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Inertial electrostatic confinement

Inertial electrostatic confinement, or IEC, is a class of fusion power devices that use electric fields to confine the plasma rather than the more common approach using magnetic fields found in magnetic confinement fusion (MCF) designs. Most IEC devices directly accelerate their fuel to fusion conditions, thereby avoiding energy losses seen during the longer heating stages of MCF devices. In theory, this makes them more suitable for using alternative aneutronic fusion fuels, which offer a number of major practical benefits and makes IEC devices one of the more widely studied approaches to fusion.

As the negatively charged electrons and positively charged ions in the plasma move in different directions in an electric field, the field has to be arranged in some fashion so that the two particles remain close together. Most IEC designs achieve this by pulling the electrons or ions across a potential well, beyond which the potential drops and the particles continue to move due to their inertia. Fusion occurs in this lower-potential area when ions moving in different directions collide. Because the motion provided by the field creates the energy levels needed for fusion, not random collisions with the rest of the fuel, the bulk of the plasma does not have to be hot and the systems as a whole work at much lower temperatures and energy levels than MCF devices.


One of the simpler IEC devices is the fusor, which consists of two concentric metal wire spherical grids. When the grids are charged to a high voltage, the fuel gas ionizes. The field between the two then accelerates the fuel inward, and when it passes the inner grid the field drops and the ions continue inward toward the center. If they impact with another ion they may undergo fusion. If they do not, they travel out of the reaction area into the charged area again, where they are re-accelerated inward. Overall the physical process is similar to the colliding beam fusion, although beam devices are linear instead of spherical. Other IEC designs, like the polywell, differ largely in the arrangement of the fields used to create the potential well.


A number of detailed theoretical studies have pointed out that the IEC approach is subject to a number of energy loss mechanisms that are not present if the fuel is evenly heated, or "Maxwellian". These loss mechanisms appear to be greater than the rate of fusion in such devices, meaning they can never reach fusion breakeven and thus be used for power production. These mechanisms are more powerful when the atomic mass of the fuel increases, which suggests IEC also does not have any advantage with aneutronic fuels. Whether these critiques apply to specific IEC devices remains highly contentious.

History[edit]

1930s[edit]

Mark Oliphant adapts Cockcroft and Walton's particle accelerator at the Cavendish Laboratory to create tritium and helium-3 by nuclear fusion.[3]

Designs with cage[edit]

Fusor[edit]

The best known IEC device is the fusor.[12] This device typically consists of two wire cages inside a vacuum chamber. These cages are referred to as grids. The inner cage is held at a negative voltage against the outer cage. A small amount of fusion fuel is introduced (deuterium gas being the most common). The voltage between the grids causes the fuel to ionize. The positive ions fall down the voltage drop toward the negative inner cage. As they accelerate, the electric field does work on the ions, accelerating them to fusion conditions. If these ions collide, they can fuse. Fusors can also use ion guns rather than electric grids. Fusors are popular with amateurs,[57] because they can easily be constructed, can regularly produce fusion and are a practical way to study nuclear physics. Fusors have also been used as a commercial neutron generator for industrial applications.[58]


No fusor has come close to producing a significant amount of fusion power. They can be dangerous if proper care is not taken because they require high voltages and can produce harmful radiation (neutrons and X-rays). Often, ions collide with the cages or wall. This conducts energy away from the device limiting its performance. In addition, collisions heat the grids, which limits high-power devices. Collisions also spray high-mass ions into the reaction chamber, pollute the plasma, and cool the fuel.

POPS[edit]

In examining nonthermal plasma, workers at LANL realized that scattering was more likely than fusion. This was due to the coulomb scattering cross section being larger than the fusion cross section.[59] In response they built POPS,[60][61] a machine with a wire cage, where ions are moving at steady-state, or oscillating around. Such plasma can be at local thermodynamic equilibrium.[62] The ion oscillation is predicted to maintain the equilibrium distribution of the ions at all times, which would eliminate any power loss due to Coulomb scattering, resulting in a net energy gain. Working off this design, researchers in Russia simulated the POPS design using particle-in-cell code in 2009.[63] This reactor concept becomes increasingly efficient as the size of the device shrinks. However, very high transparencies (>99.999%) are required for successful operation of the POPS concept. To this end S. Krupakar Murali et al., suggested that carbon nanotubes can be used to construct the cathode grids.[64] This is also the first (suggested) application of carbon nanotubes directly in any fusion reactor.

