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NEWSCIENCENEWSCIENCENEWSCIENCE creating a preferential thermionic flow with no need for a temperature difference, and can make a device with two electrode surfaces on one piece of metal and avoid the thermo- electric junction problem. When this disc is spinning fast enough, electrons can escape the outer surface but cannot escape the inner surface (300 K). Electrons escaping the outer rim end up in space essentially cold. They can drift back to the inner surface via a vacuum manifold. When they get near the inner surface, they are drawn in to replace the escaped electrons. Electrons crash into the inner surface and make it hot. So, the outer surface goes cold because it loses energetic electrons, the inner surface heats up due to electron collisions, and an electric current flows from the inner to the outer surface. The temperature difference induces a heat flow from inner to outer—a heat flow! But wait, there's more! We are spinning a disc, and so electrons entering the disc at the inside eventually move through the disc to where they are emitted; but at that time they are travelling faster due to their own kinetic energy plus the ring's outer velocity. Accordingly, the disc must be getting hotter (assuming heat is not lost via radiation and vacuum is perfect). The disc's very fast spin does many things, but is not in itself a way to produce usable electricity for external loads. Figure 3 shows a cross-section of a homopolar motor, a_ rotating thermionic electrode and a vacuum path. The disc is connected to a drive shaft. Shown on the left-hand side is the current flow through the disc, and on the right-hand side the intersecting magnetic field. The shaft is linked to an AC motor/generator wired to grid AC power. Instead of the electrons colliding into the inner surface, creating heat, the emf generated at the outer surface now pulls electrons through the disc and past the magnetic field, causing a motor effect (torque is induced). This conversion of current to torque is proved physics. As the flow of electrons is being choked (flow rate is restricted by the magnetic field), the electrons at the inner surface are absorbed without causing heating. The heat lost at the outer surface is converted to torque. To get the disc up to speed, we use a mains-synchronous motor/generator as a motor. If the grid AC is 60 Hz, then, for a 1.676-m-diameter disc, the outer surface is travelling at 316 m/s and the centripetal acceleration is an amazing 12,153 G! Once the disc is up to speed, it will tend to try to go faster as heat is converted to torque; but as the disc is coupled to the grid via the AC generator, the torque, caused by the conversion of heat, tries to advance the phase of the grid and in doing so transfers energy (electricity) to the grid. Figure 1 But for an electron to replace an _ near the inner surface, they are drawn escaped electron, we have to pull one in to replace the escaped electrons. from the right side of the ring across Electrons crash into the inner surface the thermo-electric junction—a and make it hot. potential barrier as large as the So, the outer surface goes cold thermionic work function from which because it loses energetic electrons, the electron just escaped. As this the inner surface heats up due to requires equal work, we lose all the electron collisions, and an electric benefit of the escaped electron. Thus current flows from the inner to the the device fails to produce a current outer surface. The temperature flow. Tit for tat. difference induces a heat flow from A conventional thermionic device inner to outer—a heat flow! cannot convert heat to electricity But wait, there's more! We are unless there is a temperature spinning a disc, and so electrons ifference. To eliminate the entering the disc at the inside thermocouple issue, we need to have eventually move through the disc to the same metal on each side, but then where they are emitted; but at that there is no preferential direction at time they are travelling faster due to the thermionic gap. The only way to. their own kinetic energy plus the get a preferential directional flow is ring's outer velocity. Accordingly, to have one side hotter than the other. the disc must be getting hotter A eureka moment! Can we causea (assuming heat is not lost via preferential flow direction with radiation and vacuum is perfect). The something other than heat, with one disc's very fast spin does many material type and no thermo-electric things, but is not in itself a way to barrier, and can the emf induced by produce usable electricity for external an escaping electron do work? Wow, loads. but how? Centripetal acceleration! A centrifuge! Homopolar motor reconsidered Figure 2 shows the heart of the — Invented by Michael Faraday, the new thermionic method. If this disc homopolar motor, or Faraday disc, (ring) spins very fast, there is a has been of little use as it requires centrifugally induced force at the high currents—and at high currents, outer and inner surfaces. We are brushes get hot. However, if we have assisting electrons off the ring at the a device that has no heat exhaust, outside and retarding them at the then heat generated at a brush is not inside. We have altered the work wasted; it simply gets recycled. We function of these surfaces without can theoretically make a Rotating needing different metals. This is Thermionic Generator without significant: we now have a means of _ brushes. This is analytically simple! Figure 2 50 ¢ NEXUS www.nexusmagazine.com AUGUST — SEPTEMBER 2008