Investigations on pulsed, dielectric barrier discharges in multi-filament arrangements

介质阻挡放电(DBD)是产生常压非热等离子体的一种常见方法，例如用于化学处理。分子气体混合物(如氮氧混合物)中的DBD是丝状的，即它们形成单独的瞬时放电通道。各种研究表明，脉冲操作比传统的正弦驱动操作更有效地产生反应物种。申请人对单丝排列的脉冲驱动DBD的初步调查表明，击穿和放电发展可以直接由高压脉冲宽度(预电离)控制。特别是，首次报道了迄今为止未知的新的DBD击穿机制。考虑到等离子体-化学反应是由单丝内的物理过程触发的，因此有可能以一种方式影响等离子体参数，以启动更选择性和更有效的等离子体化学过程。在实际使用的DBD装置中，会出现许多细丝，但对于单丝的结果是否可以转移到多丝排列尚不清楚。因此，悬而未决的问题不仅涉及间隙中的电击穿，而且还涉及多丝排列中体积和表面过程的相互影响。本项目的目标是解决和解决这些问题。因此，将进行从单丝排列到多丝排列的逐步过渡。为此，将利用我们在DBD配置设计方面的专业知识，开发新的、特殊的、空间固定的和自由的多丝布置。将对常压下氮气-氧气混合气体中单丝在多丝排列中的行为进行系统的研究。通过对单丝和多丝操作的比较，可以说明是否存在控制DBD击穿和动态的一般机制。此外，还将研究单个放电通道在体积和介质表面上的相互作用。其目的是阐明单丝排列的体积预电离的主导效应是否也发生在多丝排列中。对于这些调查，将使用快速成像和光谱诊断，这是在申请人的初步工作中建立的，可在INP Greifswald获得。同时，时间分辨气体分析方法将被用于研究等离子体-化学过程的动力学。结合DBD的特性，将计算出放电物理和等离子体化学之间的关系。实验研究将伴随着等离子体模拟，包括对放电时空发展、等离子体参数和等离子体化学的模拟。

Dielectric barrier discharges (DBDs) are a common method to generate non-thermal atmospheric pressure plasmas, which are used e.g. for chemical processing. The DBDs in molecular gas mixtures, such as nitrogen oxygen mixtures, are filamentary, i.e. they form individual and transient discharge channels. It was shown in various studies that the generation of reactive species is more efficient for pulsed operation than for classical sine-driven operation. Preliminary investigations of the applicant concerning pulsed-driven DBDs in a single-filament arrangement have demonstrated that the breakdown and the discharge development can be directly controlled by the HV pulse width (pre-ionisation). In particular, new, up to now unknown DBD breakdown regimes were reported for the first time.Having in mind that the plasma-chemical reactions are triggered by the physical processes within single filaments, there is the possibility to influence the plasma parameters in a way to initiate more selective and effective plasma chemical processes. In DBD arrangements which are used in practice, many filaments occur, but it is not known if the results obtained for a single filament can be transferred to multi-filament arrangements. Therefore, open questions not only concern the electrical breakdown in the gap, but also the interacting impact of volume and surface processes in multi-filament arrangements. The goal of this project is to address and resolve these issues.Therefore, the stepwise transition from a single-filament to a multi-filament arrangement will be performed. For this purpose, novel and special, spatially fixed and free multi-filament arrangements will be developed using our expertise concerning the design of DBD configurations. There will be a systematic study on the behaviour of a single filament in multi-filament arrangements in N2-O2 gas mixtures at atmospheric pressure. The comparison of both single- and multi-filament operation will allow statements concerning the existence of general mechanisms to control the breakdown and the dynamics of DBDs. Furthermore, the interaction of single discharge channels in the volume and on the dielectric surface will be investigated. The aim is to clarify if the dominating effect of volume pre-ionisation for single-filament arrangements occurs also in multi-filament arrangements. For these investigations, fast imaging and spectroscopical diagnostics will be used, which were established during the applicant’s preliminary work and are available at the INP Greifswald. Simultaneously, temporally resolved gas analysis methods will be applied to study the dynamics of plasma-chemical processes. In combination with the DBD characterisation, a correlation of discharge physics and plasma chemistry will be worked out. The experimental investigations will be accompanied by plasma modelling, which includes the simulation of the spatio-temporal discharge development, plasma parameters and plasma chemistry.