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View Diary: The Thing that is Not Cold Fusion (36 comments)

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  •  And you know this from what? (0+ / 0-)

    Wb-8 is twice the size of Wb-7, and is claimed to scale.

    .................expect us......................... FDR 9-23-33, "If we cannot do this one way, we will do it another way. But do it we will.

    by Roger Fox on Sun Apr 21, 2013 at 04:45:53 PM PDT

    [ Parent ]

    •  I know this (0+ / 0-)

      from studying the physics. The regime it operates in is heavily dominated by background, ion-neutral reactions instead of ion-ion reactions that are predicted to scale with the square of the current (or higher according to 'magic' multiple-well predictions).

      Instead, the ions react with the background gas in nothing more than beam-target interactions, same as shooting a beam of accelerated ions at a target.

      It just doesn't scale up to a reactor from an energy balance perspective.

      If you have access, this work lays it out pretty well:

      Fusion Reactivity Characterization of a Spherically Convergent Ion Focus, T.A. Thorson, R.D. Durst, R.J. Fonck, A.C. Sontag, Nuclear Fusion, Vol. 38, No. 4. p. 495, April 1998

      Let's put it this way, the basic physics behind the Polywell is simple. The technology behind the Polywell is simple. If the Polywell was a feasible reactor concept, you would see net energy producing versions already.

      •  Thorsons paper is about wire grid fusors..... (0+ / 0-)

        From D Tibbets

        Again I'm not sure why you assume there are alot of neutrals present in a Polywell. It is a given that neutrals above ~10^19 neutrals per cubic meter ( ~ 1 micron) will shut down the machine due to arcing. That taken with the target of ~ 10^22 ions per cubic meter needed for net power production mandates that there has to be a thousand ions per neutral within the machine. I believe this means that there would be 1 million ion- ion collisions per ion neutral collision. If these ion to neutral proportions cannot be maintained the whole system is a failure from the start and presumably the physicists involved (including the reviewers) would abandon the effort. I believe Bussard's work has shown this gradient (~100-1000) is possible, and Nebel's work has confirmed it ( internal densities vs external densities). This is a presumptive argument about neutrals not contributing significantly to the fusion output in the Polywell. I'm not sure how difficult it would be to directy measure this in the current low output machines, though I again assume that the review panel was satisfied that it was not a show stoper due to my above arguments, other arguments, or actual measurements.

        One reference by Univ. Wisconsin used in another thread that did some measurements of localized neutron production in a gridded fusor showed ~10% coming from the core. This means the rest was outside the grid and was probably dominated by ion- neutral collisions, but looking at it another way: 10% of the fusions were occurring in the small core volume (assume 10 cc) and 90% was occurring in the volume outside the grid ( assume 200 cc). This means that fusions per unit area was dominate in the core. While these could still be in part ion- neutral collisions I argue that the nature of the experiment suggests otherwise. In the experiment the detector saw either the core area, the grid area or a modest area outside the core (not the entire fusor volume). In the D-D fusion experiments the rate was higher in the core than in the volume around the grids, or immediately outside the grid. If the increased fusion rate was due only to the ions reaching their maximal velocity at or near the grid, then striking a neutral I would expect the counts from the unmasked tests would dominate (maximum rate and observed volume - again remember that this observed volume included the core, grid and near grid volumes. Also, the detector was seeing increasing reaction volumes as you moved out from the center. Once inside the grid the ions would be coasting or decelerating due to virtual anode formation so the fusion rate from ion- neutrals should be lower due to smaller volume and same or decreased ion velocities.

        I believe there are two ways to look at this.
        There were significant ion- ion fusion collisions in this area due to convergence (increased density) combined with increased collision speeds (head on ion- ion collisions ~ twice as fast as ion - neutral collisions with resultant larger fusion crossections).
        Or, the increased rates were only due to the convergence of ions effectively increasing the total energetic collisions weather ion- ion or ion - neutrals. The D-He3 tests also showed probable ion- target collisions presumably from He3 embedded in the grid, but this was not seen (as much) in the D-D tests. And ion-beam collisions are is irrelivant with a virtual cathode.
        The convoluted conclusions are that even in this non ion injected gridded glow discharge fusor in which there would have been a dominance of neutrals to intercept the ions and impede their confluence and direct collisions, there was evidence of significant core convergence and possibly significantly increasing core ion- ion fusion collisions. In a hand waving way, I claim that this supports my belief that ion- neutral collisions as a contribution to the fusion rate quickly becomes insignificant as the ratio of neutrals/ions drops, both because of probabilities of collisions and the magnifying (increasing only the effective ion density in the core region, while the neutrals density is not effected) benefits of any ion convergence .

