A Comparative Study of Non-Invasive Fibre Bragg Grating for Spatially and Temporally Resolved Gas Temperature Measurements in Cold Atmospheric Pressure Plasma Jets

Cold atmospheric pressure plasma jets (CAP-Jet) are successfully used in medical ther-apy for healing of chronic wounds and are widely researched in inactivation of patho-gens and in assisting in cancer therapy. A crucial parameter for these plasma applica-tions is that CAP-Jets operate at temperatures that are tolerable for biological tissues. While tools characterizing the plasma's gas temperature are well developed, there are only a few methods that work with an agreeable limit of uncertainty, complexity and limited perturbation properties to accurately determine that the studied plasma jet operates at tissue tolerable temperatures at all times. In the current work, time resolved measurements of the gas temperature in the effluent of a CAP-Jet are performed using the innovative technique of a Fibre Bragg Grating (FBG), in which the temperature dynamics is measured by a shift of the FBGs resonant wavelength through its thermo-optic coefficient. Comparing with other temporal and spatial diagnostic tools such as thermocouple measurement, Schlieren imaging, and optical emission spectroscopy, we demonstrate reliable calorimetric measurements at different plasma duty cycles. The plasma source maintains tissue tolerable temperatures inside the plasma active zone with values below 35°C at 1 cm distance from the jet nozzle. The calorimetric measure-ments have revealed that the heat power dissipation in comparison to electric energy of our plasma source is at least 50%.

冷大气压等离子体射流（Cold Atmospheric Pressure Plasma Jet，CAP-Jet）已成功应用于慢性伤口愈合的临床治疗，并在病原体灭活、辅助癌症治疗领域得到广泛研究。对于这类等离子体应用而言，核心参数之一是CAP-Jet的工作温度需处于生物组织可耐受的范围内。尽管表征等离子体气体温度的检测工具已较为成熟，但能够在不确定性、复杂度和扰动控制上达到合理阈值，且可精准确保所研究的等离子体射流始终维持组织可耐受温度的方法却寥寥无几。本研究采用创新的光纤布拉格光栅（Fibre Bragg Grating，FBG）技术，对CAP-Jet流场出口处的气体温度开展时间分辨测量：该技术通过光纤布拉格光栅的热光系数引发的谐振波长偏移，获取温度动态变化信息。相较于热电偶测温、纹影成像、光学发射光谱等其他时空诊断工具，本研究验证了在不同等离子体占空比下的量热测量结果具备可靠性。该等离子体源在等离子体活性区域内可维持组织可耐受的温度：在距射流喷嘴1厘米处，温度低于35℃。量热测量结果显示，本研究所用等离子体源的热功率耗散量至少占其输入电能的50%。