CEA Codes forum

Dear Didier,

Hello,
I'm trying to calculate beam transfer at LEBT with space charge effect.
The beam is CW(I checked CW beam checkbox), so I thought "bunch frequency" in main tab does not affect the calculation.
However, the simulated result completely change when I change bunch frequency (ex. from 0.00001MHz to 1MHz).
It seems the degree of the effect of "SPACE_CHARGE_COMP" is changed.
Specifically, when the bunch frequency is 0.0001, SPACE_CHARGE_COMP does not work and seems to be always 1.

What "bunch frequency" means in CW beam simulation ? Does it have relation with space charge effect?

The space charge is simulated in Partran multiparticle simulation and PICNIR(r,z)(2D) model is used.

best regards,

Ashikaga

Dear Ashikaga,

Yes, frequency is used for space-charge to define the longitudinal size of the space-charge frame. Usually try to have a beta*lambda size in the same order than the transverse one, in order to have mesh size close as possible to cube. If it is really too different the calculation becomes very approximate.

Regards,

Didier

Dear Didier,

Thank you for your kind reply. It helps me so much.
I understand that z-rms must be specified in order to decide z-direction mesh size in PICNIR2D.
When you said beta*lambda should be the same order than the transverse one,
lambda = [speed of light]/[bunch frequency]
is right ? And also, z-rms = beta*lambda ?

best regards,
Ashikaga

Yes exactly

Didier