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Fiber resists CERN's radiation to carry data

02 May 2007

A radiation-resistant fiber is soon to be used in the world's largest particle accelerator for essential communication links.

A radiation-resistant, single-mode optical fiber developed by Fujikura has been selected by CERN for essential communication links within the world's largest particle accelerator - the Large Hadron Collider (LHC).

The single-mode fiber will transmit data about the beam condition around the 27 km ring to the LHC control room. This information is essential for the operation of the machine, but the fiber must be able to withstand large levels of radiation that can cause radiation-induced attenuation in normal optical fiber.

"The total dose the fiber might have to withstand is 100 kGy," Fujikura's product manager, Rob Walker, told optics.org "I estimate that this is roughly equivalent to 1000 million chest X-rays." Samples of the fiber were tested up to much larger doses of 1.4 MGy, which was found to cause an increase in attenuation of only around 0.03 db/m.

Fujikura will supply 2500 km of fiber consisting of a pure silica core and fluorine-doped cladding. The fiber will also be used to collect data from the beam cleaning zones, where the radiation dose is at its highest. These zones consist of an array of collimators and absorbers that protect sensitive detectors from protons straying from the edge of the beam.

"The energy in the beam is about the same as that of a high-speed train and extreme care is needed to ensure that these beams do not damage the sensitive detectors," said Walker.

In addition, Fujikura has already supplied more than 100 km of radiation-resistant 12-way multimode ribbon fiber for data readout within the ATLAS inner detector. The location of the fiber is close to the beam pipe and expected to receive a maximum dose of 300 kGy.

The entire installation is expected to be in place for the start-up of the LHC, which is currently scheduled for December 2007. Fujikura also intends to bid for work when CERN's network is upgraded in 2014.

Fujikura also hopes to introduce its radiation-resistant fiber to other companies and projects where optical communications is required in an area of high radiation.

"We will continue to improve the operational characteristics of radiation-resistant fiber by investigating improved methods of fiber production. We also have a polyimide-coated optical fiber for use in high-temperature environments (up to 300°C)."

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