Strain Measurement in the Spallation Target Using High-Radiation-Tolerant Fiber Sensors

We describe the measurement of fast dynamic strains in the mercury target module of the spallation neutron source using customized high-radiation-tolerant fiber-optic strain sensors. The sensors are made from fluorine-doped single-mode optical fibers that demonstrated high radiation tolerance at 1300 nm. A digital phase demodulation scheme is employed in the signal interrogation system, which enables high bandwidth measurement and has an excellent adaptability to sensor output power fluctuations and sensor gap variations. Fast transient strain waveforms induced by high-energy, high-intensity proton pulses are successfully measured. The sensors have survived radiation doses of 10(9) Gy. Both measurement bandwidth and radiation tolerance of the sensors are an order of magnitude higher than their commercial counterparts.