Controlled Optimization of Mode Conversion from Electron Bernstein Waves to Extraordinary Mode in Magnetized Plasma

In the CDX-U spherical torus, agreement between radiation temperature and Thomson scattering electron temperature profiles indicates [Formula presented] conversion of thermally emitted electron Bernstein waves to the [Formula presented] mode. This has been achieved by controlling the electron density scale length ([Formula presented]) in the conversion region with a local limiter outside the last closed flux surface, shortening [Formula presented] to the theoretically required value for optimal conversion. From symmetry of the conversion process, prospects for efficient coupling in heating and current drive scenarios are strongly supported.