ZGOUBI USERS' GUIDE - HEP

4.4 Optical Elements and related numerical procedures 81 ¨³´ 1'« ³q> 1 1, ‰: extent of the linear part of an EFB.The magnetic field is calculated in polar coordinates. At any positionvertical component of the mid-plane field is calculated by 1"/Å along the particle trajectory the value of the¤ (4.4.8)ÕÔ"$Å V¡ 4 £nV o ¡V o£where , and £ ¡"$Å is the fringe field coefficient.V oCalculation of the Fringe Field CoefficientWith each EFB a realistic extent of the fringe field, (normally equal to the gap size), is associated and a fringe fieldcoefficient is calculated. In the following stands for either ³ (Entrance), ³ Œ (Exit) or (Lateral EFB).³%µ ³ ³ Šis an exponential type fringe field (Fig. 11) given by [17];'whereinis the distance to the EFB and depends on¯‡°± ¥ , and "/Å3' ² ² ² P ¨It is also possible to simulate a shift of the EFB, by giving a non zero value to the parameter SHIFT.SHIFT in the previous equation. This allows small variations of the magnetic length.' wis then changed to ² M ¨ ² T ¨Š LetŒ (respectively , ) be the fringe field coefficient attached to the entrance (respectively exit, lateral) EFB. Atany position on a trajectory the resulting value of the fringe field coefficient (eq. 4.4.9) is