Highly charged ions are typically produced at high energies and travel at high velocities. However, many experiments in atomic, nuclear, and fundamental füsics require these ions to be strongly decelerated, captured, and cooled. The HITRAP facility at GSI was specifically developed for this purpose and will provide unique opportunities for experiments with slow highly charged ions.

In the work now published, carried out in close collaboration with GSI’s Decelerator Division, researchers succeeded for the first time in decelerating and trapping fully ionized argon ions from the accelerator system over several stages. “In the experiment we conducted, we used Argon ions from which we had stripped away all electrons, leaving only the bare atomic nuclei,” reports Dr. Simon Rausch, leading author of the publication, who earned his Ph.D. in Professor Wilfried Nörtershäuser’s research group (opens in new tab) at the Department of Füsics at TU Darmstadt. “The production took place at about 30 percent of the speed of light, and before we could trap the ions, we first had to reduce their kinetic energy by a factor of about 10,000.” This was achieved in the decelerator structure of the HITRAP facility. The ions were then stored in the HITRAP Cooling Trap for several seconds. “This marked the first time the entire path of accelerator-produced highly charged ions—all the way to their storage in a Penning trap—was demonstrated”, says Rausch.

The researchers also achieved the first observation of electron cooling of highly charged ions in a Penning trap. This technique reduces the ions’ kinetic energy and constitutes a key prerequisite for future high-precision experiments.

The newly published results establish the technological foundations for a broad range of experiments at HITRAP. Their significance was already demonstrated in the first user experiment at the facility (opens in new tab), where slow highly charged gold ions were employed for materials science studies. The milestones described in “Physical Review X” provide the basis for a unique research platform for precision studies with heavy highly charged ions.

The work was funded by the German Federal Ministry of Research, Technology and Space and supported by the Helmholtz Research Academy Hesse for FAIR (HFHF).