And all that silly talk about a "lifter " not working in a vacuum? Well maybe, just maybe, its not supposed to work in a vacuum .... but this smooth disc that I have seen pictures of Townsend Brown holding. Thats no " lifter", is it Elizabeth? It took me awhile by the way, my regards. grinder
grinder wrote:And all that silly talk about a "lifter " not working in a vacuum? Well maybe, just maybe, its not supposed to work in a vacuum .... but this smooth disc that I have seen pictures of Townsend Brown holding. Thats no " lifter", is it Elizabeth?
Chris Knight wrote:The sparks Townsend observed in the tri-arcuate discs are important. In the absence of ion wind in a hard vacuum, what do you think might be the cause of such an effect?
Paul S. wrote:
So, uh, what exactly is it that's so unusual about this spark? Are sparks not supposed to happen in a vacuum? That doesn't sound right to me.
It was the ability to make a "hard" vacuum in a glass tube, achieved in 1854, that led to the discovery of X rays, the electron, and (indirectly) radioactivity. In the first half of the 20th century, vacuum tubes powered radio and television, computers, and other electronic devices, until they were largely displaced by solid-state devices, such as transistors and
Ion wind, ionic wind, or coronal wind is a stream of ionized fluid generated by a strong electric field.
Electric charges on conductors reside entirely on their external surface (see Faraday cage), and tend to concentrate more around sharp points and edges than on flat surfaces. This means that the electric field generated by charges on a sharp conductive point is much stronger than the field generated by the same charge residing on a large smooth spherical conductive shell. When this electric field strength exceeds what is known as the corona discharge inception voltage (CIV) gradient, it ionises the air about the tip, and a small faint purple jet of plasma can be seen in the dark on the conductive tip. Ionisation of the nearby air molecules result in generation of ionised air molecules having the same polarity as that of the charged tip. Subsequently, the tip repels the like-charged ion cloud, and the ion cloud immediately expands due to the repulsion between the ions themselves. This repulsion of ions creates an electric "wind" that emanates from the tip, which is usually accompanied by a hissing noise due to the change in air pressure at the tip.
In ultra high vacuum systems, some very odd leakage paths and outgassing sources must be considered. The water absorption of aluminium and palladium becomes an unacceptable source of outgassing, and even the adsorptivity of hard metals such as stainless steel or titanium must be considered. Some oils and greases will boil off in extreme vacuums. The porosity of the metallic chamber walls may have to be considered, and the grain direction of the metallic flanges should be parallel to the flange face.
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