FPN04-06

NSTX Sets New Records

February 12, 2004

The National Spherical Torus Experiment (NSTX) at the Princeton Plasma Physics Laboratory has been out of operation for the past year making repairs to a magnet that failed. It recently came back on line and, in its first full week of operations, set records for both toroidal and normalized beta. Beta is the ratio of plasma pressure to magnetic field pressure and is an important measure of fusion power density and efficiency. Using strong neutral beam heating, the NSTX team achieved toroidal betas of up to 37% and normalized betas of up to 7.

Machine performance was aided by boronization and conditioning of the neutral beam systems. High beta toroidal beta values were achieved with the plasma current being ramped to 1.3 MA. The high normalized beta was obtained through current ramp down experiments in which beta-poloidal reached 1.5. The results attained so far are encouraging indicators that target equilibrium with the most extreme values of poloidal and normalized beta can be produced to allow study of the effect of rotation on ST equilibria under these conditions.

H-mode plasmas were obtained throughout the week, with a special note that transitions were observed in double null plasmas using only one beam source for the first time. Global confinement times were calculated to be approximately twice the conventional L-mode scaling value for both L- and H-mode plasmas.

The neutral beam systems were able to support these experiments with all three sources operating at 90 keV for a total neutral power of over 6 MW.

Information on NSTX is posted at http://www.pppl.gov/projects/pages/nstx.html