On the Kinetics of the Active Zone of the Stationary SF6 Beam Discharge Plasma

The paper deals with the impact of intensive electron attachment on the kinetics of the electrons in the active zone of the stationary band-like beam discharge plasma in SF₆ which is an alternative useful plasma medium for “dry etching”. The energy distribution of the electrons in this plasma was obtained by numerically solving the Boltzmann equation which includes apart from elastic collisions, different exciting collision processes, attachment in electron collisions, direct ionization, the ambipolar loss of electrons, Coulomb interaction between electrons and of electrons with ions and the power input to the electrons by the turbulent electric field. In particular, due to the needed fulfilment of the consistent electron particle balance, for an extended region of the turbulence energy density in this plasma a large impact on the electron kinetics of the intensive electron attachment, which is the prevailing electron loss process, was found enforcing independent of the turbulence energy density always a large power input to the electrons, smooth and only slowly decreasing energy distributions even in the energy region of direct ionization.     

Statistical description of ionization potentials in dense plasmas

The Thomas-Fermi model is used to investigate the influence of the density on the energies of ions in high-density plasmas (?10²¹?10²⁶ cm^?3). This model can be used to explain the two dominant high-density effects — continuum lowering and pressure ionization — by simple energy considerations. The result shows that only the outermost electrons are affected and that the inner region of the ion is hardly influenced by the density.     

Observation of high-energy electrons from a metal target irradiated by protons with a mean energy of 25 keV

Electrons with abnormally high energies of up to 16 keV are detected from an iron target irradiated by ions (H⁺, Fe⁺, Fe²⁺, Fe³⁺) with energies ranging from 20 to 100 keV from the plasma of a high-power femtosecond laser pulse with an intensity of 10¹⁶ J/(s cm²). These electrons indicate that the energy of an incident ion is almost completely transferred to an electron knocked out of the target. In a range of 6–16 keV, the spectrum of electrons knocked out of the K shell of iron atoms by protons with an energy of 22 ± 2 keV is quasi-exponential with an exponent of 4 keV. For 8-keV electrons, the double differential cross section for ionization by such protons is estimated as 10^?7 b/(eV sr).     

Beam-plasma discharge in the propagation of a long-pulse relativistic electron beam in a medium-pressure rarefied gas

A theoretical model is given, along with a numerical analysis of the evolution of beam-plasma discharge in the propagation of a long-pulse relativistic electron beam in a rarefied gas at medium pressure. It is shown that the self-stabilization of beam-plasma discharge as a result of longitudinal inhomogeneity of the density of the discharge plasma makes it possible for the beam to traverse the beam chamber with relatively low total energy losses, including ionization losses and energy losses in the generation of oscillations. During the dissociative recombination of electrons and ions of the discharge-driven plasma, heat is released and spent in raising the temperature of the gas. The investigated collective-discharge mechanism underlying heating of the gas for a relativistic beam can be more efficient than the classical heating mechanism due to ionization losses of the beam in pair collisions of its electrons with gas particles. Zh. Tekh. Fiz. 67, 94–98 (May 1997)     

Electron spectrometry study of associative and penning ionization in laser excited sodium vapor

The first observation, by electron spectrometry, is reported in laser-excited sodium vapor of the primary low energy electrons produced by associative ionization and by Penning ionization of sodium atoms in highly excited n1 states. The sequential heating of these primary electrons has been observed in 1, 2 or 3 superelastic collisions with Na(3p) atoms. The variation of associative ionization was measured as a function of the excited state density by using inner-shell photoionization produced by synchrotron radiation. Finally, an associative ionization cross section of 3.8 X 10^-17 cm² and a Penning ionization cross section for the 5s state of 1.1 X 10^-12 cm² were found (within 50% uncertainty) for an oven temperature of 520 K.     

