What does it mean to call a collisional plasma model density-dependent?
All plasma emission models are inherently density-dependent, since the more dense the plasma, the more collisions will occur and the more emission will be generated. Since the collisions involve electrons and ions, the density-dependence due to this effect is proportional to the overall density squared. However, there is another type of density-dependence which occurs when some of the underlying assumptions for a coronal plasma break down. As the density increases, some metastable energy levels will tend to be excited (or de-excited) by collisions before sufficient time has elapsed for spontaneous radiative decay to occur. This will modify the emitted spectrum, increasing the strengths of some lines and decreasing others. The effect is subtle, and likely impossible to observe with low or moderate resolution detectors. However, high-resolution devices with E/dE > 300 will be able to detect such effects in hot plasmas.
