D. S. Belić

Absolute detection efficiencies of microchannel plates for 0.1–2.3 keV electrons and 2.1–4.4 keV Mg+ ions

The absolute detection efficiencies of detectors consisting of two microchannel plates (MCP) in a chevron arrangement, were experimentally determined for 0.1–2.3‐keV electrons and 2.1–4.4‐keV Mg+ ions. Both detectors tested included a grid with 92.5% transmission in front of the first MCP. For the measurements, the observed detector count rates were compared to the corresponding particle currents collected in a Faraday cup and measured with a vibrating reed electrometer. The electron detection efficiency of the MCP detector, including the grid, decreases from 0.82 at 0.1 keV to 0.65 at 2.3 keV for electrons incident normal to the surface. The Mg+ ion detection efficiency for the same arrangement, but with 43° incidence angle, increases from 0.49 at 2.1 keV to 0.81 at 4.4 keV.

Electron-ion collisions: Dielectronic recombination and ionization

Abstract Inelastic electron-ion collisions have been studied by using crossed-beam techniques. The effects of state mixing by extrinsic fields in the collision region were investigated for the dielectronic recombination process Mg + (3s) + e → Mg(3p, nl ) → Mg(3s, nl ) + hν . By field ionization of the Rydberg atoms produced, cross sections σ ( n ) have been measured. The observed large changes of σ ( n ) with alteration of the extrinsic field provided the first incontrovertible experimental evidence that dielectronic recombination can be changed by external fields. Absolute cross sections for electron impact single, double and triple ionization of singly and multiply charged krypton ions were measured. The energy ranged from below threshold up to 1000 eV. The influence of metastable states on the cross sections for single ionization is discussed. Contributions of inner-shell ionization with subsequent auto-ionization to double and triple ionization are identified. Connections between the three principal inelastic processes in electron-ion collisions, i.e. recombination, excitation and ionization, are pointed out. The influence of these processes on plasma-modeling calculations is briefly discussed.