Blazevic, A.

Frank, A.

Ortner, A.

Roth, M.

GSI Repository

Theoretical investigation of the charge transfer processes of heavy ions atintermediate energies interacting with a plasmaA. Ortner∗1,, A. Frank3, A. Blazevic2, and M. Roth11Technische Universita¨t Darmstadt, Germany; 2GSI Darmstadt, Germany; 3Helmholtz-Institut Jena, GermanyThe influence of the plasma properties, like plasmadensity, temperature and ionization degree, on the de-velopment of the charge state distribution of a heavy ionbeam interacting with this plasma was investigated the-oretically by a Monte-Carlo code.The charge transfer processes in plasma are quite differ-ent compared to those in cold matter due to the presenceof free electrons and ionized atoms. In cold matter, the dy-namic balance of the projectile charge state is mainly gov-erned by impact ionization of the projectile and recombi-nation with bound target electrons (non-radiative electroncapture, NREC).In plasma, the ionization processes are the same, but therates increase significantly due to a reduced screening ofthe target nucleus potential. As in a plasma, the number ofbound electrons is reduced, which consequently suppressesNREC, the recombination processes with free electrons,like radiative electron capture (REC), dielectronic recombi-nation (DR) and three-body recombination (3BR), becomemore dominant. However, due to the much smaller crosssections for free electron capture processes, the recombina-tion rates in plasma are typically dropping with higher ion-ization degrees. In addition, the plasma density is changingthe mean free path length of the projectile ions which leadsto higher collision rates and in consequence to increasingionization rates with raising density.The charge state of the projectile ion is determined bythe ionization and recombination rates which are balanc-ing each other out. After a certain interaction time in∗ a.ortner@gsi.detemperature  eV 10 50 100 150 200iondensitycm3101810191020102110221023 Ztarget123456Figure 1: The plasma parameter space investigated in ourstudy. The ionization degree of the carbon plasma is calcu-lated by solving the saha equation.the plasma the charge state distribution reaches an equi-librium and a mean charge state can be determined. Forour study we used an Ar16+ ion as projectile with an en-ergy of 4MeV/u interacting with a plasma column of 200g/cm−2. As shown in Fig. 1, the plasma parameter spacevaries from electron temperatures from 10 eV to 200 eVand ion densities of 1018 cm−3 to 1023 cm−3.temperature  eV 10 50 100 150 200iondensitycm3101810191020102110221023 Zmean out14.51515.51616.517Figure 2: Mean charge state of an Ar16+ ion beam afterinteracting with 200 μg/cm2 carbon plasma.The calculated mean charge state in plasma compared tocold gas of the same density (color bar on the left side) isshown in Fig. 2. At hight temperatures one can clearly seethe ”density effect” where the charge state increases withhigher densities. At low densities the temperature depen-dency, the so called ”plasma effect” shows the reductionof the charge state to lower temperatures. As expected,in a hot plasma, the projectile mean charge state increasescompared to the equilibrium charge state in cold matter ofthe same density. However, at low plasma temperatures,where a partly ionized plasma is predominant, both effectsare compensating each other and even a decrease of themean charge state in plasma compared to cold matter canbe observed (e.g. ρ = 5∗1020 cm−3, T = 10 eV to 50 eV).At detailed description of the code can be found in [1]. Thecode was benchmarked with experimental results [2]. Thiswork was supported by the Helmholtz International Centerfor Fair and HGS-Hire.References[1] A. Frank, PhD-Thesis, TU-Darmstadt, (2012)[2] A. Frank, A. Blazevic, W.Cayzac, A.Ortner, M.Roth et al.,Phys. Rev. Lett. 110 11 115001 (2013)GSI SCIENTIFIC REPORT 2013 PNI-PP-06doi:10.15120/GR-2014-1-PNI-PP-06 187

Theoretical investigation of the charge transfer processes of heavy ions at intermediate energies interacting with a plasma

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Theoretical investigation of the charge transfer processes of heavy ions at intermediate energies interacting with a plasma

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