN configuration during similar transitions with less pronounced density pedestal.

Effect of Geometrical Properties on Localized Surface Plasmon Resonance of Gold Nanoparticles

This work reportson plasmonic effects (i.e light scattering and absorption properties) induced by two different gold nanoparticles (AuNPs)-shaped: spherical particle and triangular particle. The scattering cross-section and electric field profiles have been investigated by using theboundary element method (MNPBEM toolbox). Two configurations: the isolated AuNPand the coupledtwo-gold NPsystem have been considered to evaluate the localized surface plasmon resonance (LSPR) in eithersingle or coupled AuNPstructures. The effect of the surrounding medium on the scattering behavior of the NPs has also been examined. Then the dependence of “hotspot” intensity on the distance between two NPs has been recognized by mapping the electric field profile. The obtained results can be used as the guidelines for synthesizing AuNP structures to employ LSPR for sensing or other applications.

Experimental observation of asymmetrical microwave jets and far-field distribution generated by a dual-material system

In this paper, we report the experimental and numerical investigation of plane wave diffraction by an all-dielectric dual-material cuboid. Edge diffraction by a cuboid leads to the generation of a narrow, high intensity beam in the near-field region called a photonic jet. We examine the dependence of the jet behavior and orientation on the materials and dimensions of constitutive parts in the microwave frequency domain. The possibility to shift and deviate the resultant microwave jet in the near-field region of such a structure depending on the size of constitutive parts is demonstrated numerically. Experimentally, we observe a shift in the spatial position of the jet. The experimental asymmetric electric field profile observed in the far-field region is attributed to the input of multiple edge waves generated by the dual-material cuboid. The presented results may be scaled at different frequency bands such as optical frequencies for designing nanostructures enabling the focusing and deviation functionality and creation of new optical devices which would satisfy the needs of emerging nanophotonic applications.

The Effect of the Axial Heat Transfer on Space Charge Accumulation Phenomena in HVDC Cables

To date, it has been widespread accepted that the presence of space charge within the dielectric of high voltage direct current (HVDC) cables is one of the most relevant issues that limits the growing diffusion of this technology and its use at higher voltages. One of the reasons that leads to the establishment of space charge within the insulation of cables is the temperature dependence of its conductivity. Many researchers have demonstrated that high temperature drop over the insulation layer can lead to the reversal of the electric field profile. In certain conditions, this can over-stress the insulation during polarity reversal (PR) and transient over voltages (TOV) events accelerating the ageing of the dielectric material. However, the reference standards for the thermal rating of cables are mainly thought for alternating current (AC) cables and do not adequately take into account the effects related to high thermal drops over the insulation. In particular, the difference in temperature between the inner and the outer surfaces of the dielectric can be amplified during load transients or near sections with axially varying external thermal conditions. For the reasons above, this research aims to demonstrate how much the existence of “hot points” in terms of temperature drop can weaken the tightness of an HVDC transmission line. In order to investigate these phenomena, a two-dimensional numerical model has been implemented in time domain. The results obtained for some case studies demonstrate that the maximum electric field within the dielectric of an HVDC cable can be significantly increased in correspondence with variations along the axis of the external heat exchange conditions and/or during load transients. This study can be further developed in order to take into account the combined effect of the described phenomena with other sources of introduction, forming, and accumulation of space charge inside the dielectric layer of HVDC cables.

The TeraFERMI Electro-Optic Sampling Set-Up for Fluence-Dependent Spectroscopic Measurements

TeraFERMI is the THz beamline at the FERMI free-electron-laser facility in Trieste (Italy). It uses superradiant Coherent Transition Radiation emission to produce THz pulses of 10 to 100 μ J intensity over a spectral range which can extend up to 12 THz. TeraFERMI can be used to perform non-linear, fluence-dependent THz spectroscopy and THz-pump/IR-probe measurements. We describe in this paper the optical set-up based on electro-optic-sampling, which is presently in use in our facility and discuss the properties of a representative THz electric field profile measured from our source. The measured electric field profile can be understood as the superimposed emission from two electron bunches of different length, as predicted by electron beam dynamics simulations.

Effects of external shed damage on voltage and electric field profile for overhead insulators

Purpose This paper aims to present simulation studies on voltage and electric field characteristics for imperfect ceramic insulators using QuickFieldTM software. Based on previous studies, it is accepted that string insulator can still serve the transmission line although imperfect of certain insulator exist in a string. However, different materials of porcelain and glass type had made these insulators own different abilities to carry electricity to be transferred to the consumers. Design/methodology/approach Cap and pin type of porcelain and glass insulators are used as the main subject for comparison. The simulation works begins with modeling a single insulator, followed by string of ten insulators with their respective applied voltage, that is, 11 and 132 kV. The insulator was modeled in alternate current conduction analysis problem type using QuickField Professional Software. Technical parameters for porcelain and glass insulator were manually inserted in the modeling. Findings This paper presents an investigation on the influence of broken porcelain and glass insulators in string for voltage and electric field characteristics. For single insulator, the voltage distribution may literally reduce when experiencing external damages; whereby the broken porcelain insulator condition is worse than the glass insulator. In terms of electric field distribution, the glass insulator is badly affected compared with the porcelain insulator, as it is pulverized comprehensively. Research limitations/implications Further work needs to be done to establish whether the experiments of these simulations study will present coequal outcomes. This study endeavors in promoting a good example of voltage and electric field characteristics across high voltage (HV) insulator with the presence of broken insulator in the string. Practical implications This study is beneficial to future researchers and manufacturing companies in strategic management and research planning when they involve in the field of HV insulators. It will also serve as a future reference for academic and study purposes. This research will also educate many people on how HV insulators work. Social implications This study will be helpful to the industry and business practitioners in training for the additional results and knowledge to be updated in the area of HV insulators. Originality/value This paper presents the analysis of porcelain and glass insulators according to their respective logic conditions when broken. Consequently, the existence of a damage insulator in a string may alter the distribution of voltage and electric field which may ultimately lead to the insulation breakdown after some time. This is because the broken insulator may cause other insulators to withstand the remaining voltage allocated for that particular insulator and may affect the insulators in terms of the life span. Therefore, the distribution of voltage and electrical field characteristics in the presence of broken insulators had been studied in this project.