During the present quarter, the emphasis of Fermilab operations has been to improve reliability and performance of its accelerators in support of the MiniBooNE experiment and Tevatron Collider Run II. Both of these efforts have been discussed in detail in previous issues of this publication. Since both parts of the program use the same chain of accelerators, up to the 8-GeV protons required for MiniBooNE, efforts to improve reliability up to that kinetic energy are common to both endeavors. The 8-GeV Booster Synchrotron, designed and built in the late 1960s, continues to be a major bottleneck that limits performance. A simple fact points toward the relevant issues: during one year of present operations, the booster will accelerate more beam to 8 GeV than previously in the history of Fermilab. Likewise, the Fermilab Main Injector is being pressed to provide sufficient proton intensities at 120 GeV to supply antiproton production while simultaneously supplying protons at 150 GeV for injection into the Tevatron for proton-antiproton collisions. Many of the problems that must be overcome to reach the operational goals for MiniBooNE and Tevatron Collider Run II ultimately show up as locations of elevated residual radioactivity with consequent impact on worker exposures. The Tevatron is especially sensitive to beam losses since the resultant quenching of the superconducting magnets poses major programmatic disruptions.
During January, an extensive maintenance shutdown of about four weeks' duration occurred. The goal was to fix a number of problems that had been identified over the past few months. A major portion of the extraction system in the booster was repaired or replaced. A rather comprehensive effort was undertaken to verify survey alignment accuracies in crucial locations. This turned out to be potentially very beneficial. At one crucial location in the Tevatron, an alignment error of approximately 1 in. was found. This error may have been in place for a long time, perhaps being "steered around" for years in the beam tuning with probable enhanced beam losses there or elsewhere in the orbits in the machine. Was this a case of the proverbial "survey to the mil and miss by an inch"? (Note: a mil is 0.001 U.S. inches, a unit still used in surveying in our decidedly "non-metric" USA.) Also, some of the Tevatron dipoles that were supposed to have magnetic fields exactly vertical in their gaps were found to be slightly "rolled"; that is, oriented such that they had a slight horizontal field component as well. Some of the Tevatron quadrupole magnets were also "rolled" slightly. Individual dipoles were found in some cases to be measurably twisted. The cause of these problems is still under investigation. One possibility is that through years of operation the extremely strong magnetic forces present in the magnets has resulted in internal movements not measured heretofore.
During this shutdown, the Beams Division Radiation Safety Group, with the help of the Beams Division Operations Department, instituted a new web-based database for tracking self-reading pocket ion chamber readings of personnel involved in various tasks. This made it possible to obtain much better tracking information correlating exposure received to group and task. Since higher beam intensities are envisioned for the future, the data collected should be invaluable for planning future work. While we will not know the total recorded exposures for this period until mid-May since our quarterly thermoluminescent "dosimeters of record" (TLDs) are read out on that schedule, early input is that the doses were controlled very well during this shutdown given the volume of radiological work that was performed. This shutdown was planned in advance over a three-month period. The dates of the shutdown were never changed. In the past, shutdown dates at Fermilab have tended to be changed in both directions, with a negative effect on careful planning. Most people at the laboratory, including the radiation safety community, believe that this well-planned shutdown was a howling success. Very few mistakes occurred and there was not much wasted motion.
Operations have not yet settled down to routine levels; however, more consistent steady periods appear to be happening. The Tevatron Collider has set a new luminosity record and the MiniBooNE intensity is approaching half of the design goal. The numbers are not quoted here because, hopefully, they will have been eclipsed by the time of publication of this newsletter.
This project continues to proceed toward completion of the associated civil construction. Significant efforts now continue to be directed toward the final resolution of a number of radiological issues mostly concerned with the control of residual activity hazards in the enclosures, plans for the control and monitoring of the release of airborne radionuclides during operations, and the control and monitoring of groundwater activation. While much work has been done in the last few years, major efforts are being made to provide clear documentation of the work. As of this writing, beam should be delivered in 21 months. There is still much to do so that this might as well be tomorrow.
Even colliding beam experiments need fixed-target beams under some circumstances. Likewise, all scientific questions cannot be addressed by them. Thus, this spring a limited portion of the Fermilab fixed-target beamlines are being revived after a hiatus of several years to support both test beams for the collider experiments and stand-alone experiments. This activity, at least for now, will occur in the old "Meson" experimental area and will utilize 120-GeV protons extracted from the Main Injector. To make this happen, the beamlines, where necessary, have been modified from their 800-GeV configuration left over from the days of Tevatron fixed-target operations. A major feature of this work is the addition of more focusing for the larger emittance beam found at lower momentum and the replacement of the right bend chain of superconducting magnets with conventional dipoles. The safety assessment documentation is presently in preparation and will include a new shielding assessment.
The following publication in the journal Health Physics will appear soon, possibly as early as the June 2003 issue: "Assessment of the Prompt Radiation Hazards of Trapped Antiprotons." Much of the same material will be presented in a talk at the San Diego meeting of the Health Physics Society in the session sponsored by the Accelerator Section. For a number of years, some have expressed an interest in storing antiprotons at low kinetic energies and even transporting them about for scientific research and speculative practical applications. The work reported looks at the technical radiological issues that would accompany such endeavors.