The cryogenic storage ring CSR

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 ± 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.

Astrochemical studies at the Cryogenic Storage Ring

“…The inner vacuum chambers-which also house the ion optical deflection elements-can be cooled by a closed-cycle liquid helium refrigerator to temperatures around 5 K. At these temperatures, most residual gas particles will be cryopumped efficiently, and therefore a very low pressure can be achieved. During the first cryogenic experimental phase, a residual gas particle number density of less than 140 cm −3 was obtained [5] (derived from lifetime studies and collisional detachment rates, as commercial pressure gauges do not allow for measurements at these low densities). Although this pressure regime is not strictly needed for all astrophysical experiments per se, it is interesting to note that with these physical conditions (with a temperature around 10 K and number densities of the order of 10 2 cm −3 ) the CSR vacuum system may be the largest laboratory on Earth that manages to closely mimick the conditions in a cold molecular cloud.…”

“…In any case, the 300 K radiation field in a room-temperature storage ring would lead to a thermal distribution spread out over many rotational states, unlike the concentration of the population in the lowest quantum states observed in low-temperature interstellar environments. With the advent of cryogenic electrostatic storage rings [3][4][5], this situation has changed. In these devices, the experimental vacuum system is cooled to very low temperatures (typically below 20 K) that resemble those prevailing in interstellar clouds.…”

Dissociative Recombination Measurements of Chloronium Ions (D2Cl+) Using an Ion Storage Ring

“…45 μeV, based on precise fitting of resonance features in the dielectronic recombination measurement of Lestinsky et al (2008) and on fragment-imaging spectra in the DR studies of Stützel (2011). The uncertainties quoted here and throughout are given at an estimated 1σstatistical confidence level.…”

Opportunities for negative ions studies at the Frankfurt Low-energy Storage Ring (FLSR)

“…However, at least the vibrational ground state can usually be reached. The rotational lowest states can only be reached in a cryogenic storage ring like CSR@Heidelberg [4] or DESIREE@Stockholm [5], where the whole storage ring is cooled to only a few Kelvin above absolute zero.…”