Re: Micro SSTC + light bulb = plasma globe. Safe( xrays ) ?

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

Original poster: "Jim Lux" <jimlux-at-earthlink-dot-net> 

At 11:57 AM 7/28/2004 -0600, you wrote:
>Original poster: Mddeming-at-aol-dot-com
>In a message dated 7/28/04 9:13:52 AM Eastern Daylight Time, 
>tesla-at-pupman-dot-com writes:
>Thanks. Btw, can someone explain why the plasma is more intense in a
>vacuum with HF HVAC than in free air(it is a better conductor)?
>
>---Eric
>
>Hi Eric,
>     Vacuum is a very poor conductor. There is no plasma in a vacuum by 
> definition.

Welll... there's vacuum, and there's vacuum.  For instance, as far as radio 
propagation goes, the ionosphere is a pretty good conductor, but it would 
also qualify as a pretty decent vacuum
http://wwwppd.nrl.navy.mil/nrlformulary/typical_plasma_parameters.pdf has data
http://wwwppd.nrl.navy.mil/nrlformulary/p41nrl.pdf has a nice figure

number density (n/cm3) is the usual thing they use to describe it (as 
opposed to pressure in torr) but.. take a look.. number densities of 10^6 
or 10^7 are glow discharges (say in a neon bulb) and that's a great conductor
Ionosphere is down around 10^5 number density(/cm^3)

Number density at STP is about 3E19.. so, number densities of 1E5 are a 
pressure of  1E-14 atmosphere.. call it 1E-11 torr, which is a pretty darn 
good vacuum.  (In thermal vacuum testing of spacecraft, we don't get 
anywhere near that...)

>  Plasma globes only work because they are low pressure, not good vacuum. 
> Tesla claimed that conduction through air was best at ~ 150 mmHg. 
> Standard light bulbs work as mini plasma globes because they are 
> backfilled to low pressure with a gas (usually N2 or Ar) to reduce the 
> rate of evaporation of the filament.
>