Tunable, unmountable, permanent-magnet-based accelerator magnet

This paper presents the concept and design of a novel accelerator magnet consisting of two concentric rings of permanent magnets arranged in a Halbach layout. By replacing one component, the device can be converted to any transverse multipole configuration. By the individual rotation of the two rings, both the strength and the direction of the field pattern can be continuously tuned in a wide range, including the special case of polarity reversal. The tuning range can be changed by a parametric change of the design. The device is split into two halves and can be easily opened to allow for its installation and removal around an existing beampipe. The performance of a quadrupole demonstrator prototype is presented, including measurement results of field quality, integrated gradient and hysteresis, and discussion of sensitivity to the remanent magnetization of the permanent magnets.