Theoretical Studies On Electron-atom Impact Excitation Process In The Whole Energy Region

Electron impact excitation cross sections of atoms or ions are the indispensable physical parameters in astrophysics studies and inertial confinement fusion research.We studied the interface of excitation cross sections calculated by different theories(i.e.partial wave expansion method,distorted wave method,first Born approximation method)from low to high energy range to get the convergent cross sections in the whole energy range.We summarized the Correction Functions from the example of electron impact excitation of helium,with which one can easily obtain cross section in the whole energy range based on the readily calculated first Born cross sections.The Correction Functions are expected to be useful in conveniently providing cross sections in the whole energy region to related research fields,such as Astrophysics and fusion energy research.More specifically,(1)The convergences of the low energy electron impact excitation cross sections of helium are checked systematically by using 5 sets of high quality target states.Our calculated cross sections are in excellent agreement with the benchmark high resolution experimental data.Transitions between excited states are also calculated,and they are expected to have the same precision as those from the ground state.We find that the normalization of experimental measurement to the theoretical calculations may not be enough,absolute measurement is important.Compared with the recommended theoretical data,which are widely used in the astrophysical studies,there is a deviation of about 10%from our results,which suggests the recommended data may need a revision.(2)We study the interface of R-matrix cross sections and the FBA cross sections.We use R-matrix method to calculate the He 1~1S-2~1S and 1~1S-2~1P transition cross sections in the energy region from low to high,and find that the R-matrix cross sections can interface directly with the FBA cross sections in high energy region.A large number of pseudo states are needed in the R-matrix calculation for intermediate and high energy region.With the energies of the pseudo states adequately corrected,we avoid pseudo resonance in our calculations.(3)We find that the distorted wave approximation can also be use to calculate the neutral atom system after adequately taking account the exchange interactions and the orthogonalization between the distorted waves and the target wavefuncions.The distorted wave approximation is more appropriate in handling the electron impact system in lower energy region,which can effective reduce the energy range of the R-matrix calculations,making it more conveniently for one to obtain the cross sections in the whole energy region.(4)Based on our calculations,we find that the ratios between the calculated cross sections and FBA cross sections have similar trend and behaviors.We summarized the Correction Functions for all 1s-ns and 1s-np transitions of helium.As the FBA cross sections can readily calculated,the Correction Functions can conveniently provide cross sections in the whole energy region to related research fields,such as Astrophysics and fusion energy research.In the last chapter we summarize the calculations of electron impact excitation cross sections of a neutral atom in the whole energy region,and give a discussion and outlook of low electron impact with ion.For the problem of an electron impact with a neutral system,it is not an easy job to treat the correlations properly.The calculations of the electron impact with the neutral He atom in this work have demonstrated that our correlations have been considered sufficiently.Therefore we can expect the calculations for the electron-ion scattering will have a better precision.We choose the calculation of a partial wave of J~?=3~-of the e+O~+system as an example to show our scenario to handle the electron-ion scattering.