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1.
建立了包括电子、离子、器壁发射二次电子以及负离子多种成分的等离子体无碰撞鞘层的基本模型,讨论了二次电子发射和负离子对1维稳态等离子体鞘层结构的影响,并且分析了多种成分等离子体鞘层内的二次电子和负离子的相互作用。结果表明：二次电子发射系数的增加和负离子含量的增加,都将导致鞘层的厚度有所减小;二次电子发射系数超过临界发射系数之后,鞘层不再是离子鞘。随着器壁材料二次电子发射系数的增加,鞘层中的负离子密度分布也逐渐增加;负离子的增加,导致二次电子临界发射系数有所增加。另外,在等离子体鞘层中二次电子发射和负离子的存在,也影响着鞘层中电子的放电特性与器壁材料的腐蚀。 相似文献
2.
Object coated with plasma has stimulated great interests of many people because of its stealth capability. The study on a conducting cylinder coated with coaxial plasma is very much, but there are little works on a conducting cylinder coated with eccentric plasma. In this article, a model for a conducting cylinder coated with eccentric unmagnetized plasma is set up, the scattering cross section of the object cylinder is studied by adopting the superposition of cylindrical wave functions and the coordinate transformation, where these wave functions are the solutions of Maxwell's equations with boundary conditions in cylindrical coordinates. The results show that the radar cross section for a conducting cylinder coated with eccentric plasma in every direction decrease obviously with an increase of the distance between two eccentric axes, but is almost not impacted by electron–neutral collision frequency of plasma, and the backscattering cross section of the target reduce with the increase of electron density. Comparing with the coaxial model, the backscattering cross section of the eccentric model has a smaller value in a wide frequency band. This is of significance for the target plasma stealth technology in practice. 相似文献
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霍尔推进器中振荡鞘层对电子与壁面碰撞频率的影响研究 总被引：5，自引：0，他引：5
利用二维粒子模拟方法研究振荡鞘层对近壁电导的影响.研究结果表明,当二次电子发射系数大于1时,鞘层处于振荡状态.在振荡鞘层状态下,电子与壁面的碰撞通量沿平行与壁面方向剧烈的周期性振荡,振荡的波长为电子静电波波长量级,电子与壁面的碰撞频率高出经典鞘层状态下电子与壁面碰撞频率1—2个数量级,此时的碰撞频率对通道中电流的贡献不可忽略.振荡鞘层相对与经典鞘层增大了电子与壁面的碰撞频率,但是振荡鞘层的存在,仍然会使一部分慢电子无法穿越鞘层的势垒而打到壁面.关键词：霍尔推进器振荡鞘层二次电子 相似文献
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采用一维无碰撞的动力学鞘层模型计算了脉冲等离子体在恒压引出时的等离子体鞘层厚度变化,分别对短脉冲和长脉冲放电时的离子源发射面演变进行了分析。结果表明：对于短脉冲放电,发射面位置的变化相对等离子体密度的变化存在一定时间的延迟;对于长脉冲的上升沿和直流放电的开启阶段,鞘层厚度变化的速度与离子初始速度相关,稳定后发射面的位置与离子初始速度和等离子体密度的乘积相关。 相似文献
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建立包括两种正离子的电负性磁鞘的流体模型,利用四阶龙格库塔法数值求解描述一维稳态等离子体鞘层的方程组,考察离子与中性粒子碰撞对一维稳态等离子体鞘层的影响.结果表明:鞘边Ar+与He+的含量比值与碰撞参数对离子马赫数的取值范围都有影响.鞘边负离子含量越少,碰撞对鞘层中带电粒子密度的影响越明显.并且随碰撞参数的加大,鞘层中电子、负离子的密度下降越快,两种正离子的密度则呈现不同的波动变化.鞘边负离子含量越多,碰撞对鞘层中两种正离子的速度影响就越明显.此外,碰撞参数越大对鞘边δ越大的鞘层中的带电粒子密度影响越大. 相似文献
6.
