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An alpha magnet implemented as a matrix, up to 3rd order. PART is used to split the magnet into halves. XS$<$n$>$ and DP$<$n$>$ allow momentum filtration at the midpoint.
Parallel capable? : yes
Parameter Name Units Type Default Description
XMAX $M$ double 0.0 size of alpha
XS1 $M$ double 0.0 inner scraper position relative to XMAX
XS2 $M$ double 0.0 outer scraper position relative to XMAX
DP1   double -1 inner scraper fractional momentum deviation
DP2   double 1 outer scraper fractional momentum deviation
XPUCK $M$ double -1 position of scraper puck
WIDTHPUCK $M$ double 0.0 size of scraper puck
DX $M$ double 0.0 misalignment
DY $M$ double 0.0 misalignment
DZ $M$ double 0.0 misalignment
TILT   double 0.0 rotation about incoming longitudinal axis
PART   long 0 0=full, 1=first half, 2=second half
ORDER   long 0 matrix order [1,3]
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 matrix-based implementation of an alpha magnet [5]. Matrices up to third order are available [4].

The parameter XMAX determines the size of the alpha, which is related to the gradient $g$ in the magnet and the central momentum $\beta\gamma$ by

x_{max} [m] = 0.07504986 \sqrt{\frac{\beta\gamma}{g [T/m]}}.
\end{displaymath} (10)

The path length of the central particle is $2.554 x_{max}$.

Because an alpha magnet has large dispersion at the midplane, it is often used for momentum filtration in addition to bunch compression. The dispersion at the center is given by the simple relation

R_{16} = -\frac{1}{2} x_{max}.
\end{displaymath} (11)

To use an alpha magnet for momentum filtration in elegant, one must split the alpha magnet into two pieces. One may then either use the scraper features of the ALPH element or other elements such as SCRAPER or RCOL.

To split an alpha magnet, one uses the PART parameter. E.g.,

! First half, with momentum filter between -5% and +2.5%
AL1: ALPH,XMAX=0.11,PART=1,DP1=-0.05,DP2=0.025
! Second half 

As just illustrated, the parameters DP1 and DP2 may be used to filter the momentum by providing fractional momentum deviation limits. These are implemented in a physical fashion by computing the corresopnding horizontal position deviations and imposing these as limits on the particle coordinates. One may also do this directly using the XS1 and XS2 parameters, which specify maximum acceptable deviations from the nominal horizontal position. XS1 is the allowed deviation on the low-energy side while XS2 is the allowed deviation on the high-energy side.

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