Electron transfer in proton-hydrogen collisions in nonideal classical plasmas

Effects of nonideality of classical plasma on the reaction: p + H(1s) → H(nlm) + p has been investigated by carrying out fully quantum mechanical calculations within the framework of a first-order distorted wave method. Scattering amplitude is calculated conveniently by employing a simple, variationally determined wave function of hydrogen atom embedded in nonideal classical plasma. A detailed study is made on the changes in electron transfer cross sections due to the nonideality of plasma varying from 0 to 4 and the incident proton energy lying between 10 and 500 keV. It has been found that nonideality of plasma causes substantial change in capture cross section.     

Ion-acoustic shock waves and their head-on collision in a dense electron-positron-ion quantum plasma

Ion-acoustic shock waves and their head-on collision in a dense quantum plasma comprised of electrons, positrons, and ions are studied. The extended Poincaré-Lighthill-Kuo perturbation method is used to derive the Korteweg-de Vries-Burgers equations for shock waves in this plasma. The dissipation is introduced by taking into account the kinematic viscosity among the plasma constituents. The effects of the ratio of positrons to ions unperturbation number density μ, the normalized kinematic viscosity ηi0, and the quantum Bohm potential H on the interaction and structure of the shock waves are investigated. It is found that there are integrally vertical downward movements for both the colliding shocks after their head-on collision, but there are no shifts of the postcollision trajectories (phase shifts). It is also found that these plasma parameters can significantly influence the collision and properties of the colliding shocks. The results may have relevance in dense astrophysical plasmas (such as neutron stars or white dwarfs) as well as in intense laser-solid density plasma experiments.     

Positronium formation for positron scattering from metastable hydrogen

Positronium(Ps) formation for positron impact on metastable hydrogen in 2s state has been studied by using the twochannel, two-center eikonal final state-continuum initial distorted wave(EFS-CDW) method. The differential, integrated,and total cross sections for Ps formation in different states have been calculated from each channel opening thresholds to high energy region. The results are compared with other theoretical calculations available in the literature. For Ps formation in s-state at intermediate and high energies, our results are in good agreement with the prediction of distorted wave theory.Those formed in p-states and the total Ps formation cross sections are reported for the first time. It is shown that the total Ps formation cross sections for positron scattering from H(2s) state are significantly larger at relatively low energies, while smaller at high energies, compared with those obtained from hydrogen in ground state.     

Electron impact excitation of hydrogen and helium in Coulomb-projected Born methods

Coulomb-projected Born methods for the theoretical study of electron impact excitation of hydrogen and helium are reviewed. The results obtained by using different forms of Coulomb-projected Born methods are compared with other theoretical and experimental results and analyzed. The inadequacy of the variable charge Coulomb-projected Born approximation (VCCPB)—the most recent form of the Coulomb-projected Born methods—in giving good results in processes where exchange is dominant is discussed in detail. The ‘modified’ VCCPB approximation obtained by modifying the VCCPB method to remove its shortcomings is also discussed and its application to electron impact excitation of 2³ s state of helium is studied.     

Investigation of the transfer ionization process in collisions of partially stripped ions on He

In this paper a projectile ion-recoil ion coincidence technique is used to investigate the transfer ionization processes in collisions of 0.22--6.30~MeV C^{q + } ions and 0.25--6.35~MeV O^{q + } ions (q=1, 2, 3, 4) with the He atom separately. The cross section ratio f of transfer ionization to single electron transfer is measured, and the dependence of f on both charge state q and energy E of the projectiles is investigated. The electron-structure and the mechanisms leading to transfer ionization affect the dependence of f on q and E. Our measurements, along with other data published previously, suggest a similar dependence of f on charge state and energy of projectile for partially stripped ions over a large energy range. The maximum value of f is approximately 0.17q^{0.60}; the energy corresponding to maximum f is about 160q^{0.60}~keV/u.     

