Greetings,

I am working with an rf-gated electron gun for < 300 ps bunch extraction inCST Studio Suite. Currently, I am using the ES-PIC solver. You may find a related topic here,

https://r1132100503382-eu1-3dswym.3dexperience.3ds.com/community/swym:prd:R1132100503382:community:39?content=swym:prd:R1132100503382:qnaquestion:pw_uFGxsTtahrYaK45SZDQI used the same gun geometry but with different voltages:

Simulation 1:

20 keV DC voltage

Bunch length extracted at the exit: ~48.4 mm

Simulation 2:

100 keV DC voltage

Bunch length extracted at exit: ~50 mm

I assume the temporal length of the bunch is calculated by the following formula: 

in which β is the Lorentz beta of the bunch (on average, of course. Because there is a small energy spread in bunches). If I use the aforementioned formula, the bunch lengths are ~600 ps for the 20 keV and ~300 ps for the 100 keV DC voltage. I use ASTRA code for particles tracking and I imported the spatial data of the bunch (there is no temporal information in CST) and I got the same 600 ps and 300 ps temporal lengths. However, I think this formula is wrong because it is known that temporal length of a bunch is independent of its Lorentz beta (at least for DC acceleration and zero velocity spread). Though we have velocity spread in here, I am not able to theoretically prove that in a drift space (i.e., gun exit) the aforementioned formula holds true. Also, I do not know if temporal length must be measured in the rest-frame of the bunch or lab-frame.

I was wondering if there is a way to extract temporal length of the bunch directly from CST to make sure that my theoretical measurements are correct.