Principle of Helical \& Nonhelical Dynamo and $\alpha$ effect in Field
  Structure model
  We explain the (non)helical dynamo process using a field-structure model
based on magnetic induction equation in an intuitive way. We show how
nonhelical kinetic energy converts into magnetic energy and cascades toward
smaller eddies in a mechanically forced plasma system. Also, we show how
helical magnetic energy is inversely cascaded ($\alpha$ effect) toward large
scale magnetic eddies in a mechanically or magnetically forced system. We,
then, compare the simulation results with the model qualitatively for the
verification of the model. In addition to these intuitive and numerical
approaches, we show how to get $\alpha$ and $\beta$ coefficient
semi-analytically from the temporally evolving large scale magnetic energy and
magnetic helicity.
