Inga Tolstikhina

Charge-changing collisions of tungsten and its ions with neutral atoms

New experimental and theoretical data on charge exchange (CE) cross sections are presented for low-energy collisions (10?500?eV u?1) of W+ and W2 + ions with H, H2 and He atoms. The CE cross sections are calculated using the ARSENY code based on the hidden crossing method. The isotope effect (mass dependence) in collisions of W+ and W2 + ions with hydrogen isotopes H, D, T is studied in the framework of the adiabatic theory of transitions in slow collisions. Furthermore, the electron loss (EL) and CE cross sections for the energy range of 1?105 keV u?1 are calculated for tungsten and its ions Wq + (q = 0?40) colliding with H, He, N, Ar and W atoms using the computer codes (CAPTURE, DEPOSIT and RICODE) based upon the Born approximation and the classical energy-deposition model. The data obtained can be used for plasma modelling, planning and interpretation of future experiments in fusion devices using tungsten as a material for the plasma-facing components.

Collisions of Be, Fe, Mo and W atoms and ions with hydrogen isotopes : electron capture and electron loss cross sections

This work is a continuation of an investigation of the collisional properties of heavy-ion plasma impurities and the elements used for the plasma facing components in fusion devices. Results on the charge-changing cross sections for W atoms and ions are published in (Tolstikhina et al 2012 J. Phys. B: At. Mol. Opt. Phys. 45 145201). Here we present the electron loss and electron capture cross sections for collisions of Be, Fe and Mo atoms and their ions with the hydrogen isotopes (H, D, T) calculated in the E = 10 eV/u–10 MeV/u energy range. The calculations are performed, accounting for the multiple-electron loss processes and the cross sections, which can contribute more than 50% to the total loss cross sections. The influence of the isotope effect (mass dependence) (Stolterfoht et al 2007 Phys. Rev. Lett. 99 103201) on the capture cross sections is also studied in the frame of an adiabatic theory of transitions in slow collisions. New data on the partial multiple-electron loss cross sections for W and W+ are presented. Calculated cross sections are compared with the available experimental and theoretical data.

X-ray spectroscopy comparison methods for diagnostics of high-temperature molybdenum plasmas

A comparison method of high-temperature plasma diagnostics, developed by Shevelko [Quantum Electron. 41, 726 (2011)] and Shevelko et al. [Plasma Phys. Rep. 34, 944 (2008)], is modified and applied for Mo laser-produced plasma analyses. This method consists in determining the electron temperature Te of the studied plasmas by comparing the spectra of the investigated radiation source with the spectra of well-diagnosed laser-produced plasmas recorded at different Te. The modified comparison method includes the theoretical modeling of X-ray spectra of laser-produced plasmas of different elements. The most complete correspondence between the structure of the theoretical spectrum and the experimental one is achieved by changing the single parameter in theoretical calculations—the electron temperature Te. Such a method made it possible to describe in detail the structure of the X-ray spectra of multiply charged Mo ions, improve the accuracy of measurements, and justify the methods used. In particular, for Mo laser plasma (3-2 transitions in Mo31+-Mo34+ ions), the electron temperatures determined experimentally by the comparison method (Te = 685 ± 55 eV) and calculated theoretically (Te = 650 eV) are in a very good agreement.

Stopping Power of Ions in Matter (SP)

This chapter is devoted to properties of the stopping power (SP)—the important quantity characterizing the energy losses of projectile ions slowing down in gaseous, solid and plasma targets. The energy losses are resulted due to atomic processes between projectiles and target particles, mainly electron-loss, capture and target ionization. Energy and target-thickness (Bragg peak) dependencies of the SP are considered. Special attention is paid to the SP in plasmas as well as to the influence of the target-density effect on the SP values.

Charge Exchange in Slow Ion-Atom Collisions. Adiabatic Approach

This chapter is devoted to consideration of electron-capture processes at very low collision velocities \(\upsilon \ll \) 1 a.u. At present time, these processes are of a high importance because of two main reasons: first, they constitute the dominant mechanisms in a low-temperature plasma for creating the impurity ions in excited states, radiation short-wavelength spectra of which are used for plasma diagnostics. Second, at low-energy collisions, electron-capture cross sections, occurring in collisions with hydrogen isotopes (H, D, and T), are strongly influenced by the so-called isotope effect which changes the cross sections values by orders of magnitude. This influence is important for estimating, e.g., the capture cross sections of tungsten atoms and ions, colliding with neutral plasma atoms, because tungsten is adopted now as the most perspective element for making walls and diverter in plasma devices aiming at magnetic plasma confinement.

Electron Capture Processes

This chapter is devoted to consideration of electron capture (EC), which is one of the most important recombination mechanisms in collisions of ions with various targets. Special features of EC are described such as the presence different atomic particles before and after collision, a preferential capture of inner-shell target electrons at high energies, the role of excited states of the projectile ion after EC, different scaling laws at low and high energies and so on. The influence of the target-density effect as well as the use of the Bragg’s additivity rule for EC cross sections are described. Information on multiple-electron capture, which is very important for many applications, is also given. EC processes at very low energies, where the molecular effects play a key role, are considered in detail in Chap. 5.

Evolution of the Projectile Charge-State Fractions in Matter

The key question arising in passage of ion beams through media is the evolution of the projectile charge-state fractions \(F_q(x)\) in matter as a function of the target thickness x. Experimental and theoretical information on \(F_q(x)\) values are required for solving many problems in atomic, plasma and accelerator physics. For example, electron-loss and capture cross sections are usually determined by measured equilibrium charge-state fractions [1, 186]. After a number of subsequent collisions with the target particles, the charge-state distribution becomes dynamically stable and reaches its equilibrium with an average (mean) charge state \(\bar{q}\). This chapter is devoted to determination of equilibrium and non-equilibrium charge-state fractions on the basis of differential balance rate equations with coefficients equal to the interaction charge-changing cross sections. The Allison three-charge-state model as well as different computer codes are considered. To solve the balance rate equations, semi-classical and semiempirical formulae for the equilibrium mean charges \(\bar{q}\) are given for ion beams passing through gaseous and solid targets.

Multiple-Electron Ionization of Atoms by Fast Heavy Ions

Single- and multiple-electron ionization of atoms and molecules, induced by fast highly charged ions, constitute an important issue in accelerator physics (the vacuum conditions) and in different applications (cancer therapy). Multiple ionization of heavy target atoms can strongly (up to 50%) contribute to the total ionization cross sections similar to projectile ionization (loss) by target atoms, Sect. 1.4. In this Chapter, various theoretical approaches for multiple-electron probabilities and cross sections for ionization of neutral atoms are considered and compared with available experimental data.

Some Applications of Charge-Changing Cross Sections and Charge-State Fractions

In this chapter, some applications of results, obtained in the previous chapters for charge-changing cross sections and equilibrium charge-state fractions, are discussed for ion-beam lifetimes, inverse population in a laser plasma, detection of super-heavy elements, and material modifications.

Lifetimes of Radioactive Heavy Ion Beams

In the previous chapter, it was discussed that for non-radioactive ion beams, the lifetimes depend on the atomic charge-changing interactions between the ion beam and residual-gas components. In the case of radioactive ion beams, the mean lifetimes depend in addition on the nuclear properties of accelerated ions, and hence, the total mean lifetime comprises both atomic and nuclear components: