ADVANCED FIELD-MEASUREMENT METHOD WITH 3 ORTHOGONAL HALL PROBES FOR AN ELLIPTICALLY POLARIZING UNDULATOR

A three-orthogonal-Hall-probe assembly with an 'on the fly' mapping me thod has been developed to characterize an elliptically polarizing und ulator (EPU). The underlying design concept is that it can measure the three real field components without any field correction under a reli able and synchronization measurement method. Therefore, the relative c entral position shift, orthogonal angle and the planar Hall effect err or between the three Hall probes should be calibrated and readjusted. Experimental results demonstrate that this method can yield an r.m.s. reproducibility of 10 G cm for the three field components and 2 G for the peak field strength. Under precision conditions this system can co mpletely measure the three on-axis field components within 2 min for a 4 m-long EPU.