A new technique for directly measuring the safety factor, or q, profile in a tokamak is described. A tightly collimated neutral beam capable of injecting approximately 100 mA of 30 keV deuterium atoms was mounted on the Adiabatic Toroidal Compressor tokamak. By proper tangential aiming of the beam a strong concentration of circulating fast ions was created at a chosen plasma minor radius. Through examination of the orbits of these ions with a multi-sight-line charge exchange detector, it was possible to measure the shifts of the orbits off magnetic surfaces, and thereby make local measurements of q. This experiement showed that when q on axis reached unity, strong internal turbulence began, and further lowering of q at the outer edge of the plasma did not lower q(0). A second result was that the measured q(0) was approximately 1.8 times larger than the q(0) deduced from the Tc(r) profile, assuming Z eff to be independent of minor radius. This suggests a significant peaking of Zeff on axis.
All Science Journal Classification (ASJC) codes
- Computational Mechanics
- Condensed Matter Physics
- Mechanics of Materials
- Mechanical Engineering
- Fluid Flow and Transfer Processes