First storage of ion beams in the Double Electrostatic Ion-Ring Experiment - DESIREE

TL;DR

This paper reports the first successful storage of ion beams in the DESIREE electrostatic ring at Stockholm University, demonstrating long storage times and analyzing decay mechanisms influenced by residual gas and space charge effects.

Contribution

It presents the first storage of ion beams in DESIREE, measures long storage lifetimes, and investigates decay dynamics including space charge effects.

Findings

Residual-gas limited storage lifetime of 448 seconds for C₂⁻ ions.

Estimated residual gas pressure in the 10⁻¹⁴ mbar range.

Observation of non-exponential decay due to space charge effects.

Abstract

We report on the first storage of ion beams in the Double ElectroStatic Ion Ring ExpEriment; DESIREE, at Stockholm University. We have produced beams of atomic carbon anions and small carbon anion molecules (C$_n^-$, $n=1,2,3,4$) in a sputter ion source. The ion beams were accelerated to 10 keV kinetic energy and stored in an electrostatic ion storage ring enclosed in a vacuum chamber at 13 K. For 10 keV C$_2^-$ molecular anions we measure the residual-gas limited beam storage lifetime to be 448 s $\pm$ 18 s with two independent detector systems. Using the measured storage lifetimes we estimate that the residual gas pressure is in the 10$^{-14}$ mbar range. When high current ion beams are injected, the number of stored particles does not follow a single exponential decay law as would be expected for stored particles lost solely due to electron detachment in collision with the residual-gas. Instead, we observe a faster initial decay rate, which we ascribe to the effect of the space charge of the ion beam on the storage capacity. %The latter effect becomes insignificant after longer storage times of typically 100-150 seconds and we then observe a constant decay rate due to residual-gas collisions.