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A Riggatron is a magnetic confinement fusion reactor design created by Robert W. Bussard in the late 1970s. It is a tokamak on the basis of its magnetic geometry, but some unconventional engineering choices were made. In particular, Riggatron used copper magnets positioned inside the lithium blanket, which was hoped to lead to much lower construction costs. Originally referred to as the Demountable Tokamak Fusion Core (DTFC), the name was later changed to refer to the Riggs Bank, which funded development along with Bob Guccione.

Conventional tokamak design

In a conventional tokamak design the confinement magnets are arranged outside a "blanket" of liquid lithium. The lithium serves two purposes, one is to absorb the neutrons from the fusion reactions and produce tritium which is then used to fuel the reactor, and as a secondary role, as shielding to prevent those neutrons from reaching the magnets. Without the lithium blanket the neutrons degrade the magnets quite quickly.

This arrangement has two disadvantages. One is that a magnetic field must be produced not only in the plasma, where it is needed, but also in the blanket, where it is not, significantly raising the construction costs. The other is that the core, where the magnetic coils penetrate the machine along its axis, must be large enough to contain the shielding, which limits the achievable aspect ratio. A higher aspect ratio generally results in better performance.

Riggatron improvement

The Riggatron re-arranged the layout of the conventional design, reducing the role of the lithium to producing tritium only. The magnets were to be directly exposed on the inside of the reactor core, bearing the full neutron flux. This precluded the use of superconducting magnets, and even copper magnets would have to be disposed in as little as 30 days of operation. The Riggatron was laid out to make this core replacement as easy and fast as possible. After removal and replacement, the magnets would then be melted down and reprocessed. Although this process would be costly, the smaller magnetized volume, the larger aspect ratio, and the reduction in complexity by avoiding superconducting magnets was a tradeoff that would, it was hoped, pay off.

Another advantage of the parameters chosen was that ignition appeared to be possible with ohmic heating alone, as opposed to more expensive systems like ion injection normally required. The first proposal, made in the late 1970s, projected that the device would be able to produce about three or four times the power in fusion reactions as it used in powering the heaters and magnets. This represents a fusion energy gain factor (or simply "fusion gain" or Q) of three or four. The project was never completed as Guccioni was unable to secure the $150 million needed to build the full-sized device (much of which would have been for a large homopolar generator).

Fusion research establishment consideration

Studies carried out at the time suggest the Riggatron was not considered as much of a "sure thing" by other members of the fusion research establishment.[1][2] Existing experimental tokamaks generally do not include a lithium blanket, and are thus fairly similar to the Riggatron in layout, yet none of these reactors is close to generating a fusion gain of one, let alone the three that was being claimed for the Riggatron. In retrospect it appears the Riggatron concept likely would not have worked, due to the various plasma instabilities that were only being discovered coincident with its design process. Interest in the Riggatron has essentially disappeared.

With the demise of the original project, Bussard moved on to new inertial electrostatic confinement fusion designs with extremely high claimed performance. This culminated in his final development of IEC before his death in October 2007 - the Polywell device.

References

Selection of a toroidal fusion reactor concept for a magnetic fusion production reactor
"Evaluation of Riggatron Concept". Archived from the original on 2007-08-21. Retrieved 2006-11-18.

Fusion power, processes and devices
Core topics

Nuclear fusion
Timeline List of experiments Nuclear power Nuclear reactor Atomic nucleus Fusion energy gain factor Lawson criterion Magnetohydrodynamics Neutron Plasma

Processes,
methods
Confinement
type
Gravitational

Alpha process Triple-alpha process CNO cycle Fusor Helium flash Nova
remnants Proton-proton chain Carbon-burning Lithium burning Neon-burning Oxygen-burning Silicon-burning R-process S-process

Magnetic

Dense plasma focus Field-reversed configuration Levitated dipole Magnetic mirror
Bumpy torus Reversed field pinch Spheromak Stellarator Tokamak
Spherical Z-pinch

Inertial

Bubble (acoustic) Laser-driven Magnetized Liner Inertial Fusion

Electrostatic

Fusor Polywell

Other forms

Colliding beam Magnetized target Migma Muon-catalyzed Pyroelectric

Devices, experiments
Magnetic confinement
Tokamak
International

ITER DEMO PROTO

Americas

Canada STOR-M United States Alcator C-Mod ARC
SPARC DIII-D Electric Tokamak LTX NSTX
PLT TFTR Pegasus Brazil ETE Mexico Novillo [es]

Asia,
Oceania

China CFETR EAST
HT-7 SUNIST India ADITYA SST-1 Japan JT-60 QUEST [ja] Pakistan GLAST South Korea KSTAR

Europe

European Union JET Czech Republic COMPASS GOLEM [cs] France TFR WEST Germany ASDEX Upgrade TEXTOR Italy FTU IGNITOR Portugal ISTTOK Russia T-15 Switzerland TCV United Kingdom MAST-U START STEP

Stellarator
Americas

United States CNT CTH HIDRA HSX Model C NCSX Costa Rica SCR-1

Asia,
Oceania

Australia H-1NF Japan Heliotron J LHD

Europe

Germany WEGA Wendelstein 7-AS Wendelstein 7-X Spain TJ-II Ukraine Uragan-2M
Uragan-3M [uk]

RFP

Italy RFX United States MST

Magnetized target

Canada SPECTOR United States LINUS FRX-L – FRCHX Fusion Engine

Other

Russia GDT United States Astron LDX Lockheed Martin CFR MFTF
TMX Perhapsatron PFRC Riggatron SSPX United Kingdom Sceptre Trisops ZETA

Inertial confinement
Laser
Americas

United States Argus Cyclops Janus LIFE Long path NIF Nike Nova OMEGA Shiva

Asia

Japan GEKKO XII

Europe

European Union HiPER Czech Republic Asterix IV (PALS) France LMJ LULI2000 Russia ISKRA United Kingdom Vulcan

Non-laser

United States PACER Z machine

Applications

Thermonuclear weapon
Pure fusion weapon

International Fusion Materials Irradiation Facility ITER Neutral Beam Test Facility

Physics Encyclopedia

World

Index

Hellenica World - Scientific Library

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