Impurity injection experiment on the TEXTOR tokamak: Effect of detached plasmas on confinement time

A marked increase in the confinement time of injected impurities was measured during detachment of the plasmas in the TEXTOR tokamak. Non-recycling, metallic elements were introduced via laser blow-off, and scaling studies were performed. As the electron density increased, a threshold was reached beyond which the decay time of the brightness of the injected impurity transition was seen to increase from 75 ms to greater than 500 ms. The detachment of the plasma appeared coincident with the onset of this long confinement regime.