Improved heating and diagnostic capabilities at the HSX stellarator

The Helically Symmetric eXperiment (HSX) has demonstrated excellent neoclassical confinement with core-electron temperatures above 2 keV, and strong trapped electron mode turbulence in the outer region enables studies of turbulent fluctuations. Several new systems and upgrades are being commissioned to improve the plasma performance and diagnostic capabilities. A 70 GHz Electron Cyclotron Resonance Heating system is being installed that will allow for plasma operation with increased densities (2x10¹⁹ m^-3) and absorbed powers (200 kW). The increased operational range will allow for the exploration of plasmas with higher normalized pressures and modified neutral penetration depths. Moreover, installation of a 20 keV neutral beam injection (NBI) system with tangential geometry is planned for direct ion heating, current drive, and fast-ion confinement studies. The HSX diagnostic suite is undergoing extensive improvements. The Thomson Scattering system has been equipped with new high-speed electronics [1] and leverages a new multi-bandpass filtering technique. A multi-channel poloidal reflectometry system is under development to facilitate the investigation of turbulent fluctuations at different positions in the plasma. Fluctuation measurements will be combined with an upgraded correlation electron cyclotron emission diagnostic to study core density and temperature fluctuations.

[1] W. Goodman et al, 2022 Rev. Sci. Instrum. 93