The OPAL Discussion Forum

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

Dear colleagues,
I am using the AWAGun-1 as a toy model. In there I have modified the emission
time to be several times longer than 1/f0 to mimic a non-pulsed cathode. As a
consequence the bunching is performed by the RF-field.

Regarding current and charge, normally one will specify the charge/bunch for
really short bunches and multiply that with f0 to get the current. In that
situation the bunch is no longer than 1/f0, i.e. it is spatially contained in
one RF period..

When the emission time is longer than 1/f0, how is the beam current, the
number of macroparticles, and their associated charge related? Normally one
would do

macroparticle_charge = (beam_current * emission_time) /
number_of_macroparticles

but I suspect 1/fo is involved (because BFREQ=f0 in the BEAM command), and I
will have to scale the beam current to have the correct charge/macroparticle.

Conversely, to eliminate f0 from the equation, should I specify the following
options

BUNCHED=False
BFREQ=1/emission_time

in the BEAM command?

What is the correct and consistent way of dealing with this issue?


Thanks,
Dragos