Super strong permanent magnet quadrupole for a linear collider

The field strength generated by permanent magnets has been further extended by introduction of saturated iron. A permanent magnet quadrupole (PMQ) lens with such saturated iron is one of the candidates for the final focus lens for an e⁺e^- linear collider accelerator, because of its compactness and low power consumption. The first prototype of the PMQ has been fabricated and demonstrated to have an integrated strength of 28.5 T with an overall length of 10 cm and a 7 mm bore radius. Two drawbacks should be considered: its negative temperature coefficient of field strength and its fixed strength. A thermal compensation material is being tested to cure the first problem. The other problem may be solved by rotating sectioned magnet bricks, but that may lead to movement of the magnetic center and introduction of multipoles beyond some strict requirements.