Bevalac Had 40-Year Record of Historic Discoveries
October 9, 1992By Judy Goldhaber
Since its commissioning almost 40 years ago, the venerable particle
accelerator has made major contributions to four distinct areas of research:
high-energy particle physics, nuclear heavy-ion physics, medical research and
therapy, and space-related studies of radiation damage and heavy particles in
space.
As the Bevatron/Bevalac neared the end of its usefulness in each of these
fields, the area of research it had pioneered moved to other facilities around
the nation. Thus, particle physics continues at accelerators such as
Fermilab's Tevatron, SLAC's colliders, and in the future, at the proposed
Superconducting Super Collider. Heavy-ion nuclear studies will be the major
focus at the new Relativistic Heavy Ion Collider (RHIC) at Brookhaven, and
experiments in heavy-ion therapy led to the design of dedicated medical
accelerators such as the Proton Cancer Treatment Center at Loma Linda
University Medical Center, and the proposed proton therapy facility at the UC
Davis Medical Center.
The original version of the accelerator, the Bevatron has been called by
physicist Ed Lofgren (who was in charge of its operation from 1954 until his
retirement from that job in 1979) "the last of the great accelerators build in
... `the Lawrence style' ... durable and adaptable. That's why it's not
surprising that the Bevatron has endured and adapted so well over the years."
The Bevatron played the leading role in three of the most important
discoveries of particle physics: experimental studies of "strange" particles
leading to the discovery of parity nonconservation (the first known example of
a lack of symmetry in nature); the discovery of nuclear antimatter (the
antiprotons and the antineutron); and the discovery of the "resonances" -- the
particle explosion of the 1960's that led to the development of the quark model
and the current understanding of the basic nature of matter.
In the 1970s, the Bevatron seemed to be nearing the end of its useful career
in high-energy physics, and there was talk of shutting it down. An LBL proposal
to replace it with a new accelerator known as the Variable Energy Nuclear
Synchrotron (VENUS) never received the necessary approval and funding.
Nevertheless, it was given a productive new lease on life through the
invention of the Bevalac, in which the Bevatron was linked to the SuperHILAC
linear accelerator. Nuclei begin their journey in the SuperHILAC and then were
passed through a transfer line to the Bevatron, where they were accelerated
almost to the speed of light.
With the later addition of an improved vacuum system and other modifications,
the Bevalac became the only machine the world capable of accelerating all of
the elements of the periodic table to relativistic energies. The Bevalac
pioneered a whole new field of physics, leading to the studies of the nuclear
equation of state and the search for "quark matter." A major discovery of this
era was the observation of compressed nuclear mater.
Also during the `70 and `80s, the use of Bevalac beams in medical and
biological research became an important part of the program. Because such ions
deposit most of their energy near the point at which they come to rest, a heavy
ion beam aimed at a deeply buried tumor can destroy the tumor without seriously
damaging tissues in its path. Bevalac beams were found to be useful in the
treatment of cancer and other diseases, especially ocular melanoma and
arteriovenous malformations in the brain.
With the closure of the Bevalac, research in heavy-ion therapy will no longer
be conducted in the U.S> but will be shifted to Japan, using technology
developed at LBL.
In 1988, LBL proposed a major upgrade of the Bevalac that would replace the
weak-focusing Bevatron with a modern strong-focusing synchrotron, greatly
increasing its beam intensity, beam quality, and other significant factors. It
also would have permitted fast switching between different kinds of beams,
allowing the machine to accommodate both nuclear science and medical
radiotherapy programs simultaneously. Had the upgrade been approved, it would
have brought the Bevalac back to the forefront of modern experimental machines
and assured its continued usefulness through the `90s and beyond.
Nevertheless, during the last few years the Bevalac achieved another important
success when its beams of heavy ions were used to mimic the conditions that
astronauts might encounter on the moon, Mars, or on interplanetary voyages.
Bevalac beams were used to calibrate and check out scientific equipment due to
be carried on satellites or shuttle missions, and Bevalac experiments led to a
better assessment of the risks associated with space flights.
It was this program that, over the past year or so, seemed to offer the best
hope for the Bevalac's continued survival. NASA, realizing that the Bevalac is
the only facility in the country capable of simulating the spectrum of
radiation native to space, argued against its closure, and for some time
considered taking over the funding of Bevalac operations from the Department of
Energy. However, in this era of tight budgets, this prospect also faded, and
the Laboratory will end operations at the Bevalac in 1993.
The closure also spells the end of a long and honorable career for the "uphill
" member of the tandem Bevalac team, LBL's SuperHILAC. Like the Bevatron, the
SuperHILAC and its predecessor the HILAC figured in several distinct epochs of
successful scientific endeavor.
Probably no other machine in physics has so ambitiously been "tinkered
upwards" in its lifetime. First built as the HILAC (Heavy Ion Linear
Accelerator) in 1957, it (along with a similar one at Yale University) was the
first machine in this country built specifically to accelerate heavy ions. The
HILAC was modified to new capabilities in 1961, 1965, and 1969, and finally
completely rebuilt into the SuperHILAC in 1971.
As HILAC and SuperHILAC, the machine figured in the discovery of five
"manmade" or elements by Al Ghiorso and his team. In recent years, the
SuperHILAC's independent research program was phased out, and it operated
principally as the injector for the Bevalac.
Over the years, LBL's Bevalac was often snatched, from seemingly inevitable
closure, to be reborn each time into a whole new productive chapter of its
career. But at last it seems to have finally used up all of its nine lives.
Looking at a model of the Bevatron prior to its construction in 1949 were (left to right) Lloyd
Smith, Ed McMillan, Ernest Lawrence, Ed Lofgren, Bill Brobeck, and Duane Shell
