Atomic Physics

Low-energy antiprotons are the ideal and perhaps the only tool to study in detail correlated quantum dynamics of few-electron systems in the femto- and sub-femtosecond time regime. Advanced storage ring and detection technologies in combination will enable, for the first time, access to kinematically complete antiproton-induced rearrangement and fragmentation measurements. These will allow to ultimately benchmark contradicting predictions of existing theories and to explicitly address the few-body Coulomb problem – one of the most fundamental, yet unsolved problems in physics.

Presently the only experimental data available from antiproton/atom collisions is on the level of total cross sections as shown in the figure below. While these measurements are already well suited for tests of existing theories, they do not allow for a full understanding of the quantum dynamics of these collisions.

Cross section of Helium ionization by antiproton impact

Cross section of Helium ionization by antiproton impact. 


The QUASAR Group has designed an in-ring spectrometer for carrying out such measurements and has also realized design studies into the USR, a compact antiproton recycler ring, as well as upgrade options for ELENA with the aim to investigate the feasibility of in-ring atomic physics experiments.


Currently involved QUASARs:



Selected publications:


V. Tzoganis, C.P. Welsch, 'Alignment of a Nozzle-Skimmer System for a Non Invasive Gas Jet Based Beam Profile Monitor', IBIC 2013, Oxford, UK(2013)

M. Putignano, C. P. Welsch, 'Numerical study on the generation of a planar supersonic gas-jet', Nucl Instrum Methods Phys Res A 667 44-52 (2012) (S0168900211020961)

C.P. Welsch, K.U. Kühnel, C.D. Schröter, and J. Ullrich, 'Sub-Femtosecond Correlated Dynamics Probed with Antiprotons', AIP Conf. Proc. 1037 (2008), p.318-33

C.P. Welsch, M. Grieser, A. Dorn, R. Moshammer, J. Ullrich, 'Exploring Sub-Femtosecond Correlated Dynamics with an Ultra-low Energy Electrostatic Storage Ring', AIP Conf. Proc. 796 (2005) p. 266-271

J. Ullrich, A. Dorn, D. Fischer, R. Moshammer, B. Najjari, M. Schulz, A. Voitkiv, C.P. Welsch,'Sub-Femtosecond Correlated Dynamics Explored with Antiprotons', AIP Conf. Proc. 793 (2005) p. 71-88