Generic time evolution of temperature T( t) and electron density n( t) during an impulsive heating process with subsequent cooling, subdivided into two time phases of (1) dominant heating ( t _s < t < t _p ) and (2) dominant cooling ( t _p < t < t _e ). The maximum of the temperature profile T _m = T( t = t _m ) occurs at time t _m , and the density has a peak value n _p = n _e ( t = t _p ) at time t _p , approximately when the temperature drops to half of the maximum value, i.e., T _p = T _m /2.