Guest Editorial: Understanding low temperature plasmas for device reliability, modulation and application to green energy strategy

Low temperature plasma stands at the forefront of green and clean energy technologies, showcasing remarkable versatility across a wide array of applications including material processing, water splitting, methane conversion, and plasma medicine. To fully harness the potential of this technology, it is imperative to deepen our understanding of the physics underlying various discharge structures.

This issue casts a spotlight on the recent strides in the field of low-temperature plasmas. We focus on key areas such as multipactor discharge, dielectric barrier discharge (DBD), plasma jet, leader, and spark. These topics are pivotal in demonstrating how low-temperature plasma technology can be leveraged in terms of device reliability, modulation and practical applications within the green energy sector.

In this collection, we have curated six papers that reflect the cutting-edge developments in this area, comprising three review articles and three original research papers. Each paper offers unique insights and contributes significantly to our understanding of low-temperature plasmas. The brief introductions to these papers, provided herein, encapsulate the essence of their research and findings.

In this comprehensive review, Peng Zhang et al. from the Michigan State University explore recent advances in multipactor discharge for both single and dual-surface geometries. The paper provides an overview of critical concepts like secondary electron emission and electron kinetics, alongside multipactor susceptibility and saturation mechanisms. It also highlights contemporary strategies for multipactor mitigation in device engineering, including modern surface coating techniques, surface conditioning, and geometric modifications. The review further covers recent developments in multipactor physics and engineering, such as novel prediction methods and the understanding of space charge effects. Finally, it discusses the potential applications of multipactor in fields such as high power microwave switches and surface cleaning.

Guangliang Chen and colleagues present a green approach to engineering high-performance electrocatalysts for water splitting through the use of low-temperature plasma. This technology, rich in reactive species, offers a unique environment for refining the physicochemical structures of catalysts via plasma milling, etching, doping and deposition. The review comprehensively summarises recent advancements in transition metal-based electrocatalysts, focusing on the enhancements made possible by DBD and radio frequency plasma technologies. These advancements not only improve plasma controllability but also pave the way for the development of cost-effective and efficient equipment. This, in turn, streamlines the plasma technology manufacturing process, allowing for precise material synthesis and modification.

Authored by Xinpei Lu and colleagues at Huazhong University of Science and Technology, this review offers a detailed chronological analysis of homogeneous DBD. It examines the effects of various parameters on DBD, its development, and the fundamental mechanisms operating in different gases. This comprehensive understanding is crucial for designing innovative experiments, enhancing our grasp of homogeneous DBD generation mechanisms. Such insights are instrumental in facilitating the creation of large-volume homogeneous DBD in air environments, a cost-effective and environmentally sustainable approach with significant applications in material processing and surface treatment.

In this insightful paper, Xuzhu Dong and the team from Wuhan University delve into the complex physical mechanisms of leader formation in plasma discharges. They aim to scrutinise the varying characteristics of discharge during both the initiation and progression of the leader under different voltage rise rates. This investigation uniquely combines theoretical plasma discharge models with empirical data gathered from a 10-m outdoor discharge experiment. This experiment, focusing on leader discharge, captures essential parameters like current, voltage and optical imagery. These measurements, particularly the current, are then integrated into the plasma model to analyse the evolution of key factors such as streamer stem temperature, conductivity and thermodynamic parameters within the leader channel.

In the realm of low temperature plasma applications, atmospheric pressure planar plumes hold significant value, particularly for the rapid modification of large-scale surfaces. Traditionally, plasma jets have been limited to producing single-mode planar plumes, characterised either by a streamer or a filamentary mode. Addressing this limitation, Xuechen Li from the Hebei University introduces an innovative plasma source in Paper 5. This novel source is capable of generating a double-mode planar argon plume. The paper focuses on a comparative analysis of the discharge characteristics, plasma parameters, and modifications induced by this double-mode planar plume, utilising a range of measurement techniques including electrical, optical and spectroscopic methods.

The dynamic nature of spark discharge plasmas, characterised by high-energy deposition and rich chemical activity, has garnered considerable interest. However, a challenge arises due to its tendency for unstable transitions at high frequencies or during extended pulse durations, which are less favourable for industrial applications. Addressing this issue, Yun Wu and colleagues from the Airforce Engineering University present a novel approach in this paper. They propose an intelligent and energy-efficient method to establish a highly repeatable and stable spark plasma source. This is achieved by automatically adjusting the voltage amplitude in response to the discharge frequency in a high-frequency pulse train, tailored to the fluid response time scale. Additionally, the paper explores the impact of various modes of electron number density increase and the modulation of voltage profiles on the system's energy efficiency.