Re: [TCML] Large Plsma Tube

["Tim Meehan" <btmeehan@xxxxxxxxx>]

Where do you guys get the big globes from?  (or even medium or small sized
globes)  Do you have to have a glass-blowing setup in order to really play
with these things or do you just order pyrex chemistry glassware?

On Dec 1, 2007 7:35 AM, Bill Lemieux <gomezaddams@xxxxxxxxx> wrote:

> PS: I forgot to mention the end-seals.  Because the ends will probably
> have to be flat, you should consider using 1/2" thick plate to span a
> 6" distance.  This is a bit on the overkill side for 15PSI of
> pressure, but better safe than sorry!  Make sure you don't introduce
> any small cracks when you drill the plates for your electrodes, and
> polish all edges to eliminate sharp edges or pits from drilling or
> cutting.  Use fine emery paper for this.
>
> Forget about using plastics for your end plates, it won't last.  Among
> other things, atmospheric helium and hydrogen will leak in (through
> the material) over the passing years... possibly changing the
> appearance of your discharge significantly. You're going to have
> problems with that using epoxy seals anyway, but if the exposed area
> of the epoxy seal is tiny and the thickness great (ie; .25") they
> ought to be good for many years.
> The higher pressure you can operate at, (approaching atmospheric) the
> slower this leak problem will be.
>
> This is why old epoxy-sealed HeNe lasers died after about ten years -
> the helium would diffuse out through the seals.  Amazingly, because
> there was still a low pressure inside the tube, you could rejuvenate
> those old tubes by sticking them in a bag of cheap balloon helium, and
> operating the tube - you'd check it every few days and eventually it
> would be working as good as new.  Take it out of the bag, and it would
> once again be good for years.  Of course, with modern diode lasers and
> even cheap hard-seall HeN lasers being so plentiful, that isn't worth
> the effort.  Epoxy-sealed HeNe lasers are worthless now.
>
>  - "Gomez"
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