Sunday, September 27, 2015

Polywell Fusion In Nine Steps

Polywell Fusion In Nine Steps

      The US has failed to dive into this technology, despite its' far reaching implications.  We still do not know if this concept will work or not.  We do not have the data, because we have failed to fund the research.  

     It is frustrating.  The nation that invented the aeroplane, went too the moon and sequenced the human genome has failed in this.  Will we look at the next great scientific challenge - and back off?  Will we let China or Russia gain an lead in an energy technology which could change the world?  We need to get moving, climate change is not waiting on us. 

     This is an update on the post “How It Works” from The Polywell Blog. That work was written in September 2012 and was based on Robert Bussards’ 2005 machine. Bussard reported finding neutrons in that paper [4, 27]. If we trust this data - then it is evidence that polywell fusion really works. The newest paper from Dr. Parks’ team only provided data for plasma trapping not fusion.  Hence, this step-by-step is theoretical at present.   If Parks findings are correct it may lead to the worlds' best plasma trap.  That gets you pretty far down the road to a fusion power reactor.  It is still early days, but we see a very promising future for this technology.

1.  Magnetic Field Turned On.  The rings inside the polywell are six electromagnets in a box. They face each other, so that their poles point into the center [3, 22].  That is the same as six north pole magnets facing one another.  In WB8, each electromagnet had 40,960 amp-turns [21].   We do not want those rings to touch - they should be externally mounted.  We also want those rings to be smooth and uniform [25].   At the center there is a pocket of no magnetic field, a null point. All of this is contained inside a vacuum chamber (in WB8 this chamber was held at a pressure is roughly 10 mtorr or less) [24]. The fields are shown below.

2.  Electrons Emitted.  Next, the electrons are drawn into the magnetic field.   Bussards' old machine did this using a second electric field to pull material in [3].  The newest work just used a plasma cannon.  In analyzing their work, I estimated there was ~6E+18 of charged particles, flung out from the emitter at ~1E9 newtons [33].  In a power plant scenario, this material would all be electrons.


3. Electrons Get Caught By Ring Fields.  When the electron gets close it starts to feel the magnetic fields. The electron starts following the magnetic fields generated by the rings.  The electron oscillates around one of these magnetic field lines, following it towards the center, giving off cyclotron radiation [4].

4. Electron Motion Inside Center.  When the electron reaches the center, its' motion becomes straighter as it passes through the null point [5]. This is the point of no magnetic fields in the middle of the rings. As it heads out the other side, it starts oscillating again. This oscillation get tighter as the electron gets farther away from the center [11, 8]. The radius of oscillation is the electron gyroradius [6]. The electron follows the magnetic field lines. These lines are drawn together, tighter and tighter at the corners. The field around the electron gets denser. The electron oscillation gets smaller and tighter. At some point, the field gets so tight that the electron hits a magnetic mirror at the cusps [6, 7, 8, 11]. The electron turns around. It heads back toward device center and repeats the motion [8, 11]. An electron should be lost after a given period of time [8].

5. Cusp Confined Plasma.  The electrons’ motion make small magnetic fields [9]. In bulk populations, this gives the plasma magnetic properties, allowing it to go diamagnetic and reject the outside field [29]. Theoretically, the plasma should form a stable system where the plasma pressure balances the magnetic pressure; a beta of one [17, 18, 25-28].  The shape of this cloud would depend on where the pressures find equilibrium, but it is commonly assumed to be a 14 point star.  The evidence of cusp confinement was the breakthrough claim of the new EMC2 paper.  They provided data (x-ray, visual and flux loop) that this effect has finally been observed in a real physical system [21]. This effect was first predicted in 1954 [3, 5, 25-28].  This is also the trapping mechanism that Lockheed Martins' Skunkworks is chasing [30].

6. Deuterium Gas Injection: The D2 gas is puffed towards the rings [3]. This is the uncharged D2 gas. This means that the gas is less affected by any electric fields. Hence, it can make it to the edge of the rings. Bussard puffed the gas in at the relatively high pressure of 3E-4 torr against vacuum pressure of 1E-7 torr [3].

7. The Deuterium Ionizes: When the D2 reaches the edge of the rings it is hit by an electron. If the electron is hotter than 16 eV [1] the D2 will become an ion. Bussard estimated that the typical electron in his device had 2,500 eV [3] at the beta=1 condition [10]. This collision heats up the deuterium and it ionizes.   The deuterium loses an electron to become the ion. The ion is positively charged and is attracted to the cloud of electrons in the center. In WB-6, this attraction created a 10,000 volt drop for the ions to "fall down"[3].

8.  Ions Fall & Collide: The charged deuterium is attracted to the electrons in the center. In WB6, it was attracted by the 10,000 volt drop. It “falls down” this hill towards the center [3]. The ion builds up 10,000 eV as it falls. Note that the deuterium ion is about 3,670 times more massive than the electron [12, 1].

9. Fusion: If two ions do collide at 10,000 eV, they can fuse. The product will be have on the order of 1 MeV [15] of energy and cannot be held by the electric or magnetic fields. It should therefore rapidly exit the rings. As the voltage increases the odds of fusion typically improves. This is measured by a fusion reactions' cross section [15]. The stated goal of NIF was to get the average plasma temperature over 10,000 eV under confinement [2].


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21. Park, Jaeyoung, Nicholas A. Krall, and Paul E. Sieck. "High Energy Electron Confinement in a Magnetic Cusp Configuration." In Submission (2014): 1-12. Http:// Web. 13 June 2014.
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23. Moynihan, Matthew J. "Modeling Plasma Emitters In Polywell Paper." Https:// Quora, 20 July 2015. Web. 25 Sept. 2015.
24.  Private communication, “What was roughly the pressure inside the machine?” Paul Sieck, July 2, 2015
25.  University of Maryland, Colloquium & Seminars, "Measurement of Enhanced Confinement at High Pressure Magnetic Cusp System", Jaeyoung Park, September 9th 2014
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30.  McGuire, Tom. "The Lockheed Marin Compact Fusion Reactor." Thursday Colloquium. Princeton Plasma Physics Lab, Princeton. 6 Aug. 2015. Lecture. 

1 comment:

  1. Do you know why typically a ring coil electromagnet is used as opposed to a pancake coil or other geometry? I know that there have been exotic one-wire coils in various geometries such as an octahedron or cube-octahedron, but is there a reason you can think of for using a ring as opposed to a pancake coil? Also, it is often said that the coil is generally contained in an Iron ring, is this done to effect the magnetic field?