|K1||double||0.0||geometric quadrupole strength|
|K2||double||0.0||geometric sextupole strength|
|K3||double||0.0||geometric octupole strength|
|K4||double||0.0||geometric decapole strength|
|K5||double||0.0||geometric 12-pole strength|
|K6||double||0.0||geometric 14-pole strength|
|K7||double||0.0||geometric 16-pole strength|
|K8||double||0.0||geometric 18-pole strength|
|E1||double||0.0||entrance edge angle|
|E2||double||0.0||exit edge angle|
|TILT||double||0.0||rotation about incoming longitudinal axis|
|H1||double||0.0||entrance pole-face curvature|
|H2||double||0.0||exit pole-face curvature|
|HGAP||double||0.0||half-gap between poles|
|FSE||double||0.0||fractional strength error|
|ETILT||double||0.0||error rotation about incoming longitudinal axis|
|N_KICKS||long||4||number of kicks|
|NONLINEAR||long||1||include nonlinear field components?|
||include classical synchrotron radiation?|
|EDGE1_EFFECTS||long||1||include entrance edge effects?|
|EDGE2_EFFECTS||long||1||include exit edge effects?|
|EDGE_ORDER||long||1||order to which to include edge effects|
A canonical kick sector dipole magnet.
||Include fringe effects (1=linear, 2=higher order)|
|INTEGRATION_ORDER||long||4||integration order (2 or 4)|
|EDGE1_KICK_LIMIT||double||-1||maximum kick entrance edge can deliver|
|EDGE2_KICK_LIMIT||double||-1||maximum kick exit edge can deliver|
||scale maximum edge kick with FSE?|
||use bn instead of Kn?|
||Order of field expansion. (0=auto)|
|B1||double||0.0||K1 = b1/rho, where rho is bend radius|
|B2||double||0.0||K2 = b2/rho|
|B3||double||0.0||K3 = b3/rho|
|B4||double||0.0||K4 = b4/rho|
|B5||double||0.0||K5 = b5/rho|
|B6||double||0.0||K6 = b6/rho|
|B7||double||0.0||K7 = b7/rho|
|B8||double||0.0||K8 = b8/rho|
||include incoherent synchrotron radiation (scattering)?|
|ISR1PART||long||1||Include ISR for single-particle beam only if ISR=1 and ISR1PART=1|
||Order of expansion of square-root in Hamiltonian. 0 means no expansion.|
||If nonzero, overrides SYNCH_RAD and ISR, causing simulation of radiation from distributions, optionally including opening angle.|
|ADD_OPENING_ANGLE||long||1||If nonzero, radiation opening angle effects are add if USE_RAD_DIST is nonzero.|
A canonical kick sector dipole magnet.
|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|
This element provides a symplectic bending magnet with the exact Hamiltonian. For example, it retains all orders in the momentum offset and curvature. The field expansion is available to fourth order.
One pitfall of symplectic integration is the possibility of orbit and path-length errors for the reference orbit if too few kicks are used. This may be an issue for rings. Hence, one must verify that a sufficient number of kicks are being used by looking at the trajectory closure and length of an on-axis particle by tracking. Using INTEGRATION_ORDER=4 is recommended to reduce the number of required kicks.
Normally, one specifies the higher-order components of the field with the K1, K2, K3, and K4 parameters. The field expansion in the midplane is . By setting the USE_bN flag to a nonzero value, one may instead specify the b1 through b4 parameters, which are defined by the expansion . This is convenient if one is varying the dipole radius but wants to work in terms of constant field quality.
Setting NONLINEAR=0 turns off all the terms above K_1 (or b_1) and also turns off effects due to curvature that would normally result in a gradient producing terms of higher order.
Edge effects are included using a first- or second-order matrix. The order is controlled using the EDGE_ORDER parameter, which has a default value of 1. N.B.: if you choose the second-order matrix, it is not symplectic.
Incoherent synchrotron radiation, when requested with ISR=1, normally uses gaussian distributions for the excitation of the electrons. Setting USE_RAD_DIST=1 invokes a more sophisticated algorithm that uses correct statistics for the photon energy and number distributions. In addition, if USE_RAD_DIST=1 one may also set ADD_OPENING_ANGLE=1, which includes the photon angular distribution when computing the effect on the emitting electron.
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
ANGLE is negative, then so are
E2. To understand this, imagine a rectangular magnet with positive
If the magnet is flipped over, then
ANGLE becomes negative, as does the bending
radius . Hence, to keep the focal length
of the edge
constant, we must also change the sign of
When adding errors, care should be taken to choose the right
ETILT parameters are used for
assigning errors to the strength and alignment relative to the ideal
values given by
TILT. One can also assign
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
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
EDGE2_EFFECTS parameters to
turn off interior edge effects.