Question about radius and cut off frequency of LSC in RFCW

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WEI-HOU
Posts: 31
Joined: 01 Mar 2018, 08:20

Question about radius and cut off frequency of LSC in RFCW

Post by WEI-HOU » 01 Oct 2018, 12:09

Hi,

I was trying to model tracking in a TESLA crymodule, with both LSCDRIFT and ZWAKE included.
Unfortunately, I could not get rid of the noise in energy distribution for small transverse radius, without cutting off the frequency at very low value and choosing very small number of bins.

For instance, with transverse radius about 10^-5, I have to set LSC_HIGH_FREQUENCY_CUTOFF0=0.1, LSC_BINS=200, sg_order=2, sg_halfwidth="4" to module just LSC in RFCW, to get rif of the noise.
LSC.png
RFCW with LSC only.
However, if I include ZWAKE together, I will see the noise in energy distribution again.
LSC_ZWAKE.png
RFCW with LSC and ZWAKE.
Is there something wrong with parameters that I used ?
I attach my scripts for your reference.

Regards
TAN
Attachments
RFCW_example.zip
example to reproduce figures attached.
(67.57 KiB) Downloaded 171 times

michael_borland
Posts: 1927
Joined: 19 May 2008, 09:33
Location: Argonne National Laboratory
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Re: Question about radius and cut off frequency of LSC in RFCW

Post by michael_borland » 01 Oct 2018, 17:15

Tan,

As the beam radius shrinks, the spectrum of LSC extends to proportionally higher frequencies. This makes the simulation more sensitive to high-frequency noise in the particle distribution. You should increase the number of particles and also consider using Halton sequences (see the manual page for &bunched_beam).

--Michael

WEI-HOU
Posts: 31
Joined: 01 Mar 2018, 08:20

Re: Question about radius and cut off frequency of LSC in RFCW

Post by WEI-HOU » 03 Oct 2018, 12:39

Hi,

Thanks a lot for your great help.
I actually have a similar problem with CSRCSBEND.
I was trying to model the CSR effect (steady state only) of a one-dimensional beam (I set emit_x and emit_y to be 10^-12).
However, the result was subjected to noise with bend angle greater than 1 degree.

In this case, should I use Halton sequence to generate particles to help reducing the noise?

Regards
Tan

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