Abstract
The feasibility of using lower-hybrid wave damping measurement as a diagnostic for energetic (above 200 keV) alpha particles has been investigated for large tokamaks like TFTR and FED devices. Detailed ray tracing calculations show that slow lower-hybrid waves can be used for TFTR, but the fast lower-hybrid wave is necessary for wave penetration into the dense plasma core of FED. It is possible to launch waves mainly damped on the energetic alpha particles whose velocity distribution function f∝(r,v,t) is related to the wave damping rate. A 1% energetic alpha-particle concentration would cause substantial wave damping measurable by FIR laser scattering systems. Preliminary estimates show that this technique should yield good temporal resolution (∼1 ms) and some spatial resolution for the alpha-particle distribution function. However, extensive computation is necessary to unfold the velocity dependence if it is at all possible.
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