Hyperfine Interact (2006) 173:93–101 DOI 10.1007/s10751-007-9547-y The HITRAP project at GSI: trapping and cooling of highly-charged ions in a Penning trap F. Herfurth · K. Blaum · S. Eliseev · O. Kester · H.-J. Kluge · S. Koszudowski · C. Kozhuharov · G. Maero · D. Neidherr · W. Quint · S. Schwarz · S. Stahl · G. Vorobjev Published online: 11 July 2007 © Springer Science + Business Media B.V. 2007 Abstract A decelerator will be installed at GSI in order to provide and study heavy nuclei without or with only few electrons at very low energies or even at rest. Highly- charged ions will be produced by stripping at relativistic energies. After electron cooling and deceleration in the Experimental Storage Ring (ESR) the ions are ejected out of the storage ring at 4 MeV/u and further decelerated in a combination of linear accelerator structures operated in reverse. Finally, they are injected into a Penning trap where the ions are cooled to 4 K by electron cooling in combination with resistive cooling. From here, the ions can be transferred in a quasi DC or in a pulsed mode to different experimental setups. This article describes the technical concepts of this project focused on the Penning trap. Keywords Penning trap · Electron cooling · QED tests · Highly charged ions PACS 07.90.+c · 12.20.Fv 1 Introduction The theory of quantum electrodynamics (QED) is better understood than most theories in modern physics. It is for instance able to predict atomic level energies F. Herfurth (B ) · S. Eliseev · O. Kester · H.-J. Kluge · S. Koszudowski · C. Kozhuharov · G. Maero · W. Quint · G. Vorobjev GSI, Planckstrasse 1, 64291, Darmstadt, Germany e-mail: F.Herfurth@gsi.de K. Blaum · D. Neidherr · S. Stahl Institut für Physik, Johannes Gutenberg Universtät, Staudingerweg 7, 55128 Mainz, Germany S. Schwarz NSCL/MSU, 1 Cyclotron, East Lansing, MI 48824-1321, USA