HITRAP Cooler Penning Trap

Electron cooling of highly charged ions (HCI) in a Penning Trap

A crucial part of the HITRAP facility is the so-called Cooler Trap, the end-point of the decelerator. After the Interdigital H-type (IH) Linac and Radio Frequency Quadrupole have decelerated the bunch to 6 keV/u, the ions can be injected into this Penning Trap where they are cooled down to 10 eV or even further down to 4 K, i.e. the temperature of the setup.

For this challenging task a 400-mm, long cylindrical trap is necessary. 21 inner electrodes allow the formation of axial nested traps and therefore the simultaneous confinement of both positive and negative charges. 10⁹ electrons are indeed used to perform electron cooling of the hot ion sample down to 10 eV, when the process is stopped to avoid excessive recombination. Further cooling is accomplished via resistive cooling, dissipating in an external tank circuit the image current induced on the electrodes by the moving ion cloud. The theoretical limit is the temperature of the environment which is kept in thermal contact with the 6-T superconducting magnet at 4 K.

The cooled sample is then extracted either in bunched or slow, quasi-continuous mode according to the needs of the experiments.