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Re: 130kW Coil Update [helium gap]
From: Jim Lux[SMTP:jimlux-at-earthlink-dot-net]
Sent: Thursday, December 11, 1997 3:19 PM
To: Tesla List
Subject: Re: 130kW Coil Update [helium gap]
Tesla List wrote:
>
> From: Greg Leyh[SMTP:lod-at-pacbell-dot-net]
> Alas, the gap is of the open frame type, far from airtight.
> As I understand it, helium actually has a lower heat capacity,
> since monatomic elements only have 5 degrees of freedom,
> where diatomic ones have 7, allowing them to carry more heat
> energy per deg C. That's why He compressors run so hot.
>
> At STP, I believe that helium gas has a much lower breakdown
> voltage than dry N2. But is this good or bad?
>
> -GL
Of course, you could always use hydrogen, which is diatomic. However,
He, while having a low specific heat, aggravated by its low density, so
you don't get many kilos in a given volume, does have a really high heat
conductivity (related to the high speed of sound in He). This is a
significant concern to deep sat divers who have to live in a He rich
environment (at several atmospheres, I grant you).
As to the breakdown voltage issue, it probably doesn't make any
difference. However, running in air, which has oxygen, does help,
particularly with copper electrodes. The copper oxide film that forms
tends to reduce the jitter of the discharge because it readily emits
electrons to get the discharge going. It also doesn't erode as fast. I
seem to recall some data where they ran rotary gaps in various gases,
and the oxygen free environments had erosion rates 5-10 times that of
oxygen containing (or any electronegative species, e.g. F or Cl, from
Freon, or SF6) (and you think you have a windage problem with air, just
try SF6)