Events at Physics |
Events on Wednesday, January 14th, 2026
- Preliminary Exam
- Tokamak Plasmas above Traditional Density Limits in the Madison Symmetric Torus
- Time: 1:00 pm - 3:00 pm
- Place: 5280 Chamberlin
- Speaker: Joseph Flahavan
- Abstract: Recent experiments in the Madison Symmetric Torus (MST) have demonstrated the capability of sustaining stable tokamak plasmas with densities far above the Greenwald limit, up to 18nG. The Greenwald limit, nG, is an empirically determined upper limit on the line-averaged electron density for stable operation of current-carrying toroidal laboratory plasmas, including tokamaks. Fusion power increases with density, making it of interest to determine the nature of MST’s ability to operate without disruptions at densities far greater than the conventional limit. When the electron density approaches 2nG, a distinct equilibrium develops with broadened electron density and nearly flat current density profiles. This happens to occur near the Sudo limit, nS, an empirical density limit observed in stellarators that is attributed to radiative collapse and is dependent on input power. Here, I present direct measurements, profile reconstructions, and fluctuation analysis across the range of densities that has been accessed in MST tokamak plasmas, 0.5 < ne/nG < 18, with a focus on plasmas near nG and nS where changes in behavior are observed. Experimental results are compared to several different theoretical models of the Greenwald density limit, including those involving enhanced edge turbulence or radiation-destabilized tearing modes.
- Host: John Sarff