Ion Optics With Oval Apertures for TCV NBI

The neutral beam injection system is a key part of the TCV machine, which is actively exploited in different experimental campaigns. Development of a new ion-optical system (IOS) for the heating beam with intermediate particle energy (up to ~38 keV) has been performed, having obtained the beam simulation results by the IBSimu code. The validity of IBSimu calculations for the existing design concepts was cross-checked with the experimental data of beam profiles and divergence. The newly developed concept of oval apertures was implemented into the geometry of beam elementary cells. Athermal–mechanical analysis was performed for the full-scale plasma grid with ANSYS. The design provides generation of ion beams with oval cross section, which helps for a better accommodation of them within rectangular or oval/elliptic beam ports, thus minimizing beam–wall interactions, which is critical for high-density neutral beams transmitted through beam ducts or ports with small dimensions. This solution also combines the advantages of ion optics with circular beamlets (high strength and geometric stability of electrodes) together with the advantages of ion optics with slit beamlets (reduced beam divergence in one direction, and increased beam current due to a combination of higher density and grid transparency). Numerical simulations of the new oval beamlet conception have demonstrated low divergence, providing reduced beam losses. Beams generated by oval elementary cells can be applied in fusion devices for plasma heating and diagnostics, as well as in high-energy experimental and industrial accelerators, where the beam duct dimensions have a moderate aspect ratio and are limited by size.