Experimental study of gas flow through curved tubes in support of disruption mitigation experiments in DIII-D

High-pressure gas injection has been shown to be an effective disruption mitigation technique in the DIII-D tokamak, offering dramatic reductions in localized power deposition and forces to the internal components due to halo currents. To date, the gas (Ar, Ne, He, or H ₂) has been injected from the magnetic low-field side of the machine through close-coupled stainless steel tubes, with relatively high gas load per shot (up to 4000 torr-L in ≈10 ms). Another option for high-pressure gas injection in DIII-D is to utilize curved guide tubes similar to those presently used for magnetic high-Held side pellet injection with exit ports on the inner wall. To demonstrate the feasibility of this option, an experimental study with different tube diameters and configurations has been carried out in the laboratory. The test results indicate that sufficiently high gas flows can be delivered through the curved guide tubes as long as the tube bore is not too restrictive (≥7.5-mm diam). The experimental results are presented and discussed relative to the disruption mitigation experiments in DIII-D.