[mcstas-users] Fermi-Chopper zero_time

[Peter Kjær Willendrup]

Hello Augustin,

On 4 Dec 2024, at 09.57, Lösch, Augustin via mcstas-users <mcstas-users at mcstas.org> wrote:

Hello everybody :),

I have a question regarding a Fermi Chopper used with a continuous source. Is there a way to use something similar to the "is first" functionality of the disk chopper component? What exactly does the zero_time option do?

Thank you for the question. I am not myself a very frequent user of FermiCopper, but I will give it a shot, potentially to stand corrected later. :-)

As I read the code, indeed the zero_time parameter allows to do something similar to the “isfirst” of DiskChopper. The 3 different modes of running the component are:

a) zero_time=0 (the default behaviour), let neutrons arrive and interact with the chopper with their “natural” arrival time.
b) zero_time=1, neutrons will receive a modified arrival time and thus increasing the probability of passing through the chopper (thus regaining some statistics)
c) zero_time=2, the chopper will auto-adapt its phase to match the time-structure of the beam (thus regaining some statistics)

All of the above should result in the same intensity transmitted.

I would say that zero_time=1 is probably what you want to use, albeit not completely as efficiently as the DiskChopper isfirst option.

Best,
Peter



Peter Kjær Willendrup
Forskningsingeniør, Specialkonsulent

DTU Physics

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Technical University of Denmark


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