Experimental Investigation Of The Intermidiate-energy P-He Collisions And Optimization Of The High-energy Electron Magnetic Spectrometer

Ionization and electron transfer occurring in ion-atom collisions havefundamental importance in the study of the dynamics and potential applications invarious fields, e.g. laboratory and astrophysical plasmas. Most of these studies wereperformed at high impact energies while the studies in the intermediate energy rangeare rare. In this work, single-electron capture and transfer ionization occurring incollisions of protons with He at energies ranging from50to100keV have beenexperimentally investigated by means of a reaction microscope. We obtained thestate-selective cross sections, revealed the importance of the electron-electroncorrelations and the dominate mechanisms in these processes. To map the high energyelectrons the magnetic system of the high-energy electron magnetic spectrometer wasoptimized.It was found that for single electron capture the ground state transfer is thedominant reaction channel, and excited states transfer has relatively smallcontributions to the cross sections. Transfer excitation process has a minorcontribution to the total cross sections. From the angular-differential cross sections forthe single transfer process, it was found that the momentum transfer mediated by theelectron is dominant because of the large contributions of small-angle scatterings,while the nucleus-nucleus interaction has a minor contribution. Compared to the singletransfer process, the transfer excitation process is more likely to take place at smallimpact parameters, which implies that the nucleus-nucleus interaction is moreimportant in this process. A comparison between the present experimental results and the theoretical calculations within the independent electron model reveals that theelectron-electron correlation effects, which are negligible in the single transfer process,manifest their importance in the transfer excitation process.For transfer ionization, the experimental results indicate that the momentumexchanges between the projectile and both the recoil ion and the electron dominate inthis process. The electron momentum distribution projected onto the scattering planedisplays some features characterized by binary encounter electron emission. Acomparison with the binary encounter model involving the binding energy effectreveals that the transfer ionization is more likely to happen in a sequential order oftransfer first and ionization second. Besides, the higher-order effect involving theinteraction between the electron and the residual recoil ion may also contribute to theelectron emission features. Another interesting observation in our data is the absenceof the cusp-shaped electrons centered at a speed equal to that of the incident projectilein the forward direction. This is contrary to the previous results. A preliminary analysisindicates that for neutralized outgoing projectile with the captured electrons in theground state the cusp does not exist and the contamination due to the double collisionscould cause the cusp-shaped electrons reported in the literature. In addition, the fullydifferential cross sections measured in the experiment provided the most rigorous testof the theories.The high-energy electron magnetic spectrometer enables one to map the emissionangle of the high-energy electrons. The beam optics of the electron spectrometer havebeen calculated and simulated in detail. We obtained the magnetic parameters fulfillingthe mapping condition and determined the magnetic system with the best resolution. Afurther investigation using the transfer matrix presented the optimum designparameters of the magnetic system.