Art Carlson wrote:...What the? The second link?? Bussard, Fusion Technology, Volume 19, March 1991???
Art, my apologies - I actually meant to say the first link, and yes they are both quite veteran papers. They do, to me at least, provide general experimental evidence (using HEPs-Polywell config) supporting basic geometry and confinement and show that these correlate 'reasonably' well with theoretical predictions. ie. no show stoppers are identified.
I agree, there is no serious attempt (in these papers at least) to extrapolate to reactor conditions. I will do some further digging.
As far as I can see, Bussard never suggested mirror confinement was adequate; I was under the impression that this has long been a known limitation and so therefore he need 'admit' nothing. (may be just a choice of words thing). He did us a mirror equation (p4 eqn 6) to estimate lower bound on containment at cusps under LOW pressure conditions.
However, he then went on to show ('admit'), how as the neutral density (identified 10degress off a cusp line) increases, so the potential (well) drops off, badly:
Because the failure of the potential to persist when the density of the neutral background far exceeds the unneutralized density that forms the potential which will also be the conditions on a reactor scenario (1,4) might be interpreted as a flaw in the concept, it was important to understand this behavior. To this end we carried out a set of studies to understand the behavior of the back ground plasma itself given in the Appendix, and then a set of studies to understand the behavior of the potential as a function of background density, electron energy, and electron current described below.
and... (p10-p11):
With no background plasma, the potential builds up to the gun energy; this potential prevents further buildup of unneutralized electrons, thus clamping the unneutralized electron density. After the background plasma has forced the potential to drop below the gun energy due to energy conservation, as discussed above, the number of unneutralized electrons is instead determined by a balance between the injected current and cusp losses.
Thereafter, the hot electron density depends on the background plasma density, only to the extent that the background might change the hot electron energy somewhat, and therefore its cusp loss rate. The fact that
the number of hot electrons does not change much with background plasma density, while the potential changes a lot, creates an apparent problem with Poisson’s equation, since del^2ϕ is proportional to the unneutralized density.
The resolution to this apparent conundrum is that as the density increases, the potential will be confined to an increasingly small sheath near the periphery, with the same excess charge producing a smaller potential.
The data shown in Figure 10a and 10b confirms this trend. The lower density run, Figure 10a, has a potential that increases fairly smoothly with radius. The higher density run, Figure 10b, has a potential that is quite flat until the sharp rise at about 65 cm. This trend is expected from the model.
... i would agree that treatment around this point seems rather scant. But, Bussards point, i believe, is that the trend is promising enough to pursue, not least, because we seem to be able to explain it, and to a greater or lesser extent, control it.
i dont see any treatment of (diamagnetic) Wiffle-ball (WB) effects anywhere here. Nor, as you rightly point out, any constructive treament of confinement 'scaling', whatever the cause. i'm certain there is adequate treatment elsewhere however, i'll dig it out.
since everyone agrees, WB formation is fundamental to feasibility, this (precise behaviour) seems to be key, still.
regarding your assertion of (R/rho) as the 'confinement enhancement ratio(?)' cf Bussards (R/rho)^2 - please could you repoint me to your derivation - i am very interested in reading though and understanding your point of view further. (though please bare with me as my own knowledge and experience of this science is considerably infererior to your own).
Art Carlson wrote:For these reasons I do strongly dispute that this paper represents the last or even the most thorough word on polywell confinement.
.
fair enough, and i wouldnt disagree (they are old papers after all). though in truth, thats not what i claimed.
Art Carlson wrote:In case you haven't noticed, I dispute Bussard up and down the block
yep, we had noticed. and it is for that reason that your learned assessments here are so highly valued.
Art Carlson wrote:Eqn. 35 uses his notation that has never made sense to me, but I believe it takes credit for recirculation that I dispute, at least when it comes to energy, not just electrons, and it ignores both the line cusps and flux conservation in the sheath leading to the point cusps. He also uses rho_e as the characteristic sheath thickness, justifying it with the simple statement (on p.9) that
This leakage radius applies for the case, valid here, of trapped electrons in a non-neutral plasma system and not for the confinement of neutral plasma, which can escape through a leakage path width comparable to the geometric mean of the ion and electron gyro radii r_e,i in the cusp field.
This statement is probably wrong, but is at best unjustified, misleading, and sloppy (The plasma is quasi-neutral, not non-neutral.).
in what way does the notation of eqn 35 (
http://www.askmar.com/Fusion_files/Some ... ations.pdf), not make sense?
it seems to me he (Bussard) is putting a general case, albeit he then qualifies with eg.
... where the parameters jo and Gj are related to others by various constraint equations...
- which seems slightly fudgy to me also. surely however, this is where we deem experimental discovery of parameters necessary.
your assertion of 'probably wrong' however, also seems to me begging some more definite proposal. did you have anything in mind?
@chrismb:
The ones in respect of Bussard's last patent?
- yes
@TallDave: thanks for the link - Photomultiplier Tubes - i had wondered how they used those for this app. what we really want though are a few measly graphs from more recent experiments, showing things are 'on-track' (or not), and to answer questions such as Art has just posed re. confinement enhancement. what are the chances of that do you suppose? Is Rick Nebel still looking in?