金属铌表面Ar/O2等离子体在线清洗的实验研究

Experimental study on on-line cleaning of Ar/O2 plasma on metal niobium surface

摘要:

超导铌腔的碳氢污染问题导致铌表面的功函数下降, 引起场致发射, 使超导腔的加速梯度恶化, 运行一段时间后必须对其碳氢污染进行清洗才能保证正常使用. 针对众多清洗装置用等离子体清洗后无法对其清洗效果进行准确、及时地判断从而控制清洗截止点, 而采用离线测试又会造成一定的二次污染的问题,本文提出了基于静电四极等离子体(Electrostatic Quadrupole Plasma, EQP)质谱分析仪及开尔文探针的等离子体清洗及在线监测装置, 成功地将等离子体清洗与残余气体监测集成并投入使用. 实验过程中, 通过在线监测清洗的副产物及功函数的变化, 证明了电感耦合等离子体源产生的密度为1016~1017 m-3的氩、氧混合等离子体, 能有效清除铌样品表面的碳氢污染, 并对铌表面进行一定的氧化改性, 将功函数由4.0 eV提升至5.3 eV左右.

Abstract:

Hydrocarbon contamination in superconducting niobium cavity results in the decrease of surface work function of niobium, field emission and the deterioration of accelerating gradient of superconducting cavity. After working for a period of time, it is necessary to clean the hydrocarbon contamination to ensure its normal running. At present, the cleaning effect after plasma processing cannot be judged accurately and timely to control the cleaning cut-off point. In addition, the off-line testing may cause some secondary pollution.Therefore, we present a plasma cleaning and on-line monitoring device based on electrostatic quadrupole plasma (EQP) mass spectrometer and Kelvin probe. The plasma cleaning and residual gas monitoring were successfully integrated and put into use. During the experiment, the changes of cleaning byproducts and work function were monitored online. It was proved that the Ar/O2 mixed plasma produced by the inductively coupled plasma source with a plasma density of 1016~1017m-3 could effectively remove hydrocarbon contaminations from niobium surface and make oxidation modification on niobium surface, raising the work function from 4.0 eV to 5.3 eV.