Modeling nitrogen plasmas produced by intense electron beams

Abstract

A new gas–chemistry model is presented to treat the breakdown of a nitrogen gas with pressures on the order of 1 Torr from intense electron beams with current densities on the order of 10 kA/cm2 and pulse durations on the order of 100 ns. For these parameter regimes, the gas transitions from a weakly ionized molecular state to a strongly ionized atomic state on the time scale of the beam pulse. The model is coupled to a 0D–circuit model using the rigid–beam approximation that can be driven by specifying the time and spatial profiles of the beam pulse. Simulation results are in good agreement with experimental measurements of the line–integrated electron density from experiments done using the Gamble II generator at the Naval Research Laboratory. It is found that the species are mostly in the ground and metastable states during the atomic phase, but that ionization proceeds predominantly through thermal ionization of optically allowed states with excitation energies close to the ionization limit.

Hybrid Modelling of Cavity SGEMP in Low Pressure Air

“…为了降低实验复杂性与成本， SGEMP 的实验研究往往通过直接注入高能电 子束来模拟光电子， 避免使用大型射线源， 即便如此， 相关实验的难度依然很高， 公开的实验数据也非常稀缺 [4]- [6] .因此，数值模拟已经成为研究 SGEMP 的重要手 段， 代表性成果是美国 Woods 等人 [7] 编制的二维模拟程序 ABORC.以往的研究中， 真空环境下的 SGEMP 一直是关注的重点 [8] .近五年左右，西北核技术研究所的 Wang 等人基于自研程序 UNIPIC-3D [9] [10] 对 SGEMP 进行模拟，该程序支持辛算 法以及共形网格 [11] ，可以有效处理系统电磁脉冲中的电子发射边界问题 [12] .国内 研究人员对其中存在的空间电荷限制效应 [13] [14] 、 壁面二次电子发射 [15] 等问题也进 行了广泛的研究 [16] . 然而，实际系统往往工作在气体环境或含有充气元器件，光电子与中性气 体间会通过碰撞电离产生大量的次级电子、离子对，次级电子又会从电磁场中获 得能量，继续与中性气体发生电离、激发等一系列反应，从而形成等离子体.实验 结果表明 [17] ，等离子体与电磁场的相互作用会使 SGEMP 的特性会发生显著变 化.Woods 等人 [18] 最早通过数值模拟研究了高空稀薄空气和预电离空气对 SGEMP 的影响， 结果表明， 随着气压升高， 空间电荷层被破坏， 系统表面电流增加 [19] .Chan 等人 [20] 与 Strasburg 等人 [21] 使用电导率模型描述稀薄空气等离子体.Pusateri 等人 [22] 基于 swarm 模型对高空核爆电磁脉冲中的二次电子进行建模.Angus 等人 [23] 建立 了零维反应动力学模型，研究电子束诱导稀薄空气等离子体中的主要反应.…”

Modeling Intense-Electron-Beam Generated Plasmas Using a Rigid-Beam Approximation

“…Some of these processes were considered in Ref. 13, and they will also be the subject of future papers. There are many additional processes which a ect the excited state populations but are not included in the plasma chemistry model used in this paper.…”

“…10 The model described in this paper is an extension of previous models developed to study the interaction of an intense e-beam with nitrogen gas. [11][12][13] The e-beam is assumed to be injected parallel to the axis of a perfectly conducting cylinder of radius lled with low-pressure nitrogen in the 1 to 10 Torr range. The usefulness of an earlier RB model was demonstrated by comparing two models for electron-gas collisions: one with collision rates computed from the reduced electric eld ( ∕ ) and a second where they were determined from the mean plasma electron energy.…”

“…In addition to this expanded plasma chemistry, the model presented in this paper extends the 0-dimensional RB model of Ref. 13 to a 1-dimensional model by allowing an arbitrary radial pro le for the electron beam. The RB model employed in this paper is described more fully in Sec.…”

“…The RB model described in this paper extends the 0-D model of Ref. 13 to a 1-D model, and expands the chemistry used in Ref. 14 to include recombination and beamimpact ionization.…”