News from Fermi National Accelerator Lab

Kamran Vaziri, Kathy Graden, Susan McGimpsey

The major activity at Fermi National Accelerator Lab (Fermilab) was a 13-week shutdown that started on August 23. The major projects for the accelerator complex during this period included the installation of electron cooling in the recycler, installation of a new focusing horn for the MiniBooNE experiment, installation of a new radiofrequency (RF) cavity in the booster, and the completion of the Neutrinos at the Main Injector (NuMI) beamline installation. A week before, the Accelerator Division Head addressed more than 150 technicians, supervisors, and trades workers in Ramsey Auditorium about the upcoming shutdown. The magic word of the meeting was definitely safety in all its aspects. It was emphasized that the most important thing is to have a very safe and effective shutdown. The idea expressed was to do the job correctly and safely. During the course of the shutdown this continued to be emphasized to Accelerator Division supervisors in their regular weekly meetings. Near the end of the shutdown, the pressure to meet the schedule increased, a phenomenon likely not unique to Fermilab. At this point the Accelerator Division management clearly instructed personnel not to overwork their personnel in a way that could cause mistakes to be made that might compromise safety. It is believed that the objectives of the shutdown were accomplished with a high level of safety achieved.

Fermilab has initiated a project called Ecool to provide higher luminosity proton-antiproton collisions in the Tevatron Collider by establishing electron cooling of antiprotons in the Fermilab recycler permanent magnet storage ring. The electrons will be provided by a pelletron accelerator and an associated beamline that heretofore had been used "off-line" in a test configuration. The task undertaken in this autumn’s shutdown included the reassembly of the pelletron and its beamline in the recycler in preparation for commissioning electron cooling in the not-so-distant future. The shutdown work focused on the section that runs through the main injector tunnel, embracing the recycler storage ring. It contains 10 electron-cooling tanks with solenoids, in which a continuous beam of electrons will mix with a stream of antiprotons to cool the antiprotons. Below the cooling section is a new beamline through which the electrons travel back to their source: the pelletron in the MI-31 building adjacent to the main injector tunnel.

The shutdown goal for the booster was to increase the number of protons that the machine can accelerate per cycle. Part of this work consisted of removing old, relatively highly activated beamline equipment and installing an additional RF cavity in the booster. The new cavity has a larger aperture that will reduce beam loss, preventing the cavity from becoming as highly activated. The other jobs consisted of magnet replacement and reconfiguration at Long 13. Two dogleg magnets, ML01 and MP01 were replaced in the area. This was done to improve machine performance and enhance machine reliability, which will lead to lower beam losses in the future as intensity demands increase. This particular region of the booster had been troublesome for a number of years. The work area exposure rates varied. For the removal process, it was 50 to 20 mR/hr. For the installation process, due to the use of mostly new components, it was 20 mR/hr, likely dominated by the activation of the enclosure itself. The resulting total effective dose equivalent (TEDE) for this job was 1464 person-mrem, somewhat less than the estimate determined in as-low-as-reasonably-achievable (ALARA) planning. Water tubing replacement work occurred at four locations in the booster lattice, denoted 13-1, 12-2, and Periods 6 and 7. The previous plastic tubing was replaced with polyetheretherketone (PEEK) tubing. The work area exposure rate at 13-1 was 20 mR/hr and 12-2 was 50 mR/hr. The TEDEs for these jobs were 97 person-mrem at 13-1 and 77 person-mrem at 12-2. At Periods 6 and 7 the previous orange "garden" hoses were also replaced with PEEK tubing. The work area exposure rate at Period 6 was 20 mR/hr and 10 mR/hr at Period 7. The TEDE for these jobs was a combined total of 15 person-mrem. This work was done to increase machine reliability and thus decrease the radiation exposure to technicians. PEEK tubing is more tolerant of the high radiation levels present during operations. The last major job was beam position monitor (BPM) replacement at locations denoted Long 6 and 7. The work area exposure rate at Long 6 was 100 mR/hr and 75 mR/hr at Long 7. The TEDE for both of these jobs was 42 person-mrem.

The MiniBooNE horn after two years of flawless operation started having problems exhibited by water leaks and electrical faults. The task of its replacement was added to the shutdown jobs on short notice. Using specifically developed safety procedures and documented dry runs, a very detailed ALARA plan was developed covering both the removal and replacement of the horn. With exacting attention to details, the old horn was placed in a doubly shielded (5-in.-thick iron) coffin, removed from its location, and transferred by truck (with a Fermilab Security Department escort) to a well-shielded storage location. The removal procedure contained 128 distinct steps. Critical factors included the tight quarters at the experimental hall and the 20-ton lifting capacities of the cranes at the removal and storage locations. It was originally expected the TEDE for this job would be 449 person-mrem. However, the measured total dose equivalent for this work was 327 person-mrem. The new horn was modified to avoid some of the water-leakage and ground-fault problems that eventually affected the original. The failure of the original horn could not really be called a major disappointment since it produced a world record of 96 million pulses.

The NuMI work in the main injector tunnel consisted of finishing all installation work, alignment, and vacuum hook-up, plus the testing of devices before the end of the shutdown. The NuMI project devoted the last week of the shutdown to testing all devices installed during the shutdown, checking the accuracy of magnetic fields, and "exercising" instrumentation. The testing will minimize access time to the tunnel when the main injector is back in operation. The NuMI beamline is ready for testing and commissioning. The beamline has many components, and the commissioning plan calls for several weeks of testing and measurements on the way to routine, high-intensity operations. The first proton beam was transported down the NuMI beamline on December 3, 2004. During this same period, the NuMI Project shielding assessment and safety assessment documents were reviewed and approved, and its accelerator readiness review was completed.

The shutdown of the Fermilab accelerator complex ended on Wednesday, November 24. Since January 2004, the peak luminosity of the Tevatron has increased 100 percent. For fiscal year 2005, the average peak luminosity of all collider stores is expected to increase to 1E32, a value achieved on July 16 for a single store. Fermilab's goal is to produce 50% more collisions than in FY 2004, with the Tevatron operating a shorter period of time because of the duration of the shutdown.