- #1
zmorris
- 13
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Hi I was about to fall asleep last night and was thinking about breakdown voltage, when electrons are pulled from the surface of a conducting plate and form a channel that discharges a capacitor. This is called a vacuum arc, some other keywords are thermionic emission and work function.
http://en.wikipedia.org/wiki/Vacuum_arc
http://en.wikipedia.org/wiki/Thermionic_emission
http://en.wikipedia.org/wiki/Work_function
http://hyperphysics.phy-astr.gsu.edu/hbase/tables/photoelec.html
The highest work function metal is platinum, so theoretically a platinum capacitor should store the most charge in a vacuum.
But it got me thinking, what if there was a way to coax the electrons into staying inside the cathode by raising the work function somehow? There might be a few ways to do this: make the surface of the cathode very cold, very smooth, or with such a high band gap that electrons want to stay where they are.
But I thought of another possibility. Perhaps Cooper pairs within a superconductor want to stay paired. For example, if electrons in the surface of the superconductor are feeling a high electric field and want to be ripped from the surface, maybe something about being paired with another electron would compel them to stay within the bulk of the superconductor. So at least theoretically, a superconductor should have a fairly high work function.
But I don't know enough about the skin effect in superconductors to know how much of the charge is near the surface, especially in DC or steady state.
http://en.wikipedia.org/wiki/Skin_effect
I also don't know how high electric fields influence the skin effect.
The best ultracapacitors right now either use a high surface area material like graphite or an electrolyte. But I'm wondering if anyone has studied how to increase the capacitance by increasing the breakdown voltage beyond 173 MV/m:
http://en.wikipedia.org/wiki/Dielectric_strength
If there was a way to catch the free electrons in the gap, maybe with a force like acceleration in a spinning capacitor, then the breakdown could be prevented because the electrons would fly off into space instead of going to the anode, so the ion channel would never form. But I imaging that any centripetal force on the electrons would be a tiny fraction of the electric field force.
So sorry this is such a general question, but does anyone know of any experiments to raise the work function of a material? This link suggests that something strange happens when a superconductor passes the critical temperature and becomes an insulator:
http://adsabs.harvard.edu/abs/1991fnps.confQT...M
I'm wondering if there might be such a thing as a semisuperconductor that has a very high dielectric in the skin so the majority of the electrons stay in the bulk and can't cross to the surface.
Any ideas on this would be greatly appreciated. Thanks for any help you can provide,
Zack Morris
http://en.wikipedia.org/wiki/Vacuum_arc
http://en.wikipedia.org/wiki/Thermionic_emission
http://en.wikipedia.org/wiki/Work_function
http://hyperphysics.phy-astr.gsu.edu/hbase/tables/photoelec.html
The highest work function metal is platinum, so theoretically a platinum capacitor should store the most charge in a vacuum.
But it got me thinking, what if there was a way to coax the electrons into staying inside the cathode by raising the work function somehow? There might be a few ways to do this: make the surface of the cathode very cold, very smooth, or with such a high band gap that electrons want to stay where they are.
But I thought of another possibility. Perhaps Cooper pairs within a superconductor want to stay paired. For example, if electrons in the surface of the superconductor are feeling a high electric field and want to be ripped from the surface, maybe something about being paired with another electron would compel them to stay within the bulk of the superconductor. So at least theoretically, a superconductor should have a fairly high work function.
But I don't know enough about the skin effect in superconductors to know how much of the charge is near the surface, especially in DC or steady state.
http://en.wikipedia.org/wiki/Skin_effect
I also don't know how high electric fields influence the skin effect.
The best ultracapacitors right now either use a high surface area material like graphite or an electrolyte. But I'm wondering if anyone has studied how to increase the capacitance by increasing the breakdown voltage beyond 173 MV/m:
http://en.wikipedia.org/wiki/Dielectric_strength
If there was a way to catch the free electrons in the gap, maybe with a force like acceleration in a spinning capacitor, then the breakdown could be prevented because the electrons would fly off into space instead of going to the anode, so the ion channel would never form. But I imaging that any centripetal force on the electrons would be a tiny fraction of the electric field force.
So sorry this is such a general question, but does anyone know of any experiments to raise the work function of a material? This link suggests that something strange happens when a superconductor passes the critical temperature and becomes an insulator:
http://adsabs.harvard.edu/abs/1991fnps.confQT...M
I'm wondering if there might be such a thing as a semisuperconductor that has a very high dielectric in the skin so the majority of the electrons stay in the bulk and can't cross to the surface.
Any ideas on this would be greatly appreciated. Thanks for any help you can provide,
Zack Morris