X-mode beam broadening in turbulent plasma.

It is shown that plasma turbulence at the edge of a fusion machine can lead to significant broadening of an X-mode microwave beam, which also impacts the performance of the heating systems and diagnostics. Based on a similar method developed for O-mode polarization, the expression for the mean microwave power distribution after the beam passes through the plasma edge turbulence is obtained, and its spatial and probabilistic distributions are analyzed. As this polarization is used for collective Thomson scattering (CTS) on ITER and for electron cyclotron resonance heating (ECRH) on ASDEX Upgrade, numerical simulations of beam broadening due to the edge turbulence are performed for the two conditions of plasma parameters, related to the planned CTS experiments on ITER and to ECRH experiments on ASDEX Upgrade. Ideas to reduce the beam broadening induced by the edge turbulence in the CTS case have been tested and are summarized in the conclusion. [ABSTRACT FROM AUTHOR]