What kind of voltage would we be looking at to repell all electrons? If I'm right, you are saying that there will still be some impacts due to upscattered electrons having more energy than others, so the repelling potential will have to be larger than the average energy. But with enough voltage, it should be possible to repell all electrons and prevent that loss current, correct? And the ion screens will prevent that recombination catalysis that you had with the alumina insulator/repellers.
The voltage required to repel electrons is dependent on their energy distribution and the strength of the magnetic field.
You need to remember that anything that screens ions will attract electrons. And vice versa.
Since, unlike vacuum tubes (generally), you need both ions and electrons to make the device work, vacuum tube type screens are not going to do you much good.
Engineering is the art of making what you want from what you can get at a profit.
But the magnetic field already insulates the electrons from the screening grid, if its positioned right (and assuming low electron cross-field transport)
jmc wrote:But the magnetic field already insulates the electrons from the screening grid, if its positioned right (and assuming low electron cross-field transport)
The greater the magnetic field the better the screening. That would keep in higher energy electrons until they had time to cool down. If the annealing theory is correct.
It may be in fact that the actual annealing takes place in the bunched beams similar to what happens in a klystron. Except you have beams whose velocity varies over the cycle so the chances that they would match velocities with stray electrons is good.
Engineering is the art of making what you want from what you can get at a profit.
Cool down? I though their larmor orbits got smaller as they cooled down. In addition to that I though that classically at least (optimistically ignoring turbulent waves) electrons had to collide with ions for a net change in position of the centres of guiding centres to take place and thus outward drift.
If you have a pressure gradient it causes perpendicular drift which can lead to changes in magnetic fields which changes guiding centers. You don't need "collisions", but the concept of pressure and collisionless doesn't make a whole lot of sense either.
The POPS device assumes no pressure gradient, but for a MaGrid to work well we certainly want an electron density gradient near the grid which implies a pressure gradient. You would hope that the drift current follows the MaGrid which leads to a slight reduction in the B field near the MaGrid but no real change in field shape. It will be interesting to see what the experiments tell us!
Having said that, even if the current does change the field shape, so long as it does so in a predictable repeatable manner the design can be adjusted accordingly.
drmike wrote:If you have a pressure gradient it causes perpendicular drift which can lead to changes in magnetic fields which changes guiding centers. You don't need "collisions", but the concept of pressure and collisionless doesn't make a whole lot of sense either.
The POPS device assumes no pressure gradient, but for a MaGrid to work well we certainly want an electron density gradient near the grid which implies a pressure gradient. You would hope that the drift current follows the MaGrid which leads to a slight reduction in the B field near the MaGrid but no real change in field shape. It will be interesting to see what the experiments tell us!
I'm not sure that is right about POPS. Wouldn't the E field provide a pressure gradient?. Also POPS is supposed to enhance the density gradient (or create one) without changing the thermal distribution at the "zero crossing" of the cycle. i.e. entropy is not changed because the compression is reversible macroscopically.
Which is pretty cool when you think about it.
Of course the reversibility can't be perfect or it wouldn't enhance collisions. Still. A Q of 10 would help. A Q of 60 would be excellent. A Q of 600 would be as good as necessary.
Engineering is the art of making what you want from what you can get at a profit.
Even open box machines have fieldines that touch the vacuum vessel wall, but because they are earthed and outside the magrid by the time the electrons hit them they have praticall zero kinetic energy.
jmc,
If I remember the "single electron" traces by indrek, electrons lose very little of their kinetic energy over a single electron lifetime, including several passes in & around the coils and through various regions of the rx, including recirculating, for instance, this one:
(sorry for the direct link Indrek)
[rest snipped]
Tom.Cuddihy
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Faith is the foundation of reason.
Surely this depends on the magnetic field strength.
Additionally it the intersections of the cusps with the solid surfaces are at electron birth potential then even large electron particle losses will not imply correspondingly large energy losses.
In principle this is identical for open and closed box machines.