M. Ikram Shabbir A. Khan A. Mushtaq M. Kamran H. U. Khan M. Zubair Khan M. Naeem 《等离子体物理论文集》2019,59(7)
The electrostatic simulations of the radio frequency (RF) heating mechanism, excitations, and ionization process of an electron plasma are carried out using a two‐dimensional (2D) particle‐in‐cell (PIC) code. RF drives with excitation frequencies of 1–15 MHz and amplitudes of 5 and 10 V were applied at two different axial positions, to the centre and to one end on the electrode stack of the ELTRAP device, at ultra‐high vacuum conditions. It is observed that the axial kinetic energy (eV) profile of the confined electrons increases with an increase of the RF excitation amplitudes, and densities from 5 × 107 to 1012 m?3 for all cases under consideration. The simulation results indicate that with continuous RF excitations, the electron heating in the beginning is higher at the trap wall of the device and extends towards the central region of the trap over a simulation time of up to 100 µs. These results on the electron heating are in good agreement with the experimental findings (optical diagnostics of ELTRAP). The heating effect is larger when the RF power is applied from the position close to one end of the trap in comparison to the central position. Monte–Carlo PIC simulations with hydrogen as a background gas are also performed to evaluate the ionization process at pressures of 10?8, 10?7, and 10?6 torr using the same electron plasma densities. The results show that at increasing pressures, the electron‐neutral collisions rate increases linearly with the background gas pressure. Increased collision frequency is obtained at higher RF drive amplitudes, which proportionally increases electron temperature, so that more ionization and secondary electrons are generated. 相似文献
7.
This work is devoted to the study of the Bohm criterion in the general case of the electron energy distribution function (EEDF). Investigations are performed by means of a Monte Carlo integration method. We resolve the cold fluid equation system describing the ion motion within the sheath, assuming collisionless conditions, singly charged and mono kinetic incoming ions (BOHM model). Results confirm that the limit ion velocity at the sheath edge to assure a monotone electric field with a positive charge over the entire sheath is vi ≥ (kTe/Mi) or εi ≥ 1/3 <εe> in the case of Maxwellian electrons. We show that in the case of a Druyvesteyn electron energy distribution, this limit is larger, it is εi ≥ 0.6 <εe>. The study is also extended to other distributions functions. Because of the large controversy in recent publications, concerning the boundary conditions at the sheath entrance, we discuss the collisionless conditions at the sheath edge according to the plasma parameters. It is shown that in a collisionless sheath, the condition ni(χ) ≥ ne(χ) can be used to determine the limit ion velocity at the sheath edge of the negatively biased collector (Langmuir probe for instance) (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
8.
Effects of plasma nonextensivity on the nonlinear cnoidal ion‐acoustic wave in unmagnetized electron‐positron‐ion plasma have been investigated theoretically. Plasma positrons are taken to be Maxwellian, while the nonextensivity distribution function was used to describe the plasma electrons. The known reductive perturbation method was employed to extract the KdV equation from the basic equations of the model. Sagdeev potential, as well as the cnoidal wave solution of the KdV equation, has been discussed in detail. We have shown that the ion‐acoustic periodic (cnoidal) wave is formed only for values of the strength of nonextensivity (q). The q allowable range is shifted by changing the positron concentration (p) and the temperature ratio of electron to positron (σ). For all of the acceptable values of q, the cnoidal ion‐acoustic wave is compressive. Results show that ion‐acoustic wave is strongly influenced by the electron nonextensivity, the positron concentration, and the temperature ratio of electron to positron. In this work, we have investigated the effects of q, p, and σ on the characteristics of the ion‐acoustic periodic (cnoidal) wave, such as the amplitude, wavelength, and frequency. 相似文献
9.
B Banerjee 《Pramana》1989,32(4):549-554
The energy density produced in a relativistic heavy ion collision is calculated within the framework of the colour tube model.
The chromoelectric field generated in the collision produces quark-antiquark pairs. The motion of these particles is described
by Boltzmann equation. The interaction between the quarks and antiquarks is approximated by introducing a relaxation time. 相似文献
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脉冲偏压上升沿特性对等离子体浸没离子注入鞘层扩展动力学的影响 总被引：1，自引：0，他引：1
等离子体浸没离子注入(PIII)是用于材料表面改性的一种廉价高效、非视线的技术.采用等离子体粒子模型,通过假设电子密度服从Boltzmann分布,求解Poisson方程和Newton方程,跟踪离子在等离子体鞘层中的运动形态及特性并进行统计分析,研究了不同上升速率和形状的6种波形上升沿对鞘层时空演化、离子注入能量和剂量的影响.结果表明,在PIII过程中,脉冲上升沿影响了等离子体鞘层的扩展,且不同波形诱导的鞘层厚度间存在最大差值.电场强度在鞘层的外边缘区域存在陡降区,离子的运动为非匀加速过程.可以通过调整脉冲关键词：等离子体浸没离子注入鞘层粒子模型上升沿 相似文献
13.