They were , where the positives and negatives are equally mixed together.[23]

quasineutral

They had evenly mixed fuel.

[23]

They were , meaning that its behavior was the same in any given direction.[23]

isotropic

The plasma had a uniform energy and temperature throughout the cloud.

[23]

The plasma was an unstructured .

Gaussian sphere

Commercial applications[edit]

Since fusion reactions generates neutrons, the fusor has been developed into a family of compact sealed reaction chamber neutron generators[78] for a wide range of applications that need moderate neutron output rates at a moderate price. Very high output neutron sources may be used to make products such as molybdenum-99[39] and nitrogen-13, medical isotopes used for PET scans.[79]

Researchers developed[80] POPS and Penning trap[35]

Los Alamos National Laboratory

In 2013 this team built a 30 cm fusor at the Saraykoy Nuclear Research and Training center in Turkey. This fusor can reach 85 kV and do deuterium fusion, producing 2.4×104 neutrons per second.[81]

Turkish Atomic Energy Authority

Hirschs original machine was a 17.8 cm diameter machine with 150 kV voltage drop across it.[12] This machine used ion beams.

ITT Corporation

has developed a commercial neutron source based on a fusor, achieving 3×1011 neutrons per second with the deuterium-deuterium fusion reaction for 132 hours of continuous operation.[39]

Phoenix Nuclear Labs

Energy Matter Conversion Inc Is a company in Santa Fe which has developed large high powered polywell devices for the US Navy.

NSD-Gradel-Fusion sealed IEC neutron generators for DD (2.5 MeV) or DT (14 MeV) with a range of maximum outputs are manufactured by Gradel sárl in Luxembourg.

[78]

Researchers at Shahid Beheshti University in Iran have built a 60 cm diameter fusor which can produce 2×107 neutrons per second at 80 kilovolts using deuterium gas.[82]

Atomic Energy Organization of Iran

Avalanche Energy has received $5 million in venture capital to build their prototype.

[83]

CPP-IPR in India, has achieved a significant milestone by pioneering the development of India's first Inertial Electrostatic Confinement Fusion (IECF) neutron source. The device is capable of reaching an energy potential of -92kV. It can generate an neutron yield of up to 107 neutrons per second by deuterium fusion. The primary objective of this program is to propel the advancement of portable and handheld neutron sources, characterized by both linear and spherical geometries.

[84]

P.T. Farnsworth, , June 1966 (Electric discharge — Nuclear interaction)

U.S. patent 3,258,402

P.T. Farnsworth, . June 1968 (Method and apparatus)

U.S. patent 3,386,883

Hirsch, Robert, . September 1970 (Apparatus)

U.S. patent 3,530,036

Hirsch, Robert, . September 1970 (Generating apparatus — Hirsch/Meeks)

U.S. patent 3,530,497

Hirsch, Robert, . October 1970 (Lithium-Ion source)

U.S. patent 3,533,910

Hirsch, Robert, . April 1972 (Reduce plasma leakage)

U.S. patent 3,655,508

Hirsch, Robert, . May 1972 (Electrostatic containment)

U.S. patent 3,664,920

R.W. Bussard, "Method and apparatus for controlling charged particles", , May 1989 (Method and apparatus — Magnetic grid fields)

U.S. patent 4,826,646

R.W. Bussard, "Method and apparatus for creating and controlling nuclear fusion reactions", , November 1992 (Method and apparatus — Ion acoustic waves)

U.S. patent 5,160,695

S.T. Brookes, "Nuclear fusion reactor", UK patent GB2461267, May 2012

T.V. Stanko, "Nuclear fusion device", UK patent GB2545882, July 2017

talk at Microsoft Research

Polywell Fusion: Electrostatic Fusion in a Magnetic Cusp

University of Wisconsin-Madison IEC homepage

IEC Overview

Summary of Physics Aspects of Some Emerging Concepts

Archived 2017-06-04 at the Wayback Machine

Fusion from Television? (American Scientist Magazine, July-August 1999)

Archived 2007-11-10 at the Wayback Machine

Should Google Go Nuclear? Clean, cheap, nuclear power (no, really)

NSD-Gradel-Fusion (Luxembourg)

NSD-Gradel-Fusion