next up previous
Next: CSRCSBEND Up: Element Dictionary Previous: CORGPIPE


A canonical kick sector dipole magnet.
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 quadrupole strength
K2 $1/M^{3}$ double 0.0 geometric sextupole strength
K3 $1/M^{4}$ double 0.0 geometric octupole strength
K4 $1/M^{5}$ double 0.0 geometric decapole strength
K5 $1/M^{6}$ double 0.0 geometric 12-pole strength
K6 $1/M^{7}$ double 0.0 geometric 14-pole strength
K7 $1/M^{8}$ double 0.0 geometric 16-pole strength
K8 $1/M^{9}$ double 0.0 geometric 18-pole 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
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 misalignment
DY $M$ double 0.0 misalignment
DZ $M$ double 0.0 misalignment
FSE   double 0.0 fractional strength error
ETILT $RAD$ double 0.0 error rotation about incoming longitudinal axis
N_KICKS   long 4 number of kicks
NONLINEAR   long 1 include nonlinear field components?
SYNCH_RAD   long 0 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.
Parameter Name Units Type Default Description
FRINGE   long 0 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
KICK_LIMIT_SCALING   long 0 scale maximum edge kick with FSE?
USE_BN   long 0 use b$<$n$>$ instead of K$<$n$>$?
EXPANSION_ORDER   long 0 Order of field expansion. (0=auto)
B1 $1/M$ double 0.0 K1 = b1/rho, where rho is bend radius
B2 $1/M^{2}$ double 0.0 K2 = b2/rho
B3 $1/M^{3}$ double 0.0 K3 = b3/rho
B4 $1/M^{4}$ double 0.0 K4 = b4/rho
B5 $1/M^{5}$ double 0.0 K5 = b5/rho
B6 $1/M^{6}$ double 0.0 K6 = b6/rho
B7 $1/M^{7}$ double 0.0 K7 = b7/rho
B8 $1/M^{8}$ double 0.0 K8 = b8/rho
XREFERENCE   double 0.0 reference x for interpretation of fn values
F1   double 0.0 Fractional field error fn=bn*xrn/n!, adds to K1 or b1.
F2   double 0.0 Fractional field error fn=bn*xrn/n!, adds to K2 or b2.
F3   double 0.0 Fractional field error fn=bn*xrn/n!, additive.
F4   double 0.0 Fractional field error fn=bn*xrn/n!, additive.
F5   double 0.0 Fractional field error fn=bn*xrn/n!, additive.
F6   double 0.0 Fractional field error fn=bn*xrn/n!, additive.
F7   double 0.0 Fractional field error fn=bn*xrn/n!, additive.

A canonical kick sector dipole magnet.
Parameter Name Units Type Default Description
F8   double 0.0 Fractional field error fn=bn*xrn/n!, additive.
ISR   long 0 include incoherent synchrotron radiation (scattering)?
ISR1PART   long 1 Include ISR for single-particle beam only if ISR=1 and ISR1PART=1
SQRT_ORDER   long 0 Order of expansion of square-root in Hamiltonian. 0 means no expansion.
USE_RAD_DIST   long 0 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.
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 $B_y(x) = B_o * (1 +
\sum_{n=1}^8\frac{K_n\rho_o}{n!}x^n)$. 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 $B_y(x) = B_o
* (1 + \sum_{n=1}^8\frac{b_n}{n!}x^n)$. 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 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: CSRCSBEND Up: Element Dictionary Previous: CORGPIPE
Robert Soliday 2014-06-26