The response of the Tore Supra edge plasma to supersonic pulsed gas injection

The response of the scrape-off layer (SOL) to supersonic pulsed gas injection (SPGI) in Tore Supra is measured by a reciprocating Mach probe. The edge density increases abruptly following injection and decays to its pre-injection value in about 10 ms. The edge temperature falls to 5–10 eV range. The perturbation appears to be toroidally symmetric. The density increase depends on the injected amount of deuterium gas, but the temperature decrease does not. The parallel Mach number changes during the density spike; the sign of the change depends on the poloidal location of the injection nozzle. We use a simple one-dimensional fluid model for the SOL to interpret the measurements. The Mach number change lasts about 10 ms as well, indicating the existence of a poloidally localized ionization source in the vicinity of the nozzle.