ANS winter 2010 Conference

[WizWom]

an entire program on Fusion energy...

http://fed.ans.org/TOFE19/program.pdf

from the "Alternate and Nonelectric Concepts" Track:
1 3:30 2618 Compact, Inexpensive Fusion Devices Using the
Inertial Electrostatic Confinement Approach
(Invited)
Gerald L Kulcinski, J. F. Santarius,
R. L. Bonomo

4 4:30 2528 Driven Fission Research Reactor Using a Cylindrical
Inertial Electrostatic Confinement (IEC) Neutron
Source
George H Miley

6 5:00 2565 Results from the Six Ion Gun Fusion Experiment Brian J. Egle, Matthew Michalak,
John F. Santarius, Gerald L
Kulcinski

No Polywell

[WizWom]

oooh, Poster session (latest results)

Experiments, Alternate Concepts, and Magnets
4
2536 Numerical Study of Ion Recirculation in an
Improved Spherical Inertial Electrostatic
Confinement Fusion Scheme by Use of a
Multistage High‐Voltage Feedthrough
Kai Masuda, Yu Yamagaki, Taiju
Kajiwara, John Kipritidis,
Kazunobu Nagasaki

[rcain]

packed agenda! very short sessions. bit heavy on the TOK stuff. good to see Miley there. oh for a Eureka announcement. someone, anyone.

anyone here going?

[WizWom]

Me. That's why I was looking at the program.

[DeltaV]

What happens in Vegas, stays in Vegas.

[rcain]

Me. That's why I was looking at the program.

lucky man. you picked out the same sessions interested me. in addition, i thought the following looked intriguing:

Development of a Simpler Stellarator Power Plant
Design
Thomas G. Brown, M. Zarnstorff,
L. Bromberg, N. Pomphrey, L-P.
Ku

Compact, Efficient Laser Systems Required to
Harness the Power of the Sun (Invited)
Andy J Bayramian, Chuck Boley,
Amber Bullington, Diana Chen,
Robert Deri, Alvin Erlandson, et
al.

Nanoscale Issues In Advanced Materials For
Inertial Fusion Technology
Santiago Cuesta Lopez, J.M.
Perlado, Maximo Victoria

Evaluation of power constraint condition for
fusion driven subcritical energy reactor
Yunqing Bai, Ming Jin, Yican Wu

look forward to hearing what you pick up.

[WizWom]

OK, I made it to the "Alternate and Nonelectric concepts" session, which was very cool.

Kulcinski presented "Compact Inexpensive Fusion devices Using the Inertial Electrostatic Confinement Approach." This was gridded fusors, and he did some detailed analysis of fusion locations and was able to get some idea of ionizations. Most interesting was finding that ~ 2/3 of fusions were occurring very close to source regions, and that ~10% of the Deuterium was reaching a negative ionization.

Miley presented his very linear design, a tube with a 15:1 length:width ratio, cathodes at the ends and anodes in the middle. The idea was to be able to insert it in a fuel element as a neutron source, and use it for subcritial pile experiments. He was talking about doing this as a low-wattage (<1kW) experiment setup for undergrads or grad students.

Miley also presented a novel stressed palladium coating for laser target fusion, with D2 diffused into the interstitial voids. The D2 then forms an additional high speed D2 source for fusion in the pellet, and increased yield.

Bromberg presented a computer design study using High-Temperature superconducting tiles to modify a simpler base magnetic field in a stellerator. The trouble was edge effects in the tiles, as the magnetic field begins degrading the superconductivity in the corners of the tiles.

Egle, a recent graduate under Kulcinski, presented "Results frm the Six Ion Gun Fusion Experiment." The 300kV energies they reached managed to match up with Hirsch's results quite well - but only when they used unfocused ion guns. Detailed investigation of fusion regions showed only 2% of fusions occurring at the intersection, the majority occurring at the wall. This implies that up-scattered deuterium ions were hitting previously neutralized ions stuck to the anode. (Up-scattered only, since the coulomb barrier for D-D fusion is 480keV).

Matsuura presented a paper on 3He and proton interactions in D-D fusion plasmas, which seemed interesting but not important. Until you get the D-D going, the 3He-p reaction is trivial.

I also attended the NIF/LIFE plenary session, where LLNL talked about their big laser and things they have managed. Still a hugely expensive boondoggle. they are pushing for 10-15 shots per second. with 150 MJ shots for a power plant. They were very happy with the engineering advanced in high energy laser lenses, they are able to have good life with 8MJ/cm^2 lenses. They do not see any possibility of aneutronic fusion.

