Normalized damping time of torsional Alfvén waves (T_d/T₀) vs. wave period (T₀) for three different situations from top to bottom: faint cell center area (FAL93-A), bright network (FAL93-F), and prominence core. The blue line indicates the wave damping due to collision of ions with neutral hydrogen atoms alone. The red line indicates the wave damping due to collision of ions with neutral hydrogen and neutral helium atoms.