BERKELEY: Farewell to the Bevatron/Bevalac

Full text: Nearly a hundred current and former Lawrence Berkeley Laboratory employees gathered at the Bevatron accelerator on 21 February to watch Ed Lofgren turn off the beam for the last time. Lofgren, in charge of the venerable machine from its completion in 1954 until his retirement in 1979, pushed a button that someone long ago labeled ''atom smasher offer'', bringing to an end four decades of accomplishment in high energy and heavy ion physics. Owen Chamberlain, who shared the 1959 physics Nobel with Emilio Segré for the discovery of the antiproton at the Bevatron, was among those present at the closing ceremony. The shutdown came 39 years to the week after Bevatron beam first circulated, and a touching moment came just after Lofgren shut the machine down when the poignant strains of the ''Taps'' salute wafted out over the PA system. The Bevatron - or Bevalac, as it was called after being linked to the Super HILAC linear accelerator in the 1970s - made major contributions in four distinct areas of research: high energy physics, heavy ion physics, medical research and therapy, and space-related studies of radiation damage and heavy particles in space. As well as the discovery of the antiproton, the early years of the Bevatron saw classic studies of the kaon, leading to a deeper understanding of both strong and weak interaction physics. With Luis Alvarez' development of Donald Glaser's original bubble chamber idea into a prolific physics technique, the Bevatron was a major focus of the heady days of resonance hunting in the late 1950s and early 1960s. Most recently the Bevalac (Bevatron-SuperHILAC combination) pioneered relativistic heavy ion physics. The central focus of this research programme was the production and study of extreme conditions in nuclear matter. Highlights include the first definitive evidence of collective flow of nuclear matter at high temperatures and densities, studies of the nuclear matter equation of state and multifragmentation, a systematic study of dilepton production, and measurements using secondary beams of light radioactive nuclei, culminating in the observation of the ''neutron halo'' of lithium-11. (This nucleus consists of nine central nucléons surrounded by a relatively distant and weakly bound neutron pair.) After the pioneering work at LBL, the relativistic heavy ion baton was taken up at still higher energies by Brookhaven and CERN, while Brookhaven's RHIC collider, now under construction, will provide the next energy step. During the past year, the impending shutdown of the Bevalac concentrated research on the properties of nuclear matter, especially dilepton production and studies of reaction dynamics using the new Equation Of State (EOS) Time Projection Chamber. The last experiment to be run was led by a collaboration from Japan, headed by Isao Tanihata, measuring the properties of radioactive beams near the proton drip line. Physics analysis of the large volume of data accumulated during this intensive year of running is now in full swing