Um, ever heard of a Paschen curve? The breakdown electric field of a gas
goes down as the pressure falls from way above atmospheric, to a minimum in
the range of .1-50 torr depending on the gas, then rises again as the
pressure falls further. At high pressure the mean free path of an electron
isn't enough to let the energy rise to the ionization potential before a
collision slows it back down so ionization is very inefficient and breakdown
field is high, and at very low pressures the gas density is low enough the
electrons make it all the way from cathode to anode without a collision with
a gas molecule so even though they have plenty of energy to ionize something
there just isn't anything to ionize so the breakdown field goes back up. In
that fun in-between region you get pretty glow discharges and all kinds of
other phenomena.
The main question the OP never answered is "what pressure are you trying to
achieve"? That will dictate the materials needed and the physical layout
needed for his voltage.
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Regards,
Carl Ijames
"WoolyBully" wrote in message
you're probably ok. Otherwise,
use the expensive glass-metal feedthrus. Be careful of partial
vacuums, it doesn't take much voltage to flash over at a partial
vacuum.
Total bullshit.
As pressure goes down, dielectric resistance goes up because the air
molecules are farther apart. So, it takes more voltage in a reduced
pressure chamber than it does at atmospheric pressures. It MAY be far
less than the first arc in a full vacuum takes, but it will still be
higher than in normal air.
The volts per mil to acquire an arc in a air lattice is 100% dependent
on pressure. That is what determines atom spacing in ANY gas.
A partial vacuum has air in the chamber. There is only one type of
"full vacuum".
A full vacuum does not have the same behavior as a chamber with an air
lattice in it. Once an arc is created, there are metallic 'gasses in the
chamber, and on surfaces and carbon trails and arc path can form and
substantiate themselves. At that point, the "full vacuum" can no longer
be claimed. At all.
So the arc in even the best chamber draw down will require a higher
voltage than it will once the very first arc occurs. After that, it
isn't really a fully vacuumed chamber any more.