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Re: Skin Effect & Primary Current?


>From: "Fred W. Bach, TRIUMF Operations" <music-at-triumf.ca>
>To: tesla-at-pupman-dot-com
>Cc: music-at-triumf.ca
>Subject: Re: Skin Effect & Primary Current?

>   Carbon doesn't cool off so fast so it can stay off for quite a
>   while.  There is some carbon in the arc vapour path. 
My understanding is: it's a refectory material, low conductivity. Does
that also imply a low emissivity? 
> Copper cools
>   faster so it can't stay off so long.  I believe there is less
>   copper vapour in the arc path than with carbon. 
Easier to ionize implying a lower molar concentration for a given
current?

> But mercury is a
>   different story, having a comparatively high vapour pressure.  I
>   don't know about the mercury *extinguishing* times, (being a heavy
>   gas I expect it's very small)
I'm outside my pratical/theoryitical experience here. I'm can argue it
both ways: mercury is heavy => it can't get out of the arc path very
fast which says that is should have a long extinguish time, or it's
very heavy, can't get out of the arc fast and therefor recombines
rapidly. More information searching;)

> but the actual time it takes to
>   strike an arc in mercury vapour is incredibly small, less than a
>   nanosecond.  Mercury wetted relays are used in line-discharge
>   pulser circuits for nanosecond pulses.  The "make" part of the
>   cycle is extremely fast.
I always guessed that mercury wetted relays were used to reduce the
bounce time. As the contacts bounced apart,upon closure, the liquid
mercury formed a thread between them, keeping them 'closed'.

>  We used these on our old Van de Graaff to
>   pulse electrons into the cathode at the top of the accelerator
>   tube. 

I'd would have liked to see the throw on that relay! How many leagues
did you say it was?;)

> I wonder if this is what von Engel was speaking of, the
>   speed of arc striking.
He was speaking of re-strike time, i.e., the off time that would not
quench the 'plasma channel'. But then, he could have been confusing
the two.
>
>>

>    Somebody ought to investigate the possibly advantageous properties
>    of mercury for fast switching.  We know it turns on fast.  I wonder
>    if it turns off as fast.
>
>
I'm having visions of an open-air, rotary paddle-wheel, mercury gap
here;)   

On the other hand, a cold-cathode fluorescent light is just what we
are talking about. Anyone out there care to steal the backlight out of
their LCD portable computer for some gap testing?

	Regards,

	jim