Fermilab Today Friday, May 11, 2007

Preparations for Magnet Repairs Proceed

The cold mass of the Q1 magnet (blue) and two of the four cartridges (red) that get attached to the cold mass and the vacuum vessel surrounding the magnet (not shown) with brackets.

Scientists and engineers from CERN, Fermilab, Lawrence Berkeley National Laboratory and Japan's KEK Laboratory are preparing for repairs of 18 sets of structural supports to Fermilab-built quadrupole magnets for the LHC accelerator under construction at CERN. On Tuesday, March 27, the structural supports to one quadrupole magnet, part of an "inner triplet" of three magnets named Q1, Q2, Q3, failed a high-pressure test in the LHC tunnel. Fermilab assembled nine inner triplets for the LHC, including one spare. They are used to focus the proton beams of the particle collider before they enter the four interaction points along the ring.

To fix the structural supports' design flaw, the team of scientists and engineers has proposed to add to each Q1 magnet and each Q3 magnet a set of four cartridges that can absorb the longitudinal force generated during the pressure test. The solution was presented to a team of experts during a review at CERN on April 24 and 25. Since then the design of the cartridge system has been refined and parts needed for the cartridges and their installation have been ordered. Detailed tests of the design are in progress. The final design reviews will take place at Fermilab and CERN over the next couple of weeks.

The cartridges are stiff mechanical springs that will be installed parallel to the cold mass. Each cartridge consists of two parts: a 1.8-meter-long rod made of Invar (a kind of steel whose dimensions change minimally in response to temperature variations) inserted into a 1.4-meter-long aluminum tube that is closed at one end. When a longitudinal force acts to push the cold mass in longitudinal direction, the cartridge holds the cold mass in place as the rod presses against the bottom of the tube. The thermal properties of the rod and tube allow the system to function through the full range of temperatures encountered by LHC magnets, from room temperature to minus 271 degrees Celsius, the temperature at which the superconducting quadrupole magnets operate.

The installation of the cartridges in the Q1 and Q3 magnet of at least one inner triplet is scheduled to be complete in early June, in time for the next pressure test. The cartridges will be inserted and mounted from one end of each magnet, without having to cut open the steel vacuum vessel surrounding the magnet. The installation can be done in the LHC tunnel, with the magnets in place. Only the inner triplet damaged during the previous pressure test will be removed from the LHC tunnel for repairs of its structural supports.

Scientists and engineers from CERN, Fermilab, Lawrence Berkeley National Laboratory and Japan's KEK Laboratory will continue to share the tasks involved in analyzing, installing and testing the triplet repairs.

LHC Magnet Update Archive

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