The DESIREE storage rings are two electrostatic ion storage rings with one common ion-beams merging section where positive/negative ion interactions can take place and be investigated.


DESIREE is an acronym for 'Double ElectroStatic Ion Ring ExpEriment' and this double ion storage ring is the main instrument of the facility. It has been built for studies of interaction processes involving atomic, molecular, and/or cluster ions. The two storage rings have circumferences of 8.6 m and they have a common section where two stored ion beams of opposite charges are merged. This makes it possible to study reactions between positive and negative ions at center-of-mass energies ranging from the keV the meV range. The two beams are stored separately, one in each ring, and at energies of tens of keV in the laboratory frame. As the rings are purely electrostatic, ions of any mass may be stored and when the rings are operated at the lowest temperature of about 10 Kelvins most molecular and cluster ions will have time to relax to low internal energies during long time storage. The residual gas pressure is of the order of 10-14 mbar which is achieved by means of condensation on the cold inner chamber walls and Ti-sublimation pumps. In addition to cold ion-ion collisions it will also be possible to study interactions between internally cold, stored, ions and laser light in parallel or perpendicular beams geometries. Four position sensitive microchannel-plate particle detection systems are currently mounted around the rings and inside the cryogenically cooled vacuum chamber – one of the detectors consist of three 75 mm diameter channel-plates with a phosphor screen anode and is mounted after the merging section to catch and register one or several neutral fragments from each individual reaction event. A second position sensitive system will catch charged fragments after the merging systems and two additional detector systems will be used for neutral reaction products due, for example, to laser interactions with ions in the outer straight sections of the two rings. In order to achieve these experimental conditions very demanding design conditions for the cryogenic and the vacuum systems have been realized. The DESIREE storage rings are described in detail in this publication.

The electrostatic elements and detectors used for the two storage rings of DESIREE: CD- Cylindrical 160o Deflectors. DE- 10o Deflectors. QD- Quadrupole Doublets. MR- Merging Region enclosed in seven drift tube electrodes. SS- Straight Sections for collinear laser interaction. ID- Imaging Detector for neutral products from the merging region. SD- Optically transparent secondary electron emission detector. MD-, MC- Movable position-sensitive detectors. D1-, D2-, D3- Beam-merging deflectors (note that the deflector plates denoted both D3 and DE bend the beam in the symmetric ring by 10o and the beam in the asymmetric ring by an angle determined by the two beam storage energies). CC-, CV- Correction elements. PU- Electrostatic pick-up electrodes. RF- Radiofrequency beam bunching electrodes. The parts of the injection lines included in this picture are situated inside the main DESIREE vacuum enclosure. Four position-sensitive detectors are mounted in DESIREE.