Re: Skin Effect & Primary Current?

>Message-ID: <199607280225.UAA21672-at-poodle.pupman-dot-com>
>Date: Sat, 27 Jul 1996 20:25:02 -0600
>To: Tesla-list-subscribers-at-poodle.pupman-dot-com
>Subject: Re: Skin Effect & Primary Current?
>From jim.fosse-at-bdt-dot-comSat Jul 27 20:12:49 1996
>Date: Sat, 27 Jul 1996 08:27:08 GMT
>From: Jim Fosse <jim.fosse-at-bdt-dot-com>
>To: tesla-at-pupman-dot-com
>Subject: Re: Skin Effect & Primary Current?

  [ big snip ]

>	" The cathode substances also fall into two groups when the
>restriking time is investigated: a circuit containing a carbon arc can
>be interrupted for up to about 1 sec at applied voltages of several
>hundred V and will restrike without change of the electrode
>separation, while a Cu arc when interrupted for 10^-3 sec or less will
>not restrike. Hg arcs at low pressure have restriking times of less
>than 10^-8 sec."
>WHAT? Mercury at 10nS. !!!! ?????  Why are Mercury Thyratrons So Slow?
>If low pressure mercury arcs quench in 10nS. why use blown Cu/N2
>gaps;) I think von Engel is off here (pun intended)

   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.  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.  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) 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.  We used these on our old Van de Graaff to
   pulse electrons into the cathode at the top of the accelerator
   tube.  I wonder if this is what von Engel was speaking of, the
   speed of arc striking.

>Although, if the 10^-3 sec number is correct for Cu, maybe we should
>consider a different electrode material? (or at least determine if we
>are close to the arc region of operation instead of just the glow
>discharge region).
>	as always; thoughts, comments, snide remarks?
>	jim

    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.

 Fred W. Bach ,    Operations Group        | Internet: music-at-triumf.ca
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