The National Spherical Torus Experiment (NSTX) (pictured and shown schematically ) at the U.S. Department of Energy’Princeton Plasma Physics Laboratory (PPPL) is yielding research results that may open an attractive path towards developing fusion energy as an abundant, safe, affordable and environmentally sound means of generating electricity. The NSTX device is exploring a novel structure for the magnetic field used to contain the hot ionized gas, called “plasma”, needed to tap this source of energy.

Future fusion power plants will contain plasmas consisting of a mixture of the hydrogen isotopes deuterium and tritium, which can undergo fusion reactions to produce helium, accompanied by a large release of energy, if a sufficient temperature and pressure can be maintained in the plasma using the insulation provided by a suitably shaped magnetic field. As shown in Fig. 1, the magnetic field in NSTX forms a plasma that is a torus since there is a hole through the center, but where the outer boundary of the plasma is almost spherical in shape, hence the name “spherical torus” or “ST”. The theory of magneto-hydrodynamics (MHD) describing the interaction of a plasma and a magnetic field shows that the plasma pressure needed to produce self-sustaining fusion in a ST can be maintained with a lower magnetic field strength. Since the cost of a fusion power plant will increase with the strength of its magnetic field, successful development of the ST approach to plasma confinement may lead to economical fusion power plants.

The mission of the NSTX is to establish the scientific potential of the ST configuration as a means of achieving practical fusion energy. If successful, the NSTX could be followed by a larger experiment to explore the issues needed for eventually harnessing fusion power continuously from a reactor. Farther down the line, there is the possibility of an ST-based compact Component Test Facility (CTF) to develop and test fusion power plant components. The NSTX research program for the next few years is designed both to explore the feasibility of these future steps for fusion development and to contribute to the success of other magnetic fusion experiments, such as the major international experiment ITER, by establishing a firm physics and technology foundation for its design and operation. The experiments on NSTX are being conducted by a collaborative research team of physicists and engineers from 30 U.S. laboratories and universities and 28 international institutions from 11 countries

Accomplishments

NSTX began operation in September 1999. As described below, through 2008, the NSTX research team has made excellent progress, both in exploring the characteristics and effectiveness of the ST configuration and in resolving scientific issues relevant for ITER and future experiments. In the process, the team has implemented numerous improvements in measurement and operational capabilities thereby opening the door to future progress in ST research.