A multiple-beam, collective scattering technique for spatially resolved measurement of plasma turbulence

Collective Thomson scattering has long been utilized to study electrostatic turbulence in magnetic confinement fusion plasmas with a view to demonstrating a causal link to the observed anomolous transport of heat and particles. However, this goal has been severly hampered by the relatively poor spatial resolution available at the dominant turbulence wave numbers using standard experimental techniques. Good spatial resolution is necessary if adequate comparison of theory and experiment is to occur. The present paper describes the basic principles of a new technique utilizing simultaneous, multiple input beams, a detector array, and coherent tomographic inversion algorithm, which can substantially improve the available spatial resolution for these important measurements. The proposed multiple beam scattering diagnostic offers a spatial resolution of ∼10 cm at a fluctuation wave number of 5 cm-1 when the angular envelope of the beams is 0.1 rad. Optical designs suitable for implementing the multiple beam diagnostic on a large tokamak have been developed