Investigation of the ozone formation process in a nanosecond microwave discharge in air and oxygen

Results are presented from an investigation of the dynamics of ozone formation in a freely localized discharge generated by a periodic train of 3-cm nanostructured microwave pulses in oxygen and air at a pressure p=3–30 Torr. Conditions for the efficient generation of ozone in air with the minimum production of nitrogen oxides are demonstrated experimentally. It is shown that when the microwave pulse repetition frequency is high, heating of the gas and the buildup of nitrogen oxides in the discharge in air reduce the ozone formation efficiency while under prolonged exposure the ozone formed initially is destroyed. The energy cost of forming ozone in oxygen and air is determined as a function of the microwave pulse length and repetition frequency and the gas pressure. The lowest energy cost of forming a single ozone molecule in these experiments is 16 eV per molecule for a discharge in air and 4 eV per molecule in oxygen. It was observed that circulating the gas through the discharge zone enhances th ozone formation efficiency. It is shown that there are optimal conditions for ozone formation as a function of the reduced electric field in the plasma. Zh. Tekh. Fiz. 67, 9–18 (March 1997)     

Beam quality of a high-power CO2 laser MOPA system

In this paper, the effects of amplification of diffraction-limited pulsed CO₂ laser radiation over several meters of amplification length on beam quality and pointing stability are documented. Millijoule pulses are amplified up to 3 J. Generation and amplification of the 10 μm wavelength pulses were performed in the discharge volume of an e-beam sustained CO₂ laser. Beam quality is measured according to the ISO/DIS 11146 standard in terms of the beam quality factor M². Fluence distributions were recorded with a beam analysing system of 100 μm spatial resolution. M² parameter values ranged up to 1.55 for amplified pulse energies of 3 J. The necessity of beam-quality restoring techniques is inferred for the multijoule pulse energy regime.     

Characteristics of a vacuum spark triggered by the transient hollowcathode discharge electron beam

The discharge characteristics of a vacuum spark triggered by the transient hollow cathode discharge (THCD) electron beam is investigated over a wide variety of discharge conditions. Two systems of the vacuum spark device have been considered-the first system powered by eight 2700-pF doorknob capacitors charged to a voltage of 40 kV (input energy of 17.6 J); while the second system employs a single 1.85-μF Maxwell capacitor discharged at a voltage of 20 kV (input energy of 370 J). The operating pressure of these systems has been varied over the range of 10 ^-2 to 10^-5 mbar in order to examine the effect of the operating pressure on the plasma formation of the vacuum spark discharge. The effectiveness of plasma heating has been found to be significantly enhanced in the two vacuum spark systems studied here. In particular, the plasma of the 17.6 J system has been observed to be heated to a condition hot enough to emit in the X-ray region when the operating pressure is reduced from 10^-2 to 10^-5 mbar. Similarly, in the case of the 370 J system, hot spot formation is also observed to occur only at a low operating pressure of 10^-4 mbar     

Generation regimes of a pulsed Nd:YAG laser with transverse LED pumping and multiloop self-pumped phase-conjugate cavity

The generation regimes in a pulsed Nd:YAG laser with transverse LED pumping and multiloop self-pumped phase-conjugate cavity on the gain gratings are studied. The differential efficiency of laser is 27% in the free-running regime at a pulse energy of up to 1 J and quality parameter M ² of no greater than 1.5. The pulse energy under passive Q-switching is no less than 60% of the pulse energy in the free-running regime at the same beam quality. The generation of the narrow-band radiation is demonstrated. A generation band of no greater than 1.2 GHz corresponds to the primary single-frequency high-power laser pulse in the free-running mode under conditions for self-Q-switching on the gain gratings. When additional elements (F ₂ ^? :LiF and Cr⁴⁺:YAG crystals) are introduced in the optical scheme of the phase-conjugate cavity, similar narrowband single-mode generation is observed in the passive Q-switching regime as a pulse train or monopulse. The laser pulse power is up to 2 MW at a pulse duration of 20 ns.     

