| Neutral Beam Injection(NBI)heating is an efficient auxiliary method for exciting and maintaining high-energy stable operation of fusion plasmas.To effectively prevent high-energy particle bombardment of the inner wall protective tiles,causing sputtering pollution of the plasma and even damaging the device structure,it is crucial to accurately detect the temperature field of the high-field side protective tiles and establish a locking protection mechanism for neutral beam injection.This will ensure timely adjustment or cessation of beam injection in case of overheating,thus safeguarding the structural integrity and plasma stability of the device.With the advancement of NBI technology towards higher energy and longer pulses,the thermal load on protective tiles has increased,demanding higher reliability in temperature measurement.Future experimental operations will entail neutron irradiation,impacting the stability of measurement circuits;moreover,higher beam energies will result in increased penetration loss energy,necessitating a more comprehensive assessment of high-field side protective tile temperature measurement techniques.This paper explores the detection methods for thermal load increase on high-field side protective tiles of the Experimental Advanced Superconducting Tokamak(EAST)under neutral beam injection.It comprehensively addresses the temperature rise of protective tiles from both the perspectives of upgraded infrared hardware measurement technology and simulation prediction of the beam spot location.In anticipation of neutron irradiation impacts in future fusion reactions,this study proposes a fiber-optic infrared temperature measurement system based on the principle of infrared thermometry.This system aims to obtain stable measurements of thermal deposit temperature rise and reliable overheating protection response,ensuring safe operation of NBI beam injection in strong neutron environments.The paper also assesses the quantitative attenuation levels introduced by the fiber-optic infrared measurement method;for the unavoidable atmospheric path in the measurement optical route,MODTRAN software was used to assess infrared signal attenuation in the atmosphere.The results show that the introduction of fiber optics maintains an accuracy of about 1%in the infrared temperature measurement monochromatic scheme,and the experimental results under the same parameters reach about 80%of the theoretical maximum value predicted by the simulation,indicating that the attenuation brought by the proposed method is within the acceptable range for measurement requirements.This study also addresses the detection needs of currently used graphite tiles and potentially upgraded metal inner wall materials in the future.It investigates the measurement accuracy of the infrared monochromatic measurement scheme at low temperatures and the interference resistance of the colorimetric temperature measurement scheme at high temperatures.Through theoretical modeling and experimental evaluation,the consistency of numerical simulation and experimental results was verified.It was found that adopting the colorimetric scheme for temperature distribution measurement of the beam spot in higher temperature environments with upgraded metal materials shows superior adaptability,solving the issue of insufficient interference resistance of the measurement system in a plasma radiation environment.To overcome the limitations of current single-point infrared temperature measurement in assessing the overall temperature distribution,this paper proposes a numerical simulation method for modeling the temperature field distribution of protective tiles under different beam injection parameters.The simulation results were compared with infrared/thermocouple measurement data,verifying the reliability of the NBI beam spot thermal deposition simulation method.The simulation process involved the use of a two-dimensional Gaussian distribution model and a Monte Carlo particle model for beam face power density distribution simulation.In addition,penetration loss was assessed based on experimental paper fitting formulas and NUBEAM simulation,and thermal deposition was simulated using Matlab’s one-dimensional heat conduction analytical model and COMSOL’s three-dimensional finite element analysis model.Finally,the thermal distribution results of the COMSOL finite element analysis model were compared with the infrared measurement values of the protective tile surface temperature,showing good consistency between simulation and infrared measurement data,thereby validating the reliability of the numerical simulation results.To address the challenges in measuring and protecting against temperature distribution and rise effects due to higher beam energy and longer pulse duration in the future,this paper innovatively proposes a protective warning strategy based on fiber-optic infrared temperature measurement and numerical simulation for measuring and protecting against the temperature rise of high-field side protective tiles.This strategy allows for the prediction of potential overheating scenarios based on set/measured parameters of beam operation and plasma,and for immediate adjustment of NBI beam injection parameters based on measurement results,ensuring safe and stable operation of EAST device experiments.The results of this research have developed detection technology for the thermal effects of high-energy particle beam injection heating in plasma radiation environments,achieving good consistency between measurement outcomes and numerical simulation results.This provides significant engineering reference value for future experiments with higher energy and longer pulse NBI beam lines.By combining real-time temperature detection of protective tiles with simulation-based prediction,this study lays a technical foundation for the digital twinning and automated operation of NBI systems,ensuring the safety of experimental devices under higher energy and longer pulse injection conditions in the future. |
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