A magnet arrangement for creating a magnetic field, comprising: a first magnet having a first surface defining a first pole and a second surface defining a second pole opposite the first pole, wherein the second surface has a higher magnetic flux density than the first surface; a second magnet spaced from the first magnet and having a third surface defining a third pole and a fourth surface defining a fourth pole opposite the third pole, wherein the third surface has a higher magnetic flux density than the fourth surface, wherein the second magnet is spaced from the first magnet to define a first gap between the second surface and the third surface, and wherein magnetic field lines of the magnetic field run from the first surface to the second surface, from the second surface to the third surface through the first gap, and from the third surface to the fourth surface; a third magnet spaced from the second magnet and having a fifth surface defining a fifth pole and a sixth surface defining a sixth pole opposite the fifth pole, wherein the sixth surface has a higher magnetic flux density than the fifth surface, and wherein the magnetic field lines run from the fourth surface to the fifth surface and from the fifth surface to the sixth surface; a fourth magnet spaced from the third magnet and having a seventh surface defining a seventh pole and an eighth surface defining an eighth pole opposite the seventh pole, wherein the seventh surface has a higher magnetic flux density than the eighth surface, wherein the fourth magnet is spaced from the third magnet to define a second gap between the sixth surface and the seventh surface, and wherein the magnetic field lines run from the sixth surface to the seventh surface through the second gap, and from the seventh surface to the eighth surface; wherein the magnetic field converges through the first magnet, then passes through the first gap, then diverges through the second magnet, then converges through the third magnet, then passes through the second gap, then diverges through the fourth magnet and then returns from the fourth magnet to the first magnet; characterised in that the second surface is arcuate, the third surface is arcuate, the sixth surface is arcuate, the seventh surface is arcuate, and that the second surface, the third surface, the sixth surface and the seventh surface share a common arc center. a first magnet having a first surface defining a first pole and a second surface defining a second pole opposite the first pole, wherein the second surface has a higher magnetic flux density than the first surface; a second magnet spaced from the first magnet and having a third surface defining a third pole and a fourth surface defining a fourth pole opposite the third pole, wherein the third surface has a higher magnetic flux density than the fourth surface, wherein the second magnet is spaced from the first magnet to define a first gap between the second surface and the third surface, and wherein magnetic field lines of the magnetic field run from the first surface to the second surface, from the second surface to the third surface through the first gap, and from the third surface to the fourth surface; a third magnet spaced from the second magnet and having a fifth surface defining a fifth pole and a sixth surface defining a sixth pole opposite the fifth pole, wherein the sixth surface has a higher magnetic flux density than the fifth surface, and wherein the magnetic field lines run from the fourth surface to the fifth surface and from the fifth surface to the sixth surface; a fourth magnet spaced from the third magnet and having a seventh surface defining a seventh pole and an eighth surface defining an eighth pole opposite the seventh pole, wherein the seventh surface has a higher magnetic flux density than the eighth surface, wherein the fourth magnet is spaced from the third magnet to define a second gap between the sixth surface and the seventh surface, and wherein the magnetic field lines run from the sixth surface to the seventh surface through the second gap, and from the seventh surface to the eighth surface; wherein the magnetic field converges through the first magnet, then passes through the first gap, then diverges through the second magnet, then converges through the third magnet, then passes through the second gap, then diverges through the fourth magnet and then returns from the fourth magnet to the first magnet;