September 23, 2008 Edition

About the Author

Paul Sampson is the group leader for Maintenance Support in the Machine Operations group in Brookhaven's Collider-Accelerator Department.

Shutdown Maintenance and Operations

By Paul Sampson

Planning and execution of shutdown work in the Collider-Accelerator Department complex has been reorganized 3 years ago by emphasizing central coordination. The system in place is modeled after the one used for scheduled maintenance days during the run, which has shown clear positive results over the past few years. (See Figure 1) The system is proving its value not only in for recording and sharing information on shutdown activities, but also in increasing the effectiveness and efficiency of the scheduled work, as exemplified by the improved smoothness in the transition from shutdown to operations in the past few runs. With the end of the shutdown for FY08 nearing and preparation work for the upcoming run in sight, a review of the ongoing activities is in order.

This shutdown had an extremely aggressive agenda as is the norm in CAD. Most all of the accelerators and facilities, including the Tandem transport, Booster AGS, AGS to RHIC transport, support buildings and RHIC itself had major work performed, and in addition, work continued on the new accelerators, EBIS and ERL.

The next NSRL (the dedicated extraction line from Booster for NASA experiments) run is fast approaching (the first running day is September 29th), and work in the AGS and Booster is wrapping up. A checkout and re-commissioning period for the Booster is currently in full swing. By the week of the 22nd, Machine Specialists in Operations will begin to tune beam parameters.

Much of the work on the accelerators was concentrated on improving efficiency, intensity and polarization for the upcoming RHIC PP run. Injector systems were modified to preserve beam polarization and to minimize losses and blow up. In RHIC itself, a new systems were installed which ultimately is expected to improve beam stability and reduce polarization loss during acceleration.

Projects for general improvement of RHIC continued. Power supply upgrades, stochastic cooling installation and polarimeter and controls upgrades were among the larger jobs. Several jobs took advantage of the fact that RHIC this year was warmed to room temperature, and included: a repair of the main magnet bus, the repair of Beam Position Monitor feed-throughs, and work on mitigation of the observed 10Hz triplet oscillation. As the run nears, the system groups will be endeavoring to complete all of the jobs originally hoped for before, as well as the many that have arisen during the shutdown of FY08.

One of the largest jobs completed in the Booster this year has been the installation of the EBIS transport line on the inside of the Booster enclosure. This was a particularly difficult undertaking since it affected the LINAC to Booster (LTB) and Tandem to Booster (TTB) lines (See Figure 2). Challenges to the Rigging, Survey, Vacuum, Water services, Instrumentation, Power supply Maintenance Support groups were met such that the line is presently installed and ready for testing. Major phases of the project included the installation of the two large dipole magnets and prep work for the vacuum bake out that followed. Delays in magnet shipping from overseas, design and delivery of instrumentation, power supply and vacuum components added complexity to the job and the start-up schedule. Injection of heavy ions via the Tandem to Booster (TTB line) is scheduled for the 24th of September and will be the final confirmation that the installation was a success and had no detrimental affect on the TTB line to which it is now connected.

One of the larger construction jobs at the Booster was the installation of the soil cap over the High Energy Beam Transport (HEBT) line above the beam-stops. These stops were originally used to prevent direct injection from the LINAC into the AGS, which has not been done since early 90’s, but are presently used to stop Polarized Protons send down the HEBT line and through the LINAC polarimeter. In order to finish this job, it was necessary to: move first the beam stops to a more favorable location inside the accelerator enclosure, then install the cap physically on the Booster berm above.

Another large effort was made in the Booster to AGS (BTA) line. Old instrumentation was resurrected and new ones installed in anticipation of studies that will take place in parallel to the NSRL run. In addition, all of the quadrupole supplies had both hardware and software calibrations checked. These studies are designed to better understand the BTA line optics, and ultimately the match between the Booster and AGS.

All of the was completed in addition to standard systems maintenance, software and hardware upgrades, and in particular the installation of and the implementation of low level RF system.