Nonradiative charge transfer in collisions of protons with rubidium atoms

The nonradiative charge-transfer cross sections for protons colliding with Rb(5s) atoms are calculated by using the quantum-mechanical molecularorbital close-coupling method in an energy range of 10 3 keV-10 keV.The total and state-selective charge-transfer cross sections are in good agreement with the experimental data in the relatively low energy region.The importance of rotational coupling for chargetransfer process is stressed.Compared with the radiative charge-transfer process,nonradiative charge transfer is a dominant mechanism at energies above 15 eV.The resonance structures of state-selective charge-transfer cross sections arising from the competition among channels are analysed in detail.The radiative and nonradiative charge-transfer rate coefficients from low to high temperature are presented.     

Collisional effects on the current-filamentation instability in a dense plasma

The collisional current-filamentation instability (CFI) is studied for a nonrelativistic electron beam penetrating an infinite uniform plasma. It is analytically shown that the CFI is driven by the drift-anisotropy rather than the classical anisotropy of the beam and the background plasma. Therefore, collisional effects can either attenuate or enhance the CFI depending on the drift-anisotropy of the beam-plasma system. Numerical results are given for some typical parameters, which show that collisional effects cannot stabilize but enhance the CFI in a dense plasma. Thus, the CFI may play a dominant role in the fast electron transport and deposition relevant to the fast ignition scenario (FIS).     

高电荷态Xe离子与He原子碰撞中的电子转移过程研究

采用位置灵敏探测和飞行时间技术研究了高电荷态Xe离子（q=15，17，19，21，23）与He原子碰撞中双电子转移截面与单电子转移截面比随入射离子电荷态的变化规律.提出一步过程假定，对扩展的经典过垒（ECB）模型进行了修正，利用修正模型计算得到的单、双电子转移绝对截面与Andersson等人和Selberg等人的实验结果很好符合，所得截面比与本实验得到的双电子转移截面与单电子俘获截面比较好符合. 关键词： 离子 原子碰撞 电荷转移 一步过程     

Influence of dynamic screening on the conductivity of hydrogen plasma including electron–electron collisions

We investigate the dynamical conductivity of dense hydrogen plasmas on the basis of the effective interaction potential (taking into account static or dynamic screening and diffraction effects). We apply a generalized Drude–Lorentz formula related to the dynamical conductivity with collision frequency. The influence of electron–ion collisions as well as the influence of both electron–ion and electron–electron collisions were taken into account via a renormalization factor. All calculations were performed on the basis of the effective potential with static or dynamic screening.     

Collisional effects on the current-filamentation instability in a dense plasma

The collisional current-filamentation instability (CFI) is studied for a nonrelativistic electron beam penetrating an infinite uniform plasma. It is analytically shown that the CFI is driven by the drift-anisotropy rather than the classical anisotropy of the beam and the background plasma. Therefore, collisional effects can either attenuate or enhance the CFI depending on the drift-anisotropy of the beam-plasma system. Numerical results are given for some typical parameters, which show that collisional effects cannot stabilize but enhance the CFI in a dense plasma. Thus, the CFI may play a dominant role in the fast electron transport and deposition relevant to the fast ignition scenario (FIS).     

Head-on collision of quantum ion-acoustic solitary waves in a dense electron-positron-ion plasma

The characteristics of the head-on collision between two-quantum ion-acoustic solitary waves (QIASWs) in a dense electron-positron-ion plasma are investigated. Using the extended Poincaré-Lighthill-Kuo (PLK) method, the Korteweg-de Vries (KdV) equations and the analytical phase shifts, after two QIASWs collision occurs, are derived. This study is a first attempt to illustrate the effects of both of the quantum diffraction corrections and the Fermi temperature ratio of positrons to electrons on the phase shifts. It is found that the electron-positron-ion plasma parameters modify significantly the phase shifts of the two colliding solitary waves.     

低能He2+-He碰撞体系转移电离机理的实验研究

利用冷靶反冲离子动量谱仪,对低能He²⁺-He碰撞反应中产生的反冲靶离子和炮弹离子进行了符合测量,根据反冲靶离子的动量,研究了转移电离过程中的电荷转移机理.实验结果表明：在20—40 keV能量范围内,靶原子上的一个电子俘获到炮弹离子的基态,另一个电子直接发射到靶的连续态的直接电离及另一个电子俘获到炮弹离子的连续态的过程(ECC)是最主要的转移电离机理,且ECC过程主要发生在大碰撞参数条件下;炮弹离子俘获两个电子处在双激发态的自电离过程的贡献很小. 关键词： 冷靶反冲离子动量谱仪 转移电离机理 离子原子碰撞     

