A magnetic structure comprises a plurality of magnetic elements configured to generate high-gradient magnetic field regions. Magnetic conductive material may be placed on or around the elements of the magnetic structure to shape and focus the high-gradient magnetic field regions. A magnetic element may be configured so as to project a magnetic field region generated by the magnetic structure. The generation and projection may be controlled. For example, one or more of the magnetic elements may be an electromagnet, or mechanical systems may be used to position the magnetic elements with respect to one another.
