The Superconducting Super Collider Project: A Summary

This appendix is a chronology of activities and decisions that led to the creation of the Superconducting Super Collider (SSC) project, and of its subsequent progress and accomplishments.

The interests of the high-energy physics community in a multi-TeV accelerator began to take shape in a series of International Committee on Future Accelerators (ICFA) workshops in 1978 and 1979, where a proton-proton collider with an energy of 20 TeV per beam was first discussed. The SSC project itself had its origins in the 1982 Snowmass Summer Study sponsored by the Division of Particles and Fields of the American Physical Society. Several other workshops, including two major ones at Cornell and Lawrence Berkeley Laboratory (LBL) on accelerator and detector technologies respectively, then provided the basis for the recommendation by the High Energy Physics Advisory Panel (HEPAP) in 1983 for "immediate initiation of a multi- TeV high-luminosity proton-proton collider project with the goal of physics experiments at this facility at the earliest possible date." This large leap forward in the scale of accelerator technology was agreed to be necessary to elucidate the physics of electroweak symmetry breaking, and hence necessary for continued progress in high- energy physics.

As a result of the HEPAP report, formal research and development support for the SSC was initiated in fall 1983, and the Department of Energy and the directors of the U.S. high-energy physics laboratories chartered a series of preliminary studies for the SSC. Thus began the National Reference Designs Study, started in December 1983, to study the technical and economic feasibility of a machine with the designated parameters of 20 TeV per beam and a luminosity of 10^33cm^-2sec^-1. By April 1984, these initial studies had been completed by a team of about 150 engineers and accelerator physicists. Three different reference designs were presented, based on three distinct types of superconducting magnets, all of which were deemed technically feasible. A preliminary cost estimate was produced for each of the designs.

The next step was the formation of the Central Design Group (CDG), based at LBL and managed by the Universities Research Association (URA) in summer 1984. This effort was directed by Professor Maury Tigner. In parallel, extensive work on prototype magnets was launched in several national laboratories--Brookhaven National Laboratory (BNL), Fermi National Accelerator Laboratory (Fermilab), and LBL, as well as the Texas Accelerator Center (TAC), studying five different designs. This effort led to the selection of a magnet design based on a single cold bore with a high field of 6.5 Tesla in 1985. Additional work on site specifications and a detailed site-independent cost estimate, as well as engineering refinements of the magnet design, led to a complete conceptual design for the project. In total, a group of roughly 250 scientists and engineers participated in the CDG and contributed to the Conceptual Design Report published in 1986. The SSC machine described in this report embodied many technical challenges. A broad-based accelerator research and development program, encompassing high-field superconducting magnets, vacuum and thermal problems associated with synchrotron radiation, beam dynamics, and energy losses had been initiated in 1984 under the CDG, and would proceed over the following decade to address these challenges. Major challenges also existed for the experimental program, and a detector research and development program, administered by the Department of Energy with assistance of the CDG, was started in 1987 and continued through 1992.

After extensive Department of Energy review, a Presidential decision to proceed with the SSC was made in January 1987 and a site selection process was initiated. A total of 43 proposals were received, 35 of which met the necessary guidelines. After examination by a committee assembled under the auspices of the National Academy of Sciences, seven proposals were selected for further Department of Energy review. The Ellis County, Texas site was announced as the preferred site by the Department of Energy in November 1988, leading to the creation of the SSC laboratory under the directorship of Professor Roy Schwitters, and the management of URA, in January 1989. A series of international advisory bodies were formed by the lab director, including the Scientific Policy Committee, the Program Advisory Committee, and the Machine Advisory Committee. The Texas National Research Laboratory Commission (TNRLC) was formed in 1987 to oversee the Texas interest in the SSC. Starting in 1990, it created a program to distribute, based on extensive peer review, approximately $100M over a period of ten years to universities in support of SSC-related research and development throughout the U.S.

One of the initial tasks of the laboratory was the creation of the site-specific conceptual design, completed in July 1990. As the site-specific design became more detailed, experience with the Hadron Elektron Ring Anlage (HERA) magnets, and simulations of the full 107 turns required for injection, led to a decision to change several aspects of the original design toward a more conservative one. Changes were proposed and agreed upon, including increasing the main ring dipole aperture from 40mm to 50mm to improve operating margins and field quality, and increasing the injection energy from 1 TeV to 2 TeV. Numerous technical experts agreed that these changes were essential for rapid commissioning and reliable operation of the accelerator. Detailed reviews of the energy and luminosity goals of the design were carried out by an Ad Hoc Committee and by a HEPAP subpanel. Both affirmed the design parameters of 20 TeV per beam and a luminosity of (10^33)(cm^-2)(sec^-1). The site- specific conceptual design, a basic construction plan, and a detailed cost estimate were then extensively reviewed by the Department of Energy Program Office as well as by the Department's Independent Cost Estimating staff, and the project cost and schedule baseline were established. As the site-specific design process was completed, the final footprint of the machine was delivered to the Department of Energy in December 1989, and in March 1990 the State of Texas began acquiring some 16,000 acres of land.

