  An external magnetic field can induce a transition in $\alpha$-RuCl$_3$ from
an ordered zigzag state to a disordered state that is possibly related to the
Kitaev quantum spin liquid. Here we present new field dependent inelastic
neutron scattering and magnetocaloric effect measurements implying the
existence of an additional transition out of the quantum spin liquid phase at
an upper field limit $B_u$. The neutron scattering shows three distinct regimes
of magnetic response. In the low field ordered state the response shows magnon
peaks; the intermediate field regime shows only continuum scattering, and above
$B_u$ the response shows sharp magnon peaks at the lower bound of a strong
continuum. Measurable dispersion of magnon modes along the $(0,0,L)$ direction
implies non-negligible inter-plane interactions. Combining the magnetocaloric
effect measurements with other data a $T-B$ phase diagram is constructed. The
results constrain the range where one might expect to observe quantum spin
liquid behavior in $\alpha$-RuCl$_3$.