The Booster will run various species of heavy ion for NSRL until November 21st, then have a short shutdown period were several jobs that remain outstanding from the summer will be completed. The largest of these is the replacement of the H- injection foils. This will require the C5 sector of the Booster to be bled up to air and baked out after installation is complete. The new “Postage Stamp” foils will decrease beam blow up during injection by minimizing the turn by turn exposure of the beam to the foil during the process.

The NASA Space Radiation Laboratory itself also underwent a major alteration. The Beam plug, used to prevent extracted beam down the line while setup in the experimental area is in progress, was upgraded for more reliable operation. The downstream end of the NSRL transport modified to accommodate future large beam experiments. This entailed the dismantling of the transport line, installing the new “Big Beam” elements and reassembly.

At present, live checkout of the Booster systems is in progress, including a “Heat Run”, where all devices are run at high power and infra red cameras are utilized in the ring to locate hot and potentially problem areas prior to running with beam. Following this a “dry run” was performed where all of the components are run with the expected beam start-up parameters.

The AGS will remain opened for the most part until December, when testing for start-up will commence. As in the Booster, many systems are undergoing maintenance, upgrade and replacement. The largest job by far at the AGS is the replacement of the Motor Generator transformers. These massive transformers, 2 at 100+Tons and 2 at 60+ Tons feed the Motor Generator’s Pulsed (acceleration) and Flattop (injection and extraction porch) banks respectively. This is the final stage of a three year improvement project. The end result will be that the ripple and transfer affects seen by the Main Magnets in the AGS ring will be greatly. This not only helps to keep beam blowup down, but reduces de-polarization effects during the acceleration cycle as well as increasing stability. At present, the formidable job of cabling these transformers is well under way. It is anticipated that the transformers will be tested in mid October.

Other work in the AGS is progressing very well. The replacement of the AGS Magnet Over-temperature system was completed earlier this shutdown. The old system was original AGS equipment and relied on melting solder (woods metal) to interlock the Main Magnet Power supply in the event of overheating. The new system is comprised of klixons with a PLC interface and will better detect cooling problems before main ring magnet could be damaged. Since a magnet replacement would cost several days of down time to RHIC, this was a highly desired upgrade.

Specific RHIC shutdown projects are presently in full swing. Several major efforts are well underway, while others are just beginning. The final installation of the 9MHz RF system was completed and tests are presently ongoing. RF, Vacuum, Survey, Water, and Instrumentation and Beam Components personnel all contributed to various stages of this successful effort. Commissioning and synchronization of this system will be one of the challenges for the start up this year.
The Instrumentation and Beam Components group, with support from vacuum, survey, cryogenics and others, have been working on several large scale projects including: Installation of one of the desired two spin flippers, CNI polarimeter upgrades in both the yellow and blue rings, continued work on stochastic cooling, BPM upgrades and repair, as well as system maintenance, checkout and support of other jobs.

The RHIC mechanical group has been busy locating and repairing existing main bus problems. In addition, planned implementation of 10Hz triplet oscillation damping is ongoing. Completion of these jobs will allow for more flexibility in the selection of magnet cycles and may allow the machine to run at a more desirable working point respectively.

The effort to further increase system efficiency and reduce downtime due to failure continues throughout the shutdown. Continued upgrades to the Main Magnet Power Supplies, quench protection detector and assembly improvements, interlock string reconfiguration and added supply chassis cooling is expected to add to past improvements in the reliability of RHIC main power supply system. Installation of dehumidifiers the tunnel and improvements to air-conditioning regulation in the RHIC alcoves should reduce moisture related problems in the ring while continued improvement of air conditioning the support buildings will aid to the reliability of all equipment. Upgrades to the MRAM for controls hardware continued and has also shown to increase the reliability of that equipment.

As the Booster start-up is completed, shutdown focus will shift to the AGS and prep for setting up Polarized Protons early next year. With the goal of improved injector beam quality underway, jobs at RHIC will be wrapped up and a startup, checkout and commissioning period will follow.

During each shutdown period a huge amount of work is planned, the scope of which ranges from scheduled maintenance to major installation and renovation. Pulling it all together in the end always proves to be a challenge. With the cooperation and assistance of all the groups at CAD and beyond we always manage to get it done.