LHCb installs bridge and beampipe section…

4 October 2006

The last large component of the Large Hadron Collider beauty (LHCb) experiment has descended into the cavern on the LHC ring, and the delicate installation of the important beryllium vacuum chambers has begun. LHCb will focus on the precision measurement of CP violation and rare decays of hadrons with b quarks, with a spectrometer covering only one side of the collisions in the LHC. Beryllium was chosen for 12 m of the 19 m long beampipe to minimize the level of background in the experiment.


The 10 tonne, 18 m long metal structure known as the bridge, which will support the LHCb tracking system, was lowered into the cavern in June. This was a challenge as there were only a few centimetres to spare as the structure was turned and moved into its final position. The bridge is made of stainless steel, which was chosen to avoid creating interference in the experiment as it is only slightly magnetic. It has rails onto which will slide the three stations of the silicon inner tracker and the three stations of the outer tracker consisting of straw-tube detectors.

More recently, at the end of August, the first beryllium section of LHCb’s beam vacuum chamber was installed. The three-day operation demanded patience and precision as the first of four sections of the beampipe was connected to the vacuum vessel of the vertex locator (VeLo). This first section comprises a conical tube of 1 mm thick beryllium, nearly 2 m long, and an 800 mm diameter spherical window made from 2 mm thick aluminium alloy. The window is connected to the conical part of the beampipe through an aluminium alloy bellow, which allows mechanical alignment once the assembly is installed.

For installation, the beampipe was placed on a frame that slides over rails to move it gently into position. A wakefield suppressor was then inserted and connected electrically, and finally the spherical window was connected to the VeLo vessel using a metal seal. After installation was completed, the system was pumped down and a leak test conducted. The aim is to reach an average pressure of 10–9 millibar with the beam passing through the beampipe.

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