# How to construct a source that produces particles with a certain bunch length and repetition rate?

Dear fluka experts and users,
I im asked to construct an electron beam source with the following characteristics:

But i can’t find a way to make a time-depended simulation ,i mean is there a way to construct a source that produces electron bunches of a certain duration eg:350fs and determine a repetition rate eg 100Hz?As far as ive read i havent found a way.Do you have any suggestions ?

Dear @el16044,
Are you interested in studying activation or prompt radiation?

Dear @amario

Hi, you do not need to do a time-dependent simulation, just implement the beam energy, its spread (almost negligible), and the transverse beam size as a function of the given emittance. The other parameters allow you to calculate the electron population to be used for normalization, depending on the considered time interval.

Dear Artemis,

We touched upon this subject in your other thread Questions about energy deposition of electron beam on tungsten target where I commented on scaling scoring results given per primary to a given beam current. Please go back to it, but let me try to explain once more.

We can probably agree that each electron in your beam, regardless of how many other electrons are with it in the bunch, will lead to the same energy deposition in the target on average. If this is so (and it is), then all you need in order to get, for example, energy deposition per bunch is to multiply your result, which is energy deposition per primary electron, by the number of electrons in 75 nC. A further multiplication by the repetition rate of the accelerator (e.g. 100 Hz, meaning 100 bunches per second) will give you the energy deposition per second (in other words, deposited power).

So, as @ceruttif mentioned above, the only relevant parameters from your table are the electron energy, the energy spread and the spatial profile (beam size). These can be defined via the BEAM card with minimal effort. The beam charge and repetition rate do not enter the simulation at all, nor do they need to, but can be used to appropriately scale the output of the simulation in order to obtain the desired quantities.

Let us know if this concept is still not clear.

P.S. The discussion would be somewhat different if you wanted to study residual radiation. There, the beam current and duration of the irradiation are of course relevant.

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Thank you very much ,i think im fully covered by your answers!