Electron kinetics in a discharge plasma produced by a focused microwave beam in free space

A study is made of the electron kinetics in a discharge plasma produced by a high-power beam of electromagnetic radiation in the centimeter-wave region under conditions approaching free space, when the dimensions of the chamber are much greater than the wavelength of the microwave radiation. Two regimes of discharge production are investigated: the regime of short microsecond pulses at a repetition rate of 200 Hz, and a single millisecond pulse regime. It is shown that at threshold values of the microwave energy flux density the electron density in the initial stages of discharge formation reaches the critical value, and that the average energy of the electrons is of the order of 1.5–3 eV. Zh. Tekh. Fiz. 67, 10–14 (June 1997)     

Scenario for output pulse shortening in microwave generators drivenby relativistic electron beams

At the present time, microwave generators driven by high current relativistic electron beams are not baked and sealed, so their inner surfaces are densely covered with molecules of gas and oil. This allows the production of microwave pulses of 10^-8 s to 10^-7 s duration, but not longer. A microwave pulse termination scenario is speculated as follows: (1) Electrons oscillating in the strong RF field near the metallic surfaces multiply owing to the secondary emission (the multipactor effect); (2) the multipactor electron bombardment stimulates desorption of gas molecules from the metallic surfaces; (3) the gas undergoes avalanche RF breakdown; and (4) the resultant plasma stops microwave generation and, since electron-ion recombination is slow, does not allow the RF field to revive. At the gigawatt power level, the characteristic time of such a scenario is much shorter than that of the cathode and collector plasma expansion and electron beam instabilities. The energy output parameters of relativistic electron microwave generators can be (and usually are) improved at high pulse repetition rates. A more radical improvement is possible using the technology typical for high vacuum tubes, i.e., baking and sealing     

Production of nitric monoxide using pulsed discharges for a medicalapplication

Nitric monoxide (NO) is widely used in medical treatment of acute respiratory distress syndrome (ARDS). The production of NO is of interest to the medical community. In the present work, NO is generated by pulsed discharges between two rod electrodes in a mixture of nitrogen and oxygen. An arc discharge having a temperature of about 10000 K was produced, which was sufficient to generate NO. Some of the important parameters affecting the production of NO have been investigated. These include the percentage of O₂ (6-94%) in the mixture of Na and O₂, the energy of the discharge (0.5-12 J/pulse), the pulse repetition rate (0.54.5 pps) and the flow rate (1.35-5.4 l/min) of the gas mixture. NO₂ produced in the discharge was successfully changed to NO using a heated molybdenum tube, NO₂ must be extracted from the gas before clinical inhalation. The concentration of ozone was completely eliminated by bubbling the gas mixture through water. A maximum of NO and a minimum of NO₂ concentrations were generated when the proportion of O₂ in the gas mixture was in the range of 20-27%. The concentrations of NO and NO₂ increased with increasing pulse repetition rate and with decreasing flow rate of the mixture. In all cases, No₂ was effectively removed using a heated molybdenum tube     

等离子体放电活化生理盐水杀菌应用研究

等离子体中含有多种活性物种可实现高效安全杀菌,活性物种与生物体相互作用多在水环境下进行.因此等离子体与水的相互作用过程研究掀起了等离子体生物杀菌的新浪潮.本文采用水中阵列放电产生等离子体活化生理盐水,利用所产生的活化生理盐水对大肠杆菌开展了杀菌消毒研究,当等离子体放电时间达到120 s时产生的活化生理盐水与大肠杆菌混合后可使大肠杆菌的存活效率降至0.001%.通过紫外-可见吸收光谱测量及化学氧化还原沉降滴定表明放电电荷及激发态氧化性活性物种与水溶液相互作用,转化为活化生理盐水中长寿命相对稳定存在的H_2O_2和O_3等氧化性物种,与大肠杆菌作用并主导主要杀菌效果.     

用Z-扫描技术研究卟啉铜偶合TiO2/SiO2有机-无机材料的非线性吸收特性

应用溶胶-凝胶技术, 成功地把5,10,15,20-四(4-磺酸苯基)卟啉铜掺杂到SiO₂/TiO₂无机凝胶中, 制备成有机-无机复合材料. 采用开孔Z-扫描技术, 使用波长532 nm、脉宽7ns的YAG脉冲激光为光源, 测定了不同浓度卟啉铜掺杂的SiO₂/TiO₂凝胶Z-扫描曲线. 应用Z扫描理论对获得的曲线进行分析与理论拟合, 得到复合材料的非线性吸收系数. 这些非线性吸收是由材料中卟啉铜的单聚体与二聚体的反饱和吸收所引起. 研究表明, 随着掺杂浓度的增大, 复合材料的非线性吸收明显增强. 掺杂浓度为1.11×10^-4 (A2), 1.48×10^-4 (A3)与3.01×10^-4 mol/L (A4)凝胶的非线性吸收系数分别为1.705×10^-11, 1.892×10^-11和4.854×10^-11 m/W. 讨论了单聚体与二聚体的浓度变化对非线性吸收的影响. 随着掺杂浓度的增加, 凝胶中二聚体与多聚体含量的增加, 导致非线性吸收系数的增大. 同时测定了无机材料对该光源的抗激光损伤阈值为～5 J/cm².     

