The History of the Holifield Heavy Ion Research Facility and the Holifield Radioactive Ion Beam Facility
by R. L. Robinson*
In late 1974 the U.S. Congress approved funding of $17.5 million for a national heavy-ion facility to be placed at Oak Ridge National Laboratory (ORNL). A year later Congress enacted a bill which named it the Holifield Heavy Ion Research Facility (HHIRF). The funds were for the design and procurement of a tandem electrostatic accelerator with terminal voltage up to 25 MV, for a building to house the new accelerator and experimental halls, for beam transport lines, and for modification of the existing Oak Ridge Isochronous Cyclotron (ORIC) to serve as a postaccelerator for beams from the tandem.
The HHIRF project was initiated in January 1975. In November 1978 the building was completed. The most prominent feature of the structure, and what has since become the dominant landmark of ORNL, is the 167-ft-high tower for housing the 100-ft-high pressure vessel that in turn houses the electrostatic accelerator. The relatively short length for an electrostatic tandem with 25-MV terminal voltage capability was made possible by employing a folded design in which the low-energy and high-energy acceleration tubes were placed in the same column structure and were coupled by a 180-degree bending magnet located in the high-voltage terminal. This folded design also resulted in a pressure vessel of smaller volume whereby less SF6 insulating gas was required. Even so, the amount necessary for optimum pressurization is 175,000 lbs.
Major milestones of the project relating to the accelerator system were:
In parallel to the activities of the HHIRF project, there were the formation of a users group and the design, purchase, and fabrication of a wide variety of experimental apparatus. The users, who numbered about 400, provided crucial guidance on types of experimental apparatus and on desired beam parameters, as well as on members to serve on the Program Advisory Committee. The users also did the majority of work related to apparatus design, oversight of fabrication, procurement, and commissioning. Major equipment available to the users included two magnetic spectrometers (one with a gas target), a 5-ft.-diameter scattering chamber, an on-line mass separator (UNISOR) with a nuclear orientation facility, a velocity filter, a close packed Compton-suppressed Ge ball (21 modules), a near 4-pi sphere of 72 NaI detectors Spin Spectrometer with the flexibility to have up to 18 of these units replaced with Compton-suppressed Ge detectors, a highly segmented charged particle array for simultaneous observation of properties of several heavy nuclei with many light nuclei, HILI, a time-of-flight facility, and a Van Hamos Crystal X-ray Spectrometer. The facility also provided a forefront computer system that was recognized by the nuclear physics community for its power for both data acquisition and data reduction.
One special subgroup of users was from thirteen universities which had formed a consortium to support and manage the activities of UNISOR with its centerpiece being the on-line mass separator. Management was done through an Executive Committee composed of one person from each of the member universities. This consortium, which in fact predated the HHIRF by three years, demonstrated how several small groups of scientists could combine their efforts effectively to undertake an exciting and mutually beneficial research program over many years.
After the initiation of HHIRF operation in 1981, the accelerator system underwent ongoing improvements in reliability and in performance. At the pinnacle of operation in 1989, the facility provided nearly 5000 hours of beam for the research program; about one-quarter of these hours were with tandem beams which were post- accelerated by the ORIC (coupled operation). New acceleration tubes which had 17% more insulating length were installed in 1988. With these a terminal voltage of 25.5 MV was achieved with an accelerated beam. This world record is significantly higher than voltage performance obtained with any other electrostatic accelerator. Throughout the years of operation there was a continuing program to develop beams of interest to the researchers. Ultimately 70 different ion species from protons to 238U were delivered for the scientific program. This too may be a world record. During the 1980s, two additions were made to the HHIRF building to accommodate the growing needs of the researchers: 1) a 2200-sq.-ft. target room for atomic physics and applications and 2) a 4000-sq.-ft. hall for counting rooms and experimental setup areas.
Maximum energies per nucleon of the beams from the HHIRF accelerators generally decreased with increasing mass. Representative cases of maximum energy (in MeV/amu) are given in the following table for tandem stand-alone and coupled operation. Maximum beam currents were strongly dependent on ion species and ranged from a few particle nanoamps to a particle microamp.
