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.