Ultrashort electron beam and volume high-current discharge in air under the atmospheric pressure

Conditions are studied under which an electron beam and a volume discharge with a subnanosecond rise time of a voltage pulse are produced in air under atmospheric pressure. It is shown that the electron beam appears in a gas-filled diode at the front of the voltage pulse in ∼0.5 ns, has a half-intensity duration of ≤0.4 ns and an average electron energy of ∼0.6 of the voltage across the gas-filled diode, and terminates when the voltage across the gap reaches its maximum value. The electron beam with an average electron energy of 60 to 80 keV and a current amplitude of ≥70 A is obtained. It is assumed that the electron beam is formed from electrons produced in the gap due to gas ionization by fast electrons when the intensity of the field between the front of the expanding plasma cloud and the anode reaches its critical value. A nanosecond volume discharge with a specific power input of ≥400 MW/cm³, a density of the discharge current at the anode of up to 3 kA/cm², and specific energy deposition of ∼1 J/cm³ over 3 to 5 ns is created.     

ϑ-pinch in extrinsic InSb

The compression of an electron-hole plasma, caused by a ?-pinch in extrinsic InSb of 140 K, was investigated by measuring the absorption of 10·6 μm radiation and the change of the magnetic flux in the sample. A plasma density of 5 × 10¹⁵ cm^?3 was hereby found. The temporal development of the plasma density indicates that the electrons and holes resulted from impact ionization in the electric field when the magnetic field was low. Since the electric field is highest at the sample surface, the ionization was limited to the outer region of the sample and the plasma was transmitted to the inner sample volume by the ?-pinch.     

Tonks-Langmuir problem for a bi-Maxwellian plasma

An analytical solution of the Tonks-Langmuir (TL) problem with a bi-Maxwellian electron energy distribution function (EEDF) is obtained for a plasma slab. The solution shows that the ambipolar potential, the plasma density distribution, and the ion flux to the wall are mainly governed by the cold electrons, while the ionization rate and voltage drop across the wall sheath are governed by the hot electrons. The ionization rate by direct electron impact is found to be spatially rather uniform, contrary to the T-L solution where it is proportional to the plasma density distribution. The temperature of hot electrons defined by the ionization balance is found to be close to that of the T-L solution for a mono-Maxwellian EEDF, and is in reasonable agreement with experiments carried out in a low pressure capacitance RF discharge. The energy balance for cold electrons in this discharge shows that their heating by hot electrons via Coulomb interaction is equalized by the cold electrons' escape to the RF electrodes during collapse of the RF sheath     

Initiation of ecton processes by interaction of a plasma with a microprotrusion on a metal surface

Evolution of rapid (～10 ns) Ohmic overheating of a microprotrusion on a surface in contact with a plasma by emission current is studied taking into account the energy carried by plasma ions and electrons, as well as Ohmic heating, emissive source of energy release (Nottingham effect), and heat removal due to heat conduction. Plasma parameters were considered in the range of n = 10¹⁴?10²⁰ cm^?3 and T _e = 0.1 eV?10 keV. The threshold value of energy transferred to the surface from the plasma is found to be 200 MW/cm²; above this value, heating becomes explosive (namely, an increase in the temperature growth rate (δ² T/δt ² > 0) and in passing current (δJ/δt > 0) is observed in the final stage at T ～ 10⁴ K and j ～ 10⁸ A/cm²). In spite of the fact that Ohmic heating does not play any significant role for plasmas with a density lower than 10 18 cm^?3 because the current is limited by the space charge of electrons, rapid overheating of top of microprotrusion is observed much sooner (over a time period of ～1 ns) when the threshold is exceeded. In this case, intense ionization of vapor of the wall material leads to an increase in the plasma density at the surface, and the heating becomes of the Ohmic explosion type. Such conditions for the formation of a micr?xplosion on the surface and of an ecton accompanying it can be created during the interaction of a plasma with the cathode, anode, or an insulated wall and may lead to the formation of cathode and anode spots, as well as unipolar arcs.     

