Focus Fusion On Slashdot

[Betruger]

Before my time. I must've caught some echoes. Thanks.

[MSimon]

Before my time. I must've caught some echoes. Thanks.

Revisit the subject if you like (start a topic). Most of us know more now than we did then. And there is a crop of newbies who might find it useful.

[Art Carlson]

Doc you can find the Rider ref. in 1. here, and I can send you a copy of that too, if you need it.
And also "Fundamental limitations on plasma fusion systems not in thermodynamic equilibrium"; I don't rememeber if this one was discussed already.

I am already familiar with the "Fundamental limitations". It's the paper I am usually referring to. (Rider's doctoral thesis is a more detailed version of the same work.)

I'm not sure I ever read the "general critique of IEC". The abstract sounds very interesting. Rider claims to have discovered not just one but "several fundamental flaws". The point about the non-Maxwellian distribution for the ions seems to have to do with up-scattering out of the well. Do Bussard/Nebel have a quantitative calculation on which to base their contention that up-scattering is tolerable? It is interesting that Rider is a sort of polywell fan, at least in a relative sense, describing it as "one of the best electron confinement systems proposed for such devices". What would most interest me is how he supports the statement that "by making exceedingly optimistic assumptions about the performance of that confinement system, the electron losses from the machine prove to be intolerable for all fuels except perhaps DT."

I do know how to visit the library, but if you are willing to enable my laziness, Betruger, then I would glady accept your offer for an electronic copy of this paper.

[Betruger]

My pleasure Doc. This isn't my field and I'm too busy thru next summer to properly learn enough to contribute, but in the mean time I'm glad to enable any kind of progress thru cogitation.

The paper's contents at a glance..

I. INTRODUCTION
II. DESIGN-INDEPENDENT PHYSICS ISSUES
A. Fusion power density
B. Energy equilibration between ion species
C. Ion thermalization
D. Ion upscattering losses
E. Bremsstrahlung radiation losses
III. DESIGN-DEPENDENT PHYSICS ISSUES
A. Spatial profiles
-1. Devices with convergence-limited core densities
-2. Devices with enhanced core densities
B. Relative importance of edge and central plasma regions
C. Total fusion power
D. Electron cusp losses
E. Electron grid losses
F. Ion grid losses
G. Electron thermalization
H. Synchrotron radiation losses
IV. RESULTS
V. CONCLUSIONS
A. Ion thermalization and upscattering losses
B. Bremsstrahlung
C. Electron cusp losses
D. Acoustic-wave compression of the core
E. Other potential problems

There are several other issues which were not examined in this paper but which would need to be carefully considered in future IEC work. These areas include the following.
Limitations on core convergence
Counterstreaming instabilities
Anisotropic instabilities
Lifetime of the potential well
Deviations from spherical symmetry in the system
Technological issues (accurate fueling deep inside well, design of direct converters (cf this Rosenbluth & Hinton paper)

F. Outlook for the future
ACKNOWLEDGMENTS
APPENDIX: ALTERNATE DERIVATION OF CUSP LOSSES

[ladajo]

Dr. Carlson,
These may help, it what they used to think (Circa 91/92), not sure if it is still what they think...

Collisional Relaxation of Non-Maxwellian Plasma Distribution in a Polywell
http://handle.dtic.mil/100.2/ADA257651

Ion Loss by Collisional Upscattering
http://handle.dtic.mil/100.2/ADA257688

Ion Loss by Collisions Outside the Core
http://handle.dtic.mil/100.2/ADA257642

Bremsstrahlung and Synchrotron Radiation Losses in Polywell Systems
http://handle.dtic.mil/100.2/ADA257895

At a minimum it gives a glimpse of where they were.

EDIT: Changed links to direct link, and added Bremsstrahlung

[Art Carlson]

My pleasure Doc. This isn't my field and I'm too busy thru next summer to properly learn enough to contribute, but in the mean time I'm glad to enable any kind of progress thru cogitation.

Thanks. Rider sure does cover a lot of ground. He repeats his conclusion that bremsstrahlung power should be greater than fusion power (by at least a factor of 1.74) in a p-B11 system. What I was most interested in was his estimate of energy loss through the cusps. Even though he used a model that I consider hopelessly optimistic (no line cusps, no sheath thickening due to flux conservation) he still finds cusp losses to be 10 times greater than fusion power. (In another model the factor is even 60.) In fact, he thinks cusps losses would be the death of the polywell even if you tried to run D-T:

However, quite likely D-T will also prove to have prohibitively
large cusp losses when one accounts for practical limitations
on how small the cusp holes can actually be made and
how many cusps are required to adequately approximate a
spherically symmetric system in order to avoid destroying
proper ion convergence

These are his reference parameters for an IEC reactor running on p-B11:

