Re: Corrected di-el strength of gas

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Bert Hickman <bert.hickman-at-aquila-dot-net> 

Hi John,

Thanks for the table. However, there's apparently more to quenching than 
can be gleaned by comparing relative dielectric strengths. Although 
dielectric strength will provide an indication of the voltage standoff, 
this parameter does not indicate how quickly a previously conducting spark 
gap will recover its dielectric strength (i.e., how well it will quench).

For example, although hydrogen has only about half the dielectric strength 
of nitrogen, it recovers more quickly from a plasma state to a 
non-conductive state, giving it superior quenching ability. Hydrogen's 
small molecules have a higher molecular speed so that heat can be removed 
more quickly from a recovering gap. Hydrogen was used for high performance 
multiple-gap switches for spark radio, and it's sometimes even used today 
for special high-power high reprate spark gaps. Hydrogen and deuterium are 
also the fastest "fill" gases available for high speed thyratron switches, 
the low pressure evolutionary cousins of spark gaps.

Best regards,

-- Bert --
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Tesla list wrote:
>Original poster: "john cooper" <tesla-at-tesla-coil-dot-com>
>I posted an error for the di-electric strength of air in a previous 
>response, the 0.4-0.7 for air was kV/mm.  Here's a new partial listing for 
>some gasses (FWIW gases and gasses are both proper)
>Air, 0.97
>Argon, 0.18
>Carbon Dioxide, 0.82 - 0.88
>Carbon Monoxide, 1.02 - 1.05
>Chlorine, 1.55
>Helium, 0.15
>*Hexafluoroethane, 1.82 - 2.55
>Hydrogen, 0.50
>Methane, 1.00 - 1.13
>Nitrogen, 1.00
>Neon, 0.16 - 0.25
>Nitrous Oxide, 1.24
>*Octafluoropropane, 2.19 - 2.47
>*Sulfur Hexafluoride, 2.50 - 2.63
>Tetrachloromethane, 6.21 - 6.33
>*used in industry and research as di-electrics
>The di-el strength of a gas is measured as a comparison to Nitrogen - 1.0
>It was surprising for me to realize that air, which doesn't provide much 
>quenching, is rated at 0.97; while Nitrogen, which quenches quite well, is 
>rated at 1.00  Not much of a difference in rating for a huge difference in 
>quenching ability.
>Neon & Helium could be an interesting alternatives to Argon for inducing 
>long streamer length although neon is more expensive than helium.
>Someone asked about CO2, they'd be better off with compressed air.
>
>
>
>.