This work presents an experimental investigation of the hydrodynamic effects induced by nanosecond and conventional spark discharges. The energy deposited in sparks in the short breakdown time (~1 mJ ...mm−1) induces hydrodynamic effects that redistribute the energy over a large volume (~1 cm3) surrounding the initial plasma channel. This process influences the subsequent formation of the ignition kernel and the initiation of combustion. The experimental results presented in this paper were obtained with a set of synchronized diagnostics including schlieren, OH planar laser induced fluorescence and electrical measurements of the energy deposited in the plasma. It is shown that the motion of the gas excited after the discharge breakdown depends not only on the total deposited energy but also on the dynamics of the energy input in the plasma. Finally, the effects of nanosecond sparks are compared with those of conventional sparks used for internal combustion engines. We show that, with 20 times less energy, the nanosecond spark produces a twice bigger excited gas volume than the conventional spark. This is because the energy deposited by the nanosecond spark during the breakdown stage is three times higher than for the conventional spark.
The formation and decay of the thermal spark generated by a single nanosecond high-voltage pulse between pin electrodes are characterized in this study. The influence of air pressure in the range ...50-1000 mbar is investigated at 300 K. By performing short-gate imaging and optical emission spectroscopy (OES), we find that the thermal sparks exhibit an intense emission from excited electronic states of N+, in contrast with non-thermal sparks for which the emission is dominated by electronic transitions of N2. Spark thermalization consists of the following steps: (i) partial ionization of the plasma channel accompanied by N2 emission, (ii) creation of a fully ionized filament at the cathode characterized by N+ emission, (iii) formation of a fully ionized filament at the anode, (iv) propagation of these filaments toward the middle of the interelectrode gap, and (v) merging of the filaments. The formation of the filaments, steps (ii) and (iii), occurs at sub-nanosecond timescales. The propagation speed of the filaments is on the order of 104 m s−1 during step (iv). For the 1 bar condition, the electron number densities are measured from the Stark broadening of N+ and Hα lines, with spatial and temporal resolution. The electron temperature is also determined, from the relative emission intensity of N+ excited states, attaining a peak value of 48 000 K. In the post-discharge, the electron number density decays from 4 × 1019 to 2 × 1018 cm−3 in 100 ns. We show that this decay curve can be interpreted as the isentropic expansion of a plasma in chemical equilibrium. Comparisons with previous experiments from the literature support this conclusion. Expressions for the Van der Waals and resonant broadenings of Hα, Hβ, and several lines of O, O+, N and, N+ are derived in the appendix.
The development of a nanosecond surface dielectric barrier discharge in air at pressures 1-6 bar is studied. At atmospheric pressure, the discharge develops as a set of streamers starting ...synchronously from the high-voltage electrode and propagating along the dielectric layer. Streamers cover the dielectric surface creating a 'quasi-uniform' plasma layer. At high pressures and high voltage amplitudes on the cathode, filamentation of the discharge is observed a few nanoseconds after the discharge starts. Parameters of the observed 'streamers-to-filaments' transition are measured; physics of transition is discussed on the basis of theoretical estimates and numerical modeling. Ionization-heating instability on the boundary of the cathode layer is suggested as a mechanism of filamentation.
The ratio of emission intensities of the second positive N2(C3Πu, v′ = 0) → N2(B3Πg, v = 0), 337.1 nm and first negative (B → (X, 391.4 nm systems of nitrogen have been measured in a nanosecond ...surface dielectric barrier discharge (SDBD). The measurements were carried out in synthetic air for a pressure range 1-3 bar for different polarities of the high-voltage (HV) pulse. For all the investigated conditions, the ratio of emission intensities at the wavelengthes 391.4 and 337.1 nm, measured experimentally, is systematically higher for the positive polarity of HV electrodes. To analyze the spatial distribution of N2(C3Πu) and (B emissions, comprehensive two-dimensional numerical modeling for P = 1 bar has been performed. The details of the formation of a narrow gap between the dielectric surface and the streamer channel in the case of positive polarity of HV electrodes are discussed. The ratio of integrated over space calculated emission intensities, , has been analyzed and compared with obtained experimental data. A good agreement was obtained for a negative polarity SDBD. For a positive polarity discharge, for all the considered conditions. Explanation for the observed effect is suggested.
