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Radiation Physics and Chemistry

Production of negatively charged atomic ions inside a linear Paul trap for the formation of antiprotonic atoms

Łukasz Kłosowski, Mariusz Piwiński, A. Linek, Małgorzata Grosbart, R. Ciuryło, M. Zawada, M. Teske, T. Sowiński, S. Alfaro Campos, Marcis P. Auzinsh, D. Bhanushali, A. Bhartia, Michael Berghold, Roberto Sennen Brusa, Krzysztof Calik, A. Camper, R. Caravita, F. Castelli, G. Cerchiari, S. Chandran, Ahmad Chehaimi, Sankarshan Choudapurkar, P. Conte, Giovanni Consolati, M. Doser, R. Ferguson, Matthias Germann, Anna Giszczak, L. T. Glöggler, L. K. Graczykowski, F. Guatieri, Natali Gusakova, F. P. Gustafsson, S. Haider, S. Ḣuck, Christoph Hugenschmidt, M. Jakubowska, M. A. Janik, Grzegorz H. Kasprowicz, Kamila Kempny, G. Khatri, Adam Ryszard Kisiel, G. Kornakov, V. Krumins, Lidia Lappo, S. Mariazzi, P. Moskal, Markus Münster, Piyush Pandey, Daniel Pęcak, Luca Penasa, F. Prelz, T. Rauschendorfer, Bharat Singh Rawat, B. Rienäcker, Volodymyr Rodin, H. Sandaker, S. Sharma, Estere Teberga, Mira Tockner, Marco Volponi, C.P. Welsch, J. Zielinski, Nicola Zurlo

Published Mar 31, 2026• 0 citations

Abstract

An effective, long-lasting, low-energy source of negatively charged ions was designed, constructed, and tested. The source uses electron dissociative attachment in electron-molecule collisions to form a set of anions inside a linear Paul trap. Iodine I 2 molecules were used to obtain pure sets of I − anions. The system was tested, providing about 1 0 5 ions produced in less than a minute, which can be stored in the trap and used in further experiments.

DOI: 10.1016/j.radphyschem.2026.113884

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An effective, long-lasting, low-energy source of negatively charged ions was designed, constructed, and tested. The source uses electron dissociative attachment in electron-molecule collisions to form a set of anions inside a linear Paul trap. Iodine I 2 molecules were used to obtain pure sets of I − anions. The system was tested, providing about 1 0 5 ions produced in less than a minute, which can be stored in the trap and used in further experiments.

The formation of Li− by dissociative attachment in e+Li2 collisions is characterized by a large cross section for electron attachment to highly vibrationally excited Li2 molecules. However, the electronic structure of the Li−2 system dictates that low energy electrons (≲0.2 eV) are needed to minimize loss processes. An alternate production route for Li− is possible via direct ion‐pair formation through collisions of highly excited (Rydberg) Li atoms. The mechanisms for ion‐pair formation will be discussed in terms of the high‐lying molecular Rydberg states of Li2.

Abstract We describe a linear Paul trap and high-voltage platform specifically designed for the trapping of a large and pure sample of anions from an external keV-energy beam. Capture and confinement in a static configuration of DC potentials was found to occur by transfer of axial to radial ion momentum due to elastic and inelastic collisions. Stability diagrams both in transmission and capture mode were recorded. The trapping efficiency was observed to be very sensitive to the axial potentials relative to the beam energy. Several 104 oxygen anions were loaded from a 2 keV primary beam and confined for several 100 s. Identification of trapped O− ions and contaminants was achieved by selective laser photodetachment.

Low-energy electron transfer in collisions between a Rydberg atom and a target molecule can result in the formation of negative ions. Depending as to the properties of the target molecule the electron may be bound in a localized molecular orbital (valence-bound) or bound by its dipole potential in a diffuse orbital located at the positive end of the dipole (dipole-bound). Here we examine the properties of valence-bound and dipole-bound negative ions created through electron transfer in collision with Rydberg atoms, in particular, their lifetimes, collisional properties and electric-field-induced detachment characteristics. Intercomparison of the various data also leads to new insights into electron attachment to molecules that can support both valence-bound and dipole-bound negative ion states.

We produce large numbers of low-energy ions by photoionization of laser-cooled atoms inside a surface-electrode-based Paul trap. The isotope-selective trap's loading rate of $4\ifmmode\times\else\texttimes\fi{}{10}^{5}\phantom{\rule{0.3em}{0ex}}{\mathrm{Yb}}^{+}\phantom{\rule{0.3em}{0ex}}\mathrm{ions}∕\mathrm{s}$ exceeds that attained by photoionization (electron-impact ionization) of an atomic beam by three (six) orders of magnitude. Traps as shallow as

0.13\phantom{\rule{0.3em}{0ex}}\mathrm{eV}

are easily loaded with this technique. The ions are confined in the same spatial region as the laser-cooled atoms, which will allow the experimental investigation of interactions between cold ions and cold atoms or Bose-Einstein condensates.

In order to demonstrate laser cooling on negatively charged ions, it is necessary to confine the ions in a region free of strong magnetic fields. In the course of this thesis, the pre-existing design of a linear Paul trap was modified and taken into operation. The new design possesses two additional end cap electrodes whose shape provides effective axial confinement without blocking optical access to the trapped particles. The influence of these end cap electrodes on the trapping potential was simulated and compared to experimental results. Measurements with AU- ions show that the trap allows storage of ions for multiple hours. Analysis ofthe storage time suggests that the loading process heats up the trapped ions. The lifetime τHot of the hot ions was determined to be 23(3) min. After thermalization, the lifetime increases to 75(2) min. Measurements of the ion cloud’s radius provide an estimation of the equilibrium temperature T∞ ≈5000 K. The experimentally determined time constant of the cooling process is τcool = 41:6(4) s.