Accurate Thermal Analysis Method For Complex Pixel Detectors

In order to meet the requirement of particle location resolution for high-energy physics experiments in the future,pixel detectors that distributed around vertices are widely used in various high-energy physics experiments.With the increase of position resolution and layer number of pixel detectors,high-power and densely stacked pixel detectors will rapidly increase the structure temperature,resulting in chip failure and decreased detection accuracy.In order to solve the conflict of temperature,power consumption and stacked layout and obtain better detection performance,thermal design of pixel detector is a core problem in pixel detector research.However,for complex pixel detectors,traditional numerical methods are often unable to accurately simulate the model structure of complex pixel detectors due to limited computational conditions.Meanwhile,material parameters,air gap,contact mode and other factors that are difficult to accurately obtain and simulate will also lead to deviation between the calculated results and the actual values,making it difficult for the numerical method to carry out effective quantitative research.In order to better analyze the thermal properties of complex pixel detectors,this paper proposes microelement-integral equivalent method and thermal resistance correction method for the simulation of large pixel detectors that composed of multiple repeatable complex pixel elements and the correction of model accuracy.In the microelement-integral equivalent method,the equivalent model of pixel detector is constructed by the transformation of the geometry and parameters of pixel element,which can greatly reduce the computational cost caused by the complex structure of the pixel elements in the pixel detector on the premise of ensuring the accuracy of the model.In the thermal resistance modification method,the heat transfer model containing a boundary heat source is simplified and analyzed as a thermal resistance network.based on a set of temperature measurements located at participating surfaces.The equivalent correction of the total thermal resistance between two temperature surfaces can be achieved by correcting a certain term of thermal resistance in the heat flow transfer path,so as to obtain the true heat transfer rate.This method can effectively replace unknown thermal conductivity factors,such as materials,gap and contact,and improve the accuracy of the model.Through the research of ALICE ITS2 pixel detector,the microelement-integral equivalent method and the thermal resistance correction method are verified.The results show that the equivalent model of inner detector has good consistency with the original model in temperature value and temperature field distribution,and the maximum temperature difference is kept within 0.2?.When the thermal resistance correction method was used to correct the model parameters,the average temperature error between the numerical results of the model and the experimental results in the inner detector was reduced from 5.6 ? to 1.63?,and the maximum temperature error was reduced from 8.12?to 2.70?.The above research proves that these methods can be applied to the thermal analysis of complex pixel detectors effectively and accurately.The thermal analysis and related design of the latest generation of ALICE ITS3 pixel detector were carried out by the microelement-integral equivalent method and the thermal resistance correction method.The effects of convective heat transfer coefficient,ambient temperature,power density,ratio of power consumption,length of power consumption zone,detector length and thermal conductivity on detector operating temperature were studied.In addition,a scheme is proposed to solve the high temperature problem in the power consumption region of the detector through the thermal conduction structure of the cold source.The results show that when the thermal conductivity of the detector is increased from 5.9 W K-1m-2 to 100 W K-1m-2 and a cold source is used,the maximum temperature difference between the detector and the maximum temperature will be optimized from 40.6,23.0? to 33.8,16.3?.