Re: Skin Effect & Primary Current?
>From: "Fred W. Bach, TRIUMF Operations" <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
> 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
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
> 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
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?