Ignition of a Deuterium Micro-Detonation with a Gigavolt Super Marx Generator

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1. The problem is bracketed by two experiments and by the fuel. The Centurion-Halite experiment demonstrated ignition of a deuterium-tritium micro-explosion with no more than a few megajoules; the Mike test demonstrated a pure deuterium explosion above 10⁶ megajoules — and in both cases a fission bomb supplied the ignition energy. Winterberg wants pure deuterium because deuterium-tritium depends on lithium and puts about 80 percent of its energy into neutrons that activate the reactor, whereas the raw material for deuterium is ordinary water, everywhere abundant, and the reaction releases much less energy into neutrons. The price is a far higher ignition energy.Abstract; Section 1, Introduction; Section 2, Solution in between two extremes, Fig. 1

2. The central move replaces a sphere with a rod. For deuterium-tritium the condition for propagating burn in a sphere is a density-radius product of at least 1 gram per square centimetre; for deuterium-deuterium it is at least 10, and with an optimal ignition temperature about ten times higher the ignition energy for a deuterium sphere works out around 10⁴ megajoules — beyond any laser or particle beam. But at a beam current of about 10⁷ amperes the beam’s own magnetic field entraps the charged fusion products inside a thin deuterium cylinder, so the sphere condition is replaced by the same product taken along the length of the rod, and the gain then depends only on how long the rod is.Section 2, equations 1 to 3

3. The ignition numbers close. Single GeV protons would pass straight through, but an intense beam is stopped by the proton-deuteron two-stream instability sharpened by a collisionless magnetohydrodynamic shock: in hundredfold-compressed deuterium, with a number density about 5 by 10²⁴ per cubic centimetre, the stopping length is about 1.2 by 10⁻² centimetres. A rod length of about 0.6 centimetres then satisfies the burn condition, and the ignition energy comes out at about 10¹⁶ erg — one gigajoule or less — which is what the 10⁷ ampere gigavolt proton beam delivers in 10⁻⁷ seconds. At thousandfold compression, already reached in laser fusion experiments, the ignition energy is ten times less.Section 2, equations 4 and 5

4. The reason the voltage has to be a gigavolt is a pair of settled results. For a capacitor of a given size, the energy stored and the power released both go as the square of the voltage. And a beam is easy to focus only while its current stays below the Alfvén limit, which is 17 kiloamps for electrons but 31 megamps for protons — so a 10⁸ ampere electron beam from a 10 megavolt Marx generator is hopelessly above the limit, while a 10⁷ ampere proton beam accelerated through a billion volts sits below it and carries 10¹⁶ watts, which is enough to ignite deuterium.Section 3, The Importance of High Voltages for Inertial Confinement Fusion, equations 6 to 10

5. The machine is specified, not gestured at. About 100 coaxial capacitors, each 15 metres long and built as a magnetically insulated transmission line, are charged by two conventional Marx banks each to plus and minus 5 megavolts, decoupled, and then switched in series by spark gaps to produce 1 gigavolt along a 1.5 kilometre evacuated vessel. Breakdown is held off by magnetic insulation — the condition being that the magnetic field in gauss exceeds 300 times the electric field in volts per centimetre, so an axial field of 2 by 10⁴ gauss insulates up to 9 by 10⁷ volts per centimetre — and the current pulse from the closing spark gaps raises an azimuthal field that insulates further as it runs down the line.Section 4, Super Marx Generator; Figures 3 to 6

6. What to watch is whether anyone builds it, and Winterberg is explicit about why he thinks the alternatives will not carry a power plant: the photon burst from a high-gain micro-explosion destroys the laser that lit it, heavy-ion beams have a stopping problem in the target, and deuterium-tritium sends 80 percent of its yield into 14 MeV neutrons. He sets the neutron-free hydrogen-boron reaction aside on the grounds that it cannot be ignited at realistically attainable pressures, which leaves pure deuterium. The stand-off problem is already answered in the design — the stiffness of a GeV proton beam lets the target sit a comparatively large distance from the wall of the confining cavity — so the open item is the machine, and the result that would settle it is one pure-deuterium micro-detonation ignited without fission.Abstract, closing sentence; Conclusion

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How to cite it

Friedwardt Winterberg (2008) Ignition of a Deuterium Micro-Detonation with a Gigavolt Super Marx Generator doi:10.1007/s10894-008-9189-3

Where it sits in the curriculum

• Fusion machines: pinches, focus devices and inertial drivers