Synchrotron radiation losses not considered a problem

[olivier]

This question is puzzling me : why did Dr Bussard not consider synchrotron radiation losses to be a problem for Polywell systems ?
On the one hand I read the following in in Bremsstrahlung Radiation Losses in Polywell Systems, EMC2-0891-04, Robert W. Bussard and Katherine E. King:

Bremsstrahlung is a more pervasive constraint than synchrotron radiation because the latter can be reflected by bounding metal walls.

On the other hand, Figures 3.a,b on the last page of Bremsstrahlung and Synchrotron Radiation Losses in Polywell Systems, EMC2-1291-02, Robert W. Bussard and Katherine E. King display dashed curves, for fusion power to synchrotron radiation power ratio, that are constantly below unity for p-11B fuel.
I remember scareduck previously addressing ion synchrotron radiation on this forum, but I could not find any answer.

[scareduck]

Interesting report. One of the things Bussard always claimed was that getting p-11B to work was that it was just a matter of ramping up the well depth and altering the fuel ratio to run the device boron lean (IIRC). But figure 2b shows his calculations seemed to indicate that as you pushed the well depth (the two charts show the difference between 10 keV and 100 keV), bremsstrahlung radiation losses more than equal fusion power. So I think you have it slightly backwards in that these charts show that bremsstrahlung radiation is a problem, not synchrotron radiation, as both charts show areas where Pfs > 1.

Edit: my bad, I noticed you said figures 3a and 3b, which were for a bremsstrahlung-optimized fuel mixture. In figure 2a he shows an area where the ratios are > 1.

[olivier]

In other words, what is actually puzzling me is :

• -Bremsstrahlung is considered the #1 problem.
  -Then it is sensible to begin by optimizing fuel mixture for bremsstrahlung.
  -In doing so, we seem to have a problem with synchrotron radiation (Fig 3 a,b).
  -Now, looking at Figure 2 which is for a 50:50 fuel mixture, we get in the best case a Pfb of 2 and a Pfs of 4 or 5, which leaves but a narrow margin.

One could think of curves optimized for synchrotron radiation or sync. rad. + bremsstr. And if it were too difficult with p-11B, we could start with D-3He and dig the moon, or with D-T and cope with neutrons, and why not?
What I am trying to say is that this a highly multidimensional optimization problem (fuel mixture, electron injection energy, virtual anode height, which result from the coils magnetic field, dimensional factors, and so on). Wouldn't it be nice to put together the most influential factors, how they interact with each other and how they influence the global performance of the system ? I do not know if that should take the form of an Excel spreadsheet, a mindmap, a text document...
Not that I am not confident that EMC2 Corp. have a clear view of all these parameters. My point is that it would help educate newbies (like me) and strengthen arguments in favor of the Polywell concept.
I am also very conscious (i) that these studies are 15 year old, (ii) that a lot of work has been done since, (iii) that Polywell physics is complex and therefore its theory is incomplete and evolving.

[scareduck]

It seems that much would also have to change in light of the 2000 Miley, Chacon, et al. paper as well regarding the effects of different well geometries.

[TallDave]

Like the above, Nebel has said there's an optimum mixture:

. The theory says that you can beat Bremstrahlung, but it's a challenge. The key is to keep the Boron concentration low compared the proton concentration so Z isn’t too bad. You pay for it in power density, but there is an optimum which works. You also gain because the electron energies are low in the high density regions.

Not sure about the specifics.

Nebel has also pointed out that parabolic wells (Chacon) gave very different results than square ones (Rider), which he thought tended to indicate we need experimental data to understand what's really going on. One of the known unknowns that may or may not kill this.

[olivier]

Thank you for the reference. Some good scientific reading for a cloudy summer day!

[Roger]

Nebel has also pointed out that parabolic wells (Chacon) gave very different results than square ones (Rider), which he thought tended to indicate we need experimental data to understand what's really going on.

What about a spiked tip well ?

Heres a nice spike on a graph:
http://bp2.blogger.com/_CLJS75_Cnao/Rid ... risons.jpg


Interesting, so who is to say a truncube parabolic well would be the same as a truncdodec parabolic well.

In fact didnt Indreks objections concern one of his pix that had 4 circular points in the well area, I wonder of those 4 points would represent a Square well (Rider).

And if so, that would provide Indrek with a significant tweak for further simulations. And reason to build a WB-dodec.

Think of it as "tuning the well", which is something that can come in handy when designing your carburetor, and/or switching to PB-11 fuel.

So it looks like the shape of the well can dictate the amount of Brem. SO we need a list of factors that can shape the well.