入射电子能量对低密度聚乙烯深层充电特性的影响

高能带电粒子与航天器介质材料相互作用引起的深层带电现象, 一直是威胁航天器安全运行的重要因素之一. 考虑入射电子在介质中的电荷沉积、能量沉积分布以及介质中的非线性暗电导和辐射诱导电导, 建立了介质深层充电的单极性电荷输运物理模型. 通过求解电荷连续性方程和泊松方程, 可以得出不同能量 (0.1–0.5 MeV) 电子辐射下, 低密度聚乙烯 (厚度为1 mm) 介质中的电荷输运特性. 计算结果表明, 不同能量的电子辐射下, 介质充电达到平衡时, 最大电场随入射能量的增加而减小; 同一能量辐射下, 最大电场随束流密度的增大而增加. 入射电子能量较低时 (≤ 0.3 MeV) , 最大电场随束流密度的变化趋势基本相同. 具体表现为: 当束流密度大于3× 10^-9 A/m²时, 最大场强超过击穿阈值2×10⁷ V/m, 发生静电放电 (ESD) 的可能性较大. 随着入射电子能量的增加, 发生静电放电 (ESD) 的临界束流密度增大, 在能量为0.4 MeV时, 临界束流密度为6×10^-8 A/m². 当能量大于等于0.5 MeV时, 在束流密度为10^-9–10^-6 A/m²的范围内, 均不会发生静电放电 (ESD) . 该物理模型对于深入研究深层充放电效应、评估航天器在空间环境下 深层带电程度及防护设计具有重要的意义. 关键词： 高能电子辐射 低密度聚乙烯(LDPE) 介质深层充电 电导特性     

Hard X-ray emission by clusters in an intense femtosecond laser field during collective recombination

We consider the new mechanism of X-ray generation by clusters under irradiation by femtosecond laser pulses, the so-called collective photorecombination. We develop the theory of the photo-recombination of electrons that pass from atomic clusters at the outer ionization to the ground level of a homogeneously charged cluster. Such a cluster is considered to be a quantum potential well. The dipole approximation is inapplicable for this process. We conclude that X-ray photons in collective photorecombination on a charged cluster as a whole have an energy that is much larger than that for photorecombination on separate atomic ions inside the cluster. For a typical cluster of 2.25 × 10⁶ electrons, with a radius R = 300 Å, and a number density of plasma electrons n _e = 2 × 10²² cm^?3, we find that at a 5% outer ionization of this cluster, the energy of hard X-ray photons is 7.2 keV.     

Gas-filled electron diode based on a glow discharge

Stable ignition and sustention of a pulsed discharge with a current of up to 180 A and duration of 12 μs at a pressure of 10⁻¹–10⁻² Pa are achieved in a glow-discharge plasma cathode with the help of an auxiliary initiating discharge. An electron emission current density of up to 100 A/cm² and accelerating voltageof 15 kV are obtained in a gas-filled diode based on this type of a plasma cathode. An electron beam witha neutralized space charge can be transported almost without losses in a weak axial magnetic field alonga plasma channel formed due to the gas ionization by the accelerated electrons over a distance of up to 30 cm.     

Generation of multiply charged refractory metals in an electron-cyclotron resonant discharge in a direct magnetic trap

The possibility of additional ionization of refractory metal ions in the vacuum arc plasma injected to a magnetic trap due to additional heating of electrons by microwave radiation under the conditions of electron-cyclotron resonance is demonstrated. High-power short-wave radiation of gyrotrons used in experiment makes it possible to work with a higher (on the order of 10¹³ cm⁻³) density of the plasma and to ensure the confinement parameter at a level of 3 × 10⁸ cm⁻³ s at an electron temperature sufficient for multiple ionization.     

Internal ionization in 41Ca

The internal ionization accompanying the first-forbidden unique electron-capture decay of ⁴¹Ca was investigated. The integrated probability of electron ejection with energy greater than 38keV was found to be (0.17 ± 0.02) × 10⁻⁵ per K-capture. In this energy range, the measured spectrum of ejected electrons is fairly close to predictions of the simple theory of Primakoff and Porter, and of the relativistic theory of Mukoyama et al. By a model-dependent extrapolation of this spectrum toward low energies, the total probability of internal ionization in ⁴¹Ca was estimated and compared with relevant experimental results for other isotopes.     