[D Tibbets]

.....

Egle, a recent graduate under Kulcinski, presented "Results frm the Six Ion Gun Fusion Experiment." The 300kV energies they reached managed to match up with Hirsch's results quite well - but only when they used unfocused ion guns. Detailed investigation of fusion regions showed only 2% of fusions occurring at the intersection, the majority occurring at the wall. This implies that up-scattered deuterium ions were hitting previously neutralized ions stuck to the anode. (Up-scattered only, since the coulomb barrier for D-D fusion is 480keV).......

I don't have the credentials to speak with any authority, but I have a gut feeling from the little I have read, that the conclusions presented need to be considered carefully.
As for the coulomb barrier being at 480 KeV, that may be correct, but it ignores the quantum uncertainty, that allows profuse D-D fusions at much lower energies (like 10 KeV, or energies of ~ 30-60 KeV for the good amateur fusors).


Dan Tibbets

[WizWom]

.....

Egle, a recent graduate under Kulcinski, presented "Results frm the Six Ion Gun Fusion Experiment." The 300kV energies they reached managed to match up with Hirsch's results quite well - but only when they used unfocused ion guns. Detailed investigation of fusion regions showed only 2% of fusions occurring at the intersection, the majority occurring at the wall. This implies that up-scattered deuterium ions were hitting previously neutralized ions stuck to the anode. (Up-scattered only, since the coulomb barrier for D-D fusion is 480keV).......

I don't have the credentials to speak with any authority, but I have a gut feeling from the little I have read, that the conclusions presented need to be considered carefully.
As for the coulomb barrier being at 480 KeV, that may be correct, but it ignores the quantum uncertainty, that allows profuse D-D fusions at much lower energies (like 10 KeV, or energies of ~ 30-60 KeV for the good amateur fusors).

Your "Gut" is wrong. The reason they can fuse is because of the Maxwellian distribution being both below and above the "mean" energy, which is reported.
Improved formulas for fusion cross-sections and thermal reactivities - H.-S. Bosch and G.M. Hale 1992 goes into it in more detail.

Their paper report the d-d coulomb barrier at 210 keV; they use a significantly more sophisticated model.

The coulomb barrier in my text-book is fairly straightforward and derives from Maxwell's equation and the strong force equation. As such, it is (to a first approximation) 1.2*(charge 1)(charge 2)/[(atomic mass 1)^(1/3)+(atomic mass 2)^(1/3)]
This formula take into consideration the quantum uncertainty in the locations of the nuclei; it leaves out some effect, obviously.

[D Tibbets]

Wizworm. My 'gut' feeling was referring to the conclusion that the experment indicated beam target fusion. My statement about the classical fusion crossection needing to be modified by quantum mechanics is based on the following Text.

PLASMA PHYSICS AND
FUSION ENERGY
Jeffrey P. Freidberg
Massachusetts Institute of Technology 2007

From pages 48-49

"The classical picture of the dependence of σ on v, or equivalently Kcm, is illustrated in Fig. 3.8. The crucial feature is the hard barrier at 288 keV," [referring to D-T fusion] "a quite high value. Any particle with a lower energy will not undergo a nuclear fusion collision. As compared to the actual situation, this is a pessimistic result.
Nuclear quantum mechanical effects The correct cross section for fusion collisions involves nuclear quantum mechanical effects. The reason is that the region of strongest nuclear interactions occurs on the scale length of the nucleus. On such small-scale lengths classical physics does not apply and it is necessary to include nuclear quantum mechanical effects. The most important effect is that on nuclear scale lengths nuclei exhibit both particle like and wavelike properties. The wavelike properties introduce three qualitatively new modifications to the simple classical hard-sphere model.

First, in the quantum mechanical regime, the “tunneling effect” is present. A simple example of tunneling occurs when a sound wave is reflected off an insulating acoustic tile. Even if the insulator is perfectly lossless, sound waves still penetrate into the material, although with exponentially decreasing amplitude. If the tile is thin enough some sound energy will emerge from the back of the insulator; energy will have “tunneled” its way through. In terms of the cross section, “tunneling” is equivalent to barrier penetration. In other words, even for kinetic energies below the Coulomb cutoff, there is still a finite probability of interaction. The 288 keV is not a hard cutoff. Intuitively, the further below the cutoff, the lower is the probability of interaction.

