10.27 EMITTANCE—Applies a linear transformation to the beam to force the emittance to given values.

Applies a linear transformation to the beam to force the emittance to given values.
Parallel capable? : yes
GPU capable? : no
Back-tracking capable? : no






Parameter NameUnitsType 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.

ENERGY