Deflection of Interferometry Beams due to Transverse Refractive Index Gradient in SST-1

TL;DR

This paper analyzes how transverse plasma density gradients in tokamaks cause deflection of THz interferometry beams, affecting measurement accuracy, through analytical and ray tracing methods for different plasma shapes.

Contribution

It provides analytical and numerical methods to evaluate beam deflection caused by plasma density gradients in tokamaks, aiding in accurate electron density diagnostics.

Findings

Refractive bending depends on plasma shape and density gradient.

Ray tracing confirms analytical predictions for D-shaped plasmas.

Beam deflection can impact diagnostic accuracy in tokamak measurements.

Abstract

Far Infrared interferometry is the main diagnostics method for electron density measurements in medium sized tokamaks. The transverse density gradients of plasma produce refractive effect, and the probing radiation does not propagate along a straight line and gets deflected. Therefore, it is necessary to evaluate the plasma effect on beam direction to verify if the used wavelength is compatible with the machine geometry. This paper presents the analytical results of refractive bending of THz beam due to transverse density gradients for circular and elliptical cross section plasma. The results from ray tracing integration to calculate refractive bending in D-shaped plasmas are also presented.