The magnetohydrodynamic kink instability is observed and identified experimentally as a poloidal flux amplification mechanism for coaxial gun spheromak formation. Plasmas in this experiment fall into three distinct regimes which depend on the peak gun current to magnetic flux ratio, with (I) low values resulting in a straight plasma column with helical magnetic field, (II) intermediate values leading to kinking of the column axis, and (III) high values leading immediately to a detached plasma. Onset of column kinking agrees quantitatively with the Kruskal-Shafranov limit, and the kink acts as a dynamo which converts toroidal to poloidal flux. Regime II clearly leads to both poloidal flux amplification and the development of a spheromak configuration.PACS numbers: 52.55. Ip,52.35.Py,52.30.Cv The spheromak [1, 2] is a simply-connected plasma configuration in which the magnetic fields are largely determined by dynamo-driven plasma currents. Because of its topological simplicity and ease of formation, the spheromak is of interest as a magnetic fusion confinement scheme [3]. Spheromak formation has traditionally been explained by Taylor's hypothesis [4] that a turbulent magnetohydrodynamic (MHD) system relaxes to a state of minimum magnetic energy subject to the constraint of constant magnetic helicity. While this hypothesis has successfully explained the existence and many equilibrium properties of spheromaks, it says nothing about the actual 3D dynamics underlying the relaxation process, e.g., for coaxial gun spheromaks, the dynamo mechanism which converts injected toroidal flux into required poloidal flux [5]. The dynamics must be 3D because Cowling's theorem [6] shows that purely axisymmetric processes cannot accomplish this. This Letter experimentally identifies the MHD kink instability [7] as a 3D mechanism which converts toroidal to poloidal flux in a coaxial gun system, thereby leading to spheromak formation. This mechanism should also be of fundamental importance to coaxial helicity injection in spherical tori [8], relaxation in reversed-field pinches [4], solar coronal plasma instabilities [9], and astrophysical jets [10].Plasmas in this experiment fall into three regimes depending on peak λ gun = µ 0 I gun /ψ gun (where I gun is the gun current and ψ gun is the bias poloidal magnetic flux intercepting the inner gun electrode), with (I) low values resulting in a straight plasma column with helical magnetic field along the symmetry axis, (II) intermediate values leading to kinking of the column axis, and (III) high values leading immediately to a detached plasma with B tor ≫ B pol . Onset of column kinking agrees quantitatively with the Kruskal-Shafranov limit [7], and the kink acts as a dynamo which converts toroidal to poloidal flux. Regime II clearly leads to both poloidal flux amplification * Now at: Los Alamos National Laboratory, Los Alamos, NM 87545 and magnetic field profiles consistent with spheromak formation. These results are qualitatively consistent with recent time-dependent resistive MHD nu...