An apparatus for measuring the transport time of impurity particles in a plasma includes a spectrometer, a system for the spatially-resolving conversion into charge of light exiting the spectrometer, an integrator circuit for the spatially-resolving integration of the charge, as well as a display screen that presents the integrated charge as a series of spectral lines. The integrator circuit is assembled from discrete components. Thus, the transport of plasma impurities can be properly measured.