From the start of the Main Injector project, we recognized that at the injection and extraction points the old Main Ring quadrupole magnets would eventually be a limit to the aperture, and thus to the amount of beam that could be handled. Proton Driver design studies in 2000 and 2002 led to a conceptual design by Vladimir Kashikhin. As the NuMI turn-on approached, the issue of increased intensity in the Main Injector became more of an issue. In addition to increasing the intensity, the NuMI installation also added another extraction point, and the SY120 program further complicated operations. So, in February 2004 we kicked off the WQB project with a review of the conceptual design.

For about six months, we held periodic meetings as AD physicists and engineers sorted out the requirements for the magnets and TD engineers and physicists explored design ideas. Weiren Chou led the effort from the accelerator side, concentrating on accelerator physics requirements. Dave Johnson analyzed apertures. Bruce Brown added the perspective of magnet physics. Leon Bartelson represented the electrical engineering and Lucy Nobrega was in charge of installation issues. From TD, Vladimir did the magnetic design, and John Carson started on the mechanical design. John Zweibohmer worked with a steel vendor to find the appropriate material, and Hank Glass represented the magnet measurement effort. I tried to hold it all together. Ioanis Kourbanis, as head of the Main Injector Department, had the final word.

During the conceptual design stage, the basic parameters of the magnet were established. Around September 2004 we began procuring the steel, the laminations, and the conductor, and TD began the detailed mechanical design. We had found that we could push the design beyond the original concept, opening the aperture further. While the main focus was on the four high energy extraction points from the Main injector, we agreed that it was worth installing magnets at the injection point and the two transfer points with the Recycler, for a total of seven magnets plus two spares. Jim Jablonski, a designer/drafter, joined the project, making 3-D models on his computer, then making detailed drawings of parts for fabrication. Once the components were defined, Bill Robotham and Marianne Battista designed the tooling needed to fabricate the major subassemblies, and Linda Alsip managed the purchase of all the parts. Bob Jensen translated the drawings into detailed instructions for the technicians.

Fabrication started in February 2005, although there were technical details of fabrication still to work out. But the biggest concern was how the strength of these magnets would compare with the strength of those they were replacing. To keep all the Main Injector quadrupoles in synchrony, the new magnets had to run on the same bus as the rest of the ring, and produce the same magnetic field to focus the beam, as the rest of magnets. The larger aperture meant that the magnetic field inside the steel yoke would be different, and we were dealing with unfamiliar steel. We have had reliable computer programs for calculating the field in the middle of a magnet (a 2-dimensional problem) for decades. But we are only slowly gaining confidence in our calculations of the field at the ends, for both strength and shape (a 3-dimensional problem). Facing a fairly tight schedule without time for extensive work on a prototype magnet, we designed the end of the magnet steel to be adjustable. Recognizing that these magnets might not behave exactly the same as the other magnets throughout the whole acceleration cycle, we also built in a trim coil to allow fine adjustments in the strength, up to 2% of the total.

In May 2005, with some critical design issues still unresolved, John Carson retired and Bill Robotham took over as lead engineer. In late July, the first magnet was delivered to Magnet Test Facility, wearing only its primer coat of paint and missing a number of details. With the first measurements, we quickly realized that although the magnetic behavior was as expected, a design defect limited the current at which it could be run. While more detailed measurements proceeded, the design was refined and another magnet was completed to the new design. By the end of August, the problem was resolved and initial measurements were made up to the full current. Subsequent detailed measurements demonstrated that the magnet did indeed meet the specifications, and the steel at the ends of the magnet did not need to be adjusted.

Fabrication of more magnets continued through the fall, along with magnetic measurements, further refining our understanding of the magnet. Several insights on the installation process led to further minor changes to the design and modifications to the magnets already built. We began moving completed magnets to MI-60 Service Building, ready for installation, in January 2006. The last dabs of paint and official stickers were put on the last magnet for installation in early February. The two spare magnets are also nearing completion.

Dan Smith has managed the crew of about a dozen technicians who have had their hands in the project at one time or another. We especially valued the vacuum impregnation skills that Junior Jones brought to the job. Bill Robatzek hand-crafted the intricate interconnections at the ends of the magnets. Ted Beale's incoming inspection team made sure all the parts met our specifications, and Les Peters's group moved the parts around as needed. Mark Thompson at MTF has conducted most of the measurements. Mike Tartaglia has taken over analysis of magnetic measurements, and Joe DiMarco has also contributed some specialized measurements. In AD, Linda Valerio has been responsible for installation since April 2005.

—David Harding, Technical Division