        In a clean fusor that is pumped down to a good vacuum and then filled with ions from an ion gun , any residual neutrals should be in a minority, perhaps by a factor of several hundred (eg: pump down to ~0.1 micron, the turn on the ion guns on and operate at ~10 microns). Any neutrals added would be from recombinations (a two way street), out gassing (that is why I stipulated a 'clean' fusor) or neutrals knocked off the walls or grid. Unless these were neutral deuterons that had been loaded/ embedded in the metal, these sputtered ions and neutrals would not be contributing to any fusion, but be poisoning the system.

        Your claim that Bussard was ignorant of neutrals contributions to the system, while convenient for your position, is not supported by facts. Bussard has discussed neutrals in several contexts in the papers which I have read.

        .................expect us......................... FDR 9-23-33, "If we cannot do this one way, we will do it another way. But do it we will.

        by Roger Fox on Mon Apr 22, 2013 at 08:53:43 AM PDT

        [ Parent ]

      •  This is standard scaling, no? (0+ / 0-)
        the scaling of power with size goes as the seventh power of the machine radius, while the gain scales as the fifth power
        It applies to Tokamaks and IEC devices.
        “A generalized scaling law for the ignition energy of inertial confinement fusion capsules.”  M. C. Herrmann, M. Tabak, and J. D. Lindl, Nuclear Fusion 41, 99 (2001).

        Cheng, Baolian. “Thermonuclear Ignition Criterion and Scaling Laws for ICF Capsules.”  Invited Talk. Lawrence Livermore National Laboratory, Livermore California. Mar. 2013. Lecture.

        BTW Thorson got his PHD at U of Wis under Kulsinkski. Thorsons fusor severly underperformed Bussards fusor by a hundred fold. Kusinkskis recent work using ion injectors designed by Andrew Seltzman has confirmed Hirsch and Bussards work, not Thorsons.

        Bussard, Robert W. "The Advent of Clean Nuclear Fusion: Superperformance Space Power and Propulsion." 57th International Astronautical Congress (2006).

        And even Thorsons work showed Fusors work in 3 separate modes.

        .................expect us......................... FDR 9-23-33, "If we cannot do this one way, we will do it another way. But do it we will.

        by Roger Fox on Mon Apr 22, 2013 at 09:09:19 AM PDT

        [ Parent ]

        •  Of course they 'work' (0+ / 0-)

          in the sense of producing fusion reactions. Thorson showed how, with the power losses, they will never be able to scale to net power producing facilities.

          You never answered my question though. Since the physics and technology behind the fusor and polywell are so simple, where are the working, power-producing reactors? Do you honestly think that, if the technlogy and physics 'worked' that some bored millionaire, a power company, wouldn't have had their engineers put one together over a weekend?

          All we get are future promises and hidden work. Stories about classified research, and a dearth of peer-reviewed articles.

          Seltzman described an active grid cooling system to improve IEC performance, yet didn't explain how this could possibly work in a reactor, and the pressures he operated at were in the same regime as Thorson, thus still subject to the issue with background reactions.

          Also, one of the issues rarely addressed is the impact of the transverse velocity imparting a finite angular momentum to the ions, necessarily causing the central point to 'defocus' and smearing out any potential well structures.

          Listen, I understand the attraction of the fusor and related devices. They are simple to understand, simple to construct, and relatively inexpensive. They produce real neutrons and nifty pictures with a tantalizing promise of clean energy.

          But this is also their weakness, to some extent. They are so simple that to not have a working reactor, decades after the idea was formed, kinda tells you that there is some fundamental difficulty that physics doesn't let you overcome.

          •  Why, you do know the the Navy has a publishing (0+ / 0-)

            embargo on EMC2........

            So you are asking me to speculate.

            Okay, Wb-8 is twice the size of Wb-7. They didnt pay for a 3 meter P-b11 polywell, they paid for a 60cm Wb-8, but Wb-8 running D-D did scale according to statements from DR Park.

            SO how does Thorsons fusor paper apply to a polywell?

            .................expect us......................... FDR 9-23-33, "If we cannot do this one way, we will do it another way. But do it we will.

            by Roger Fox on Mon Apr 22, 2013 at 11:09:41 AM PDT

            [ Parent ]

            •  The base pressure (0+ / 0-)

              operating regimes studied by Thorson are in the same range as what little there has been published by the polywell experiments. Therefore, the ion-neutral collisions and charge exchange losses would be comparable between the fusor and the polywell.

              This is even before you start considering the extremely short electron confinement time due to the losses from the cusp fields and the enormous amount of power needed to maintain your electron population.

              Yes, I realize there is a publication embargo, one might ask why this research is being funded by the Navy instead of the Department of Energy. Short answer, you can make high energy neutrons which have various uses, but you won't make energy.

              It's easy to make whatever claims you might want if you're not publishing your results. This should, in and of itself, generate skepticism.

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