CO2 conversion by thermal plasma with carbon as reducing agent: high CO yield and energy efficiency Hot!
A key problem in CO2 conversion by thermal plasma is suppressing the inverse reactions, CO+O→CO2 and CO+0.5O2 →CO2 , to simultaneously obtain high CO yield and energy efficiency. This can be done by quickly quenching the decomposed gas or rapidly taking away free oxygen from decomposed gas. In this paper, experiments of CO2 conversion by thermal plasma with carbon as a reducing agent are presented. Carbon quickly devoured free oxygen in thermal plasma decomposed gas, and not only is the inverse reaction completely suppressed, but the discharge energy to form oxygen atoms, oxygen molecular, and thermal energy is also reused. A CO2 conversion rate of 67%–94% and the corresponding electric energy efficiency of about 70% are achieved, both are much higher than that seen so far by other plasma implementations.
Nonreciprocal properties of 1D magnetized plasma photonic crystals with the Fibonacci sequence
In this paper, the nonreciprocal properties of a novel kind of 1D magnetized plasma photonic crystals (MPPCs) with the Fibonacci sequence are investigated. The isolation of the proposed 1D MPPCs is also used to analyze the nonreciprocal properties. Compared to the conventional 1D MPPCs with periodic structure, the nonreciprocal performance can be significantly improved. The effects of several parameters of the proposed 1D MPPCs on the nonreciprocal properties are studied by the transfer matrix method, which includes the incident angle, order of the Fibonacci sequence, plasma frequency, plasma cyclotron frequency and plasma filling factor. The obtained results show that the nonreciprocal propagation properties can be improved by increasing the values of the plasma cyclotron frequency and incident angle, but they will worsen by blindly increasing the order of the Fibonacci sequence, plasma frequency and filling factor of plasma. The peaks of transmittance also are obviously reduced. In addition, the value of isolation will increase with increasing the incident angle, order of Fibonacci sequence, plasma frequency and plasma filling factor. However, when the plasma cyclotron frequency is increased, the value of isolation will be increased at lower frequencies, but is almost unchanged at higher frequencies.
Negative refraction in a rotational plasma metamaterial
The features of negative refraction are investigated by using a rotational plasma metamaterial. It is assumed that the plasma metamaterial is composed of plasma and dielectric material periodically. The analytical results show that the plasma density, plasma filling factor, and rotation angle significantly changed the properties of negative refraction. Interestingly, the plasma metamaterial without exhibiting negative refraction effect will show negative refraction when rotating the optical axis of the metamaterial, while the range of incident angle for negative refraction will be reduced or even disappear for the plasma metamaterial exhibiting negative refraction effect when rotating the optical axis. Moreover, the full-angle negative refraction can be obtained by specific rotation angle and plasma density. The effects of plasma density, plasma filling factor and the rotation angle on the properties of THE negative refraction effect are also explored and discussed in detail.
The residual zonal flow in tokamak plasmas with a poloidal electric field
In a tokamak plasma with auxiliary heating by cyclotron waves, a poloidal electric field will be produced, and as a consequence influence the residual zonal flow (RZF) level. The poloidal electric field can also be induced through biasing electrodes at the edge region of tokamaks. Numerical evaluation for a large aspect ratio circular cross section tokamak for the electron cyclotron wave heating indicates that the RZF level decreases significantly when the poloidal electric field increases. Qualitatively, the ion cyclotron wave heating is able to increase the RZF level. It is difficult to apply the calculation to the real cyclotron wave heating experiments since we need to know factors such as the plasma profiles, the exact power deposition and the cross section geometry, etc. It is possible to use the cyclotron wave heating to control the zonal flow and then to control the turbulence level in tokamak experiments.
Estimation of magnetic island width by the fluctuations of electron cyclotron emission radiometer on J-TEXT
The width of a magnetic island is an important parameter for the quantitative analysis of magnetohydrodynamic-related physics. An electron cyclotron emission radiometer (ECE) is a powerful tool that can be used to obtain this width, which can usually be determined from the flat temperature distribution at the O-point phase or the maxima temperature perturbation. An improved method to estimate the width of a magnetic island is proposed in this paper, and it is independent of calibration. With this method and the existing 24-channel ECE system, the width of a rotation magnetic island can be estimated. Additionally, by filtering the fluctuation ECE signal, the evolution of the magnetic island can be obtained. The results of this method are consistent with those of the integrated magnetic probe signals, which represent the relative change of the magnetic island.
