In-situ quantification of NO synthesis in a warm air glow discharge by WMS-based Mid-IR QCL absorption spectroscopy

Nitric oxide (NO) is one of the most crucial products in the plasma-based nitrogen fixation process. In this work, in-situ measurements were performed for quantifying the NO synthesis spatially in a warm air glow discharge, through the method of Mid-infrared quantum cascade laser absorption spectroscopy (QCL-AS). Two ro-vibrational transitions at 1900.076 cm-1 and 1900.517 cm-1 of the ground-state NO(X) were probed sensitively by the help of the wavelength modulation spectroscopy (WMS) approach to increase the signal/noise (S/N) level. The results show a decline trend of NO synthesis rate along the discharge channel from the cathode to the anode. However, from the point of energy efficiency, the cathode region is of significantly low energy efficiency of NO production. Severe disproportionality was found for the high energy consumption but low NO production in the region of cathode area, compared to that in the positive column zone. Further analysis demonstrates the high energy cost of NO production in the cathode region, is ascribed to the extremely high reduced electric field E/N therein not selectively preferable for the processes of vibrational excitation or dissociation of N2 and O2 molecules. This drags down the overall energy efficiency of NO synthesis by this typical warm air glow discharge, particularly for the ones with short electrode gaps. Limitations of further improving the energy cost of NO synthesis by variations of the discharge operation conditions, such as discharge current or airflow rate, imply other effective manners able to tune the energy delivery selectively to the NO formation process, are sorely needed.

Влияние предыонизации на микроканальную структуру искрового разряда в воздухе в промежутке острие-плоскость

The initial phase of a spark discharge in the gap between the pin (cathode) and a plane 1.5 mm long in atmospheric pressure air under conditions of preliminary photoionization by an auxiliary discharge was investigated by the method of shadow photography. In the absence of preionization, the discharge from the first nanoseconds after breakdown is an aggregate of a large number of micron-diameter channels. It was found that the electron concentration resulting from preionization, estimated at 108  109 cm-3, increases the degree of uniformity of the discharge channel in the near-cathode region; however, in the near-anode region, the channel remains microstructured. Within the framework of the mechanism of microstructure formation due to the instability of the ionization wave front, a criterion for the formation of a uniform discharge is obtained and an explanation of the results obtained is presented.

Формирование микроканальной структуры искрового разряда в воздухе в промежутке острие-плоскость"

The formation of the microchannel structure of a spark discharge in the gap spike (cathode)-plane of 1.5 mm length in the air of atmospheric pressure was studied by the method of shadow photography. The images with the concurrent descent of microchannel diameter sand the number of microchannel increase in the cathode region on the time interval of 5 ns were recorded. The obtained data are explained in the frames of the microstructure formation mechanism at the expense of the front instability of the ionization wave. The parameters characterizing the process of the microstructure formation are estimated, and they agree with the experimental data.

An Investigation of Exposure to the Eyes and Thyroid of Personnel Near to Patient in Abdominal Radiography: A Phantom Study

Abdominal radiography is beneficial in a variety of clinical situations. Prior to the introduction of multiplanar imaging, it was considered as the main examination for gastrointestinal pathology. However, the radiation dose received is considered high since it is equivalent to the dose of at least 75 chest radiographs. Personnel including staff or relatives may be required to assist patients in many conditions, increasing unnecessary radiation and the likelihood of radiation-induced cancer. The purpose of this study was to determine the radiation dose received by personnel when eyes and thyroid are exposed during abdominal radiography. The Rando and body phantoms were used to represent personnel and patients in this experimental approach. The dose was measured as entrance surface dose (ESD) by using TLD-100, which was positioned at the Rando phantom's eyes and thyroid. The study included a total of twenty exposures, five times at each of four distinct sites. The mean doses (eyes/thyroid in mGy) were (0.083/0.081), (0.090/0.087), (0.093/0.092), and (0.092/0.089), respectively, at locations 1, 2, 3, and 4. The results indicated that there was no correlation between organ and location affecting ESD measurement (p=0.960). There was no significant difference in dose between the two organs (p=0.355), with the mean difference in the eyes being 0.002 more than in the thyroid. The proximity of the eyes to the tube source contributed for the increased dose observed at the eyes. Though ESD was substantial for location pairings 1 vs. 3 (p=0.001) and 1 vs. 4 (p=0.015) owing to the anode-cathode phenomena. In conclusion, personnel should avoid the tube source and cathode region, since they give a greater dose of radiation, particularly when the personnel are closest to the patient and does not have eyes or thyroid protection.

