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Multi-layered Secondary




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From:  Jim Lux [SMTP:jimlux-at-earthlink-dot-net]
Sent:  Wednesday, March 25, 1998 10:38 AM
To:  Tesla List
Subject:  Re: Multi-layered Secondary


> 
> ----------
> From:  Alfred C. Erpel (Home) [SMTP:aerpel-at-pil-dot-net]
> Sent:  Tuesday, March 24, 1998 6:14 PM
> To:  Tesla List
> Subject:  RE: Multi-layered Secondary
> 
> 
> > From:  Jim Lux [SMTP:jimlux-at-earthlink-dot-net]
> > Sent:  Monday, March 23, 1998 10:32 AM
> > To:  Tesla List
> > Subject:  Re: Multi-layered Secondary
> 
> > The "resonance transformer" 1+ MeV x-ray sources developed at GE by
> > Charlton in the 30's used just such a coil. A series of 125 air core
> > pancake windings were connected in series and resonanted at 180 Hz. The
> 180
> > Hz was generated by a clever saturating transformer running from the 3
> > phase 60 Hz supply. The spacing of the pancakes was not uniform, by the
> > way. The total L was calculated at around 15,000 H and the C was 50 pF.
> The
> > system developed 55 mA peak secondary current at 1000 kVp (i.e. 55 kW).
> The
> > losses in the system ranged from around 1 kW at 1 MV output to about 4
kW
> > at 2 MV (i.e. as the square of the voltage/current). The load current
was
> 3
> > mA.
> 
> 	I've wondered about winding a huge coil (stacked series pancakes) which
is
> resonant at 60 Hz. No more spark gap.
There is a scheme for doing this that was developed for HV testing of power
equipment. It basically uses an auto transformer and a large HV inductor
that is resonated at 60 Hz. The typical Q would be around 50, so the
resonant rise is substantial. The advantage is that the stored energy is
lower, so once the test object breaks down, the voltage drops rapidly (sort
of like a current limited NST).  The practical problem is making the
inductor: e.g. insulating it for the MV or so. An iron core would make it
easier to make, although you'd have to look at the trade off between
weight/cost of iron and weight/cost of copper.  Also the resonating
capacitor has to hold off the full voltage. Typically they use a
pressurized gas capacitor.

>   	This would be truly dangerous, 1 zap and you probably wouldn't get a
> second chance.
I suspect that the 180 Hz system is basically in the same category. The
stored energy in 15 kH at 55 mA is about 20 Joules. Potentially lethal, but
probably not (it's about what is stored in the on camera flash unit in one
of those disposable cameras, which darkroom operators get zapped by all the
time). 

Of course, the average power is fairly high: 20 Joules * 180 = approx 4 kW,
which at 1 MV will certainly do you in..

> 
> > The system was in a steel tank with Freon 12 at 60 psig for insulation.
> The
> > entire system (a portable Xray generator) was 3 ft in diameter, 4 ft
high
> > and weighed about 1500 lb. A 20 cfm blower circulated the gas when
running
> > at 1.25 MV.
> 
> 	Funny what was once considered portable (1500 lbs.)  I know of a
portable
> x-ray unit that weighs 35 lbs. including the suitcase it is carried in. 
The
> x-ray head itself, with handle, removes from the suitcase, while the
power
> remains in the suitcase attached to the head via cable. Head weighs about
14
> lbs.
Yes, but does it generate 1 MeV x-rays? My vet has a portable x-ray
machine, but it works at 100 kV or so. You could get 1 MeV x-rays with less
weight with some sort of accelerator, I suppose.  The 1500 lbs included the
vacuum pumps for the beam tube, etc. Actually, I'm sort of impressed that
it was that light. The steel tank alone must have weighed a bit, even
though the pressure wasn't all that high.