The Study Of Energy Loss And Effective Charge Of Low-energy Ion Beams In Low-density Hydrogen Plasma

The interaction between ion beams and plasma has been one of the important subjects in high-energy-density(HED)physics research.The energy loss of ion beams in plasma is one of key physical problems in the frontier fields of inertial confinement fusion(ICF)driven by ion beams,high-energy-density matter generation,self-sustain burning of fusion and astrophysics research and so on.In the low energy regime,the energy-loss process of ion beams in plasma is very complex,which is a necessary stage of fast ignition driven by ion beams and high-energy-density matter generation.However,the related experimental investigation is scarce.Therefore,for the low energy regime,the systematic and detailed studies of energy loss of ions in plasma are necessary.The experiments in the dissertation have been performed at the 320 k V high voltage experimental platform at Institute of Modern Physics,Chinese Academy of Sciences(IMP,CAS)in Lanzhou.The energy losses of protons and helium ion beams with low energy penetrating through a hydrogen gas discharging plasma have been measured by a position sensitive detector with time resolution,and energy-loss data with high precision have been obtained.Based on these measurements,the dependence of the effective charge of these ions on energy loss is studied in detail.Moreover,empirical formulae are applied to extract the effective charge,and the existing theoretical models are tested according to experimental results.The detailed investigations and main results are as following:1.Energy losses of protons with 90 and 100 keV energies penetrating through a hydrogen plasma target have been studied.It is found that the energy loss of protons in the plasma is obviously larger than that in cold gas.The comparison between theoretical calculations and experimental data shows that the effective charge remains 1 for the protons with the energy greater than or equal to 100 keV,while the charge-state evolution effect for protons with the energy lower than 100 keV needs to be taken into account.The effective charge calculated by modified empirical formulae for 90-keV protons is 0.92.2.Energy losses of helium ions with 100 and 125 keV/u energies penetrating through a hydrogen plasma target have been studied.Compared to protons,energy loss for helium ions with the same energy per nucleon is larger.The theoretical predictions indicate that energy loss for heavy ions is strongly dependent on the effective charge.The theoretical predictions with traditional effective charge model are unable to describe effectively the experimental results.However,ab initio theoretical simulations involving almost all the atomic states and the main atomic processes are well in agreement with experimental data.This indicates that excited projectile states play an important role in the stopping process in plasma.3.In order to measure in situ ion energy loss in future,the X-ray emission in near Bohr velocity ion-atom collisions has been measured.The results imply that,not only the direct ionization results in X-ray emission,but also the vacancy transfer of quasimolecular model plays a dominant role in inducing X-ray emission.