M. Druetta

Beam-gas study of low velocity highly ionised titanium in the EUV using microchannel plates

Abstract Position sensitive detection was used to record spectra of Ti XIII and XII emitted by a low velocity titanium beam after one and two electron capture in a gas cell. A three meter quasi-grazing-incidence spectrometer was equipped with two 25 mm microchannel plates coupled with a sensitive anode encoder. The detector was successively positioned to record EUV radiations in the wavelength range from 30 to 60 nm. Observed lines are unambiguously assigned to transition in Ne-like and Na-like titanium.

Sequential photoionization of ions using synchrotron radiation and a Penning ion trap

Abstract Sequential photoionization has the potential of making available for study highly charged low energy ions. Synchrotron radiation was used to create a multicharged xenon ion target for further ionization by synchrotron radiation inside a Penning ion trap. Evidence of sequential photoionization was seen, though the yields were small. Improvements in the apparatus and radiation from third generation synchrotrons are expected to increase sequential photoionization yields significantly.

Sensitivity calibration of a VUV spectrometer using cross section measurements

Abstract Spectra produced in low-energy collisions between multicharged ions and neutrals have been used for the calibration of the detection efficiency of a vacuum-ultraviolet (VUV)-spectrometer-multichannel-plate (MCP) detector system. This method is now competitive with others due to the availability of ECR sources and new data on line emission cross sections. Results are shown with a 3 m VUV spectrometer, two gratings and MgF 2 -coated or uncoated MCP in the 8–130 nm spectral range.

Excitation cross section measurements of doubly excited states produced in low energy collisions between multicharged ions and neutrals

Abstract 5–60% N 5+ (1s2s 3 S) metastable beam fraction has been produced. Single-electron capture from this state will give doubly excited 1s2s nl 2,4 L states. The quartets are metastable with respect to Coulomb autoionization and transitions between these doubly excited quartet states have been observed by photon spectroscopy. 1s2p nl states are also observed (TE process). Absolute emission and excitation cross sections have been measured.

Subshell selective electron capture in collision of Oq+ (q = 6, 7) with H2, He at 10q keV☆

Abstract Absolute cross sections for electron capture into different ( n , l ) subshells have been determined for O 6+ + He and O 7+ + He/H 2 collisions. The n = 4 level of O VI are predominantly populated, while the n = 3 and n = 4 of O VII are nearly equally populated. Transitions between doubly excited quartet states of O VI are observed, they are obtained by one electron capture on the 1s2s 3 S O 6+ metastable state.

Radiative decay following low energy charge exchange collisions at the Agrippa facility

Abstract From radiative decay observed in the X and VUV domain, it is possible to determine the (n, l) substate populations and deduce their excitation cross sections. We consider here the case of different projectiles of charge +8. For some of them, we show σnl for single capture from H 2 and He, as a function of energy. From the spectra it is recognized that double capture followed by radiative decay is effective. Observed transitions — of the same nature as dielectronic recombination satellites — are the signature of this process. Finally, in the case where energy levels are not known since the capture is a selective process, radiative decay appears thus as a means for basic spectroscopic studies.

Charge exchange spectroscopy of Xeq+(q = 7–8) + He collisions

Abstract Charge exchange collisions between Xe q + ( q = 7–8) and He have been studied by optical spectroscopy at 15 q keV energy. New identifications in Xe VII and Xe VIII are reported and level energies are deduced. ( n , l ) cross sections have been measured.

Electron transfer collision studies on stored ions produced by synchrotron radiation

Abstract Studies of electron transfer collisions of low energy stored ions with target atoms have been carried out as a function of the well depth of the Penning ion trap. The ions were produced by vacancy cascades following inner-shell photoionization by synchrotron radiation. The ion storage data, following an analysis based on the details of the ion production, storage, and collision processes in the trap, provides information for optimizing the accuracy of electron transfer rate coefficient measurements when several charge state are present. Low trap well depths exceeding a well-defined minimum value are the most useful.

Neutral density measurements at the plasma edge of the Tore Supra tokamak with carbon charge exchange lines

Abstract Direct measurements of the neutral (hydrogen) density n0 in tokamak plasmas are almost completely lacking. Thus, indirect information via charge exchange spectroscopy (CX) of sensible intensity ratios of impurity (carbon) ions are used. Two methods are used for the evaluation of the n0. The first method is based on ground state transitions of CV and the second on CX-recombination of completely ionized carbon (C6+). CX-recombination occurs at the interface between the hot plasma and the cold periphery. Consequently, plasma situations with a cold and dense edge where n0 is naturally high are analyzed. These cold edge plasmas are characterized by the appearance of a highly radiating region at the inner wall of the tokamak (Marfe). The inferred Marfe neutral density is between 1017 and 1018 m−3. In addition, the changes of this radiating zone induced by the ergodic divertor (ED) of Tore Supra are studied: an n0 of 1016 m−3 is deduced inside the ergodized region where the CV line is emitted.

One and two electron transfer at low collision energy: Spectroscopic case studies

Abstract A comparative study of single and double electron transfer is made considering ions with an initial charge of 8 + (O8+, Ne+ , Ar8+) colliding with He at energies of a few keV/amu. It is shown that even though single capture populates n = 4, the dynamics of the process is different. Furthermore double capture being possible, mostly via a two step process in one collision, it appears that stabilization changes significantly in these three cases from mostly autoionizing to mostly radiative.