Düsseldorf 2007 – scientific programme

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A: Fachverband Atomphysik

A 11: Poster I - Collisions with electrons and ions

A 11.4: Poster

Tuesday, March 20, 2007, 16:30–18:30, Poster B

Cold electron beams for high-resolution storage-ring electron collision spectroscopy. — •Michael Lestinsky, Jens Hoffmann, Dmitry Orlov, and Andreas Wolf — Max-Planck-Institut für Kernphysik, D-69117 Heidelberg

High-resolution electron collision spectroscopy uses a merged beams arrangement with a magnetically guided electron beam in heavy ion storage rings to observe resonant processes such as dielectronic recombination of atomic and dissociative recombination of molecular ions. At low energies, energy resolutions can reach down to 0.5 meV with a photocathode source. At higher energies the achievable resolution is limited by the energy spread parallel to the overall motion of the beam, usually expressed by the longitudinal temperature kT_||.

The influence of realistic acceleration arrangements, employing magnetic transverse expansion and a long section for slow (adiabatic) acceleration (0.45 m), has been systematically investigated at the cold electron target of the TSR Heidelberg. At a beam energy of 4 keV, lower limits of kT_|| of 29 µeV and 11 µeV were realized at the two current extremes of 10 mA and 0.05 mA, respectively. For fast acceleration, the temperatures were found to be higher by up to 25%. A guiding field of 0.06 T was used to keep the rise of kT_|| by electron scattering low, so that expected effects of the acceleration structure became visible. The results help to guide the layout of future high-resolution beam devices, such as at the NESR at GSI/FAIR or at the CSR Heidelberg.