• Phi_well = 900 kV
• T_i0 = 300 keV
• T_e0 = 138 keV
• n_ce = 5e17 cm^-3
• B = 8.5 T
• Fuel mixture = 5:1 p:B11
• r_c = 3 cm
• (ln Lambda)_average = 16
• <sigma*v> = 2.39e-16 cm^3/s
• E_fus = 8.7 MeV
• N_cusps = 8
• k_H = 2
• P_fus = 1.9 GW(t)
• P_brems / P_fus = 10.5 or 61.1, depending on the model
• Ion fusion rate / loss rate = 3e-2 (for p)
• ( tau_i,loss / tau_fus ) = 330 (for B11)
• tau_ii / tau_fus = 5e-3 (for p), 7e-4 (for B11)
• tau_ee / tau_e_loss_cusp = 7e-5

Rider is hard-headed, but also an eternal optimist. His concluding words are these:

It is hoped that discussion of these problems with IEC
will lead to the discovery of more radical and fundamental
methods for circumventing them without losing the attractive
engineering simplicity of IEC devices. Certainly it would be
very welcome to have a fusion approach which could be
thoroughly proven in fairly small-scale, simple experiments
and yet could scale up to an economically attractive reactor
capable of using D-3He and perhaps even more advanced
fuels.

[Betruger]

And Drs Bussard and Nebel are among his acknowledgments.

I'm curious if anyone knows how one could (if possible) find a copy of those two unpublished reports: “Evaluation of Proton-Based Fuels for Fusion Power Plants” (Reports TRW-FRE-006 and TRW-007, TRW, Redondo Beach, CA, 1981) by J. D. Gordon et al.

[chrismb]

TRW 'merged' with Lucas (as both had aerospace and automotive division) then the conglomerated aerospace parts got mostly sold to Northrop Grumman, as TRW had a thriving satellite business that they wanted. So Northrop are the ones to ask now. TRW used to be into everything, I don't think Northrop would've had the same interest and would probably have binned such things.

(I seem to recall Northrop owned the whole lot for a finite period of adminstrative time, and sold the automotive divisions on to a holding complany. So if you have a car made in around 2002 then it may technically have 'Northrop Grumman' auto parts in it!!)

[chrismb]

Rider is hard-headed, but also an eternal optimist.

I'm not sure that's entirely true. He changed his whole fields of interest to bio-sciences after this fusion work!

His PhD preface reads;

"..the author...advises future graduate students working on their theses to avoid accidentally demolishing the area of research in which they plan to work after graduation."

[MSimon]

chris,

I can't imagine why any one would have wanted Lucas. Unless it was for the replacement part (about once a week) business.

I had a Triumph 650 (a very fine bike to ride - not so fine to keep running) with Lucas electrics and I was always replacing something on the electrical system.

OTOH I was riding in the San Francisco Bay area and met a LOT of really nice Hells Angels who would stop when they saw a bike breakdown and offer assistance.

[D Tibbets]

My pleasure Doc. This isn't my field and I'm too busy thru next summer to properly learn enough to contribute, but in the mean time I'm glad to enable any kind of progress thru cogitation.

Thanks. Rider sure does cover a lot of ground. He repeats his conclusion that bremsstrahlung power should be greater than fusion power (by at least a factor of 1.74) in a p-B11 system. What I was most interested in was his estimate of energy loss through the cusps. Even though he used a model that I consider hopelessly optimistic (no line cusps, no sheath thickening due to flux conservation) he still finds cusp losses to be 10 times greater than fusion power. (In another model the factor is even 60.) In fact, he thinks cusps losses would be the death of the polywell even if you tried to run D-T:

However, quite likely D-T will also prove to have prohibitively
large cusp losses when one accounts for practical limitations
on how small the cusp holes can actually be made and
how many cusps are required to adequately approximate a
spherically symmetric system in order to avoid destroying
proper ion convergence

These are his reference parameters for an IEC reactor running on p-B11:

• Phi_well = 900 kV
• T_i0 = 300 keV
• T_e0 = 138 keV
• n_ce = 5e17 cm^-3
• B = 8.5 T
• Fuel mixture = 5:1 p:B11
• r_c = 3 cm
• (ln Lambda)_average = 16
• <sigma*v> = 2.39e-16 cm^3/s
• E_fus = 8.7 MeV
• N_cusps = 8
• k_H = 2
• P_fus = 1.9 GW(t)
• P_brems / P_fus = 10.5 or 61.1, depending on the model
• Ion fusion rate / loss rate = 3e-2 (for p)
• ( tau_i,loss / tau_fus ) = 330 (for B11)
• tau_ii / tau_fus = 5e-3 (for p), 7e-4 (for B11)
• tau_ee / tau_e_loss_cusp = 7e-5

......

