The magnetic core material of the inductor dislpays high permeability and saturation of the flux density. In order to avoid saturation of the iron core at high currents and/or high flux density an air gap must be provided. The air gap length, in conjunction with the length of the magnetic circuit, defines the effective permeability of the inductor. This is evident in the B(H) characteristic shown in the animation where a larger air gap results in the reduction of the effective permeability. 

Adding an air gap to an inductor reduces the value of its inductance for the same number of turns, but allows a higher maximum current before saturation of the magnetic core is reached.

• Increase the air gap length to reduce the effective permeability as shown in the B(H)-characteristic.
• Reduce the air gap length to increase the amount of magnetic energy. As shown in the animation, almost the entire stored magnetic energy is concentrated in the air gap.
• Change the number of turns. More turns will increase the inductance (time behavior shown as L(t)).
• Change the load resistor to increase the current. With higher current, the core will go into saturation. In this case you can see the ripple in the time behavior of the inductance L(t).
• Change the time slider to visualize the current paths in the power circuit.