Schematic of NSTX in 2002                                National spherical Torus Experiment (NSTX) in January 2001
 

The National Spherical Torus Experiment (NSTX) is an innovative magnetic fusion device that was constructed by the Princeton Plasma Physics Laboratory (PPPL). It is being used to study the physics principles of spherically shaped plasmas -- hot ionized gases in which nuclear fusion will occur under the appropriate conditions of temperature, density, and confinement in a magnetic field. Fusion is the energy source of the Sun and all the stars. Scientists believe it can provide an inexhaustible, safe, and environmentally attractive source of energy on earth. These experiments are being performed by a national team comprised of twenty-one fusion research institutions throughout the U.S. Scientists from Europe, Japan and Russia also participate in the research.

NSTX (http://nstx.pppl.gov/index.html) produces plasma that is shaped like a sphere with a hole through its center, different from the "donut" shaped plasmas of conventional tokamaks. This innovative plasma configuration may have several advantages, a major one being the ability to confine a higher plasma pressure for a given magnetic field strength. Since the amount of fusion power produced is proportional to the square of the plasma pressure, the use of spherically shaped plasmas could allow the development of smaller, more economical fusion reactors. NSTX's attractiveness may be further enhanced by its ability to produce a high "bootstrap" electric current. This self-driven internal plasma current would significantly reduce the power requirements of externally driven plasma currents required to heat and confine the plasma.

The mission of the NSTX program is to establish the scientific potential of the spherical torus configuration as a means of achieving practical fusion energy.

The low toroidal field of spherical torus results in plasmas with different parameters from those in conventional aspect ratio tokamaks. This in turn leads to new challenge for making some measurements and new requirements for others. The following sections are taken from a recent DOE diagnostics proposal solicitation and provide a brief description of the topical areas, for which enhanced measurement capabilities are required and which guide the UC Davis development activities
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I. Measurement of Transport and Turbulence-physical process that govern heat, particle and momentum confinement;
II. Measurement of Macroscopic MHD Stability Properties- role of magnetic structure in plasma pressure and bootstrap current;
III. Measurement of Wave-Particle Interactions- role of electromagnetic waves, modes and energetic particles in sustaining and controlling hot plasmas;
IV. Measurement of Startup, Ramp-up and Sustainment Process- physical process of magnetic flux generation and sustainment;
V. Measurement of Boundary Physics- interface between fusion plasmas and normal temperature surroundings;
VI. Measurement of Physics Integration Processes- physics synergy of external control and self-organization.