Study of obliquely propagating electron acoustic shock waves with non-extensive electron population
Obliquely propagating electron acoustic shock waves in magnetized plasma composed of stationary ions, cold and non-extensive hot electrons are investigated by deriving Korteweg–de Vries Burgers (KdVB) equation. The tangent hyperbolic method is used to solve the KdVB equation in dissipative medium. The dissipation effect is introduced in the model by means of kinematic viscosity term. The analytical calculations of the KdVB equation shows that the structures (amplitude, velocity and width) of the shock waves are modified significantly with kinematic viscosity (η0), obliqueness (kz) and magnetic field (ωc). Since plasmas are ubiquitously permeated with magnetic field, it is pertinent to explore the characteristics of KdVB equation in a magnetized plasmas.
Breakdown characteristics of CF3I/N2/CO2 mixture in power frequency and lightning impulse voltages
Trifluoroiodomethane (CF3I) and its mixtures are believed to be prospective alternatives to sulfur hexafluoride (SF6 ), which has been included as a greenhouse gas. In this paper, the breakdown properties of a CF3I/N2 /CO2 mixture with the volume fraction of CF3I fixed at 10% are investigated under power frequency and lightning impulse voltages. The experimental result shows that N2 possesses higher power frequency and negative lightning impulse breakdown voltages than CO2, but the power frequency and more negative lightning impulse breakdown voltages of the CF3I/N2 /CO2 mixture do not increase with the content of N2. For the purpose of explaining this abnormal phenomenon, the ionization energies and excitation energies of CF3I, N 2 and CO2 are calculated. The computation results indicate that the ionization energy of CF3I is lower than the first excitation energy of N2, but higher than the lowest excitation energy of CO2, which means that CF3I molecules are easily ionized by metastable N2 molecules. The first excitation energy of N2 is too high, which hinders its application as the buffer gas of CF3I.
High-power microwave propagation properties in the argon plasma array
The argon plasma induced by the L-/C-band high-power microwave (HPM) is investigated theoretically and experimentally. Influences of the microwave power, pulse width, polarization and the plasma electron density on the protection performance of the plasma array against HPM are studied. The results show that the effect of HPM is caused by energy accumulation, with the gas breakdown emerging only after a short time. The attenuation of the wave by the plasma array with the tubes off can reach approximately 23 dB at 1.3 GHz. It can also be obtained that the protection performance of the plasma array against the TE wave is better than that against the TM one. The plasma array shows better protection performance in the L-band than in the C-band. In addition, the attenuation of 5.6 GHz HPM can reach 30 dB when the tubes are turned on in the experiment. The research shows that the plasma array has protection ability against HPM.
Degradation and mineralization of ciprofloxacin by gas–liquid discharge non-thermal plasma
A typical quinolones antibiotic ciprofloxacin (CIP) in aqueous solution was degraded by a gas–liquid discharge non-thermal plasma system. The discharge plasma power and the emission intensity of the excited reactive species (RS) generated in the gas phase were detected by the oscilloscope and the optical emission spectroscopy. The effects of various parameters on CIP degradation, i.e. input powers, initial concentrations addition of radical scavengers and pH values were investigated. With the increase of discharge power, the degradation efficiency increased but the energy efficiency significantly reduced. The degradation efficiency also reduced under high concentration of initial CIP conditions due to the competitive reactions between the plasma-induced RS with the degradation intermediates of CIP. Different radical scavengers (isopropanol and CCl4) on ·OH and H· were added into the reaction system and the oxidation effects of ·OH radicals have been proved with high degradation capacity on CIP. Moreover, the long-term degradation effect on CIP in the plasma-treated aqueous solution proved that the long-lived RS (H2O2 and O3, etc) might play key roles on the stay effect through multiple aqueous reactions leading to production of ·OH. The degradation intermediates were determined by the method of electrospray ionization (+)-mass spectroscopy, and the possible degradation mechanism were presented.
Plasma ignition threshold disparity between silver nanoparticle-based target and bulk silver target at different laser wavelengths
Plasma ignition threshold of nanoparticle-based and bulk silver targets was measured in air. The plasma was initiated by a Nd:YAG laser at wavelengths of 355, 532, and 1064 nm. The plasma ignition was monitored utilizing the prominent Ag I line at 546.5 nm. Lower ignition thresholds of the nanoparticle-based silver target were estimated at 0.4±0.02, 0.34±0.04, and 0.27±0.035 J cm−2 coupled with the different laser wavelengths, respectively. In contrast, the bulk silver target plasma exhibited an order of magnitude higher ignition threshold. A three orders of magnitude enhanced emission intensity from the nano-based target over the bulk target was achieved at lower levels of laser irradiation. A reduction of the thermal diffusion length of the nanosilver was assumed in order to theoretically predict this reduction in the plasma threshold. In addition, the effect of self-reversal on the resonance lines was taken into consideration.
