The Columbia Non-neutral Torus (CNT) is a small

stellarator A stellarator confines Plasma (physics), plasma using external magnets. Scientists aim to use stellarators to generate fusion power. It is one of many types of magnetic confinement fusion devices. The name "stellarator" refers to stars because ...

at the

Columbia University Columbia University in the City of New York, commonly referred to as Columbia University, is a Private university, private Ivy League research university in New York City. Established in 1754 as King's College on the grounds of Trinity Churc ...

Plasma Physics Plasma () is a state of matter characterized by the presence of a significant portion of charged particles in any combination of ions or electrons. It is the most abundant form of ordinary matter in the universe, mostly in stars (including th ...

Laboratory designed by Thomas Sunn Pedersen with the aid of Wayne Reiersen and Fred Dahlgren of the

Princeton Plasma Physics Laboratory Princeton Plasma Physics Laboratory (PPPL) is a United States Department of Energy national laboratory for plasma physics and nuclear fusion science. Its primary mission is research into and development of fusion as an energy source. It is know ...

to conduct the first investigation of non-neutral plasmas confined on magnetic surfaces. The experiment, which began operation in November 2004, is funded by the

National Science Foundation The U.S. National Science Foundation (NSF) is an Independent agencies of the United States government#Examples of independent agencies, independent agency of the Federal government of the United States, United States federal government that su ...

and the

United States Department of Energy The United States Department of Energy (DOE) is an executive department of the U.S. federal government that oversees U.S. national energy policy and energy production, the research and development of nuclear power, the military's nuclear w ...

in the form of a Faculty Early Career Development (CAREER) award.

Technical design

CNT, which is housed in a cylindrical

vacuum chamber A vacuum chamber is a rigid enclosure from which air and other gases are removed by a vacuum pump. This results in a low-pressure environment within the chamber, commonly referred to as a vacuum. A vacuum environment allows researchers to c ...

made of 316

stainless steel Stainless steel, also known as inox, corrosion-resistant steel (CRES), or rustless steel, is an iron-based alloy that contains chromium, making it resistant to rust and corrosion. Stainless steel's resistance to corrosion comes from its chromi ...

, measures 60 inches in diameter and stands 75 inches tall. The empty chamber is capable of reaching a pressure of 2x10⁻¹⁰

Torr The torr (symbol: Torr) is a Pressure#Units, unit of pressure based on an absolute scale, defined as exactly of a standard atmosphere (unit), atmosphere (101325 Pa). Thus one torr is exactly (≈ ). Historically, one torr was intended to be ...

. CNT is unique in its simple geometry. Magnetic surfaces are created using only four

electromagnetic coil An electromagnetic coil is an electrical Electrical conductivity, conductor such as a wire in the shape of a wiktionary:coil, coil (spiral or helix). Electromagnetic coils are used in electrical engineering, in applications where electric curre ...

s – two interlocking coils inside the chamber, and two poloidal field coils outside the chamber. The two interlocking coils have a radius of .405m, and the angle between them can be manually selected to be 64°, 78°, or 88°, allowing for different shear and rotational transform values, and magnetic surface configuration. The poloidal field coils have a radius of 1.08 m. The coils are powered by a 200 kW power supply and are capable of producing

magnetic fields A magnetic field (sometimes called B-field) is a physical field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular ...

of 0.01–0.2T. The configuration of CNT creates a very low aspect ratio of 1.9, the lowest of any stellarator built.

Research

Thomas Sunn Pedersen is the principal investigator of CNT, which studies several areas of theoretical and experimental non-neutral plasma physics. These include the equilibrium of non-neutral plasmas,

transport Transport (in British English) or transportation (in American English) is the intentional Motion, movement of humans, animals, and cargo, goods from one location to another. Mode of transport, Modes of transport include aviation, air, land tr ...

and confinement, and ion-related instabilities. The CNT theory program is run by Pedersen and Prof. Allen Boozer, also at Columbia University. First studies on CNT showed the successful creation of magnetic surfaces with the simple four coil design. At sufficiently low neutral pressures and sufficiently high magnetic field strengths, the plasmas are essentially pure electron plasmas and are

macroscopic The macroscopic scale is the length scale on which objects or phenomena are large enough to be visible with the naked eye, without magnifying optical instruments. It is the opposite of microscopic. Overview When applied to physical phenome ...

ally stable with confinement times of up to 20 ms. Transport is driven by collisions with neutrals as well as E x B drift along insulating rods inserted into the plasma. At higher neutral pressures (10⁻⁷ Torr and above), an ion related instability is observed, with a frequency in the 10–50 kHz range, and a poloidal mode number ''m'' = 1. The CNT group installed a conducting boundary in August 2007 to study its effects on confinement times, and to allow measurements in the absence of internal rods. Future plans for CNT include the study of electron-positron plasmas confined on magnetic surfaces and further studies of partly neutralized plasmas.

References

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External links

CNT homepage

at

Department of

Applied Physics Applied physics is the application of physics to solve scientific or engineering problems. It is usually considered a bridge or a connection between physics and engineering. "Applied" is distinguished from "pure" by a subtle combination of fac ...

and

Applied Mathematics Applied mathematics is the application of mathematics, mathematical methods by different fields such as physics, engineering, medicine, biology, finance, business, computer science, and Industrial sector, industry. Thus, applied mathematics is a ...

Fu Foundation School of Engineering and Applied Science The Fu Foundation School of Engineering and Applied Science (also known as SEAS or Columbia Engineering; historically Columbia School of Mines) is the engineering and applied science school of Columbia University, a private research university ...

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