Excitation of hydrogen atom by ultrashort laser pulses in optically dense plasma

The features of excitation of a hydrogen atom by ultrashort laser pulses (USP ) with a Gaussian envelope in optically dense plasma at a Lyman‐beta transition are studied theoretically. The problem is of interest for diagnostics of optically dense media. USP have two doubtless advantages over conventional laser excitation: (a) the USP carrier frequency is shifted to the region of short wavelengths allowing exciting atoms from the ground state and (b) the wide spectrum of USP allows them to penetrate into optically dense media to much longer distances as compared with monochromatic radiation. As actual realistic cases, two examples are considered: hot rarefied plasma (the coronal limit) and dense cold plasma (the Boltzmann equilibrium). Universal expressions for the total probability of excitation of the transition under consideration are obtained in view of absorption of radiation in a medium. As initial data for the spectral form of a line, the results of calculations by methods of molecular dynamics are used. The probability of excitation of an atom is analysed for different values of problem parameters: the pulse duration, the optical thickness of a medium, and the detuning of the pulse carrier frequency from the eigenfrequency of an electron transition.     

Post collision interactions and polarization effect in (e, 2e) collisions of helium

A modified distorted-wave Born approximation (DWBA) method is used to calculate the triple differential cross sections (TDCSs) in a coplanar asymmetric geometry for the electron impact single ionization of a He (1s²) atom at intermediate and lower energies. The post-collision interaction and the polarization effect in (e, 2e) collisions of helium are considered in the calculations. The polarization potentials from the damping method and density functional theory (DFT) are compared. Theoretical results are compared with the recent experimental data.     

Electron structure of interstitial hydrogen inα-Zr

The impurity-induced charge density in jellium is calculated by solving the Schr?dinger equation self-consistently. The resulting phase shifts have been used to estimate the value of residual resistivity for dilute Zr-H system, which comes out to be 0.50 μΘ cm/at.%. An alternative form of one-parameter-screened Coulomb potential, which is more suitable than the customary Thomas-Fermi potential, is suggested. The calculated self-energy by using new potential is found close to its value obtained by Darbyet al.     

弱电离大气等离子体电子碰撞能量损失的理论研究

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     

Electron excitation processes in low energy collisions of hydrogen-helium atoms

The electron excitation processes of $rm H(1s) + He(1s^{2}) to H(2s/2p) + He(1s^{2})$ are studied in impact energy range of 20—2000 eV/u by using the quantum-mechanical molecular orbital close-coupling (QMOCC) method. Total and state-selective cross sections have been obtained and compared with the available theoretical and experimental results. The results agree well with available measurements in the overlapping energy regions overall. The comparison of our results with other theoretical calculations further demonstrates the importance of considering a sufficient number of channels. The datasets presented in this paper, including the excitation cross sections, are openly available at https://www.doi.org/10.57760/sciencedb.j00113.00083.     

低能Ar9+离子与Na原子碰撞反应中的多电子转移过程

利用近代物理研究所新建的原子物理实验平台,采用位置灵敏探测和散射离子-反冲离子飞行时间符合技术,研究了180 keV的Ar9+离子与Na原子碰撞中的多电子转移过程,对实验结果做了分析和简单的讨论,并同修正后的分子库仑过垒模型结果进行了比较.     

Changes of the electron dynamics in hydrogen inductively coupled plasma

Changes of the electron dynamics in hydrogen （H2） radio-frequency （RF） inductively coupled plasmas are investigated using a hairpin probe and an intensified charged coupled device （ICCD）. The electron density, plasma emission intensity, and input current （voltage） are measured during the E to H mode transitions at different pressures. It is found that the electron density, plasma emission intensity, and input current jump up discontinuously, and the input voltage jumps down at the E to H mode transition points. And the threshold power of the E to H mode transition decreases with the increase of the pressure. Moreover, space and phase resolved optical emission spectroscopic measurements reveal that, in the E mode, the RF dynamics is characterized by one dominant excitation per RF cycle, while in the H mode, there are two excitation maxima within one cycle.