Magnetic field gradient apparatus and apparatus for separation

A magnetic field gradient apparatus, especially a unidirectional magnetic field gradient apparatus, for generating a magnetic field having a magnetic field gradient in a direction perpendicular to a first plane defined by a first axis and a second axis transverse to the first axis, wherein the first axis and the second axis are in the first plane, and the magnetic field is obtained by having a current distribution of a current in the first plane with a current direction of the current distribution alternating between opposite directions parallel to the second axis with a period λ along the first axis, and wherein the magnet apparatus comprises:

• leg sections extending along the second axis and arranged besides each other along the first axis, wherein a distance (d) between adjacent leg sections is λ/6, and a width of a leg section having an adjacent leg section on either side is λ/3, as seen along the first axis, wherein the leg sections comprise a conductor for the current;
• and
• a controller configured to control current through the respective leg sections,
• wherein the leg sections and the controller are arranged to provide a current direction in adjacent leg sections in opposite directions to obtain the current direction of the current distribution alternating between opposite directions parallel to the second axis with the period λ along the first axis.