Alcator C-Mod

Gregory Wallace

Updated: 07/14/06

In a tokamak, the poloidal field responsible for confining the plasma is generated by the toroidal current in the plasma.  Most tokamaks, including CMOD, depend on an ohmic transformer as the primary means of driving toroidal current in the plasma.  A transformer works by changing the magnetic flux through a conducting loop (i.e. the plasma), thus inducing a current in that loop.  This works well for short pulses, but an ohmic transformer cannot sustain steady-state plasma operation due to the fact that the magnetic flux cannot increase infinitely.

The Lower Hybrid Current Drive (LHCD) experiment on CMOD aims towards steady state operation by driving current in the plasma with radio frequency waves. These "lower hybrid waves" propagate in one direction around the torus, damping on electrons traveling in the same direction at roughly the same speed.  This gives rise to a population of super-thermal electrons traveling in one direction around the torus, thus creating a net current.

My research currently focuses on experimental aspects of the LHCD system such as determining the antenna coupling and current drive efficiency, arc detection, and pushing towards higher power and more current drive.