MODELING OF OSCILLATORY AND ROTARY TRAJECTORIES OF ELECTRONS IN GRADIENT MAGNETIC FIELD MAGNETRON GUN

The motion of electrons in cylindrical magnetic field with variable strength along the axis is considered. The formation of a beam with energy of 55 keV in the longitudinal direction during its transport in solenoidal magnetic field with large gradient has been studied. The bifurcation regimes of the dynamics of particles during their move-ment along the transport axis both forward to the target and back to the cathode region are considered. The operat-ing modes of the gun are obtained, in which the particle experiences the "bottleneck" effect and returns to the cath-ode region. It is shown that for given electron energy and fixed magnetic field, the parameter that determines the reflection of the particle is the polar angle of entry with respect to the axis of the cylindrical magnetic field. The re-sults of numerical simulation on the motion of the electron flow are presented.

Cylindrical model of electrochromic colouration of hydrated vanadium pentoxide thin films with point contacts

This article analyses experiments on the kinetics of the internal electrochromism of thin (micron) films of hydrated vanadium pentoxide xerogel with point contacts. It describes a cylindrical model of electrochromic colouration, which was used to evaluate the concentration of the colour centres in the initial film and after additional hydrogenation of this film by plasmaimmersion ion implantation.When we compared the calculated values of the concentration of colour centres with the equilibrium concentration of protons in the xerogel, we saw that the mobility of the protons migrating from the depth of the film to the cathode region, which are involved in the electrochemical reaction, was not a determinant of the electrochromism kinetics.The rate of electrochromic colouration could be increased by the formation of layered film structures based on hydrated vanadium pentoxide, which have increased overall electron conductivity and, as a consequence, low faradaic resistance of the electrochromic cathodic reaction.

Influence of the cathode region preionization on the operating parameters of the eptron

Investigations of the operating parameters of a plasma-cathode switch based on a capillary discharge in helium and neon in the burst mode are presented. An increase in the efficiency of the switch is demonstrated when an additional preionization pulse is applied at a low pulse repetition frequency (5 kHz). The compression ratio of voltage pulses more than 300 is achieved at a pulse repetition frequencies less than 40 kHz.

SYNTHESIS OF 3,3´-(1,4-PHENYLENE)BIS(1-(4-R-PHENYL)-5-PHENYL-5,6-DIHYDRO-1,2,4,5-TETRAZINIUM) PERCHLORATES

A series of 3,3'-(1,4-phenylene)bis(1-4-R-phenyl)-5-phenyl-5,6-dihydro-1,2,4,5-tetrazinium) perchlorates containing hydrogen, methyl, bromio, methoxy, acetyl and nitro groups (R = H, Me, Br, OMe, COMe, NO2) as substituents were obtained as a result of a three-stage synthesis from terephthalic aldehyde. The synthesis of tetrazinium salts was carried out by reaction of the corresponding formazans with formalin in the presence of perchloric acid in dioxane. Formazans were obtained by reaction of terephthalic aldehyde phenylhydrazone with arenediazonium tosylates in a mixture of DMF and pyridine. The usage of arenediazonium tosylates made it possible to extremely simplify the segregation and purification of formazans. The phenylhydrazone was synthesized according to the standard procedure from terephthalic aldehyde and phenylhydrazine/hydrochloric acid in aqueous dioxane. The formazans and tetrazinium perchlorates were isolated in individual state and characterized by elemental analysis, IR, UV, 1H and 13C NMR spectroscopy data. The process of electrochemical reduction of tetrazinium perchlorates was studied using the method of cyclic voltammetry (CV). Thus, the CV curves of all salts in the cathode region contain two one-electron reduction peaks, which are related to the sequential formation of a radical cation and a biradical. It was found that electron-donating substituents (R = Me, OMe) in the aromatic ring at position 1 facilitate the reduction of tetrazinium cation, while electron-withdrawing substituents (R = COMe, NO2) hinder this process. On this basis, it was suggested that the corresponding bis-verdazyl radicals should be easily formed in the presence of electron-donating substituents in the aromatic ring at position 1. Thus, 3,3´-(1,4-phenylene)bis(1-(4-R-phenyl)-5-phenyl-5,6-dihydro-1,2,4,5-tetrazinium-1) perchlorates are perspective precursors of symmetric biradical systems based on verdazyl radicals.

Simulation studies on the RF gun saturated emission

The emission of a short high charged electron bunch in a radiofrequency gun was simulated. The numerical model is supplemented by a positive charge arising and dynamically changing during emission in the cathode region The numerical results are compared with experimental data.