Design of a microwave back-scattering diagnostic for lower-hybrid waves on TST-2

Non-inductive plasma start-up with lower-hybrid waves has been investigated on the TST-2 spherical tokamak at the University of Tokyo. The current drive efficiency drops dramatically above the density that is roughly consistent with the wave accessibility limit. For a more quantitative analysis, wave measurement in the plasma core is important. A new microwave back-scattering diagnostic is being fabricated for this purpose. The design of the back-scattering system and the analysis of the expected signal level are presented. The actual wave measurements will also be presented if available.