The high- k poloidal scattering system for NSTX-U

R Barchfeld; C W Domier; Y Ren; R Ellis; P Riemenschneider; N Allen; R Kaita; B Stratton; J Dannenberg; Y Zhu; N C Luhmann Jr

doi:10.1063/1.5035410

The high- k poloidal scattering system for NSTX-U

Rev Sci Instrum. 2018 Oct;89(10):10C114. doi: 10.1063/1.5035410.

Authors

R Barchfeld¹, C W Domier¹, Y Ren², R Ellis², P Riemenschneider¹, N Allen², R Kaita², B Stratton², J Dannenberg¹, Y Zhu¹, N C Luhmann Jr¹

Affiliations

¹ Department of Electrical and Computer Engineering, University of California, Davis, California 95616, USA.
² Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA.

PMID: 30399655
DOI: 10.1063/1.5035410

Abstract

An 8-channel, high-k poloidal far-infrared (FIR) scattering system is under development for the National Spherical Torus eXperiment Upgrade (NSTX-U). The 693 GHz poloidal scattering system replaces a 5-channel, 280 GHz high-k toroidal scattering system to study high-k electron density fluctuations on NSTX-U. The FIR probe beam launched from Bay G is aimed toward Bay L, where large aperture optics collect radiation at 8 simultaneous scattering angles ranging from 2° to 15°. The reduced wavelength in the poloidal system results in less refraction, and coupled with a new poloidal scattering geometry, extends measurement of poloidal wavenumbers from the previous limit of 7 cm^-1 up to >40 cm^-1. Steerable launch optics coupled with receiver optics that can be remotely translated in 5 axes allow the scattering volume to be placed from r/a = 0.1 out to the pedestal region (r/a ∼ 0.99) and allow for both upward and downward scattering to cover different regions of the 2D fluctuation spectrum.