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CERN and IHEP collaborate well on Beam-loss Monitors System
:: 23 October, 2007
The circulating beams will store an unprecedented amount of energy when the LHC is in operation. If even a small fraction of this beam deviates from the correct orbit, it may induce a quench in the superconducting magnets or even cause physical damage to system components. The LHC beam-loss monitoring (BLM) system is the key to protecting the machine against dangerous beam "losses" of this kind.
The BLM system generates a beam abort trigger when the measured rate of lost beam exceeds pre-determined safety thresholds. The lost beam particles initiate hadronic showers through the magnets, which are measured by monitors installed outside of the cryostat around each quadrupole magnet. About 4000 BLMs – mainly ionization chambers – will be installed around the LHC ring. They are the result of a successful collaboration between CERN and the Institute for High Energy Physics (IHEP) in Protvino, Russia. CERN developed the monitors and IHEP manufactured them during the past year, using industry-produced components.
Signal speed and robustness against aging were the main design criteria. The monitors are about 60 cm long with a diameter of 9 cm and a sensitive volume of 1.5 l. Each one contains 61 parallel aluminium electrode plates separated by 0.5 cm and is filled with nitrogen at 100 mbar overpressure and permanently sealed inside a stainless-steel cylinder. They operate at 1.5 kV and are equipped with a low-pass filter at the high-voltage input. The collection time of the electrons and ions is 300 ns and 80 μs, respectively.
The radiation dose on the detectors over 20 years of LHC operation is estimated at 2 × 108 Gy in the collimation sections and 2 × 104 Gy at the other locations. To avoid radiation aging, production of the chamber components included a strict ultra-high vacuum (UHV) cleaning procedure. As a result, impurity levels from thermal and radiation-induced desorption should remain in the range of parts per million. Standardized test samples analysed at CERN periodically helped to check the cleaning performance.
The team at IHEP designed and built a special UHV stand to ensure suitable conditions for building the monitors. They performed checks throughout the production phase and documented the results. The quality of the welding is a critical aspect, so the team tested all of the welds for leak tightness at several stages. They also monitored constantly the vacuum and the purity of the filling gas. It was necessary to test the components before welding, and the assembled monitors during and after production, to ensure that the leakage current of the monitors stayed below 1 pA. Overall, IHEP achieved a consistently high quality for the monitors during the whole production period and kept to the tight production schedule. Tests at CERN's Gamma Irradiation Facility of all 4250 monitors found fewer than 1% to be outside of the strict tolerance levels.
About European Organization for Nuclear Research
The European Organization for Nuclear Research (French: Organisation européenne pour la recherche nucléaire), commonly known as CERN (see Naming), pronounced [sɝn] (or [sɛʀn] in French), is the world's largest particle physics laboratory, situated just northwest of Geneva on the border between France and Switzerland. The convention establishing CERN was signed on 29 September 1954. From the original 12 signatories of the CERN convention, membership has grown to the present 20 member states. Its main function is to provide the particle accelerators and other infrastructure needed for high-energy physics research. Numerous experiments have been constructed at CERN by international collaborations to make use of them.
The main site at Meyrin also has a large computer centre containing very powerful data processing facilities primarily for experimental data analysis, and because of the need to make them available to researchers elsewhere, has historically been (and continues to be) a major wide area networking hub.
CERN currently has approximately 2600 full-time employees. Some 7931 scientists and engineers (representing 500 universities and 80 nationalities), about half of the world's particle physics community, work on experiments conducted at CERN.
As an international facility, the CERN sites are not officially under Swiss or French jurisdiction, and some company vehicles have diplomatic number plates.
About Large Hadron Collider
The Large Hadron Collider (LHC) is a particle accelerator and collider located at CERN, near Geneva, Switzerland (46°14′N, 6°03′E). Currently under construction, the LHC is scheduled to begin operation in May 2008.[1] The LHC is expected to become the world's largest and highest energy particle accelerator. The LHC is being funded and built in collaboration with over two thousand physicists from thirty-four countries, universities and laboratories.
When activated, it is hoped that the collider will produce the elusive Higgs boson particle — often dubbed the God Particle — the observation of which could confirm the predictions and 'missing links' in the Standard Model of physics, and explain how other elementary particles acquire properties such as mass. The verification of the existence of the Higgs boson would be a significant step in the search for a Grand Unified Theory which seeks to unify the four fundamental forces: Electromagnetism, Strong Force, Weak Force, and Gravity. The higgs boson may help to explain why gravity is comparatively weak when contrasted with the other three fundamental forces.
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Tags: LHC , beam , orbit , beam-loss monitoring (BLM) , CERN , High Energy Physics , IHEP , ultra-high vacuum (UHV). ,
