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The cylindrical beam collimators that shave off unwanted portions of the proton beam
:: 27 July, 2007
A team of SLAC engineers and machinists recently brought one small component, which may someday be a part of the Large Hadron Collider (LHC), from paper to reality. The proposed device under development at SLAC will rotate the cylindrical beam collimators that shave off unwanted portions of the proton beam. It is no bigger than a six-pack of soda and topped with a collection of precision gears.
"It's an intricate little monster," SLAC machinist Kim Cook said of the device. "It took a lot of teamwork to transform a 23-pound block of stainless steel into such a complicated device."
The device is a small but important piece of the proposed collimator. When the LHC is up and running, the collimator edges will occasionally be struck by errant protons and stripped of some of their surface metal. When this hopefully rare event happens, the newly built support and gear cluster will rotate the collimator to present an undamaged surface to the beam.
Depending on the actual conditions seen at the LHC, and the relative merits of the SLAC collimator as compared to other designs being developed by CERN, 72 of these "intricate little monsters" may be produced as part of Phase II collimation upgrade program of the LHC..
Creating such a complicated device for the LHC requires massive amounts of teamwork and cooperation. Through months of collaboration and communication, a team of SLAC engineers and machinists are developing the collimator prototype. The support and gear cluster is now traveling the country to demonstrate how challenges of the LHC can be solved.
"The piece operates in a vacuum, but it wasn't built in a vacuum," SLAC engineer Steve Lundgren said with a grin. "I was consulting Kim several times a week, asking how we could design the piece to make fabrication procedures easier."
In addition to Cook and Lundgren, seven other SLAC employees helped produce the part. Gene Anzalone took the concept and configured it into a manufacturable device, Eric Doyle performed stress analysis, Roland Kurz machined some of the gears and Pete Franco provided wire work. Hugh Reynolds, Rafael Huerta, and Paul Tomasi also provided carefully crafted parts for the beam collimator rotator.
"We don't just make parts," said Kim. "We create tools to help engineers and scientists succeed."
News Inside News
SLAC's LARP Phase II Collimator Program
When Jim Strait of Fermilab gave a seminar at SLAC in 2003 about technical challenges at the Large Hadron Collider (LHC) as part of the SLAC Scenarios series, he highlighted the issue of LHC collimation. Collimators are blocks of material that form small openings through which a beam must pass. They scrape away beam tails, delivering only the clean core of the beam to experiments, and, as the tightest hole in the transport line, protect more easily damaged devices.
In the LHC collimation system, the 7 TeV 350 MegaJoule proton beam—energetic enough to melt 1,000 pounds of copper—will pass through a series of adjustable ~3 millimeter wide gaps formed by the edges, or jaws, of ~1 meter long blocks. In normal operation the jaws must stay aligned to the level of 25 microns, the diameter of a human hair, while efficiently removing 90 kW of errant protons, twice the beam power of the SLAC Linear Collider (SLC).
As if that wasn't enough, Jim's challenge was to come up with a scheme to deal with the rare, but eventual, problem of the accidental pre-firing of the fully-energized beam abort kicker magnet system, which would slam a MegaJoule of protons into a jaw in 200 nanoseconds. This photo shows what about half a MegaJoule of 16 GeV electrons can do to a 1 meter long block of copper, a typical material for collimator jaws.
As it happens, the pre-ILC X-band e+e- linear collider under development at SLAC until 2004 had a similar collimator damage challenge. After investigating several approaches, Joe Frisch proposed a design based on rotatable metal cylinder jaws, which Eric Doyle then prototyped and tested (see above image). If errant beam damaged the surface, the cylinder jaws would be rotated a bit to present a clean new surface to the beam. What began as a simple suggestion in 2003 that the LHC adopt a similar design, has led to SLAC joining U.S. LARP, the LHC Accelerator Research Program, with the task of designing and building a prototype "Phase II Collimator" for delivery to CERN in 2009.
The LHC is being equipped for start up operation with a collimation system based on rectangular carbon jaws. The carbon is sufficiently transparent that it will survive a beam abort system misfire, but lacks the resistivity and efficiency needed for the LHC to achieve its design luminosity. Empty slots have been left in the LHC lattice for improved "Phase II" collimators.
Doyle, along with Steve Lundgren, Gene Anzalone, Lew Keller, Yunhai Cai and Tom Markiewicz have designed and calculated the performance characteristics of a rotatable 1-meter long 14-centimeter diameter copper jaw with 12 kilowatts of cooling capacity that should meet the LHC's requirements and provide enough circumference for 20 accidents. The design relies heavily on SLAC's manufacturing expertise and the SLAC klystron department's superb brazing skills. Small test pieces of the jaw have been used to verify the design and manufacturing procedures and construction of the first full-length jaw is in progress. Thermal-mechanical tests will begin this fall. If beam tests in 2009 show that the SLAC design can handle the challenge, CERN will construct 32 devices from our plans and install them in the LHC, where SLAC staff will help commission them.
In The Images-
1.Steven Lundgren (left) and Kim Cook with their "intricate little monster," a beam collimator rotator recently built by a team effort at SLAC.
2.LARP Phase II Collimator Program
Release link: http://today.slac.stanford.edu/
Tags: Large Hadron Collider (LHC) , cylindrical beam collimators , proton beam , collection of precision gears , stainless steel , stress analysis , collimator rotator ,
