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 similar to100% conversion of thermally emitted electron Bernstein waves to the X mode. This has been achieved by controlling the electron density scale length (L-n) in the conversion region with a local limiter outside the last closed flux surface, shortening L-n 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.