Analysis of pellet propellant gas expansion in the test bench of the ITER DMS Support Laboratory

The analysis of the gas expansion in the test bench of the ITER DMS Support Laboratory is discussed. For this purpose, numerical FEM simulations were performed during the design phase of the laboratory. These are compared with experimental data, that have been obtained after the construction of the test bench was finished. The numerical and experimental results have been found to agree well. Both indicate the emergence of pressure waves in the acceleration barrel. These contribute to the pellet detachment from the barrel wall. Supersonic velocities have been also observed in the simulations, and an indirect indication for their presence has been found in the experimental results. The main processes during the propellant gas expansion inside the propellant gas recovery chamber are discussed, and a rough estimate for the amount of gas entering the flight tube of the test bench before the pellet is presented.