{'fraction_non_alphanumeric': 0.021164021164021163, 'fraction_numerical': 0.0, 'mean_word_length': 6.211864406779661, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Prebreakdown negative streamers in liquid nitrogen: propagation characteristics and their influence on microsecond breakdown

Further clarification of streamer-induced breakdowns in liquid nitrogen has been attracting increasing attention owing to their potential applications in superconducting systems and cryoplasmas. In this work, negative streamers in microsecond discharges were investigated using a high-speed multiple-frame imaging technique. Different external voltages, gap lengths, hydrostatic pressures, and pin tips were employed to initiate various streamers, namely bush-like streamers, single pinecone-like streamers, dendritic streamers, and filamentary streamers. Furthermore, abundant hybrid streamers involving streamer transition and combination were observed. The diversity of negative streamers may be related to the pin morphology. Generally, it was found that thinner streamers, especially filamentary streamers, could take place more frequently with higher breakdown probability under stronger filed and lower pressure. However, bush-like streamers gradually played a more dominant role upon increasing the pressure, and they were unable to cause breakdown. Moreover, several intermittent weak discharges were recorded during the growth of streamers, which might be responsible for the streamer transition and propagation. Additionally, given the evolution of streamers branches after breakdown and the influence of pressure on streamers characteristics, it was speculated that high-pressure gas could be involved inside the streamers. The possible mechanism of streamer propagation and resultant breakdown were further explored based on the analysis of streamer protrusions.