Electrostatic Storage Ring Research Articles

Dissociation Energy forC2Loss from Fullerene Cations in a Storage Ring

We have stored positively charged fullerene ions C(+)(n) (n even, from 48 to 70 and 76), C(2+)(60) and C(2+)(70) in an electrostatic storage ring and have measured the rate of emission of neutral fragments as a function of time. In the time range of the measurements, 50 micros to a few milliseconds, the rate decreases strongly due to radiative cooling of the molecules. Using the cooling rate predicted from a dielectric model, we have extracted the dissociation energies for C(2) loss from the measurements. As expected, the energies are largest for the "magic" fullerenes, C(50), C(60), and C(70), and the value of 9.8+/-0.1 eV for C(2) loss from C(+)(60) is in reasonable agreement with theory and with other recent experiments.

Lifetime measurement ofHe−utilizing an electrostatic ion storage ring

The electrostatic heavy-ion storage ring, ELISA is utilized to measure the lifetime of the metastable $1s2s2p{}^{4}{P}_{5/2}$ level of the ${\mathrm{He}}^{\ensuremath{-}}$ ion together with the average lifetime of the ${}^{4}{P}_{1/2}$ and ${}^{4}{P}_{3/2}$ levels. This storage ring allows lifetime measurements to be performed without the influence of magnetic fields, and at temperatures below $\ensuremath{-}50\ifmmode^\circ\else\textdegree\fi{}\mathrm{C},$ which reduces the photodetachment of ${\mathrm{He}}^{\ensuremath{-}}$ due to blackbody radiation. The lifetime of the ${}^{4}{P}_{5/2}$ level is determined to be $365\ifmmode\pm\else\textpm\fi{}3 \ensuremath{\mu}\mathrm{s},$ in agreement with, but more accurate than, a previous magnetic storage ring measurement, and 6% longer than the lifetime recently reported utilizing an electrostatic ion trap [Wolf et al., Phys. Rev. A 59, 267 (1999)]. The average lifetime of the ${}^{4}{P}_{1/2}$ and ${}^{4}{P}_{3/2}$ levels is determined to be $11.1\ifmmode\pm\else\textpm\fi{}0.3 \ensuremath{\mu}\mathrm{s},$ in agreement with theoretical predictions, but about 25% longer than the reported value from the electrostatic ion trap experiment.

A prototype storage ring for neutral molecules.

The ability to cool and manipulate atoms with light has yielded atom interferometry, precision spectroscopy, Bose-Einstein condensates and atom lasers. The extension of controlled manipulation to molecules is expected to be similarly rewarding, but molecules are not as amenable to manipulation by light owing to a far more complex energy-level spectrum. However, time-varying electric and magnetic fields have been successfully used to control the position and velocity of ions, suggesting that these schemes can also be used to manipulate neutral particles having an electric or magnetic dipole moment. Although the forces exerted on neutral species are many orders of magnitude smaller than those exerted on ions, beams of neutral dipolar molecules have been successfully slowed down in a series of pulsed electric fields and subsequently loaded into an electrostatic trap. Here we extend the scheme to include a prototype electrostatic storage ring made of a hexapole torus with a circumference of 80 cm. After injection, decelerated bunches of deuterated ammonia molecules, each containing about 106 molecules in a single quantum state and with a translational temperature of 10 mK, travel up to six times around the ring. Stochastic cooling might provide a means to increase the phase-space density of the stored molecules in the storage ring, and we expect this to open up new opportunities for molecular spectroscopy and studies of cold molecular collisions.

Small Electrostatic Storage Rings; also for Highly Charged Ions?

Two years ago, a small electrostatic storage ring ELISA (ELectrostatic Ion Storage ring, Aarhus) was put into operation. The design of this small 7 m circumference ring was based on electrostatic deflection plates and quadrupoles. This is in contrast to the larger ion storage rings, which are based on magnetic focusing and deflection. The result is a small, relatively inexpensive, storage ring being able to store ions of any mass and any charge at low energy (< 22 keV). The average residual-gas pressure is around 10-11 mbar resulting in storage times of several tens of seconds for singly charged ions. The maximum number of singly charged ions that can be stored is a few 107. Several experiments have already been performed in ELISA. These include lifetime studies of metastable ions and studies of fullerenes and metal-cluster ions. Lasers are also used for excitation of the circulating ions. Heating/cooling of the ring is possible. Cooling of the ring leads to significantly lower pressures, and correspondingly longer lifetimes. A change of the temperature of the vacuum chambers surrounding the ion beam also leads to a change of the spectrum of the black-body radiation, which has a significant influence on weakly bound negative ions. At the time of writing, at least two other electrostatic storage rings are being built, and more are planned. In the following, the electrostatic storage ring ELISA will be described, and results from some of the initial experiments demonstrating the performance will be shown. The relative merits of such a ring, as opposed to the larger magnetic rings and the smaller ion traps will be discussed. The potential for highly charged ions will be briefly mentioned.

Stability of the ground state vinylidene anion H2CC-

A technique to measure very low collisionless decay rates of ionic species has been applied at a new electrostatic storage ring to obtain the rate for spontaneous rearrangement of the vinylidene anion to neutral acetylene. The measurement yields a rate of k(0) = (0.009+/-0.006) s(-1), corresponding to a natural lifetime of the vinylidene anion of tau(0) approximately 110 s.

A storage ring for polar molecules

An electrostatic storage ring for polar molecules is proposed, including an analysis of the ring dynamics, loading, and losses for experimentally practical parameters. It is shown that storage lifetimes on the order of 103–104 s can be expected for methyl fluoride under reasonable operating conditions. A design for the storage ring is presented along with potential applications to molecular beam steering, molecular collision physics, and surface deposition and lithography. Other approaches to molecular storage are also briefly discussed.

ELISA, and electrostatic storage ring for atomic physics

The design of a new type of storage ring for heavy ions using electrostatic deflection and focusing devices is described. At low energy, where the velocity is low for heavy ions, electrostatic bends and quadrupoles are more efficient than magnetic ones. Furthermore, electrostatic devices are more compact and easier to construct than magnetic devices. These and other features, e.g. no magnetic fields, makes such storage rings attractive for many atomic-physics experiments, and also for basic research in neighboring fields such as chemistry and biology.