Radiation Tests on optical fibres for the LHC machine  

T. Wijnands, D. Ricci CERN EN department

Fraunhofer INT

First radiation test on optical fibres

December 2002 :First radiation test on SM and MM fibres– ~400 Gy total dose (SPS target area)– RIA : a few dB/km @ 400 Gy– Conclusion was : RIA is not an issue !

Total dose test with 60Co source

March 2005 :Verification of attenuation data with 60Co source:– 1310 nm and 1550 nm– Ge-P doped a-SiO2 fibres from Draka NK Cables Ltd

manufactured using the MCVD (Modified Chemical Vapour Deposition) process

_ Ge-doped a-SiO2 fibres from Draka Fibre Technology BV manufactured using the PCVD (Plasma Chemical Vapour Deposition) process

Radiation Induced attenuation

Dose rate : 1 kGy per hour

Ge-doped fibres

Radiation Induced attenuationGe-doped fibres

After annealing at room temperature

LHC cleaning sections

2005 : Difficult situation in the LHC– Many SM optical fibres are passing through LHC cleaning sections– Dose rate is ~10 kGy/year– Maximum attenuation (BPM/BLM system) 7 dB/km– For Ge-doped fibres 7dB/km RIA corresponds to 600 Gy !– LHC operational in 2007 !

Start of search for SM radiation hard optical fibres

LHC cleaning sections

2005 : Difficult situation for fibres in the LHC !– Many SM optical fibres are passing through LHC cleaning sections– Dose rate is ~10 kGy/year– Maximum attenuation (BPM/BLM system) 7 dB/km– For Ge-doped fibres 7dB/km RIA corresponds to 600 Gy !– LHC operational in 2007 !

Start of search for SM radiation hard optical fibres for LHC

T. Wijnands et al. TWEPP 2007 Prague

Lessons learned

– RIA is caused by TID– Test results in SPS (complex radiation field) near identical to 60Co.– Production process is very special– Small manufacturing changes may cause large variations in RIA– QA is crucial for the series production and includes sample testing– QA is crucial when you test on RIA (procedure, test setup , samples)

• How to address QA for small batches of radhard fibres ?• What fibres can be used for applications > 100 kGy ?• What if T = 5 Kelvin ?• What coating ?• How to achieve compatibility with blowing technique ?• Can we also find radhard MM fibres ?• Can we use light at 850 nm ?

M&O and new applications

Radiation test of SM Optical Fibres

25 January 2010 :3 random samples from LHC series production :– RRSMFB 110A – RRSMFB 630A– RRSMFB 380A one sample from the 3 was selected for the test

11 February 2010 :Start of irradiation test up to 5 MGy:– 1310 nm and 1550 nm– Room temperature– Light power 10 mW– Dose rate 220 Gy/min

4 March 2010 :End of first irradiation test