Enhancing Anion Trapping Efficiency: Simulation of a Novel Deceleration Stage for the Borealis Experiment*

The AEgIS collaboration at CERN’s Antiproton Decelerator aims to measure the gravitational acceleration of antihydrogen more precisely. Cold anions can sympathetically cool the antiprotons used in antihydrogen creation. Laser cooling is ideal for cooling anions to the needed temperatures. While it’s well-established for cooling neutral and positive ions, anions are more challenging due to their electronic structure. Yet, some molecular anions like C2⁻ show potential.

The Borealis experiment, initiated by AEgIS to laser cool C2⁻, produces and directs C2⁻ bunches from an ion beam into an ion trap, during which significant losses occur. Hence, a new pulsed deceleration tube was designed and simulated using finite element analysis software. The current static deceleration tube slows anions but does not narrow their kinetic energy spread. With its unique geometry the new tube narrows kinetic energy spread, resulting in more efficient trap loading. The performance was compared with a simpler alternative geometry. The ideal tube could decelerate a C2⁻ anion beam from 1700 eV to less than 1 eV and reduce the energy spread from 50 eV to 1 eV. The simpler alternative was less effective, achieving final energies and spreads of 2-3 eV. It was also seen that the combination of voltages on each electrode can help focus the beam.

This work brings Borealis closer to improving anion losses, with the ultimate goal of laser cooling a negative molecule for the first time.