Rigorous evaluation of the edge-focusing wiggler based on the magnetic field measurement

The edge-focusing (EF) wiggler, which produces the strong field gradient for transverse focusing incorporated with the normal wiggler field, has been fabricated to evaluate its performance rigorously with the magnetic field measurement. It is a five-period planar wiggler with an edge angle of 2° and a period length of 60 mm. The magnetic field in the wiggler is measured using Hall probes at four different wiggler gaps. It is experimentally confirmed that a high field gradient of $1.0\mathrm{T}/\mathrm{m}$ is realized, as designed, along the beam axis in the EF wiggler. The magnetic field gradient of the EF wiggler is derived as a function of the magnetic gap. The field gradient decreases with increasing magnet gap more slowly than the peak magnetic field does for the present experimental model. An analytic formula for the field gradient of the EF wiggler is derived and it is shown that the slope of the field gradient with the magnet gap can be changed by varying the magnet width of the EF wiggler.