The properties of a collisionless plasma sheath are investigated by using a fluid model in which two species of positive ions and secondary electrons are taken into account. It is shown that the positive ion speeds at the sheath edge increase with secondary electron emission(SEE) coefficient, and the sheath structure is affected by the interplay between the two species of positive ions and secondary electrons. The critical SEE coefficients and the sheath widths depend strongly on the positive ion charge number, mass and concentration in the cases with and without SEE. In addition, ion kinetic energy flux to the wall and the impact of positive ion species on secondary electron density at the sheath edge are also discussed. 相似文献
14.
The double layer like potential jumps have been observed in a double plasma device. They do not correspond to a switching
of plasma potential from one metastable state to another but are caused by the ionisation of a very minute amount of the gas
that inevitably leaks into the system during the probe movement. 相似文献
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半圆形容器等离子体源离子注入过程中离子动力学的两维PIC计算机模拟 总被引：2，自引：0，他引：2
利用两维particle-in-cell方法研究了半圆形容器表面等离子体源离子注入过程中鞘层的时空演化规律. 详尽考察了鞘层内随时间变化的电势分布和离子密度分布规律,离子在鞘层中的运动轨迹和运动状态,得到了半圆容器内、外表面和边缘平面上各点离子注入剂量分布规律,获得了工件表面各点注入离子的入射角分布规律. 研究结果揭示了半圆容器边缘附近鞘层中离子聚焦现象,以及离子聚焦现象导致工件表面注入剂量分布和注入角度分布存在很大不均匀的基本物理规律.关键词：等离子体源离子注入鞘层两维particle-in-cell方法离子运动轨迹 相似文献
17.
On characteristics of sheath damping near a dielectric wall with secondary electron emission 
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下载免费PDF全文 A preliminary investigation is conducted to study the characteristics of sheath damping near a dielectric wall with secondary electron emission (SEE). Making use of the linear analysis of the sheath stability, we have found two major contributions to the sheath damping, one similar to the Landau damping in uniform plasmas and another determined by local electric field and electron density of the steady-state sheath. It indicates that in a classical sheath regime the damping in the sheath region monotonically increases towards the wall and decreases with the enhancement of SEE effect. In order to verify the theoretical analysis, sheath oscillation processes induced by an initial disturbance are simulated with a time-dependent one-dimensional (1D) sheath model. Numerical results obtained are consistent with the theoretical analysis qualitatively. 相似文献
18.
弱电离大气等离子体电子碰撞能量损失的理论研究 总被引：1，自引：0，他引：1
在前期计算电子能量分布函数的基础上, 求出弱电离大气等离子体中各碰撞反应过程的电子能量损失. 由于在弹性碰撞中电子-重粒子能量交换很少, 同时氮气、氧气分子又有很多能量阈值较低的转动、振动能级存在, 因此在大气等离子体中弹性碰撞电子能量损失所占份额很小(直流电场下小于6%). 研究发现, 弱电离大气等离子体中在不同能量区间占主导的能量损失过程不同. 随着有效电子温度(或约化场强)增加, 占主导的电子能量损失过程依次为转动激发、振动激发、电子态激发、碰撞电离、加速电离产生的二次电子. 在约化场强E/N=1350 Td (或有效电子温度为14 eV)附近, 平均电离一个电子所需的能量最小, 约为57 eV. 因此可以根据不同的需求调节电场强度, 从而达到较高的能量利用率.关键词：弱电离大气等离子体碰撞反应过程电子能量损失 相似文献
19.
Influence of ion species ratio on grid-enhanced plasma source ion implantation 总被引：1，自引：0，他引：1 下载免费PDF全文
下载免费PDF全文 Grid-enhanced plasma source ion implantation (GEPSII) is a newly proposed technique to modify the inner-surface properties of a cylindrical bore. In this paper, a two-ion fluid model describing nitrogen molecular ions N_2^+ and atomic ions N^+ is used to investigate the ion sheath dynamics between the grid electrode and the inner surface of a cylindrical bore during the GEPSII process, which is an extension of our previous calculations in which only N_2^+ was considered. Calculations are concentrated on the results of ion dose and impact energy on the target for different ion species ratios in the core plasma. The calculated results show that more atomic ions N^+ in the core plasma can raise the ion impact energy and reduce the ion dose on the target. 相似文献