The second wavelike effect is that at nuclear distances two nuclei can actually pass through one another. A nuclear reaction can thus be thought of as the interaction of two closely coupled waves. If the relative velocity of the particles (waves) is very large (i.e., Kcm 288 keV), the time available for a closely coupled interaction is very short, thereby reducing the probability of a fusion collision. Therefore the fusion cross section should decrease for large increasing relative velocities.

The final wavelike effect concerns the possibility of resonance. Under certain conditions of geometry and relative velocity the combined potential energies of the two colliding nuclei can exhibit a resonance. The net result is that under such conditions there is an enhanced probability of a nuclear reaction occurring, corresponding to an increased cross section. This is in fact the situation for the D–T interaction."

The energy spread (thermalization) of the particles is an entirely different issue.

Dan Tibbets

[WizWom]

Wizworm. My 'gut' feeling was referring to the conclusion that the experment indicated beam target fusion. My statement about the classical fusion crossection needing to be modified by quantum mechanics is based on the following Text.

As I said, your Gut is wrong. On this, also - the fusion rate decreases precipitously as the focus improves.

[chrismb]

As I understand it, I don't know where this 400/200keV stuff has come from.

The Coulomb barrier for two deuterons touching is around the 40 MeV range. If two such deuterons came together at that energy, though, they should smash each other up into bits - no fusion.

Essentially all nuclear fusion (bar a few parts per million of the multi-sigma outliers in the M-B distribution - which only applies to thermal plasmas mind, not electric fusion) seen in solar and terrestrial fusions is down to quantum tunnelling, as far as I understood it....

Here are the equations;

http://burro.cwru.edu/Academics/Astr221 ... ulomb.html

In regards whereabouts fusion comes from in an 'electric fusion' device, even if you get piles of hot ions flapping around, the charge-exchange cross-section with backgrounds is so high that one should anticipate that the majority of fusions are fast neutrals into the walls/structures of the device. (Hence why I would want to see this excluded as the source of neutrons in Polywells before I sign away any more credence to the whole scheme.)

[D Tibbets]

Most of my 'Gut' feeling is due to discrepencies, or rather variations in conclusions from the same lab and others. The D-D fusion has been shown to be greatest (per unit volume) in the center of one of their fusors, suggesting a dominance of beam- beam fusion in that system. With D-He3, the grids themselves seem to dominate (beam- target fusion). Until these differences are explained, I am leery of blanket statements.

I would add, that the multiple beam intersection in the center scheme of this system ( like the Hirsch efforts) are delicate. I assume the focus and aiming of the beams is critical. If not within specks, some or most of the ions may not converge to the intersecting center, so the proportion of the ions in each beam participating in chances for fusion would decrease, In that case defocusing the beams may actually help within some limits. I would like some assurance that this was not the mechanism for their findings.

Concerning Chrismb's comment about charge exchange and neutral ion collisions having dominate effects in a fusor. This is certainly true where neutrals are the dominate species in the system. This applies in the glow discharge fusors. In ion gunned fusors operating at lower pressures (thus fewer neutrals) this picture starts to change. In a Polywell, where the ions are contained within the Wiffleball, while any neutrals are free to drift throughout the vacuum chamber. the ions are extremely dominate, so charge exchange and non charge exchange neutral collisions are proportionately much less significant. This requires good vacuum pumping to remove these background neutrals to permit the ion concentration levels to dominate the collisions and to have a useful density of these ions for reasonable fusion rates. Another issue may be negatively charged ions in a fusor plasma (that also has been reported at U. Wissconson). As this is charged, it would be contained, but if significant numbers are present and if charge exchange between it and a routine positively charged ion results in two neutrals, it might change the picture somewhat. It all depends on the prevalence of these particles compared to the positively charged deuterium ions (in this case) in the system. If a pair of neutrals was produced in this fashion they would leave the Wiffleball within ~ 1 pass, so it would not build up in the core (Wiffleball). It would essentially be a small, tiny(?) adjustment to the background neutrals within the system.

Dan Tibbets

[icarus]

chrismb:

Essentially all nuclear fusion ....... seen in solar and terrestrial fusions is down to quantum tunnelling,

Interesting viewpoint. So we can lay the thermonuclear fusion (aka Hydrogen) bomb at the feet of Bohr, Heisenberg and Feynman as their child ... (curie, rutherford and einstein can take a grand-parent role).

[Tom Ligon]

Jumping in late without checking to see if anyone posted it (I did notice the subject matter was apparently touched on):

https://lasers.llnl.gov:443/about/missi ... ture/life/