The experimental realization of a Kitaev model on the honeycomb lattice has been a major topic in a condensed matter physics because the model uniquely provides exactly solvable quantum spin liquid ground states regarding fractionalized Majorana fermions. The newly discovered alpha-RuCl3 forming a perfect honeycomb lattice with Ising-like spin-spin interaction has strong indications that it lies in proximate to a Kitaev spin liquid phase. Although the material exhibits antiferromagnetic ordering below 6.5 K, the hidden Kitaev physics in the ordered ground state is still ambiguous, and an external magnetic field can give a control parameter for addressing Kitaev Physics. We propose inelastic neutron scattering study on the alpha-RuCl3 single crystal to explore the magnetic field driven quantum phase transition and quantum criticality.