The cryogenic reaction microscope
Pfeifer Divison
Research Group (AG) Moshammer/Dorn
With the successful commissioning of the cryogenic storage ring CSR, our institute possesses a worldwide unique machine to store beams of atomic and molecular ions and to cool them down to extremely low temperatures (below -263°C or 10 K). Conditions similar to deep space are thus available in the laboratory. Now, questions such as “What happens when a cold molecule collides with an atom? How much energy is released (or required) when an electron is transferred from one atomic or molecular particle to another during a collision?” can be investigated.
The world-first cryogenic reaction microscope, called the CSR-REMI, was developed for the CSR. This combined electron and ion spectrometer enables fundamental investigations of quantum dynamics in the field of atomic and molecular physics. For example, it is possible to characterize the cooling processes of molecules and clusters by measuring ejected photoelectrons emitted, or to detect, the recoil ions and electrons, produced in collisions between the cold ion beam and a neutral gas jet with high efficiency and resolution, in coincidence with the molecular fragments of the cold CSR molecular ions. Other possible applications range from structure determinations of molecular ions with photoelectron spectroscopy to femtosecond time-resolved experiments on molecules in prepared states using established pump-probe techniques.
The figure provides an overview of the CSR with the position of the CSR-ReMi highlighted. To illustrate the complex mechanical structure of the CSR ReMi, a cut view of the ReMi is shown below the schematic figure. At the center of the spectrometer, the stored ion beam (magenta) interacts with a laser pulse or the neutral gas jet. The charged fragments can be detected by the two detectors (electrons are detected by the upper detector and ions by the lower one; the particle trajectories are shown schematically). This central, inner part will be cooled down to below 10 K. Thermal shields (dark and light blue) serve for thermal insulation against the outer CSR vacuum chamber that is at room temperature. Water and liquid helium for cooling are provided via pipes. The coils (yellow) generate a homogeneous magnetic field around the spectrometer, and in addition correct the track of the stored ion beam (magenta). A third detector within the cryogenic area enables the detection of neutral fragments in the forward direction.
In memory of Dr Claus Dieter Schröter, without his many years of dedicated work and outstanding expertise the CSR-ReMi would never have been possible.