High‐field launch electron‐cyclotron heating experiments in a bumpy torus

The midplane microwave heating system in the ELMO Bumpy Torus (EBT) [in P r o c e e d i n g s o f t h e S i x t h I n t e r n a t i o n a l C o n f e r e n c e o n P l a s m a P h y s i c s a n d C o n t r o l l e d N u c l e a r F u s i o n R e s e a r c h, 1976 (IAEA, Vienna, 1977), Vol. II, p. 145] was supplemented with power launched from the high‐field side of the fundamental resonance by an antenna in the magnet coil throat. Up to 43 kW of polarized (extraordinary mode), 28 GHz power was successfully launched with one antenna. Measurements were made of changes in the core and hot‐electron ring plasma parameters when throat‐launch power was added. In sharp contrast to initial expectations, the bulk core‐plasma parameters were degraded while the ring parameters, in the launch cavity, were improved. These results are consistent with a modified picture of electron‐cyclotron heating (ECH) in EBT. A picture of localized microwave absorption and particle losses is supported by additional measurements.