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EMITTANCE

Applies a linear transformation to the beam to force the emittance to given values.
Parallel capable? : yes
Parameter Name Units Type Default Description
EMITX $M$ double -1 horizontal emittance
EMITY $M$ double -1 vertical emittance
EMITNX $M$ double -1 horizontal normalized emittance
EMITNY $M$ double -1 vertical normalized emittance
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 allows changing the emittance of a beam during tracking. It is intended to be used to modify the emittance ``slightly'' to agree with, for example, experimental measurements.

The LCLS provides an example application: we track a beam from a photo-injector simulation through a laser/undulator beam heater and then through the entire linac. The beam emittance and twiss parameters are measured at a diagnostic downstream of the laser heater. We can insert an EMITTANCE element and a TWISS element at the location of the diagnostic to force the beam properties to the exact values that are measured. This compensates for imperfect modeling of the photo-injector while allowing us to conveniently model the system between the photo-injector and the point at which the emittance is measured.


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