[/quote]

I understand that Rider's papers were in the mid to late 1990's. Is this more recent?
Unless it was later than 2005 I'm assuming that WB6 type recirculation was not figured into the equation. Bussard admitted that the electron confinement was inadequate through WB5 , and predicted break even was only a reasoned possibility once effective recirculation was introduced with WB6.
Does Rider figure bremsstrahlung on a thermalized electron population, or a dominantly radial electron direction that is cold in the center and hot on the periphery? I believe this is one of the necessary conditions for Polywell to work. If so, Rider's conclusions are presumably correct for the assumptions he made, but does not match the Polywell assumptions.

Also, a 5 to 1 ratio of P to B11 was quoted. I think (?) I have heard of a 10 to 1 ratio proposed by someone. This would presumably help the bremsstrahlung some but also decrease the fusion rate, so I don't know if there would be any net gain.

Is the 'Phi_well = 900 kV' the potential well depth? This seems high if it is. The machine could be run as low as the 75 KeV resonance peak for P-B11.
If most fusions result from beam- beam collisions I think that the potential well would only need to be 37.5 KeV to have an equivalent collisional energy of 75KeV since the crossections are based on beam- target collisions. Am I confused on this point?


Dan Tibbets

[Betruger]

Is this more recent?

Late '94. I don't know when was Rider's PhD.

[Art Carlson]

I understand that Rider's papers were in the mid to late 1990's. Is this more recent? Unless it was later than 2005 I'm assuming that WB6 type recirculation was not figured into the equation. Bussard admitted that the electron confinement was inadequate through WB5 , and predicted break even was only a reasoned possibility once effective recirculation was introduced with WB6.
Does Rider figure bremsstrahlung on a thermalized electron population, or a dominantly radial electron direction that is cold in the center and hot on the periphery? I believe this is one of the necessary conditions for Polywell to work. If so, Rider's conclusions are presumably correct for the assumptions he made, but does not match the Polywell assumptions.

Rider quickly dismissed using electric fields to reflect the electrons lost through the cusps using much the same arguments as I did: What reduces problems with the electrons aggravates problem with the ions. If recirculation helps anyway, then it helps reduce the cusp losses, but not the bremsstrahlung. The bremsstrahlung power he cites is for Maxwellian electrons, but only after he first shows that the the electron distribution will rapidly thermalize. He mentions that trying to maintain a non-thermal distribution by bleeding off particles will aggravate energy losses that are already too high. I think he has all the bases covered.

Also, a 5 to 1 ratio of P to B11 was quoted. I think (?) I have heard of a 10 to 1 ratio proposed by someone. This would presumably help the bremsstrahlung some but also decrease the fusion rate, so I don't know if there would be any net gain.

The optimum fuel ratio to minimize P_brem/P_fus is n_1:n_2 = Z_1:Z_2.

Is the 'Phi_well = 900 kV' the potential well depth? This seems high if it is. The machine could be run as low as the 75 KeV resonance peak for P-B11. If most fusions result from beam- beam collisions I think that the potential well would only need to be 37.5 KeV to have an equivalent collisional energy of 75KeV since the crossections are based on beam- target collisions. Am I confused on this point?

Rider goes to a good deal of effort at the beginning to explain why you can't really take advantage of any resonances in the cross section. I'm not sure, but his well depth may have been optimized in light of ion losses through up-scattering.

[JLawson]

chris,

I can't imagine why any one would have wanted Lucas. Unless it was for the replacement part (about once a week) business.

I had a Triumph 650 (a very fine bike to ride - not so fine to keep running) with Lucas electrics and I was always replacing something on the electrical system.

OTOH I was riding in the San Francisco Bay area and met a LOT of really nice Hells Angels who would stop when they saw a bike breakdown and offer assistance.

Lucas wasn't known as "The Prince of Darkness" for nothing. Their alternators and oil pumps came in two versions - about to fail and dead out of the box...

I was convinced for a while that Lucas sent their worst stuff over to the US to get even for the War of Independence. But they've had fun with the locals, too...

http://www.mez.co.uk/lucas.html

I especially like the 1482 amp slo-blow fuse... Should we start up a petition to make sure no Lucas components are used in Polywell research?

[MSimon]

chris,

I can't imagine why any one would have wanted Lucas. Unless it was for the replacement part (about once a week) business.

I had a Triumph 650 (a very fine bike to ride - not so fine to keep running) with Lucas electrics and I was always replacing something on the electrical system.

OTOH I was riding in the San Francisco Bay area and met a LOT of really nice Hells Angels who would stop when they saw a bike breakdown and offer assistance.

Lucas wasn't known as "The Prince of Darkness" for nothing. Their alternators and oil pumps came in two versions - about to fail and dead out of the box...

I was convinced for a while that Lucas sent their worst stuff over to the US to get even for the War of Independence. But they've had fun with the locals, too...

http://www.mez.co.uk/lucas.html

I especially like the 1482 amp slo-blow fuse... Should we start up a petition to make sure no Lucas components are used in Polywell research?

Perhaps we can get them to chase an ITER contract where the real money is. But that would be evil.