In plasma spraying, instabilities and fluctuations of the plasma jet have a significant influence on the particle in-flight temperatures and velocities, thus affecting the coating properties. This work introduces a new method to analyze the stability of plasma jets using high-speed videography. An approach is presented, which digitally examines the images to determine the size of the plasma jet core. By correlating this jet size with the acquisition time, a time-dependent signal of the plasma jet size is generated. In order to evaluate the stability of the plasma jet, this signal is analyzed by calculating its coefficient of variation c_v. The method is validated by measuring the known difference in stability between a single-cathode and a cascaded multi-cathode plasma generator. For this purpose, a design of experiment, covering a variety of parameters, is conducted. To identify the cause of the plasma jet fluctuations, the frequency spectra are obtained and subsequently interpreted by means of the fast Fourier transformation. To quantify the significance of the fluctuations on the particle in-flight properties, a new single numerical parameter is introduced. This parameter is based on the fraction of the time-dependent signal of the plasma jet in the relevant frequency range.

在等离子喷涂中，等离子射流的不稳定性和波动对飞行中的颗粒温度和速度有重大影响，从而影响涂层性能。这项工作介绍了一种使用高速摄影技术分析等离子流稳定性的新方法。提出了一种方法，该方法以数字方式检查图像以确定等离子流芯的尺寸。通过将该射流尺寸与采集时间相关联，产生了等离子体射流尺寸的时间相关信号。为了评估等离子体射流的稳定性，通过计算其变化系数c _v来分析该信号。通过测量已知的单阴极和级联多阴极等离子体发生器之间的稳定性差异来验证该方法。为此目的，进行了涵盖各种参数的实验设计。为了确定等离子体射流波动的原因，获得了频谱并随后通过快速傅里叶变换对其进行了解释。为了量化波动对粒子飞行特性的影响，引入了新的单个数值参数。该参数基于在相关频率范围内等离子流的时间相关信号的分数。