Accelerator Update
Work on Beamline X27, RF Power Supply Focus of Spring Shutdown
June 10, 2009
Jim Murphy
Accelerator & Operations Division
jbm@bnl.gov
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Another successful shutdown has been completed! Both the VUV & X-Ray rings came up without a hitch and are in full operation. Because of a rain delay of the substation maintenance, the bake-out of the X-Ray Ring superperiod 6 had to be accelerated. As a result, we were able to complete our X-Ray maintenance tasks and begin conditioning two full days ahead of schedule. Kudos to all for the extra effort.
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Highlights of the spring shutdown include replacement of the X27 mask with one having an upstream water-cooled aperture that shields the downstream vacuum flange from synchrotron light. Despite the tight working quarters, this task went very smoothly. A new water-cooled aperture and water-cooled mask was installed immediately downstream of the X27 dipole exit port. This new aperture will collimate photons that were previously impacting the inboard side of the X27 mask housing and raising the local chamber wall temperature to approximately 145 degrees C, leading to elevated local stress that cycled with every fill of the X-Ray Ring. The long-term effect of this cycling stress was the development of a vacuum leak in the gasket of one of the mask housing flanges. Upon disassembly, the inside of the X27 mask vacuum chamber had an obvious thermal imprint in the vicinity of the vacuum leak, confirming beam-tracing studies. Post-maintenance X-Ray Ring commissioning with the new water-cooled aperture installed has shown that this solution was successful in reducing the "hot spot" temperature to a quite satisfactory value of approximately 40 degrees C. After satisfactory operational results are received from the X27 users, a similar approach will be used to reduce beam heating on the X7 front end mask during the December 2009 shutdown.
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Another difficult task completed during the shutdown was the replacement of the X-Ray RF system 3-plate power supply. The old power supply weighed about 3,000 pounds, and had to be lowered from the roof to the ground. The replacement power supply traveled in the opposite direction and weighed nearly as much. Thanks to careful work planning and the expertise of the NSLS and rigging staff, this task was completed successfully and safely.
Also on the spring schedule was the start of the installation of a front end interlock master reset system. Beamlines X1 through X6 have been completed and the rest will be done during monthly maintenance days and the winter shutdown. This system will help us fill the rings sooner following major power interruptions by giving us the ability to reset all of the front end interlocks through one key switch instead of having to reset each front end locally. Significant effort also went into preparation for a new X17 endstation enclosure, replacement of a cooling valve for the X-Ray RF system 1 cavity, installation of improved service rack fan guards, and a long list of routine preventative maintenance. Two of the three remaining original (early 1980s vintage) 300 liter/sec ion pumps in the Booster Ring were replaced during the May 2009 shutdown. At this point, six of the seven planned ion pump replacements have been accomplished, leaving only one final pump to be replaced in the December 2009 shutdown.
The manual liquid nitrogen (LN2) fill system was replaced with a new auto-fill station system designed by Cryotech International Inc. This new system automatically fills any of the standard LN2 dewars in use at NSLS simply by pushing a "start" button after making the input and exhaust connections. When the dewar is filled, the system notifies the user to retrieve it via an automatically generated email message. Users also can view the LN2 fill station area in real time via a web camera.
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The NSLS vacuum monitoring system is being restructured to provide a comprehensive, real-time display for accurate diagnostic and troubleshooting purposes. The plan is to replace the hot and cold ion gauge controllers with ones that provide better readout capability, and to increase the total number of ion gauges in each ring for more accurate average readings. During the May 2009 shutdown, an additional ion gauge was added to the X28 front end during the period of time when X-Ray super-period 6 was vented for the X27 dipole heating remediation work. The vacuum group is planning to provide real-time facility vacuum status information, tentatively on channel 14 of the NSLS CCTV monitors. The NSLS website also will be used to provide vacuum information. Both beta test versions are presently viewable while construction is continuing.
Efforts to prepare for the addition of a new branch beamline at X17A also were undertaken during the May 2009 shutdown. NSLS-assigned electricians and NSLS technicians removed and relocated electrical and fluid lines, regulators, fixtures, and conduit. During this shutdown, vacuum racks were consolidated and relocated, PUE/BPM rack relocation work was started, and the X17A experimental floor was surveyed for the new X17A hutch and X17 transport enclosure modifications to accommodate the new X17A beamline. The preliminary design of the X17A beamline was presented at a review conducted at the NSLS on April 30, 2009. After the final beamline engineering and design work is completed, the new X17A beamline will be installed in phases during future shutdown periods.
In earlier X-Ray Ring injection studies, it was established that a significant amount of Booster beam is lost in a relatively short region around the extraction area, where we have limited steering ability. To address this, a compact, C-frame, pulsed trim magnet was designed, built, measured, and installed in the Booster-to-X-Ray extraction line to aid in reducing beam losses during the injection process. The effort was spearheaded by Xi Yang of NSLS Accelerator Physics Group. The magnet was designed by George Rakowsky, built by Mike Lehecka, and measured by Dave Harder of the NSLS Magnet Measurement Group, while the pulsed current supply was implemented by Pete Zuhoski from Electrical Engineering, assisted by electrical technicians Mike Fulkerson and Pete Davila. Installation was assisted by the Mechanical Tech Group.
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Design challenges included extremely tight space and thus a concern for magnetic interaction with the adjacent booster quadrupole, which was analyzed by 3D magnetic modeling. The new trim magnet provides about 1 mrad kick in both horizontal and vertical directions. To allow simple convection air cooling, the trim magnet operates in pulsed mode, powered on only for ~10 ms during beam extraction.
The magnet was installed during the 2008-09 winter shutdown and it has undergone successful commissioning in spring of 2009. With optimized kick settings injection rates approximately doubled, reducing the X-Ray Ring refill time to a record five minutes. Additionally, operating with the new magnet reduces radiation levels in some locations by up to a factor of three. Efforts are underway to include this trim into our regular operations.
We would like to congratulate and welcome a new, yet familiar, member to the NSLS Electrical Engineering staff. Barrett Clay, who recently earned a Bachelor's degree in electrical engineering from Stony Brook University, has been promoted to the engineering staff. We all look forward to having Barrett add to his many accomplishments in this new role as Electrical Engineer.
Many thanks to the NSLS staff and the BNL Plant Engineering teams for the successful and safe completion of the Spring Maintenance period.