Re: Effect of UV on topload

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

Original poster: "Paul Nicholson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <paul-at-abelian.demon.co.uk>

Jim wrote:
> UV is certainly going to knock some electrons off from
> photoelectric effect.  Off hand, though, I wouldn't think that
> the effect is very big for aluminum, etc

Steve Greenfield wrote:
> If it were enough to change Q by a meaningful amount I'd also
> expect it to make breakdown require less voltage, too.

Terry wrote: 
> But the sun would heat the coil "considerably" which may hide
> any solar effects. 

Mike wrote:
> If he doesn't,  I will let him make use of one of my mercury
> vapor UV lamps

Thanks for the various comments.

Well we know that UV lamps discharge electroscopes, and an EPROM
erases much quicker under a lamp than outside under the Sun, so 
I guess a lamp would have more chance of affecting a coil, and with
less heating effect.

The leakage current, if any, would be proportional to the flux of
photons with energy greater than some work function, rather than
the amount of energy in the coil, or to its topvolts.  So I suppose
it would affect the Q less at high power than low power.  It would
show up, perhaps, only as a slight linearisation of the tail end of
an otherwise exponential ringdown, as the constant current leakage
became a larger percentage of the total loss.

Looks like another experiment to add to the list then, unless anyone
can see a reason why it's not worth trying?  For a given UV lamp and
coil+topload, it should be possible to measure the total leakage
current by charging the resonator up with a few kV of DC and
timing the linear rampdown.  That would give enough info to
calculate the effect on Q.

And we're left with the corollary,

e) Does shining UV onto the topload lower the position of the variac
at which breakout starts?

I suppose no amount of photo-electrons will help if there's just not
enough surface field for avalanche multiplication.  But given a coil
that's already starting to break out, perhaps incident UV will 
increase the amount of streamers by providing more seeds for
avalanche.

And what's the effect of UV on the streamers themselves?  Can they
become more branched, or bushier?   Hmm, perhaps not, I suppose the
extra few photoelectrons would be negligible compared with the
torrent of free electrons already in the streamer.

Having seen an electroscope sit there for ages holding a charge, and
then rapidly discharge the moment a lamp was turned on, I can't help
thinking that it would be at least worth checking to see if UV
illumination has an effect on TCs.

Well, some food for thought, and some experiments to try for those
with a UV lamp, TC, flyback circuit + EHT tripler, and a stopwatch.
--
Paul Nicholson
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