Abstract
Positive breakdown streamers have been investigated in a short (5 mm) point-plane gap in cyclohexane and n-tridecane with and without the additives N,N-dimethylamine (DMA) with low ionization potential and azobenzene with a not quite as low ionization potential but a very low lowest excitation level. The effects off additives are fairly similar to what is known from longer gaps with DMA or pyrene added: the additives caused reduced breakdown voltage, significantly increased acceleration voltage and increased streamer velocity around breakdown. Molecule for molecule, azobenzene has less effect than DMA. The ratio between the acceleration and the breakdown voltage is significantly higher than in long gaps, though. Nonetheless, tests in short gaps are sufficiently good for screening (a large number of) liquid combinations.The two base liquids without additives, and also neat trichloroethene and DMA have been tested with and without a tube causing spatial restriction of the streamer. Restriction causes increased breakdown voltage and promotes the fastest streamer modes.
Highlights
Positive breakdown streamers have been investigated in a short (5 mm) point-plane gap in cyclohexane and n-tridecane with and without the additives N,N-dimethylamine (DMA) with low ionization potential and azobenzene with a not quite as low ionization potential but a very low lowest excitation level
It is usually non-breakdown streamers that are studied in small gaps, and nonbreakdown streamers are usually of the slow type (20 m/s up to a few hundred meters per second) often designated 1st mode streamers or a somewhat faster type (1-3 km/s) designated 2nd mode [4]
It has been observed that a high degree of branching of 2nd mode streamers increases Va [1,5,6,7], and so far it seems that a small concentration of constituents or additives with significantly lower ionisation potential than the bulk of the liquid leads to increased branching [1,3,5,6,7].The liquid dependent branching tendency of typically nonbreakdown streamers can be studied in small gaps [1,3]
Summary
Positive breakdown streamers have been investigated in a short (5 mm) point-plane gap in cyclohexane and n-tridecane with and without the additives N,N-dimethylamine (DMA) with low ionization potential and azobenzene with a not quite as low ionization potential but a very low lowest excitation level. For some liquids the effect of spatially restricting the streamers with a tube (limiting how much branching is possible) has been studied.
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