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A sector dipole implemented as a matrix, up to 2nd order.
Parallel capable? : yes
Parameter Name Units Type Default Description
L $M$ double 0.0 arc length
ANGLE $RAD$ double 0.0 bend angle
K1 $1/M^{2}$ double 0.0 geometric focusing strength
E1 $RAD$ double 0.0 entrance edge angle
E2 $RAD$ double 0.0 exit edge angle
TILT $RAD$ double 0.0 rotation about incoming longitudinal axis
K2 $1/M^{3}$ double 0.0 geometric sextupole strength
H1 $1/M$ double 0.0 entrance pole-face curvature
H2 $1/M$ double 0.0 exit pole-face curvature
HGAP $M$ double 0.0 half-gap between poles
FINT   double 0.5 edge-field integral
DX $M$ double 0.0 misaligment of entrance
DY $M$ double 0.0 misalignment of entrance
DZ $M$ double 0.0 misalignment of entrance
FSE   double 0.0 fractional strength error
ETILT $RAD$ double 0.0 error rotation about incoming longitudinal axis
EDGE1_EFFECTS   long 1 include entrance edge effects?
EDGE2_EFFECTS   long 1 include exit edge effects?
ORDER   long 0 matrix order
EDGE_ORDER   long 0 edge matrix order
TRANSPORT   long 0 use (incorrect) TRANSPORT equations for T436 of edge?
USE_BN   long 0 use B1 and B2 instead of K1 and K2 values?
B1 $1/M$ double 0.0 K1 = B1/rho, where rho is bend radius
B2 $1/M^{2}$ double 0.0 K2 = B2/rho
GROUP   string NULL Optionally used to assign an element to a group, with a user-defined name. Group names will appear in the parameter output file in the column ElementGroup

Some confusion may exist about the edge angles, particularly the signs. For a sector magnet, we have of course E1=E2=0. For a symmetric rectangular magnet, E1=E2=ANGLE/2. If ANGLE is negative, then so are E1 and E2. To understand this, imagine a rectangular magnet with positive ANGLE. If the magnet is flipped over, then ANGLE becomes negative, as does the bending radius $\rho$. Hence, to keep the focal length of the edge $1/f = -\tan E_i /\rho$ constant, we must also change the sign of $E_i$.

When adding errors, care should be taken to choose the right parameters. The FSE and ETILT parameters are used for assigning errors to the strength and alignment relative to the ideal values given by ANGLE and TILT. One can also assign errors to ANGLE and TILT, but this has a different meaning: in this case, one is assigning errors to the survey itself. The reference beam path changes, so there is no orbit/trajectory error. The most common thing is to assign errors to FSE and ETILT. Note that when adding errors to FSE, the error is assumed to come from the power supply, which means that multipole strengths also change.

Special note about splitting dipoles: when dipoles are long, it is common to want to split them into several pieces, to get a better look at the interior optics. When doing this, care must be exercised not to change the optics. elegant has some special features that are designed to reduce or manage potential problems. At issue is the need to turn off edge effects between the portions of the same dipole.

First, one can simply use the divide_elements command to set up the splitting. Using this command, elegant takes care of everything.

Second, one can use a series of dipoles with the same name. In this case, elegant automatically turns off interior edge effects. This is true when the dipole elements directly follow one another or are separated by a MARK element.

Third, one can use a series of dipoles with different names. In this case, you must also use the EDGE1_EFFECTS and EDGE2_EFFECTS parameters to turn off interior edge effects.

next up previous
Next: SCATTER Up: Element Dictionary Previous: SAMPLE
Robert Soliday 2014-06-26