Excited atoms in argon gas discharge plasma

General principles are discussed for a gas discharge plasma involving excited atoms where electron-atom collision processes dominate. It is shown that an optimal kinetic model of this plasma at not large electric field strengths can be based on the rate constants of quenching excited atom states by electron impact. The self-consistent character of atom excitation in gas discharge plasma is important and results in the tail of the energy distribution function of electrons being affected by the excitation process, which in turn influences the excitation rate. These principles are applied to an argon gas discharge plasma where excitation and ionization processes have a stepwise character and proceed via formation of argon atom states with the electron shell 3p ⁵4s.     

Production of a large-volume plasma by a hot-cathode arc

Probe measurements reveal that the plasma produced by a hot-cathode arc contains two groups of electrons, with temperatures 4 and 10 eV, with a density of 10¹⁰–10¹¹ cm^–3. These electrons are distributed uniformly over a volume of 0.2 m³. The discharge voltage is found as a function of the gas pressure and the heater current. Low-temperature regimes of the deposition of TiN coatings on metals and insulators after a plasma processing of the articles are described. The design of the discharge system is discussed.Institute of High-Current Electronics, Siberian Branch, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 115–120, March, 1994.     

霍尔漂移对阳极层霍尔等离子体加速器电离效率的影响

以洛伦兹变换方法为基础,分析了阳极层霍尔等离子体加速器中电子的霍尔漂移,结果表明在交叉场中,霍尔漂移并不总是存在的,E/B的比值大于光速时,霍尔漂移将不存在.进一步的分析表明,霍尔漂移也并不总是回旋形式的,不同的电磁场配置以及不同的电子初始能量将带来不同形式的漂移,包括回旋形式,波浪线形式,甚至直线形式.电磁场的配置也决定着霍尔漂移的速度,在很大程度上影响着电子的能量,这就决定了放电时的电离效率.对不同电磁场配置进行数值模拟发现,合理的电磁场比值能够得到更好的电离效率(对于氩,这个数值大约为4×10⁶).不同的气体,根据其电离碰撞截面与电子能量的关系,都有不同的合理比值.     

约化场强对氮-氧混合气放电等离子体演化特性的影响

采用零维等离子体动力学模型,计算了不同约化场强条件下N₂/O₂放电等离子体的演化特性.结果表明,平均电子能量与约化场强有着近似的线性关系,在约化场强为100 Td时,平均电子能量约为2.6 eV、最大电子能量达35 eV;约化场强是影响电子能量函数分布的主要因素.气体放电过程结束后,振动激发态氮分子的粒子数浓度不再变化,电子激发态的氮分子、原子和氧原子的粒子数浓度达到一峰值后开始降低;放电结束后的氧原子通过复合反应生成臭氧.约化场强升高,由于低能电子减少的影响,振动激发态氮分子的粒子数浓度降低,当约化场强由50 Td增加75 Td,100 Td时,粒子数浓度由3.83×10¹¹ cm^-3降至1.98×10¹¹ cm^-3和1.77×10¹¹ cm^-3,其他粒子浓度则相应增大. 关键词： 等离子体 约化场强 粒子演化 数值模拟     

Numerical simulation of super-short pulsed discharge in Helium with particle-in-cell Monte--Carlo collisions technique

This paper reports that a simulation of glow discharge in pure helium gas at the pressure of 1.333×10³ Pa under a high-voltage nanosecond pulse is performed by using a one-dimensional particle-in-cell Monte Carlo collisions (PIC--MCC) model. Numerical modelling results show that the cathode sheath is much thicker than that of anode during the pulse discharge, and that there exists the phenomenon of field reversal at relative high pressures near the end of the pulse, which results from the cumulative positive charges due to their finite mobility during the cathode sheath expansion. Moreover, electron energy distribution function (EEDF) and ion energy distribution function (IEDF) have been also observed. In the early stage of the pulse, a large amount of electrons can be accelerated above the ionization threshold energy. However, in the second half of the pulse, as the field in bulk plasma decreases and thereafter the reverse field forms due to the excessive charges in cathode sheath, although the plasma density grows, the high energy part of EEDF decreases. It concludes that the large volume non-equilibrium plasmas can be obtained with high-voltage nanosecond pulse discharges.