Streamer-to-filament transition is a general feature of high pressure high voltage (HV) nanosecond surface dielectric barrier discharges. The transition was studied experimentally using time- and ...space-resolved optical emission in UV and visible parts of spectra. The discharge was initiated by HV pulses 20 ns in duration and 2 ns rise time, positive or negative polarity, 20-60 kV in amplitude on the HV electrode. The experiments were carried out in a single-shot regime at initial pressures P > 3 bar and ambient initial temperature in air, N2, H2:N2 and O2:Ar mixtures. It was shown that the transition to filamentary mode is accompanied by the appearance of intense continuous radiation and broad atomic lines. Electron density calculated from line broadening is characterized by high absolute values and long decay in the afterglow. The possible reasons for the continuous spectra were analyzed.
Nanosecond surface dielectric barrier discharge (nSDBD) is an efficient tool for a multi-point plasma-assisted ignition of combustible mixtures at elevated pressures. The discharge develops as a set ...of synchronously propagated from the high-voltage electrode charged channels (streamers), with a typical density up to a few streamers per millimetre of the length of the electrode. In combustible mixtures, nSDBD initiates numerous combustion waves propagating from the electrode. Very little is known about nSDBD at high pressures. This work presents a comparative experimental study of the surface dielectric barrier discharge initiated by high-voltage pulses (U=±(20-60) kV) of different polarities in air at elevated pressures (P=1-6 atm). Discharge morphology, deposited energy and velocity of the discharge front propagation are analysed. Differences between the discharges of positive and negative polarity, as well as the changes in the discharge morphology with changing of a gas mixture composition,
Double Deeply Virtual Compton Scattering (DDVCS) is the only experimental channel for the determination of the dependence of the Generalized Parton Distributions (GPDs) on both the average and the ...transferred momentum independently. The physics observables of the electron induced di-muon production reaction
e
→
±
p
→
e
±
p
μ
+
μ
-
off unpolarized hydrogen are discussed. Their measurement with the high luminosity and large acceptance SoLID spectrometer at the Thomas Jefferson National Accelerator Facility, using polarized and unpolarized positron and electron beams at 11 GeV is investigated. This experimental configuration is shown to provide unprecedented access to the GPDs with the determination of the real and imaginary parts of the Compton Form Factor
H
in an unexplored phase space, and to enable an exploratory investigation of higher twist effects.
Reactor experiment for neutrino oscillation (RENO) began data-taking from August 2011. It successfully observed reactor antineutrino disappearance in April 2012 to measure the smallest mixing angle ...of θ13. Two identical detectors, one at near location and the other at far location, are constructed at the Yonggwang nuclear power plant in South Korea, to compare the observed reactor neutrino fluxes. Each RENO detector is filled with 16 mass tons of Gadolinium loaded liquid scintillator (GdLS) in the neutrino target region, and with 28 mass tons of unloaded liquid scintillator (LS) in the γ-catcher region surrounding the target. LS was developed to satisfy chemical, physical, optical properties, and safety requirements. Linear alkyl benzene (LAB) was chosen as a solvent because of its high flash-point, sufficient light yield, and being environmentally friendly. GdLS is carefully developed to keep a long attenuation length and high light yield for a long time period. In this paper, we report the characteristics and mass production of the RENO LS and GdLS.
The CLAS12 Geant4 simulation Ungaro, M.; Angelini, G.; Battaglieri, M. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
04/2020, Letnik:
959, Številka:
C
Journal Article
Recenzirano
Odprti dostop
The Geant4 Monte-Carlo (GEMC) package is used to simulate the passage of particles through the various CLAS12 detectors. The geometry is implemented through a database of Geant4 volumes created ...either through the GEMC native API, by the CLAS12 geometry service, or imported from the CAD engineering model. The truth information is digitized with a plugin mechanism by routines specific to each detector and includes the use of the CLAS12 calibration database constants to produce both ADC and TDC response functions. Theoretical models that produce the generated events interface with GEMC through the LUND data format. The merging of simulated data with real random trigger data provides a mechanism to include both beam and electronic background into the simulation of generated events to accurately model beam data from the CLAS12 detector. The performance of simulation is demonstrated by comparison with the experimental data.
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