The necessary Environmental Impact Statement was completed by the end of 1990, and was issued following the Record of Decision. First major construction at the SSC site began in 1991 at the N15 site, home of the Magnet Development Lab (MDL), the Magnet Test Lab (MTL), and the Accelerator Systems String Test (ASST) facilities. These facilities, upon completion, represented fully-equipped work areas of 200,000 square feet, capable of producing 25 magnets per year (needed for the various specialized magnets for the accelerator) and testing ten dipole magnets simultaneously. The superconducting magnet program, with the goal of producing 50mm dipole magnets for the string test, was initially carried out by a collaboration among the existing laboratories (BNL, Fermilab, LBL). A total of 20 dipoles were produced, 13 at Fermilab and seven at BNL. These magnets were built in collaboration with staff from industrial partners: General Dynamics at Fermilab and Westinghouse at BNL. Six full-length prototype quadrupoles were built at LBL, and an additional five by the industrial partner Babcock and Wilcox. All of these magnets performed well, satisfying the required operating margins and field quality. A first major milestone, the string test, involved the operation of a string of five dipoles and a quadrupole, the basic half-cell of the accelerator, in the ASST facility. This was completed in August 1992. It was followed by a second phase test with a full-cell of ten dipoles and two quadrupoles. Meanwhile, the MDL was building further prototype magnets, innovative work on corrector magnet technology was being done, and design and prototyping work for the very challenging final focus magnets was going ahead.

Detailed design and early construction work was proceeding on all major machine components. "The conventional construction for the first stage of the injection complex, consisting of the ion source and a linear accelerator stationed in a 250-meter tunnel, was complete." The first circular accelerator in the chain, the Low Energy Booster (LEB), consisting of a 600-meter circumference ring filled with resistive magnets, was designed and 90% of the tunnel complete. The next element in the sequence, the Medium Energy Booster (MEB), consisting of a ring of 4.0 kilometers in circumference, again using resistive magnet technology, was designed and excavation of the tunnel had started. The third and final accelerator before entering the large collider rings, the High Energy Booster (HEB), consisting of 10.8 kilometer circumference tunnel filled with superconducting magnets, was under design. Finally, for the 87.1 kilometer circumference collider ring, the excavation of seventeen shafts was complete, and the tunnel boring, begun in January 1993, had proceeded rapidly, with 77,065 feet (roughly 23 kilometers) completed by fall 1993.

In parallel with the creation of the laboratory, the establishment of the experimental program for the SSC began with the call for Expressions of Interest in early 1990. The international experimental community responded by submitting a total of 21 Expressions of Interest for experiments covering a wide range of topics. The initial experimental program was to consist of two large, general-purpose detectors and several smaller, more specialized experiments. Letters of Intent for the large experiments were prepared by November 1990, and the task of defining the experimental program proceeded. By late 1991, two large collaborations, GEM (formed in June 1991) and SDC (formed in September 1989), had converged on complementary detector concepts. After review of their Letters of Intent, both were approved to proceed with more detailed conceptual designs and to write Technical Design Reports. This led to the submission of the SDC Technical Design Report in April 1992, and the GEM Technical Design Report in April 1993. The SDC detector received Phase 1 Department of Energy approval in October 1992, and GEM was in the process of undergoing similar review in fall 1993. In total, a community of roughly 2,000 scientists and engineers from more than 200 institutions world-wide were involved in these two detector projects. A broad-based program of research, development and engineering, addressing instrumentation issues relevant for the SSC experimental program, was carried out over many years, producing advances in all areas of high-energy physics instrumentation. This provided confidence that the very ambitious experiments planned for the SSC could succeed.

Beyond the physics mission of the SSC, there was a program of educational outreach to high school students and teachers, colleges, and universities. The substantial investment in research and development for experimental instrumentation helped the ailing university high-energy physics infrastructure, in addition to the large number of significant improvements in detector technology that resulted.

Progress on the project was the fruit of many years of dedicated work and investment by many. A substantial number of scientists and engineers had relocated to Texas in order to construct this new facility. A total laboratory staff of over 2,000 employees, including more than 250 foreign scientists and engineers from 38 countries, was assembled. The SSC experimental program, which had broad international participation from the beginning, had benefitted from the substantial investment in SSC detector research and development. Operation at luminosities of (10^33)(cm^-2)(sec^-1), which a decade before had seemed formidable, now was seen as entirely feasible for the major detectors detailed in the technical design reports, as well as for the collider itself. For both the accelerator and experimental systems, there were no technical show-stoppers when the project was terminated.

Everybody who worked to create the SSC can be proud of their very impressive technical achievements.