Operating budgets from 1984 through 1988 remained essentially constant; nevertheless, through a variety of economic measures, it was possible to continue operation of the accelerators with near maximum utilization. But the budget cuts in ensuing years were too large to make this possible. FY 1990-1992 were years of staff reduction, compromises in maintenances, and reduced research hours (4092, 3535, and 2616 hours in FY 1990, FY 1991, and FY 1992, respectively). In the summer of 1989 amidst these budget cuts came the very exciting news that a siting committee appointed by DOE recommended that the Gammasphere be placed at the HHIRF. Considerable manpower from the ORNL Physics Division was immediately redirected to this project. But this good news was more than offset a year later when a panel formed by NSAC at the request of DOE recommended that if one of three major DOE heavy-ion laboratories needed to be shut down due to budgetary constraints, it should be the HHIRF. The users of the HHIRF, who represented universities of many states, felt strongly it was scientifically unwise to eliminate the HHIRF, and took their concerns to the U. S. Congress. In this process they contacted 70 Representatives and 15 Senators from 21 states who filled 60% of the positions on committees that determined the budget for DOE. As a result of these efforts Congress stipulated that DOE fund the HHIRF during FY 1992. This additional year gave the HHIRF staff the time necessary to fully develop the concept of modifying the accelerator system for producing radioactive ion beams (RIBs). This idea was first proposed in late 1990 when it was realized that the HHIRF had the appropriate two accelerators with the proper shielding to produce RIBs using the ISOL (isotope separation on line) technique. The RIBs would be produced by intense beams of light ions from the ORIC interacting with nuclei in thick targets; the extracted RIBs would then be accelerated by the 25-MV tandem with energies sufficiently high for ions with atomic masses up to 80 to be used for studies in nuclear physics and astrophysics. This project was approved by DOE for funding in FY 1993-1995. Following the last experimental run of the HHIRF in July 1992, the staff focussed their full effort on the necessary alterations of the facility. Because of the change in emphasize of research, the facility name has been changed to the Holifield Radioactive Ion Beam Facility (HRIBF). The HRIBF was dedicated in December 1996.
Another plus for the HRIBF was that funds of $2.2 million for a state-of-the-art recoil mass spectrometer (RMS) were in place with major funding provided by DOE, ORNL, ORAU, the State of Tennessee, Vanderbilt University, and The University of Tennessee. Also, ORNL allocated $1.2 million for a new 4000-sq.-ft. experimental hall to house the 70-ft.-long RMS. Although the RMS was originally planned for the HHIRF, it is an ideal tool to observe nuclei of isotopes very far from the valley of beta stability produced by RIB-induced reactions. The new experimental hall was completed in August 1994 and named Robinson Hall. The RMS has been operational since late 1996.
A second recoil separator based on two large velocity filters was transferred from Daresbury Laboratory in the United Kingdom to ORNL via an international agreement signed in April 1994. This Daresbury Recoil Separator (DRS) arrived at ORNL in late 1994, and its installation as the basis for an astrophysics experimental station began early in 1995. The first beam was put into this device in June 1997, and a series of commissioning experiments with stable beams were conducted to optimize the DRS performance for measurements of nuclear reactions that will help improve our understanding of stellar explosions.
Although the life of the HHIRF was prematurely shortened by budgetary problems, it still was a very valuable resource over its eleven years of operation to a large body of scientists, both in terms of their research and in the training of future scientists. The following statistics give a sense of its contributions. The HHIRF provided 38,827 hours of beam-on-target for 635 different experiments. Of these, 9,537 hours were with coupled operation. There were 640 researchers from 148 institutions involved in one or more of the HHIRF experiments. Of these, 200 were graduate students and 38 undergraduates.
A history of the HHIRF would not be complete without mention of the unique Joint Institute for Heavy Ion Research (JIHIR) which was formed, funded, and managed jointly by ORNL, The University of Tennessee (UT), and Vanderbilt University. It is housed in two buildings adjacent to the HHIRF. Funds for one of the two buildings and a major portion of the annual budget of $250,000 were provided by The University of Tennessee through a Center of Excellence grant from the State of Tennessee. The mission of the JIHIR was to enhance and stimulate the scientific environment of the HHIRF. It fulfilled its mission principally by: 1) operating a dormitory facility for users of the HHIRF (approaching occupancy of 2000 person-nights per year), 2) sponsoring workshops at the JIHIR, and 3) supporting a guest program (of the order of 50 guests were partially or fully supported each year). In particular, the JIHIR was responsible for a strong theoretical effort that complemented the HHIRF experimental programs. The JIHIR now plays a similar role for the HRIBF.
* This history was written by Russell Robinson. Russell served as the Scientific Director of the HHIRF from June 1983 until he was forced to retire for health reasons in 1994. It has been updated by Jerry Garrett.
For questions about this page please contact the HRIBF User Liaison.
This file last modified Sunday November 20, 2005