Undulator magnet array and undulator

An undulator magnet array comprising:

• a first magnet array and a second magnet array disposed parallel to each other with an interval therebetween so as to lie opposite to each other, a magnetization direction of magnets contained in the first magnet array and a magnetization direction of magnets contained in the second magnet array changing, in a plane through the first and second magnet arrays, periodically along a magnet arrangement direction of the respective magnet arrays,
• wherein
• the first magnet array is formed by coupling together a first shifted magnet array and a first reference magnet array each containing a first plurality of magnets, and the second magnet array is formed by coupling together a second reference magnet array and a second shifted magnet array each containing a second plurality of magnets,
• the first shifted magnet array is disposed opposite the second reference magnet array, the first shifted magnet array being shifted relative to the second reference magnet array by a predetermined shift amount in a predetermined direction parallel to the magnet arrangement direction as compared with in a reference state where an amplitude of a periodic magnetic field produced by the first and second magnet arrays is maximized, and
• the second shifted magnet array is disposed opposite the first reference magnet array, the second shifted magnet array being shifted relative to the first reference magnet array by the predetermined shift amount in the predetermined direction as compared with in the reference state.