The Cryogenic Storage Ring CSR

TL;DR

The paper presents the design, construction, and operation of a cryogenic electrostatic storage ring capable of storing ions for extended periods at very low temperatures, enabling advanced experiments on ion collision and fragmentation processes.

Contribution

This work introduces a novel cryogenic storage ring with long storage times and low residual gas pressure, facilitating new experiments in ion physics at cryogenic temperatures.

Findings

Storage times of several minutes up to nearly an hour for ions at 60 keV.

Residual gas pressure below 10^-14 mbar, enabling low-collision experiments.

Observation of momentum distribution broadening over 1000 seconds.

Abstract

An electrostatic cryogenic storage ring, CSR, for beams of anions and cations with up to 300 keV kinetic energy per unit charge has been designed, constructed and put into operation. With a circumference of 35 m, the ion-beam vacuum chambers and all beam optics are in a cryostat and cooled by a closed-cycle liquid helium system. At temperatures as low as (5.5 $\pm$ 1) K inside the ring, storage time constants of several minutes up to almost an hour were observed for atomic and molecular, anion and cation beams at an energy of 60 keV. The ion-beam intensity, energy-dependent closed-orbit shifts (dispersion) and the focusing properties of the machine were studied by a system of capacitive pickups. The Schottky-noise spectrum of the stored ions revealed a broadening of the momentum distribution on a time scale of 1000 s. Photodetachment of stored anions was used in the beam lifetime measurements. The detachment rate by anion collisions with residual-gas molecules was found to be extremely low. A residual-gas density below 140 cm$^{-3}$ is derived, equivalent to a room-temperature pressure below 10$^{-14}$ mbar. Fast atomic, molecular and cluster ion beams stored for long periods of time in a cryogenic environment will allow experiments on collision- and radiation-induced fragmentation processes of ions in known internal quantum states with merged and crossed photon and particle beams.