NSTX produces one megampere plasma current

December 20, 1999

Plainsboro, New Jersey -- On Tuesday, December 14, the National Spherical Torus Experiment (NSTX) at the U.S. Department of Energy's Princeton Plasma Physics Laboratory (PPPL) produced a one million ampere plasma current -- a new world record for a spherical torus device. Producing this plasma current sets the stage for the Laboratory to create and study plasma conditions that are relevant to the production of fusion energy.

Secretary of Energy Bill Richardson said, "I'm delighted that the NSTX experiment has met this technical milestone nine months ahead of schedule. We can now begin the scientific investigations that the machine is designed to do."

One million amperes is the highest plasma current ever produced in a spherical torus device. The previous record is 310,000 amperes achieved in a smaller spherical torus device called START -- the Small Tight Aspect Ratio Tokamak -- built by Culham Fusion Laboratory of U.K.

In the interior of the sun and other stars, matter is converted into energy by the fusion, or joining, of nuclei of light atoms to form heavier elements. At PPPL, physicists use a magnetic field to confine hot, ionized gas, called plasma, for research on fusion. Scientists hope eventually to use the energy produced by fusion for the production of electricity. Compared to fossil fuels and fission, now used in commercial power plants, fusion would have distinct advantages, including an inexhaustible fuel supply; no contribution to acid rain or global warming; and inherent safety, with minimal production of waste.

NSTX, which began operating in February, is designed to test the physics principles of spherical torus plasmas. It produces a plasma that is shaped like a sphere with a hole through its center. This configuration may have several advantages, a major one being the ability to confine a higher plasma pressure for a given magnetic field strength. This could lead to a less expensive development path for fusion energy.

A large current flows inside the NSTX plasma and heats the plasma in the same way the current heats an electric toaster or light bulb. This plasma current also produces a magnetic field so that the resulting magnetic field line spirals around inside the plasma. The spherical torus provides a special shape in these magnetic field lines that is calculated to contain high-temperature plasmas efficiently.

The production of a one-million-ampere plasma current on NSTX required the appropriate plasma shaping, such as the width and height of the cross section of the plasma torus. Proper plasma shaping helps eliminate plasma instabilities. By October of 1999, the NSTX team had produced all of the desirable plasma shapes that they plan to use on NSTX, also a key aspect of preparation for research.

NSTX is a proof-of-principle experiment -- a relatively inexpensive device, which will create conditions suitable for the study of fusion-energy-relevant plasma behavior and advanced plasma heating and current-drive techniques. It is not planned to produce significant fusion energy in this device.

NSTX Program Director Martin Peng said, "The goals of the next few years of research on NSTX are to produce high-quality scientific results and excellent plasma performance. If successful, NSTX will have an impact on the design of future devices. These machines would extend the temperatures, densities, and other plasma parameters to the levels necessary for fusion energy production."
PPPL, which is funded by the U.S. Department of Energy and managed by Princeton University, is a collaborative national center for science and innovation leading to an attractive fusion energy source. As the nation's steward for plasma science, the Department of Energy is the largest supporter of research in this important field that has connections to astrophysics, space physics, and materials science.

DOE/Princeton Plasma Physics Laboratory

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