# Interaction of slow HCI with gaseous targets: absolute x-ray emission cross sections and contribution of multi-capture processes

Martino Trassinelli, T. Kirchner, E. Lamour, L. Maunoury, J. Mérot, J.Y. Pacquet, Christophe Prigent, J.M. Ramillon, R. Reuschl, J.P. Rozet, et al.

## ► To cite this version:

Martino Trassinelli, T. Kirchner, E. Lamour, L. Maunoury, J. Mérot, et al. Interaction of slow HCI with gaseous targets: absolute x-ray emission cross sections and contribution of multi-capture processes. XXVII International Conference on Photonic, Electronic and Atomic Collisions (ICPEAC 2011), Jul 2011, Belfast, Ireland. pp.082010, 10.1088/1742-6596/388/8/082010 . in2p3-00769581

HAL Id: in2p3-00769581

https://in2p3.hal.science/in2p3-00769581v1

Submitted on 20 May 2025

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# Interaction of slow HCl with gaseous targets: absolute x-ray emission cross sections and contribution of multi-capture processes

To cite this article: M Trassinelli et al 2012 *J. Phys.: Conf. Ser.* **388** 082010

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# Interaction of slow HCI with gaseous targets: absolute x-ray emission cross sections and contribution of multi-capture processes

M. Trassinelli<fnref n="1" />*, T. Kirchner<fnref n="2" />, E. Lamour<fnref n="1" />, L. Maunoury<fnref n="3" />, J. Mérot<fnref n="1" />, J.-Y. Pacquet<fnref n="3" />, C. Prigent<fnref n="1" />, J.-M. Ramillon<fnref n="3" />, R. Reuschl<fnref n="1" />, J.-P. Rozet<fnref n="1" />, S. Steydli<fnref n="1" /> and D. Vernhet<fnref n="1" />

**Synopsis** Collisions of 15 keV/q Ar¹⁷⁺ ions with a gaseous jet have been studied by high-resolution x-ray spectroscopy techniques. Absolute x-ray emission cross sections and initial population mechanisms on singly and multiple excited states are extracted.

Rydberg states of Highly Charged Ions (HCI) are formed in low energy collisions with atoms or molecules following the capture process of one or several electrons. Subsequent to the interaction, the excited HCI stabilize via a combination of radiative decay (either direct or via cascades) and autoionization giving rise to photons and electrons emission. It is well established that this chain of phenomena takes place in fusion plasma environments [1].

Recently, we have investigated the collision of 15 keV/q Ar¹⁷⁺ ions with either argon atoms or nitrogen molecules. The effusive gaseous jet used is formed at the exit of a cylindrical capillary connected to a reservoir at a given pressure. Both its density and angular profile have been modeled from calculations [2]. The HCI beam with a continuous current up to 2 enA was provided by the ARIBE facility (GANIL, Caen). At the interaction zone, the ion beam envelope was regularly controlled by an imaging system including an alumina foil and a CCD camera. The collision gives rise to the emission of helium-like x-ray transitions recorded by solid-state detectors fully characterized [3]. To reach high precision in the measurements of Lyman intensities, we also employed a high-transmission high-resolution Bragg spectrometer (resolution ~2 eV at 3 keV). Finally, great care has been taken to ensure the single collision condition excluding all multiple step processes that could contaminate our experimental data.

To extract absolute measurements of x-ray emission cross sections, determination of the ion beam – effusive jet overlap is mandatory and we used an integrated method established previously [4]. A first estimation gives a cross section of 8 × 10⁻¹⁵ cm<fnref n="2" /> for nitrogen target. This value agrees within 30% with previous measurements [5] obtained with a completely different experimental apparatus. While it concerns absolute value, this comparison corroborates perfectly our result.

Thanks to the high-resolution power of the crystal spectrometer, we are able to separate all the ¹s np → ¹s<fnref n="2" /> transitions from n=2 to 9 with an un-

preceded accuracy compared to previous experiments [6,7] (see Fig 1). From these spectra, applying precise calculations of the cascade processes, initial population mechanisms can be resolved. Beyond the preferential *n* quantum number, we determined the *n* distribution population of the excited states for the single-capture process. In addition, the levels in which multi-capture processes occur are extracted as well as their contribution compared to single-capture. A preliminary result exhibits a maximum of the contribution of the single-electron capture of 15% for both systems studied. Close coupling calculations on the level of the independent-particle model confirm that multi-electron processes play an important role in this collision system.

<figure><img src="image_6.png" /><figcaption>Fig. 1. ¹s np → ¹s<fnref n="2" /> transitions (from n=2 to 9) induced by the collision of 15 keV/q Ar¹⁷⁺ ions with N₂ target.</figcaption></figure>

## References

[1] H. Tawara, in *The Physics of Multiply and Highly Charged Ions*, edited by F. J. Currell (Dordrecht) 1, 103 (2003)

[2] D Vernhet, Thèse d'Etat (1990)

[3] E Lamour et al, Rev. Sci. Instr. **80**, 023103 (2009)

[4] K Wohrer et al, Rev. Sci. Instr. **71**, 20 (2000)

[5] H Tawara et al, Phys. Rev. A **64**, 042712 (2001)

[6] S Knoop et al, J. Phys. B **41**, 195203 (2008)

[7] F I Allen et al, Phys. Rev. A **78**, 032705 (2008)

<footnote n="1">¹INSP-UMR CNRS 7588, Université Pierre et Marie Curie, Paris, France</footnote>

<footnote n="2">²Department of Physics and Astronomy, York University, Toronto, Ontario, Canada</footnote>

<footnote n="3">³GANIL, Caen, France</footnote>

<footnote>*E-mail: martino.trassinelli@insp.jussieu.fr</footnote>