[Nixie]

I have a 100 kV 30 mA X-ray tube, and I'd like some pointers as to building a switching supply (in the last few years they've become common in X-ray machines), as a 3 kW X-ray transformer is too expensive and heavy for shipping.

I'm using this with a digital camera photographing a scintillation screen for cone beam tomography (yep, it's pretty much a DIY CT scanner).

Thanks for any advice. And I'm very well aware of the dangers of X-rays and have dosimetry indicators, as well as the need for oil-filled enclosures of the HV stuff, etc., so no patronising remarks please.

 

[kevin gilmore]

As this is one of the things i nominally do for a living i have a lot of
experience in this area. At this point i'm not even sure that you know
what it is that you do not know.

1) 100kv at 30ma is 3000 watts of heat. The xray tube absolutely requires
lots of water cooling. 4 litres per minute at 20C. Even in short burst mode
it still requires cooling water as the anode gets very hot very fast.

2) Since the base of the xray tube absolutely has to be at ground this means
that the filament power (which is also significant) needs to sit at the
-100kv rail. Of all the problems building a supply this is the biggest problem.

3) The specialized cable and pogo stick that fits into the tube is also
a significant problem. The power supply end of the cable uses a connector
that is both expensive and hard to find.

The leaders in the field of these kinds of switchers are siemens, bertan and
spellman. Of all the supplies the spellman is the best by far and also the
smallest by far. Still it is 6 inches high, standard rack width wide and
3 feet deep. And weighs over 80lbs and is fully encased in silicone. The
siemens is more than double the size and 4 times the weight.

All these supplies are high frequency switchers, but are not all that
efficient. The siemens supply needs 220 vac single phase at 45 amperes.
The siemens supply is the only one that is oil filled, all the rest of
the supplies these days are silicone encased.

I do have a spare siemens supply laying around if you really want to
try and hurt yourself. Complete with cable and pogo stick. I don't
have any extra tube housings at the moment. You pay for shipping.
And sign a release waver.

The X-ray tube is the easy part. I gave a spare working one with an
interesting lineage to Ray Samuels. He may still have it.

Pictures of the insides of an X-ray supply can be supplied if you want
to really know what you are up against.

 

[the_villain]

Very interesting. Although I'm an engineer I have only faint idea about what you are talking about. So,please go on with the discussion. I wonder how it would turn out in the end. Very graceful from Mr. Gilmore. And please Nixie inform us what was the outcome.

 

[Nixie]

Hi Kevin, thanks for replying.

I've seen a self-contained 15 mA 70 kV X-ray source that plugs into a 115 V outlet and was ony cube only a foot on the side (the guy was gonna give it to me for $150, but I figured I'd like a bit more power). Considering I only need occasional short bursts, fraction of a second each. Shouldn't the very low duty cycle I need allow a smaller supply to be built?

I'm certainly interested in trying out other X-ray tubes. What are the current and voltage on the spare one you have? Does it make a decently focused image?

BTW, my first picture was by running a TV sweep tube cold cathode, with inverted polarity, on 80 kV at a couple of mA (NST+multiplier), and I still managed to expose film. Blurry image was the result, but still neat, so I just had to get a real source.

 

[Clutz]

I'm just a bit curious- what are you trying to build a DIY X-ray machine for (or more correctly, CT)?

Cheers,
Clutz

 

[kevin gilmore]

quote
I've seen a self-contained 15 mA 70 kV X-ray source that plugs into a 115 V outlet

That is still 1 kilowatt of power. Filament warmup time is still in the 30
second to 1 minute range. If this is a home built thing i would stay far
far away from it. The high voltage tank on the siemens units alone are
about 6 inches x 8 inches x 15 inches. Burst mode supplies like this are
completely uncontrollable.



Running a tube cold cathode you are lucky to get 10 microamps. the
difference between this and a real xray tube running at rated power
and current is probably more than 10 million to 1. I'm now relatively sure
you don't have even the slightest clue how dangerous these things are.

The tubes i use are up to 60kv at up to 50ma. They are fine focus tubes
that produce an xray beam strong enough to permanently fog your cornea
in less than 50 milliseconds. And give you a 3rd degree burn that likely
won't heal in 1 second.

I'll post the model numbers and a few pictures on monday. The power
supplies are huge for a reason. The high voltage cable is also rather
large in diameter due to the high voltages involved.

Here is a rather huge picture of our fearless leader holding one of these
tubes. This is a dual exit tube, one hole is fine focus, the other is line
focus. (moly, lambda=1.34 angstrom)

http://gilmore.chem.northwestern.edu/g9f20531.jpg

 

[jamont]

oh boy, irradiating donuts again...

 

[Nixie]

Quote:

Originally Posted by kevin gilmore If this is a home built thing i would stay far far away from it.

Of course.

Quote:

I'm now relatively sure you don't have even the slightest clue how dangerous these things are.

You've given me such warnings in another context (lower voltage, higher current, UV instead of X-rays), when I wasn't called Nixie. Yet, I'm still here.

The spare supply you have, what is the output, and size and weight? I may be better off spending on shipping than buying one locally.

jamont, your comment is disrespectful and you should apologize.

Clutz, for the same reason some people build tesla coils, or audio electronics.

 

[erix]

Quote:

Originally Posted by Nixie You've given me such warnings in another context (lower voltage, higher current, UV instead of X-rays), when I wasn't called Nixie. Yet, I'm still here.

Please have your next-of-kin post pictures of your remains.

ok,
erix

 

[Nixie]

Kevin, can you please post schematics if you have them of a switching supply?

 

[kevin gilmore]

here is the block diagram
http://gilmore.chem.northwestern.edu/sxray.jpg

Now which of the 72 pages do you want.

All the magic happens inside the main tank anyway and
there is no schematic for that.

 

[Nixie]

I'm just curious as to the general principle of operation of that 'magic'.

 

[peranders]

Moderators, is this thread appropiate? A person who don't know anything (or at least too little, despite the remark at the end of the first post) about 100 kV devices seeking advice?

Over at some other forum this thread would have have been removed right away....

BTW: I worked with X-ray many years back. Those tubes was fed with up to 140 kV, nothing to fool around with.

 

[Nixie]

Thanks for your concern, peranders, but discussing this here would only decrease the chance of me harming myself.

 

[skyskraper]

im with peranders and the others in having concern.

xray's are hardly something you just learn how to build on a forum. i reckon something like that if you want to know about it, then go to uni/college and do it properly. it's hardly like making a potato cannon, or building a stun gun from a disposable camera.