温稠密钛电导率计算

温稠密物质是惯性约束核聚变、重离子聚变、Z箍缩动作过程中物质发展和存在的重要阶段. 其热力学性质和辐射输运参数在聚变实验和内爆驱动力学模拟过程中有至关重要的作用. 本文通过建立非理想Saha方程, 结合线性混合规则的理论方法模拟了温稠密钛从10^-5-10 g·cm^-3, 10⁴ K到3×10⁴ K区间的粒子组分分布和电导率随温度密度的变化, 其中粒子组分分布由非理想Saha方程求解得到. 线性混合规则模型计算温稠密钛的电导率时考虑了包括电子、原子和离子之间的多种相互作用. 钛的电导率的计算结果与已有的爆炸丝实验数据相符. 通过电导率随温度密度变化趋势判断, 钛在整个温度区间, 密度0.56 g·cm^-3时发生非金属相到金属相相变. 对于简并系数和耦合系数的计算分析, 钛等离子体在整个温度和密度区间逐渐从弱耦合、非简并状态过渡到强耦合部分简并态.     

吸附在活性炭、三氧化二铝和硅胶上分子的核弛豫研究

本文提出核与电子偶极相互作用和自旋扩散两种作用在被吸附到固体多电子表面上的分子弛豫起着重要作用,给出了自旋晶格弛豫时间(T_1e)和相关时间(τ_c)的关系:T_1e,-kτ_c/1+ω₀²τ_c²)^1/2,式中k对给定固体是常数。吸附在硅胶上甲苯的弛豫数据可用此式描述。得到了甲苯中甲基在不同温度下的τ_c。,它们在374K到240K间的相关时间在3.56×10^-9 s到5.76×10^-8 s范围。由此计算出其活化能为15.0kJ/mol。     

Control of gigawatt REB pulse duration using gas injection

A technique for controlling the voltage and current pulse duration of a gigawatt relativistic electron beam (REB) was investigated. The pulse duration of a beam of 250 keV and 10 kA was controlled from 60 ns to 10 ns by injecting gases (air,, argon, and hydrogen) into the diode gap at a pressure ranging from 10^-5 torr to 10^-1. The observed dependence of the pulse duration on the nature and pressure of the gas is explained in terms of volume ionization of the gas by beam electrons. It is concluded that the pulse duration is governed by the time at which the plasma density created by the beam reaches a critical value of the order of beam electron number density     

Barrier Discharge The Transferred Charge and Ozone Synthesis

We have undertaken an experimental investigation of the influence of the conditions of barrier discharge implementation such as: the discharge gap value, the type of gas, and the polarity and dielectric permittivity of the dielectric electrode on the value of charge transferred in a micro-discharge. It is shown that the increase in the specific capacitance of the electrodes leads to proportional increase in the transferred charge value, reaching 100–200 nC in a discharge gap 1 mm, in air. In this case the amplitude and duration of a current pulse in the microdischarge reach, respectively, 10 to 15 A and 40 ns. It is also demonstrated that in air with increase in the discharge gap value one can observe a decrease in the efficiency of the ozone synthesis whereas in oxygen there exists a more complicated dependence: the maximum of efficiency is observed at a discharge gap value of 0.7 to 1.0 mm.     

Simulation study of a capacitively coupled plasma torch array

Using capacitively coupled electrical discharges, an array of three plasma torches powered by a single 60-Hz source are lit up simultaneously to produce a dense plasma in the open air. The discharge voltage and current of each torch is measured for three cases of one to three torches being lit up in the array. The results determine the ν-i characteristic of the discharge which indicates that the torch is operating in a diffuse are mode. The torch array is modeled by an equivalent circuit for simulating its operation. The simulation results of the discharge voltage and current of a torch are shown to agree well with those from the experimental measurements for the three cases. The lump circuit model is then used to carry out numerical simulations of the discharge for a broad parameter space of plasma species. By fitting the simulation results, a function giving the parametric dependence of the consumed average power density 〈P〉 on the normalized average electron density 〈n_e〉 maintained in the plasma is determined to be 〈P〉 48 〈n_e〉 ^1.9α_^0.4(W/cm³), where 〈n_e〉 is normalized to 10¹³cm^-3 and α_, the electron-ion recombination coefficient normalized to 10^-7 cm³·s^-1, is used as a variable parameter in the simulation     

