Joseph Chikva wrote:
D Tibbets wrote:
Direct conversion is an extremely widely used and successful process. I am referring of course to ion rocket engines, Cathode ray tubes, etc, etc.
I agree. Ion rocket motors are extremely widly used.
D Tibbets wrote:
I am referring .....................Cathode ray tubes, etc, etc.
So. you think that stream of alphas or particles or plasma should bombard some plate without deceleration?
Concerning the second point, I do not think alphas should bombard some plate before deceleration. They should fly by some negatively charged plate and thus give up a portion of their energy. This could be a ~ 2 million volt plate and thus absorb ~ 2 million eV of KE from the alpha. This may represent ~ 1/4th of the KE of the mixture of alphas. By adding more plates additional energy could be harvested. It would be next to impossible to to collect all of the KE but ~ 80-90% may be reasonable. The trick is to ground the decelerated alphas, before the next plate becomes dominate and actually accelerates the alpha. It involves a complex mixture of geometry, spacing "diverter" magnetic fields, shielding and Gauss Law effects may be used just as with the Magrid and electrons. Note that the pos.magrid actually accelerates the alphas once they are outside the magrid. But outlying venetian blind type electrodes that are negatively charged (combined with Guass law considerations and / or clever use of grounding plates and magnetic fields, etc).
The Polywell has natural collectors, they are called the cusps. And I think Debye considerations may apply in a neutral ambipolar flow of plasma. But this does not apply to a Polywell. The electrons at thousands of eV energy are far different than alphas at millions of eV KE. They are not closely coupled with each other. They do effect each other but not in a dominate fasion.
I envision a collector grid as something like this. At increasing radii, the magrid, then a low voltage negative or grounded plate with magnetic fields that will divert the electrons to a grounded surface. They will curve in a magnetic field more do to their lower KE and lower momentum. The high energy alphas will be diverted some but to a much smaller extent. Subsequent electrodes will slow them as the alphas pass and pull away from them, until the alpha has lost enough momentum that they curve and hit a grounding plate, perhaps alternating with the charged plates. I am assuming that electron separation and collection is necessary so that they are not accelerated to millions of eV. As mentioned, this is easy because of the huge difference in momentum of the electrons compared to the alphas. Similar separation is done in ion guns, etc.
Consider the TV. The electrons do not hit the accelerating plates. That would defeat the purpose. Electrons are boiled off of an electrode, accelerated past one or more anodes, focused and guided (so that they do not hit the anodes) with magnetic fields, the electrodes then stream on to hit the phosphors on the screen. A direct conversion grid is exactly the same with some variation. Alphas escaping through a cusp are the equivalent of the charged particles near the phosphor screen. They are traveling fast due to their fusion birth KE. They are focused by the cusp into a beam with some degree of dispersion. The cathodes in this case and are decelerated, and they hit the ground with much of their kinetic energy harvested. The multiple electrodes succeed in sequentially accelerating or decelerating the charged particle due to Gauss law effects, and/or careful shielding effects.
I admit this is a complex problem, but there are many examples of practical devices. Think of linear and circular accelerators. They work with more than one electrode (from the charged particle's perspective) to sequentially impart KE to the charged particle. The reverse (deceleration) is the same.
As for what a direct conversion grid might look like consider the device produced by the MIT scientists (or was that Columbia graduates.
http://www.physics.usyd.edu.au/~khachan ... LEtalk.pdf
Look at slide (figure)15