Re: triggered spark gap in a vacuum?

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

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-uswest-dot-net>" <jimlux-at-earthlink-dot-net>



Tesla list wrote:
> 
> Original poster: "sundog by way of Terry Fritz <twftesla-at-uswest-dot-net>"
<sundog-at-timeship-dot-net>
> 
>  Hi all!
> 
>  I have a question about a triggered sparkgap in a vacuum, similar to the
> thread on the home-made vacuum gaps.
> 
>  It would basically be the same as Brian and Ross's trigatron, only with
> hookups to pull a vacuum on it, and the vent/backfill.  (so a hydrogen gap
> can be tested better).

You'll need to pull a pretty good vacuum on it to make it work very well.
Do you have access to a library with old IEEE journals?  I can give you
some review references on vacuum spark gaps that you'll find useful for
design. 

> 
>    The question I have is concerning radiation generation.  I only intend to
> run up to 30kv DC on this, but as I understand it (limited knowledge, I'm a
> computer geek, not a physicist), that's plenty enough voltage to generate
> Xrays.  The electrodes will probably end up being tungsten carbide, with a
> lot of aluminum and brass hardware.


You've got it... Vacuum + HV = Xrays... no two ways about it.  Doesn't
really matter what the materials are.


> 
>   I don't like the idea of irraidating myself, nor having to explain to the
> others in my house exactly *why* a spark gap has to be wrapped in lead
> blankets :/  The idea of growing any more toes isn't too hot either ;)  I'm
> not paranoid about getting a dose of xrays, but want to be informed as to
> what I'm tinkering with.

Your Xrays will be "soft" at only 30 keV, which means that you don't need
much shielding (the case of the spark gap will probably be enough). BTW,
You don't have to worry about more toes.. it would be your offspring that
would show up with the genetic defects, and as a male, all of your damaged
genetic material gets flushed away after a few months (why they are much
more paranoid about women and radiation than men: Women have all their
potential offspring's genetic material from birth, so all those eggs get a
cumulative rad dose).  Others are far more knowledgeable than I about
radiation safety, and I'd encourage you to find some and talk about it.
There are a lot of bad things that can happen, even with soft xrays, if the
dose is high enough.

Practically speaking, I wouldn't worry too much, but, if you are going to
fool with HV and vacuum, you DO need to get a handle on it, so that you can
make an informed decision about safety.

> 
>   What are the pressures required in general for xray production, the
> voltages and materials commonly involved?  I want to work with this, but I
> don't want to put myself in any more danger (than the HV supplies, caps,
> police, etc.)  The gap isn't designed yet, so there won't be any "Oops,
> guess I'd better change that" involved.  I want to be fully informed what
> I'm getting into with the thing.

As for pressure: when the mean free path starts to get as long than the
distance between electrodes, you start to get the possibility of an
electron hitting the anode at full speed, which is what causes the xrays.
Remember that it is MEAN free path, so you get some radiation at higher
pressures.  At STP, though, the MFP is so short that the odds of an
electron actually making it all the way to the anode is very small.

If you think about it, a color TV accelerates electrons through a 25-30 kV
potential with a VERY good vacuum, so there is great potential for
radiation hazard.  This is why the glass on the CRT faceplate is loaded
with lead (several pounds of it: enough that it is economically worthwhile
to reclaim it for the value of the lead). The much publicized xray from TV
hazard was mostly from the HV rectifier tubes, though, and leaded glass
envelopes pretty much solved it (as well as solid state rectifiers...).
> 
>
Thanks!               Shad