常壓脈衝電弧噴射式電漿的診斷

Abstract

本研究進行在常壓下運用直流脈衝式電源產生的電弧噴射式電漿之檢測。檢測包含放電區域的電漿電性及噴流下游區域的電漿熱性質及光學性質。放電區之電性檢測包含電壓及電流探棒測量放電區域的電壓電流波形。下游之檢測包含利用熱電偶測量噴流下游氣體溫度以及利用光譜儀分析噴流下游放射光譜，並使用高速攝影機記錄電漿之外觀變化。 電漿放電的電壓及電流波形顯示每個脈衝週期均會產生類似輝光放電轉變為電弧放電的過程。高速攝影機影像亦顯示，電漿在每個脈衝週期內經歷某種放變型態的改變。綜合以上結果可判斷此電漿在每個週期內均產生輝光放電轉變至電弧放電的過程。 放電區域之電性分析發現，隨著施加電壓增加，輝光放電轉變至電弧放電較快，氣體流量對此過程影響較不明顯；電漿消耗功率隨著施加電壓增加而增加；隨著施加電壓增加及氣體流量減少，電弧放電的電流較低。固定工作週期等同於固定輸入能量，因此固定工作週期下，電漿電性不隨脈衝頻率改變。 噴流下游之熱性質及光學性質分析發現，隨著施加電壓降低及氣體流量增加，噴流下游氣體溫度下降；噴流下游激發態分子密度受到放電區域的初始密度及衰退影響，在高流量時衰退的密度較少，因此噴流下游的激發態分子密度均隨著施加電壓及氣體流量增加而增加。大氣擴散對噴流下游的影響為產生急冷效應，使得活性粒子衰退量增加，且會反應生成NO，光譜分析顯示噴流下游的放射光譜含有N2、NO及N2+的放射光系統。固定工作週期等同於固定輸入能量，因此固定工作週期下，電漿噴流熱性質及光學性質均不隨脈衝頻率改變。 以上結果均可以熱效應及動力效應改變對比電場解釋。熱效應即為溫度增加激發態分子的密度亦增加，對比電場增加使得電漿反應性增高，動力效應為激發態分子密度增加，改變電子游離反應速率，對比電場增加使得電漿反應性增加 根據實驗結果，本系統可藉由改變施加電壓或氣體流量，獨立調整噴流氣體溫度及噴流下游激發態分子的密度。在製程中，前述兩種性質影響了製程的效能，此系統可藉由改變操作變因，調整電漿噴流性質以達特定製程所需之效能。

Diagnostic studies of an arc plasma jet (APJ) sustained by DC pulse power operated at atmospheric pressure were performed. Plasma characteristics studied included electric properties in the discharge region, thermal and optical properties at the jet downstream. A voltage probe and a current probe were used to measure the voltage and current waveforms, respectively, of this APJ in the discharge region. Multiple thermocouples were used to measure the downstream jet temperature. A spectrometer was used to obtain the emission spectrum at the jet downstream. A high speed camera was used to observe the change of the appearance of APJ over the pulse period. The voltage and current waveforms show that the APJ undergoes a glow-to arc transition within each pulse power period. Such a transition is further confirmed by taking images using a high-speed camera, in which the plasma appearance is not uniform in time visually in the time scale of a fraction of a period. Electrical analysis in the discharge region shows that the voltage at which the glow-to-arc transition occurs and the arc current both decreases with the increase in the applied voltage and the decrease in the flow rate. Power consumption of this APJ increases with the applied voltage and remains nearly constant with the change of the flow rate. At a given duty cycle, the power frequency has little effects on the electrical characteristics. Thermal analysis of jet downstream showed that the jet temperature decreases with the decrease in the applied voltage and the increase in the flow rate. Optical measurements reveal that the downstream excited state species were controlled by both their initial density in the discharge region and their decay upon formation. High applied voltage results in a high initial density of excited state species while high flow rate gives a smaller decay of excited state species in the axial direction. As a result, the increase of the applied voltage and the flow rate gives a higher downstream excited state species density. The diffusion of the ambient air into the jet downstream causes both a more rapid decay of active species and the formation of NO through the quench by and the reaction with oxygen, respectively. N2, N2+ and NO light emission system were observed in downstream optical emission spectra. At a given duty cycle, the power frequency has only a little effect on the downstream characteristics. Experiment results show that the plasma reactivity increases with the increase in the applied voltage and the flow rate, while jet temperature decreases with the decrease in the applied voltage and the increase in the flow rate. These trends allows for a nearly independent control of the reactive species densities and the temperature by carefully modulating the operating conditions. This allows for the APJ to be operated with a large process window in a controllable manner.