Impuritry Pellet Injector (TESPEL)
TESPELs (tracer-encapsulated solid pellet) consist of a polystyrene (CH(C6H5)CH2−) outer shell (d = 0.5 - 0.9 mm), filled with tracer particles in the core (d = 0.1 - 0.2 mm). They are injected into W7-X core plasma by means of a helium driven pneumatic pipe gun. As soon as a TESPEL enters the plasma edge, the surface of the polystyrene shell ablates and emits radiation of excited/ionized hydrogen and carbon. At some instant the polystyrene shell will be eroded completely and immediately the inner metallic impurity will be exposed to the plasma. Then the metallic impurity particles start to emit their own radiation.