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 7m c ircumference ring was based on electrostatic deflection plates and quadrupo les, This is in contrast to the larger ion storage rings, which are based o n magnetic focusing and deflection. The result is a small, relatively inexp ensive, 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 char ged ions. The maximum number of singly charged ions that can be stored is a few 10(7). 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 cha nge 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 writin g, at least two other electrostatic storage rings are being built, and more are planned. In the following, the electrostatic storage ring ELISA will b e described, and results from some of the initial experiments demonstrating the performance will be shown. The relative merits of such a ring, as oppo sed to the larger magnetic rings and the smaller ion traps will be discusse d, The potential for highly charged ions will be briefly mentioned.