Kinetic Instability of Anisotropic Drift Wave Accompanied by Field Aligned Currents in Solar Coronal Loop

Solar coronal loops are frequently accompanied by the field-aligned currents, which drive instabilities if the drift velocity u₀> v_A the Alfvén velocity. For our choice of parameters, the critical threshold value of u₀/v_A is~3.0 for growth and the corresponding current filling factor~10^-3-10^-4. Below this value we are no longer in the kinetic regime. The coronal loops also have short-scale density gradients within each loop. The electron resonance in the presence of density gradient causes the drift mode to grow. We study the effect of these two free energy sources, the electron drift and the density gradient, in the presence of temperature anisotropy T_⊥α > T_||α. These effects simultaneously exist in the coronae. Using gyrokinetic theory, we investigate the influence of these effects, examine how they interplay with each other and study the consequent growth of the magnetosonic wave. We observe that kinetic instability driven by density gradient can be suppressed by field-aligned currents. The temperature anisotropy with chosen signatures causes further stabilizing effect. The results may prove useful to study the heating mechanism of solar coronal loops, acceleration of particles and confinement of particles in the thermonuclear reactors.     

测量电子自旋——晶格弛豫时间T1的技术问题

本文讨论应用连续波方法测量电子自旋——晶格弛豫时间T₁的实验技术问题。分析液氮翻滚使T₁测量结果很不一致的原因,提出用吹冷气冷冻样品方法,可以解决液氮翻滚对测量T₁所产生的影响.用改进的方法测量ZnS:Mn、Cu粉末样品的T₁,获得重复性较好的实验结果。     

Comparison of the filamentation and the hollow-core fiber characteristics for pulse compression into the few-cycle regime

The gas-filled hollow-core fiber compression and the optical filamentation technique are compared experimentally in a parameter regime suitable for intense few-cycle pulse generation. In particular, pointing stability, spectral properties, and spatial chirp are investigated. It is found that in the case of filamentation, the critical parameter for pointing stability is gas pressure inside the generation cell whereas for the hollow-core fiber it is alignment that plays this role. The hollow-core fiber technique yields spectra that are better suited for chirped-mirror pulse compression whereas filamentation offers higher throughput and prospects for easy-to-implement self-compression. We present spectral phase interferometry for direct electric-field reconstruction (SPIDER) measurements that directly show the transition in the spectral phase of the output continua into the self-compression regime as the gas pressure is increased. PACS 42.65.Re; 42.65.Jx; 42.65.Tg     

分子间多量子相干横向弛豫时间(和自扩散系数)测量的参数优化和数据处理方法

针对测量横向弛豫时间T₂的CPMG脉冲序列和我们所设计的可同时测量高极化单组份单 峰核自旋体系n阶分子间多量子相干横向弛豫时间T_2,n和自扩散系数D_n的改进的CRAZED脉冲序列,分析了影响测量T₂、T_2,n（或D_n）的各种因素,并着重从技术方面讨论了准确测量T_2,n和D_n的实验参数优化和实验数据处理方法.     

Pressure dependence of plasma parameters in medium-vacuum nitrogenarc discharge with the titanium cathode

The plasma properties of a medium-vacuum nitrogen arc discharge from a titanium cathode were studied. The arc chamber use was 400 mm in diameter and 600 mm in length. The cathode diameter and thickness were 64 and 25 mm, respectively. The experimental conditions are given as follows: pressure range=1×10^-3~2×10^-1 torr; N₂ gas flow rate=6 ml/min; arc current=50 A. Electric probe characteristics are measured as a function of pressure and distance from the cathode surface. The analytical results obtained show that the electron energy distribution takes 1-Mx at pressures above 1×10^-2 torr but 2-Mx at pressures under 4×10^-2 torr and that the electron density has a maximum value at a certain pressure. The Ti⁺, Ti⁺⁺, and N ⁺₂ ion spectral intensities are measured as a function of pressure and distance from the cathode surface. On comparison of these results and the electron density, the Ti⁺ spectral intensity turns out to be proportional to that of the electron density. This suggests that the major ion in the plasma volume is of the Ti⁺ species     

Optimization of ozone generation

The generation of ozone under homogeneous conditions is described by a system of kinetic equations. We supposed a certain time dependence of electric field intensity inside a discharge gap. We computed the dependence of efficiency of the ozone generation on both the width and the maximum intensity of electric pulse.