"Cooler" Storage Ring, Electron Cooling (1983-2003)

Description and History

G.I. Budker at the INP in Novosibirsk proposed in 1966 that the phase space of an ion beam orbiting in a storage ring can be reduced with a co-moving electron beam of matched velocity. By the 1980’s this principle of ‘cooling’ was in use for storing anti-protons at CERN and FNAL.

Robert Pollock at IUCF recognized that this new technology could benefit nuclear physics research. The new experimental environment featured an intense stored beam circulating through a thin internal target. A proposal to build such a machine at IUCF to explore this new environment was approved by the NSF for 6.6 M$, starting February 1983.

The necessary building addition was completed in 1985 and in April 1988 the first cooled beam was orbiting in the ring. The construction involved about 50 people.

The Cooler storage ring featured an RF cavity to accelerate a stored proton beam to 500 MeV, i.e., beyond the pion production threshold in nucleon-nucleon collisions. In fact, for a while, the highest-energy electron-cooled beam in the world circulated in the Indiana Cooler.

Beam from the cyclotron was injected into the Cooler on a time-share basis with other experiments. Vertically polarized proton and deuteron beams were available. An arrangement of longitudinal magnetic field solenoids, a so-called Siberian snake, made non-vertical beam polarization possible. The first demonstration of such a scheme was accomplished with the Cooler in 1989.

Internal targets included solid targets (with limitations), gas jet targets and polarized atoms injected into ‘storage cells’ (open tubes around the beam to increase target density).

A new ion source and a Cooler injection synchrotron (CIS) were commissioned in 2000, making the Cooler independent of the cyclotron. With this addition, the Cooler reached its peak performance with about 1.5 mA of polarized proton or deuteron beam stored.

The last beam was orbiting in the ring at the end of July 2002.

The Cooler history is recounted in “The Indiana Cooler”: A Retrospective, Annu. Rev. Nucl. Part. Sci. 57, 1 (2007).

During its life, the Cooler delivered about 3000 8-hour shifts for research. Two thirds were devoted to nuclear and particle physics, the rest was mostly used for beam studies. A summary of the research and a complete list of references are given in Annu. Rev. Nucl. Part. Sci. 57, 1 (2007).

The fourth international conference on Nuclear Physics at Storage Rings (STORI99) was held in Bloomington in September 1999. The proceedings were published as AIP Conference Proceedings no. 512. Previous meetings in this series were held in Lund (1991), St. Petersburg (1994) and Bernkastel-Kues (1996).

Measurement of a finite cross section for the reaction dd→απ⁰ near threshold. This process violates the conservation of isospin and charge symmetry. This experiment made use of the unique benefits of the Cooler environment and provided a dignified termination of the Cooler project. The result is reported in E.J. Stephenson et al., Phys. Rev. Lett. 91, 142302 (1993).

Contact: Edward Stephenson and Andy Bacher

Polarized Internal Target Experiments

Polarized atomic beam targets are an excellent match for the Cooler environment. An atomic beam source (ABS), constructed at the University of Wisconsin and installed in the Cooler in 1988, provided polarized hydrogen, as well as tensor- or vector-polarized deuterium targets. Since the internal polarized target was combined with polarized beams and Siberian snakes (providing longitudinal beam polarization) unprecedented studies of the spin dependence of nuclear reaction became possible. During a 14 year period a large number of experiments were carried out by a collaboration (PINTEX) involving the U of Wisconsin, the U of Western Michigan, the U of Pittsburgh, the New Mexico State U, the Forschungszentrum Jülich, Germany, Indiana U and IUCF.

Contact: Hans-Otto Meyer