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

stellarator A stellarator is a plasma device that relies primarily on external magnets to confine a plasma. Scientists researching magnetic confinement fusion aim to use stellarator devices as a vessel for nuclear fusion reactions. The name refers to the ...

at the

Columbia University Columbia University (also known as Columbia, and officially as Columbia University in the City of New York) is a private research university in New York City. Established in 1754 as King's College on the grounds of Trinity Church in Manhatt ...

Plasma Physics Plasma ()πλάσμα
, Henry George Liddell, R ...

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 known ...

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 National Science Foundation (NSF) is an independent agency of the United States government that supports fundamental research and education in all the non-medical fields of science and engineering. Its medical counterpart is the National ...

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 manages the research and development of nuclear power and nuclear weapons in the United Stat ...

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 con ...

made of 316 stainless steel, 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 unit of pressure based on an absolute scale, defined as exactly of a standard atmosphere (). Thus one torr is exactly (≈ ). Historically, one torr was intended to be the same as one " millimeter of merc ...

. CNT is unique in its simple geometry. Magnetic surfaces are created using only four electromagnetic coils – 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 is a vector 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 to its own velocity and to ...

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 movement of humans, animals, and goods from one location to another. Modes of transport include air, land ( rail and road), water, cable, pipelin ...

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 phenomena a ...

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 to be a bridge or a connection between physics and engineering. "Applied" is distinguished from "pure" by a subtle combination ...

and

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

Fu Foundation School of Engineering and Applied Science The Fu Foundation School of Engineering and Applied Science (popularly known as SEAS or Columbia Engineering; previously known as Columbia School of Mines) is the engineering and applied science school of Columbia University. It was founded as th ...

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