The Atomic & Molecular Physics Group develops new Ion Trapping methods as well as related Mass Spectrometric techniques for further analysis of the trapped particles.
These are applied to solve questions from various areas of nuclear, atomic and molecular research, such as
- What are the structures of exotic, short-lived atomic nuclei?
- More specific: How were the elements in the Universe created?
- What are the heaviest (“superheavy”) elements and what are their properties?
- What are the structures and properties of aggregates of a few up to several hundred or thousand metal atoms, also called metal (nano-)clusters?
- How do they interact with photons, electrons, atoms and molecules?
- More specific: How many extra electrons can be packed onto a cluster of a given size, i.e. how far can an isolated nano-capacitor be charged up?
Implemented in 2016, the Greifswald MR-ToF setup is based on a multi-reflection time-of-flight (MR-ToF) mass spectrometer, an ion-storage device which is also referred to as an electrostatic ion beam trap (EIBT). Two opposing electrostatic mirrors are utilized to reflect trapped ions back and forth and thus utilize a drift tube hundreds to thousands of times. At identical total energies, ions with different mass-to-charge ratios will exhibit different revolution periods und thus different overall flight times for a fixed number of laps. The device’s precision and mass resolving power can thus be increased by elongating the flight path of investigated ions.
ClusterTrap has been designed to investigate properties of atomic clusters in the gas phase with particular emphasis on the dependence on the cluster size and charge state. The combination of cluster source, ion traps and time-of-flight mass spectrometry allows a variety of experimental schemes including collision-induced dissociation, photo-dissociation, further ionization by electron impact, and electron attachment. Positively or negatively singly-charged clusters are produced in a laser-ablation source and accumulated in a radiofrequency ion trap. Then, the cluster ion bunch is transferred via a quadrupole ion deflector into a Penning trap and there prepared and subjected to one or several reaction steps. In the Penning trap, a superconducting magnet provides a homogenous magnetic field (Bz = 12 T), which confines the ions in the plane perpendicular to the magnetic field lines. For axial ion confinement, a voltage potential is applied to a stack of cylindrical electrodes, providing a harmonic trapping potential U(z). The center ring electrode is azimuthally split into 8 segments to allow for application of radial excitation fields (e.g. dipolar, quadrupolar and octupolar) and therefore manipulation of the amplitude of the radial ion motions in the trap (cyclotron motion and magnetron motion). The cylindrical geometry of the trap allows for easy axial access for different interaction methods with stored cluster ions (e.g. laser radiation, exposure to electron beams). Subsequently, the product ions are analyzed by time-of-flight (ToF) mass spectrometry.
The intense pulsed positron source (IPPS)
The goal of the intense pulsed positron source is the development of a device for the accumulation and storage of large amounts of positrons (~10^12 e^+), at low positron energies (<1 eV) and for long times (>1 h).
The project (IPPS) is part of the APEX (A Positron Electron EXperiment) collaboration which pursues the formation of the first large scale, low Debye-length electron-positron plasma. The high intense beam of the neutron-induced positron source Munich (NEPOMUC) will be guided into a buffer-gas trap and accumulator. There, the positrons are decelerated by buffer-gas collisions with N_2 and cooled by a cooling gas (SF_6 or CF_4) and afterwards stacked in the accumulator forpulses of up to 10^9 positrons. Then the positrons are guided into the high-field multi-cell trap which further accumulates the positron pulses until a total charge of up to 10^12 e^+ is reached. The actual pair-plasma experiments take place within the trap. Its main component is a levitating super conducting coil, which creates a confining magnetic field for both electrons and positrons (APEX). In a parallel approach a tabletop stellarator (EPOS – electrons and positrons in an optimized stellerator) will be developed which addressess complement questions of a pair plasmas.