标题： 正负直流辉光放电：用于表征水表面自组织图案的对比研究 显示英文标题

标题： Positive and negative DC glow discharges: a comparative study to characterize self-organized patterns on water surface

摘要： 等离子体放电中的自组织模式（SOP）源于电场、反应性粒子和带电粒子之间复杂的相互作用，这种相互作用由非线性等离子体动力学驱动。 尽管已有研究探索了不同配置下的SOP形成，但尚未对正负直流辉光放电进行系统的比较以解释为何SOP仅在极化为负时形成。 本研究旨在通过比较正负直流辉光放电与接地水表面相互作用时的电学、光学和光谱特性来分析SOP的形成机制。 因此，确定了气体温度、电场和反应性粒子分布的关键差异。 对于正直流辉光放电（PGD），气体温度保持在350-370K范围内，而整个间隙内的归一化电场始终低于100Td。 等离子体主要由OH和N2*物种主导，其激发来源于低场环境中的电子直接撞击和能量传递。 强电离和电场梯度的缺乏导致液体表面的空间均匀发射层，从而形成无自组织的圆形均匀等离子体（CUP）模式。 相比之下，当电流超过15mA时，仅在负直流辉光放电（NGD）下出现SOP。 这些放电呈现归一化电场，在阴极针1毫米处峰值为485Td，中央间隙下降至低于100Td，并在靠近水面处上升到460Td。 在那里，等离子体层仍含有OH和N2*物种，但也存在N2+离子，后者对SOP的形成至关重要。 SOP形态随间隙大小变化：在7mm时，图案从斑点过渡到细丝，图案直径和厚度分别高达5.5mm和210{\mu }m。 使用表面活性剂降低水表面张力会减小SOP尺寸并改变图案形态。 显示英文摘要

摘要： Self-organized patterns (SOP) in plasma discharges arise from the complex interplay of electric field, reactive species and charged particles, driven by non-linear plasma dynamics. While studies have explored SOP formation in various configurations, no systematic comparison of positive and negative DC glow discharges has been conducted to explain why SOP form exclusively when polarization is negative. This study aims to analyze SOP formation mechanisms by comparing electrical, optical and spectral properties of positive and negative DC glow discharges interacting with a grounded water surface. Key differences in gas temperature, electric field and reactive species distribution are hence identified. For positive DC glow discharges (PGD), the gas temperature remains in the 350-370 K range, while the reduced electric field remains below 100 Td across the gap. The plasma is dominated by OH and N2* species, whose excitation results from direct electron impact and energy transfer in a low-field environment. The absence of strong ionization and electric field gradients leads to a spatially homogeneous emission layer on the liquid surface, resulting in a circular uniform plasma (CUP) pattern without self-organization. In contrast, SOP emerge exclusively under negative DC glow discharges (NGD) at currents above 15 mA. These discharges present a reduced electric field, peaking at 485 Td at 1mm from the cathode pin, dropping below 100 Td in the central gap and rising to 460 Td near the water surface. There, the plasma layer still contains OH and N2* species but also N2+ ions, the latter being critical for SOP formation. SOP morphology evolves with gap size: at 7 mm, patterns transition from specks to filaments, with pattern diameter and thickness as high as 5.5 mm and 210 {\mu}m respectively. Lowering water surface tension with surfactants reduces SOP size and modifies pattern morphology.