Polywell

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Polywell (Greek-English: roughly "multiple trough") is a nuclear fusion reactor concept that comes from Robert W. Bussard . It belongs to the so-called Inertial Electrostatic Confinement (IEC) fusion concepts such as B. the Farnsworth-Hirsch fusor , because the ions intended for fusion are held together by an electric field . However, this field is not generated by high-voltage electrodes , but by an electron cloud , which in turn is enclosed in a more or less spherically symmetrical magnetic field .

The Polywell development work is carried out by EMC2 Fusion Development Corporation and funded by the US Navy . So far, space propulsion systems, but also power generation, have been named as the intended use.

description

In a high vacuum container , a number of identical, three-dimensionally arranged ring-shaped coils generate a centrally symmetrical magnetic field. A cloud of electrons is enclosed by this field in the manner of a magnetic mirror and forms an electrical potential well . Positively charged ions are fed to this region, accelerated from the potential gradient towards the center point and should circulate on closed orbits long enough for a sufficient number of nuclear fusion reactions to take place when they collide. Details about the type and arrangement of the electron and ion sources have not yet been published.

Physical remarks

The accumulation of electrons and ions in the electrostatic fusion devices is only partially comparable with the thermal plasma of other fusion concepts such as fusion by means of magnetic confinement or inertial fusion . In these the plasma is created by collisions of neutral atoms or molecules with each other, so it is electrically neutral and thermally in equilibrium. In the case of Polywell etc., on the other hand, a small excess of electrons is necessary to create the potential well for ion inclusion, so the plasma is not neutral. It is also not in thermal equilibrium, i.e. it cannot be described by a temperature , since electrons and ions come from separate sources with given kinetic energies and move in the field with location-dependent and locally directed speeds.

Relatively high ion velocities occur near the center of the potential well. Therefore, energy losses in the plasma due to bremsstrahlung can become important. This would be particularly significant in the boron-11 proton fusion reaction (see Nuclear Fusion Reactor # Alternative Concepts ), which Bussard suggested to use because it does not generate free neutrons . He argued that the losses due to bremsstrahlung would only be 1/12 of the generated fusion energy with this fuel, because the high velocities in the center and the resulting small cross-section for Coulombic collisions of the ions made a significant deceleration there unlikely. In contrast, Todd Rider demonstrated in 1995 that the losses from bremsstrahlung with this fuel would exceed the production of fusion energy by at least 20%.

Trials and results

In 2006 Bussard reported on the test setup WB-6 (" Wiffleball 6"). This had six ring coils, arranged on the surfaces of an imaginary cube (diameter approx. 30 cm). With WB-6, up to 1 billion deuterium-deuterium fusion reactions per second have been achieved. This corresponds to a fusion power of about 0.6 milliwatts; the electrical power requirement of the apparatus during the experiment should have been at least a few hundred watts.

At EMC2, the WB-7 and WB-8 systems were then built and operated. Possibly (only indistinctly shown in a figure) at least in WB-7, eight coils in an octahedron or 12 coils in a dodecahedron arrangement were used in order to get closer to spherical symmetry . With reference to the rights of the client US Navy, EMC2 refuses to publish exact details and measurement results. The WB-8 apparatus, which is currently (2011) in experimental operation, should show excellent plasma confinement properties, according to the company's report.

According to Bussard, a reactor with a radius of 1.5 meters would achieve a net energy gain of many megawatts.

Individual evidence

  1. ↑ Web site emc2fusion.org
  2. ↑ Thomas J. Dolan: Review Article: Magnetic Electrostatic Plasma Confinement (PDF; 3.4 MB). Plasma Physics and Controlled Fusion 36 (1994), pp. 1539-1593.
  3. ^ Robert W. Bussard: Bremsstrahlung Radiation Losses in Polywell Systems. (PDF; 428 kB) EMC2, 1991, Table 2, p. 6.
  4. ^ TH Rider: Fundamental Limitations on Plasma Fusion Systems not in Thermodynamic Equilibrium . Dissertation. Ed .: MIT. 1995, p. 161-2 (English, archive version from June 29, 2007 ( Memento from June 29, 2007 in the Internet Archive ) [PDF; 18.7 MB ]). , see also: T. Rider: A general critique of internal-electrostatic confinement fusion systems. MIT, 1995.
  5. ^ Robert W. Bussard: The Advent of Clean Nuclear Fusion: Superperformance Space Power and Propulsion. ( Memento of September 29, 2011 in the Internet Archive ) (PDF; 990 kB) 57th International Astronautical Congress (IAC) , Valencia (Spain) 2006.
  6. ^ Alan Boyle: Fusion goes forward from the fringe. In: CosmicLog. May 10, 2011, archived from the original on March 18, 2012 .;
  7. ↑ ENERGY / MATTER CONVERSION CORPORATION. In: recovery.gov. 2011, archived from the original on October 4, 2013 .;
  8. ↑ Bussard, Robert: The Advent of Clean Nuclear Fusion: Superperformance Space Power and Propulsion ( Memento from September 29, 2011 in the Internet Archive ) (PDF; 990 kB), p. 2.

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