## 3 Results and Discussion
### Isotope Production Irradiation
The temperature compensation scheme based on Equation (1) assumes no time delay in the response of the two input signals; therefore, inadequately compensated increases in body temperature of the pressure transducer would be realized as decreases in the reported pressure value. As the pressure transducer warmed, the correction due to the increase in temperature may not have been subtracted correctly from the pressure signal. The disagreement between the pressure readings was expected to only be temporary and to revert back to an error of 0 psi once the FBG-based pressure transducer returned to a steady-state temperature. This was observed during the experiment by pressure readings collected several minutes after the conclusion of the test and at the beginning of the subsequent test once transducer temperatures stabilized. The second isotope production irradiation experiment was conducted following the same protocol as the first one with the FBG-based temperature probe now retracted by 2 mm so that its tip was removed from the wall of the target body. The proton beam current was increased stepwise to the same maximum value but with shortened dwell times at each set point. The temperature and pressure measurements are illustrated in Figure 7. The retracted temperature probe reported dynamic readings compared to the first experiment. This agreed with the assumption that in the previous experiment the temperature probe reading was affected by the thermal mass of the target body. With the temperature probe inserted into the target liquid, the temperature readings demonstrated the same level of dynamic behavior as both the FBG-based and reference pressure transducer signals, which confirmed that the fluid temperature and pressure were physically coupled. The dynamic temperature signal was understood to be a measurement of the cavitation and convection currents that occur in a liquid target. At a beam current of 20 \(\mu\)A, the highest measured temperature in the target water was 94.75 \({}^{\circ}\)C. The same behavior of divergence between the FBG-based and reference pressure transducer signals occurred at around 300 s into the test, as observed in the first experiment. Overall, the experiment successfully demonstrated the efficacy of the FBG-based temperature probe and pressure transducer in proton beam applications. More design and calibration developments are required to improve accuracy of the pressure readings. No significant performance degradation due to exposure to proton radiation was observed. A subsequent experiment was conducted to explore the behavior of the FBG-based temperature probe in an empty target cavity, i.e., the proton beam was allowed to strike the inserted probe without the thermal mass and cooling provided by the target water. As expected, the temperature sensor reacted to the increased beam current immediately with a significantly shorter response than when the target water was present. When the beam current was set to 10.5 \(\upmu\)A, the FBG-based temperature probe reported a value of 129.70 \({}^{\circ}\)C when the signal was suddenly lost. The target was disassembled to investigate the cause of the failure. Inspection of the individual components revealed that the Inconel sheath of the sensor had melted and deformed, thereby mechanically destroying the fiber and FBG, see Figure 8. It should be noted that while the Inconel sheath has a melting temperature \(\sim\)1250 \({}^{\circ}\)C, the FBG-based temperature sensor can operate in temperatures up to 1000 \({}^{\circ}\)C.  
Figure 8: FBG-based temperature probe inserted in the target body after irradiation in an empty target cavity. The damaged tip can be seen in the center of the target. Figure 7: Results from the second isotope production experiment illustrating the results of an irradiation of naturally abundant water. The black curve shows the set point proton beam current. The red curve represents the readings of the reference pressure transducer attached to the target body.