Charge transfer processes in slow, highly charged ion-atomic hydrogen collisions are important for understanding the physics of edge and diverter plasmas and analyzing charge exchange diagnostics. However, it is difficult to obtain the accurate cross sections experimentally. Furthermore, it has been known that the well-established scaling law [1] for charge transfer cross sections in highly charged ion-multielectron target collisions cannot be adopted for atomic hydrogen and alkaline metal targets that have only one valence electron. Therefore, I have constructed a simulation code based on the classical trajectory Monte Carlo (CTMC) method and calculated charge transfer cross sections for atomic hydrogen and alkaline metal targets.

The basic concept of the CTMC code is similar to that developed by Olson and coworkers [2][3]. In the present code, the equations of motion are solved numerically for three charged particles involved, incident ion, target core and target electron, by using the traditional fourth-order Runge-Kutta method [4]. Firstly, I have calculated total electron capture cross sections in highly charged ion-atomic hydrogen collisions at the collision velocity of 0.1 a.u. For incident ions, highly charged I^q+ (q=5-53), and bare Os⁷⁶⁺ and U⁹²⁺ ions are considered to study the initial charge dependence of the cross sections. In addition to atomic hydrogen, I have carried out the calculations for alkaline metal targets (Na, K and Cs), which can be assumed to be quasihydrogenic, at the collision energy of 1.5q keV. It took typically 10-20 hours to obtain a cross section with the statistical uncertainties within ±2%.

In the present CTMC calculations, it has been found that the qualitative features of the electron capture cross sections for hydrogen and quasihydrogenic targets are consist with those for multielectron targets. The cross section can be scaled as σ ∝qP^-2, where q is the incident ion charge and P is the ionization energy of target electron. However, the amplitude is smaller than the scaling law by about three times. It is noted that the scaling relation of σ ∝qP^-2 is predicted from the extended classical over barrier model for capture processes [1].

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