My answers to rcain

Discuss how polywell fusion works; share theoretical questions and answers.

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Joseph Chikva
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Joined: Sat Apr 02, 2011 4:30 am

My answers to rcain

Post by Joseph Chikva »

rcain wrote:
Joseph Chikva wrote:
rcain wrote:do you have any numbers which show it WILL/IS a problem for Polywell? i do not think so.
There in Polywell are typical conditions for creation of this type of instability: electron beam enters into background plasma consisting from two spices: electron spice and ion spice.
Nebel in his article investigated electron-electron streams interaction and claims that electron-electron 2-stream instability is not issue for Polywell. This he says is due to big angular (so thermal) component of motion of electron spice.

I know three ways for softening of impact on plasma of this type of instability:
1. high relativistic factor of at least one stream
2. strong axial mag field
3. wide velocity spread of at least one stream

So, Nebel's conclusion about electron-electron 2-stream is well understood for me because large angular component corresponds to the third mentioned way.

But ions will not have wide thermal motion velocities spread initially.

Concerning scaling law, you always can say that your device is not big enough and only this is a reason of your negative result (absence of scaling). But in reality you have not constant beta but have beta as a function of many factors and beta's value varies from nil to not one but e.g. 0.7 in real working conditions. And no outgassing and degassing or influence of those are minimal and more significant are mainly instabilities observed in any size devices.
Hi Joe,

Unlike, some others, I do not dismiss your questions - they are good questions i think and I think you are right not to simply 'trust' the word of others quoting Jesus - I mean Nebel and Bussard.

I think you will only be satisfied when

a) you have worked through equations yourself - although equations for stability in particular are not easy, nor certain - I'm sure you know. Theoretical Two-stream, Weiebel, etc is just small part of it - manifestation in real machines whole different picture.

b) you (we) have seen good (repeatable and reviewed) experiments that show how instability can be avoided or corrected.

I cannot give you either of these. And I am not qualified in this field - very few people on the planet are.
Hi again rcain,
answer on a)
there are quite many people on the planet having the skill to consider theoretically stability problem (when they consider taken separately already known certain type of instability).
See for example here: http://nonneutral.pppl.gov/ , push the “people” button I ensure you that any of those people has such skill and I know some of them.

answer on b)
if we particularly talk about two-stream instability, that is developing constantly and finally causing bunching of beam (stream) on separate “clots”. So, we will have the certain “lifetime” between beginning of streams interaction and bunching.
You would ask: what we will have between two mentioned moments? We will have emmitanse growth that will increase the phase volume.
You would ask: how we can to slow down the development of this type of instability?
An answer is: it is possible by either of three mentioned by me ways:
1. high relativistic factor of at least one stream
2. strong axial magnetic field
3. wide velocity spread of at least one stream
Because 2-stream instability would be the main concern of my fusion idea I’ve read a lot of related literature but could not find more ways. Quite may be I do not know something but I see that at least here the most people here are even less aware in this problem.

And when I’ve read the paper of Dr. Nebel about damping of electron-electron 2-stream instability, I’ve seen that this type of instability there will be damped by 3rd way as without doubt background electron population in Polywell will have high thermal motion component (and, so, wide spread). This is the so called “Landau Damping”.

And after that I am asking:
what about electron-ion 2-stream instability if initially (before occurring of thermalization) ions in Polywell will not have wide velocity spread, how we can apply axial magnetic field in spherical geometry and if we know that neither streams are relativistic?
Not a legit question?
rcain wrote:viewtopic.php?t=593
-Tall Dave recounting Rick Nebel's response to Art Carlson's similar concerns about two-stream instability and other issues.
Nebel’s words:
4. The machine does not use a bi-modal velocity distribution. We have looked at two-stream in detail, and it is not an issue for this machine. The most definitive treatise on the ions is : L. Chacon, G. H. Miley, D. C. Barnes, D. A. Knoll, Phys. Plasmas 7, 4547 (2000) which concluded partially relaxed ion distributions work just fine. Furthermore, the Polywell doesn’t even require ion convergence to work (unlike most other electrostatic devices). It helps, but it isn’t a requirement.
And it is very interesting why Nebel says so: “The machine does not use a bi-modal velocity distribution” if that does?
As a proof of my words and as a proof that Nebel didn’t mean so too we can consider a paper which he wasn't too lazy to write.
Two-dimensional electron-electron two-stream instability of an inertial electrostatic confinement device
http://pop.aip.org/resource/1/phpaen/v1 ... ypassSSO=1
If not use bi-modal velocity distribution, why to consider the possibility of two-stream of one type and why not to consider another and more dangerous in Polywell’s case type?

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