Just like a fridge, you only need the lights on in the LHC tunnel when you’re in there; but the emergency lights are part of an essential safety system if you ever need to evacuate.
Fortunately, tunnel evacuations are very rare, but if you work there, you need to know that you can rely on the emergency lighting to guide you to safety.
When the LHC machine is operating, it’s a harsh environment – people are most definitely not allowed access – and the lighting systems need to withstand the effects of radiation to ensure that they will still work when the LHC is switched off and people are allowed back in the tunnel to carry out routine maintenance.
Changes to lighting regulations mean that the current low pressure sodium lighting system which was installed for LEP, the LHC’s predecessor, is becoming obsolete; replacement parts are difficult to find because manufacturers are no longer producing them. CERN needed to find a solution, not just for the 27 km LHC tunnel, but for the whole of the accelerator complex.
“We need a mass market solution that’s cheap and available from multiple sources,” explains project engineer, James Devine.
Initially, 10 different products based on LED lamps were tested in a radiation environment; most lasted less than five minutes. The sole survivor was dissected to see how it was made.
“We looked at the way the power converter was made – most LED products use switch mode power supplies which are very sensitive to radiation – but this one used a bridge rectifier,” says James. “That’s basic technology from the early days of electrical engineering.”
Since then, James has been working with two companies (one British, one French) to incorporate this design for a radiation hard power supply into their products. Both companies are specialist suppliers of tunnel lighting, and both manufacture emergency lighting systems. However, neither had produced a product especially for radiation environments.
The new lighting system has been installed at LHC point 7 – radiation-wise, the hottest access point of the accelerator. After two years it is still working well and has been so successful that as the LEP-era lighting fails, it is being replaced with the new system.
James’ design for the power supply has recently been granted funding from CERN’s Knowledge Transfer Fund to enable further development to increase the energy efficiency and extend the lifetime.
The design is now available under the CERN Open Hardware Licence, a licence devised at CERN aiming specifically at facilitating the dissemination of hardware designs. “This means that any manufacturer can use and modify OHL designs freely”, explains Myriam Ayass, legal advisor in the CERN Knowledge Transfer Group and author of the CERN Open Hardware Licence, “and if his modifications are distributed, this must be under the same OHL conditions, thereby fostering competition and innovation in the market place.”