[sdiy] OT: Today's toxic mess

[Terry Michaels]

Message text written by "danial stocks"
>...so the anode spins to 
take the heat away from being just dumped in one area, which would most 
likely melt it even tho it is made of tungsten.. I have a rotary anode one 
and you can see a ring etched around the anode where the electrons strike..
Cheers,
Dan<

Hi Dan:

Your're right.  There is so much energy in the elecron beam of a high power
X ray tube, it will burn right through the tungsten disk in seconds if the
disk were to stop rotating.    The tungsten rotor is spun at high speed by
a rotating magnetic field supplied by a ring of electromagnets placed
around one end of the tube, since you can't make a rotary joint to the
outside that is absolutely vacuum tight. 

 Like any high vacuum tube, all internal parts of the tube must be
spotlessly clean and free of grease, oil, fingerprints, etc. to prevent
outgassing, which will contaminate the vacuum over time.  Here is an
interesting design question:  How do you make bearings that have are not
oiled or greased, but will support the tungsten disk which spins at very
high speeds in a total vacuum, at high temperatures,  inside a glass
envelope where you can't get at it to replace it if it goes bad, and work
reliably for years?

Terry Michaels