Figure 3: Fifteen-ion crystals for different axial potentials.
From: Control of the conformations of ion Coulomb crystals in a Penning trap
Experimentally obtained images of 15-ion crystals (left of each panel) compared with computer simulations (right of each panel). By increasing the axial confinement, a linear string is transformed into a zigzag structure, then a 3D crystal and finally a planar structure. Each image is labelled with the value of the normalized axial trapping frequency, 
(the trap becomes unstable when this quantity is equal to unity). There is a 100-μm scale bar in the bottom right-hand pane, which applies to all the images.
