The Synchrotron Radiation Center (SRC), located in Stoughton, Wisconsin and operated by the University of Wisconsin–Madison, was a national synchrotron light source research facility, operating the Aladdin storage ring. From 1968 to 1987 SRC was the home of Tantalus, the first storage ring dedicated to the production of synchrotron radiation.
History
The Road to SRC: 1953–1968 15 universities formed the Midwest Universities Research Association (MURA) in 1953 to promote and design a high energy proton synchrotron, to be built in the Midwest. With the intent of constructing a large accelerator, MURA purchased a suitable area of land with an underlying flat limestone base near Stoughton, Wisconsin, about 10 miles (16 km) from the Madison campus of the University of Wisconsin. MURA's first accelerator was a 45 MeV synchrotron, built in a concrete underground "vault", mostly for radiation protection purposes. A small electron storage ring, operating at 240 MeV, was designed by Ed Rowe (Ednor Marsh Rowe, 1927-1996) and collaborators as a test facility to study high currents, and construction of this ring started in 1965. However, in 1963 President Johnson had decided that the next large accelerator facility would not be built at the MURA site, but in Batavia, Illinois; this became Fermilab. In 1967 MURA dissolved with the storage ring incomplete and with no further funding. The researchers, feeling teased by fate (and the government backers) named the machine after the mythological figure Tantalus, famed for his eternal punishment to stand beneath a fruit tree with the fruit ever eluding his grasp. In 1966 a subcommittee of the National Research Council, which had been investigating the properties of synchrotron radiation from the 240 MeV ring, recommended it be completed as a tool for spectroscopy. A successful proposal was made to the US Air Force Office of Scientific Research, and the ring was completed in 1968—the first storage ring dedicated to the production of synchrotron radiation. With the demise of MURA, a new entity was created to run the facility: the Synchrotron Radiation Center (SRC), administered by the University of Wisconsin.
Tantalus: 1968–1987
Tantalus had a circumference of just over 9 metres (30 ft), and, with an energy of 240 MeV, had a critical energy of slightly under 50 eV. It achieved its first stored beam in March 1968. Initial operations were very difficult, with only about 5 hours per week of usable beam, and currents of less than 1 mA. Initial users came from three groups, who took turns using their commercial monochromators on the one available beamline. On August 7, 1968, this first dedicated storage ring based synchrotron radiation facility produced its first data when Ulrich Gerhardt of the University of Chicago, carried out simultaneous reflection and absorption measurements on CdS over the wavelength range 1100-2700 Å. In 1972 the building was enlarged to accommodate new beamlines, and by 1973 there were ten ports, and beam currents were up to about 50 mA. A new injector, a 40 MeV microtron, was installed as an injector in 1974, replacing the original MURA accelerator that had been used until that point, and within a year currents exceeded 150 mA, with typically over 30 hours of beam per week. A stored beam of 260 mA was achieved in 1977. In October 1974 the National Science Foundation took over funding from the Air Force. Initial monochromators were commercial instruments with drawbacks for use at a synchrotron. SRC started a program of instrument development, both to take advantage of the unique properties of synchrotron radiation and to make beamlines available to users without their own instruments. Such users became known as "general users", while groups with their own beamlines became known as Participating Research Teams (PRTs). This model has become widely used at other facilities, where PRTs are also denoted Collaborating Access Teams (CATs) and Collaborating Research Groups (CRGs). PRTs have been used extensively by US scientists at US facilities but by 2010 were somewhat out of favor. The CRG in Europe, however, remains as an important and successful means of flexible access. For two decades Tantalus produced hundreds of experiments and was a testing ground for many synchrotron techniques still in use. Current synchrotron facilities can be very large, while Tantalus was not, and its small building, even after the 1972 expansion, was crowded with equipment and researchers. Users worked in very close quarters and the close proximity combined with the relative isolation of the facility, made cross fertilization of ideas unavoidable. The atmosphere was open, friendly, and informal, although not particularly comfortable physically, The heating system in one washroom did not work, so, to avoid frozen pipes, users just left the door wide open. After someone posted a sign alerting users to the policy, an international contest began, with each person translating the message into their own language. A copy of this sign was included as part of an NSF funding request as evidence of Tantalus's growing international impact. Research during those early years was dominated by optical spectroscopy. In 1971 an IBM research group produced the first photoelectron spectra using Tantalus, a milestone in the development of photoemission spectroscopy as a research tool. The tunability of the radiation allowed researchers to disentangle a material's ground-state electronic properties. In the mid-1970s the increasing beam current from the ring gave intensity levels sufficient for angle-resolved photoemission spectroscopy, with a joint Bell Labs–Montana State University group conducting the earliest experiments. As an experimental technique, angle-resolved photoemission developed rapidly and had an important conceptual impact on condensed-matter physics. Gas-phase spectroscopy was another successful field at SRC, starting from early absorption studies of noble gases. With the new Aladdin storage ring operating, Tantalus was officially decommissioned in 1987, although it was run for six weeks in the summer of 1988 for experiments in atomic and molecular fluorescence. The storage ring was disassembled in 1995, and half the ring, the RF cavity and one of the original beamlines are now in storage at the Smithsonian Institution.
Aladdin, the early years: 1976–1986
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