DBD plasma assisted atomic layer deposition alumina barrier layer on self-degradation polylactic acid film surface
In this work, the plastic of polylatic acid (PLA) film is coated by alumina (Al2O3) through dielectric barrier discharge plasma assisted atomic layer deposition (DBD PA-ALD) for the proposal of the barrier property enhancement. The influence of ALD Al2O3 thickness on properties of barrier, mechanical, optical and degradation is investigated in detail. It is obtained that the growth rate of Al2O3 in DBD PA-ALD is as quick as 0.12 nm/cycle. After coated ～40 nm Al2O3, the water vapor transmission rate of PLA is reduced by two orders of magnitude. Additionally, it is noticed that the tension strength of the coated film is improved slightly, whereas the light transmission rate is decreased with the increase of Al2O3 thickness. The degradation test shows that Al2O3 coating almost does not affect the self-degradation rate of PLA film
Insight into the remaining high surface energy of atmospheric DBD plasma-treated polyethylene web after three months’ aging
In this paper, we report the modification of polyethylene (45 μm in thickness) webs through a roll-to-roll dielectric barrier discharge plasma treatment in an open atmospheric environment. Our work differs from the normal adopted corona discharge treatment at an atmospheric pressure, in that three monomers: allylamine, acrylic acid, and ethanol, are inlet into the discharge zone by argon (Ar) carrier gas. As a comparison, Ar plasma treatment is also carried out. We focus on the aging properties of treated plastics in the open air. It is found that the modified webs can retain the surface energy as high as 50.0±1 mN m-1 for more than three months. After characterization of the as-prepared and aged samples by the surface roughness, the wettability, and the chemical structure, the mechanism of retaining high surface energy is then presumed. We think that the initial high surface energy just after plasma treatment is correlated to the grafted functional groups, while the over 50.0 mN m-1 remaining surface energy after three month aging is due to the stable concentrations of oxygen-contained and nitrogen-contained groups by post-reaction on the surfaces.
Comparative study on breakdown characteristics of trigger gap and overvoltage gap in a gas pressurized closing switch
Gas pressurized closing switches are one of the most important elements in FLTD-based
systems. Improving the trigger performance of gas switches is useful for optimizing the output
parameters and the reliability of the FLTD. In this paper, the breakdown characteristics of the
trigger gap and the overvoltage gap are studied experimentally. The reasons for the different
breakdown performance of the two gaps are also investigated. The results show that
the breakdown delay of the trigger gap is more influenced by the trigger voltage, while the
breakdown delay of the overvoltage gap is more influenced by the working coefficient and
always higher than that of the trigger gap. The jitter of the trigger gap is more influenced by the
trigger voltage and accounts more than 60% of the total switch jitter, while the jitter of the
overvoltage gap is hardly changed with the trigger voltage as well as the working coefficient and
maintains less than 1.4 ns. It is proved that the discharging product from the trigger gap can
effectively reduce the breakdown delay and jitter of the overvoltage gap. Based on that, the effect
and improvement of pre-ionization on the two gaps are also studied. It is concluded that the jitter
of the trigger gap reduces obviously when the pre-ionization is added, while the pre-ionization
almost has no effect on the jitter of the overvoltage gap. The jitter of the overvoltage gap is about
two times higher than the trigger gap in the pre-ionizing switch.
Silicone-coated polyimide films deposited by surface dielectric barrier discharges Hot!
Hybrid dielectric barrier discharges are investigated for plasma generated on the surface of a dielectric layer, where two conducting electrodes of high voltage and ground are formulated on the upper and bottom surfaces. Using a flexible thin polyimide-film of a thickness ranging from 25 to 125 μm, a plasma is generated with a voltage of about 1 kV and a frequency of 40 kHz. However, the surface of the dielectric layer was etched through a chemical reaction involving plasma oxygen radical species, and thus the polyimide films failed readily, resulting in dielectric breakdown within short operating time ranging from a few minutes to several tens of minutes, based on the film thicknesses of 25 μm and 125 μm, respectively. These plasma erosions were prevented by coating the polyimide surface with a 25 μm thick silicone paste. The silicone- coated film surface was then reinforced remarkably against plasma erosion as the organic polymer was vulnerable to chemical reaction of the plasma species, while the inorganic silicone exhibited a high chemical resistance against plasma erosion.
Effect of radio-frequency substrate bias on ion properties and sputtering behavior of 2 MHz magnetron sputtering
The effect of radio-frequency substrate bias on ion properties and sputtering behavior of 2 MHz magnetron discharge was investigated. The ion velocity distribution function (IVDF), the maximum ion energy and ion flux density were measured at the substrate by a retarding field energy analyzer. The sputtering behavior was investigated by the electric characteristics of target and bias discharges using voltage–current probe technique. It was found that the substrate bias led to the decrease of sputtering power, voltage and current with the amplitude <7.5%. The substrate bias also led to the broadening of IVDFs and the increase of ion flux density, made the energy divergent of ions impacting the substrate. This effect was further enhanced by increasing bias power and reducing discharge pressure.