The OPAL Discussion Forum

["Dragos Constantin" <dragos.constantin AT gmail.com>]

Hi All,
I have a model where I am emitting electrons at the beginning of a set of
adjacent RF cavities. The emission time lasts a few RF cycles and mimics
continuous electron injection from a thermionic electron gun. As expected some
of the macroparticles are pushed back during the bunching process, and some of
these macroparticles will continue to propagate in the negative z-direction
past the emission point.

What is the best way to discard the particles that move in the negative z-
direction? I am thinking to discard any particle that propagate behind the
cathode (the emitting surface).

The second issue relates to the initial coordinates of the reference particle.
I know the reference particle starts in (x,y,z)=(0,0,z_start). Is there a way
to specify the (x,y) coordinates for the reference particle starting point?
Depending on the simulation input parameters, sometimes I loose the reference
particle after several RF cavities. More generally what is the best strategy
to make sure the reference particle 'survives'?

Thanks,
Dragos