Micro-bunching particle tracking

[Hwang, Ji-Gwang]

Dear Borland and every-body.

Hello. I simulate the linac tracking using real beam distribution.
This beam distribution get from injector simulation using parmela.
The bunch was micro-bunched by buncher cavities. This figure is attached.
It has 10% energy deviation with ~125 MeV.

General case, the momentum deviation has <0.05% at the end of Linac.
So, I make some optimization run.ele file for minimize the deviation. I attached it.
It contain the optimize the phase for the energy and deviation at the end of Linac.
But it has 3% momentum deviation after optimized.I think it is caused by the micro-bunched beam.
How to decrease the momentum deviation? and How to confirm the beam emittance of each slices?

Have a nice days. and Best regard.

From Hwang Ji-Gwang

[michael_borland]

Ji-Gwang,

Can you also post the input particle file?

--Michael

[Hwang, Ji-Gwang]

Dear Michael Borland

I attached the beam input file.

Sincerely yours

Hwang, Ji-Gwang

[michael_borland]

Ji-Gwang,

The problem is not that you have a train of bunches, but that the individual bunches are too long to allow achieving the energy spread you want. You need an energy slit upstream of the linac to remove the low-energy tail, since it makes for a very long bunch.

In your input file, you allow all the phases to vary independently, but don't vary the voltages. This is very constrained since you are also targeting a specific final energy. You don't need to vary all the phases and voltages independently, however. Varying them in a ganged fashion is completely equivalent and much faster. (A sum of sine waves at a common frequency is equivalent to a single sine wave at the same frequency.) See the attached file.

--Michael

[Hwang, Ji-Gwang]

Dear Michael Borland

Thanks for your reply. I agree with your opinion.
So, I attached the "PFILTER" element at the upstream of the linac.
But The bunch distribution at the end of linac has still long tail. So, I will test many things.

Have a nice day.

From Hwang Ji-Gwang