Columbia Non-neutral Torus
Encyclopedia
The Columbia Non-neutral Torus (CNT) is a small stellarator
at the Columbia University
Plasma Physics Laboratory designed by Thomas Sunn Pedersen with the aid of Wayne Reiersen and Fred Dahlgren of the Princeton Plasma Physics Laboratory
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
and the United States Department of Energy
in the form of a Faculty Early Career Development (CAREER) award.
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
.
CNT is unique in its simple geometry. Magnetic surfaces are created using only 4 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 64o, 78o, or 88o, allowing for different shear and rotational transform values, and magnetic surface configuration. The poloidal field coils have a radius of 1.08m. The coils are powered by a 200 kW power supply and are capable of producing magnetic fields of 0.01-0.2T. The configuration of CNT creates a very low aspect ratio of 1.9, the lowest of any stellarator built.
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
ally stable with confinement times of up to 20 msec. 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.
Stellarator
A stellarator is a device used to confine a hot plasma with magnetic fields in order to sustain a controlled nuclear fusion reaction. It is one of the earliest controlled fusion devices, first invented by Lyman Spitzer in 1950 and built the next year at what later became the Princeton Plasma...
at the Columbia University
Columbia University
Columbia University in the City of New York is a private, Ivy League university in Manhattan, New York City. Columbia is the oldest institution of higher learning in the state of New York, the fifth oldest in the United States, and one of the country's nine Colonial Colleges founded before the...
Plasma Physics 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
Princeton Plasma Physics Laboratory is a United States Department of Energy national laboratory for plasma physics and nuclear fusion science located on Princeton University's Forrestal Campus in Plainsboro Township, New Jersey. Its primary mission is research into and development of fusion as an...
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
National Science Foundation
The National Science Foundation is a United States government agency that supports fundamental research and education in all the non-medical fields of science and engineering. Its medical counterpart is the National Institutes of Health...
and the United States Department of Energy
United States Department of Energy
The United States Department of Energy is a Cabinet-level department of the United States government concerned with the United States' policies regarding energy and safety in handling nuclear material...
in the form of a Faculty Early Career Development (CAREER) award.
Technical Design
CNT, which is housed in a cylindrical vacuum chamberVacuum chamber
A vacuum chamber is a rigid enclosure from which air and other gases are removed by a vacuum pump. The resulting low pressure, commonly referred to as a vacuum, allows researchers to conduct physical experiments or to test mechanical devices which must operate in outer space...
made of 316 stainless steel
Stainless steel
In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....
, measures 60 inches in diameter and stands 75 inches tall. The empty chamber is capable of reaching a pressure of 2x10-10 Torr
Torr
The torr is a non-SI unit of pressure with the ratio of 760 to 1 standard atmosphere, chosen to be roughly equal to the fluid pressure exerted by a millimetre of mercury, i.e., a pressure of 1 torr is approximately equal to 1 mmHg...
.
CNT is unique in its simple geometry. Magnetic surfaces are created using only 4 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 64o, 78o, or 88o, allowing for different shear and rotational transform values, and magnetic surface configuration. The poloidal field coils have a radius of 1.08m. The coils are powered by a 200 kW power supply and are capable of producing magnetic fields of 0.01-0.2T. The configuration of CNT creates a very low aspect ratio of 1.9, the lowest of any stellarator built.
| Parameter | Value |
|---|---|
| ne | 1012-1014 m−3 |
| Te | 1-100 eV |
| B | 0.01-0.2T |
| R | 0.3m |
| a | 0.1m |
| P | 10−10 Torr |
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, transportMagnetorotational instability
The magnetorotational instability or MRI is a fluid instability that arises when the angular velocity of a magnetized fluid decreases as the distance from the rotation center increases. It can also be known as the Velikhov-Chandrasekhar instability or Balbus-Hawley instability in the literature;...
and confinement, and ion-related instabilities
Plasma stability
An important field of plasma physics is the stability of the plasma. It usually only makes sense to analyze the stability of a plasma once it has been established that the plasma is in equilibrium. "Equilibrium" asks whether there are net forces that will accelerate any part of the plasma...
. 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
Macroscopic
The macroscopic scale is the length scale on which objects or processes are of a size which is measurable and observable by the naked eye.When applied to phenomena and abstract objects, the macroscopic scale describes existence in the world as we perceive it, often in contrast to experiences or...
ally stable with confinement times of up to 20 msec. 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.
External links
- CNT homepage
- CNT publications at Columbia UniversityColumbia UniversityColumbia University in the City of New York is a private, Ivy League university in Manhattan, New York City. Columbia is the oldest institution of higher learning in the state of New York, the fifth oldest in the United States, and one of the country's nine Colonial Colleges founded before the...
Department of Applied PhysicsApplied physicsApplied physics is a general term for physics which is intended for a particular technological or practical use.It is usually considered as a bridge or a connection between "pure" physics and engineering....
and Applied MathematicsApplied mathematicsApplied mathematics is a branch of mathematics that concerns itself with mathematical methods that are typically used in science, engineering, business, and industry. Thus, "applied mathematics" is a mathematical science with specialized knowledge...
, Fu Foundation School of Engineering and Applied ScienceFu Foundation School of Engineering and Applied ScienceThe Fu Foundation School of Engineering and Applied Science is a school of Columbia University which awards Bachelor of Science, Master of Science, Master of Financial Engineering, Doctor of Philosophy, Doctor of Science, Doctor of Engineering degrees in engineering, applied physics and applied...