TRWAKE on the beam

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simona.bettoni
Posts: 42
Joined: 06 Jul 2011, 03:14

TRWAKE on the beam

Post by simona.bettoni » 26 Oct 2022, 06:19

Dear all,
I have a general question concerning the computation of the effect of the wakefield on the beam. I am presently running some simulations misaligning elements along a linac. I am comparing the results with another code, which is giving more pessimistic results.
A possibility pointed out by the developer of the other code is a possible different way of implementing the effect of the wakefield (transverse in this case) on the beam.
How does Elegant do this?
Does it the convolution of the bunch with the Green function, and after it computes a kind of "average offset" for the entire bunch or does it compute the kick of each slice along the bunch, and after (where the beam sees another wakefield) does use the different offsets to compute the effect on the beam?
Many htanks for any feed-back on this,
Simona.

michael_borland
Posts: 1797
Joined: 19 May 2008, 09:33
Location: Argonne National Laboratory
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Re: TRWAKE on the beam

Post by michael_borland » 27 Oct 2022, 16:56

Simona,

Elegant's method is as follows:
1. Create a position-weight charge histogram. This gives Q*<x> for a series of slices i, where Q is the charge in the slice and <x> is the average position in the slice.
2. Convolve the weighted charge histogram with the Green function, giving the transverse voltage at the slices.
3. For each slice, apply the voltage to each particle in the slice.

There's no use of offsets, which I don't think would make sense. The reference system is the center of the vacuum chamber, not the centroid of the bunch.

--Michael

simona.bettoni
Posts: 42
Joined: 06 Jul 2011, 03:14

Re: TRWAKE on the beam

Post by simona.bettoni » 28 Oct 2022, 03:06

Michael,
all clear. Many thanks for your explanation.

I meant that the offset of the beam (with respect to the RF cavity) is used to compute the kick that (at this point) each slice gets. I badly expressed myself.

Thanks also for the very prompt reply, and have a nice day.

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