Simple characterization method of small high gradient permanent magnet quadrupoles

The application of quadrupoles with high or ultra-high gradient and small apertures requires a precise control over harmonic components of the field. A simple, fast, low cost measurement method on small size PMQs (Permanent Magnet Quadrupoles) is described. It is based on the same principle of the familiar "rotating coil technique", but in this case, profiting of the small dimensions of the PMQ, it consists in rotating the PMQ itself instead of the coil. In such way a gain on accuracy and measure time is obtained. It has been applied to characterize a set of commercial PMQs with a gradient around 200 T/m and an internal radius of 3.5 mm to be mounted in a SCDTL (Side Coupled Drift Tube Linac) structure for the acceleration of a proton beam from 7 to 12 MeV. This structure has been developed in the framework of the Italian TOP-IMPLART (Intensity Modulated Proton Linear Accelerator for Radiotherapy) Project. Copyright © 2014 CC-BY-3.0 and by the respective authors.