RFQ fieldmap simulation with TraceWin

[Shuo]

Dear Didier,

1. I understand that Toutatis is the dedicated code for RFQ simulations. However, I would still like to cross-check the results by tracking particles through an RFQ field map in TraceWin.
In September 2024, I asked a similar question about using an RFQ field map in TraceWin. At that time, you kindly suggested adjusting the RF phase so that the beam is centered in phase at the RFQ output, with ϕ close to 0. However, with the latest version of the software, this approach does not seem to work in the same way.
Could you please give me some advice on how to properly use an RFQ field map in TraceWin with the current version?

1.png (666.1 KiB) Viewed 37 times

2. I am trying to reproduce the RFQ 3D field-map benchmark described in the paper (https://journals.aps.org/prab/abstract/ ... .28.044602). In the paper, the authors reduce the beam frequency by 16, reduce the initial phase width by 16, and reduce the current by 16, so that the bunch period is increased while the physical longitudinal bunch length and charge per bunch remain unchanged.

For my 200 MHz RFQ case, I used:

Bunch frequency = 12.5 MHz
Current = 0.625 mA
Phase_new = Phase_old / 16
Energy unchanged

My RFQ 3D field-map lattice is:

Drift 0.00001 10
FREQ 200
Field_map 00700 3622.000 0 5.065 0.0 1.0 0.0 0.0 Iproton
Drift 0.00001 10
END

But it is not work for me: Beam energy much too low (<1e-6 eV)

My question is: in this RFQ field-map case, should the lattice command FREQ remain at the physical RFQ frequency, 200 MHz, or should it also be reduced to 12.5 MHz? More generally, how can TraceWin distinguish the bunch frequency used for space-charge periodicity from the RF field frequency used by the field map?

Thank you very much.

Shuo

RFQ_3D_Fieldmap.zip

(61.12 MiB) Downloaded 3 times

[Didier]

Hi,

the frequency defined in main page correspond to bunch frequency.
And unless otherwise specified, this will also be the RF frequency of the structure; otherwise, simply add the "FREQ 200" command to the dat file.
That said, in your case, this isn’t necessary, as the RF frequency will obviously be that of the beam. And finally, I get the impression that the simulation is working very well. I don't see any problem.

Regards,

Didier

[Shuo]

Hi Didier,

In my side,the transverse phase space is very different between the RFQ field map and Toutatis:

2.png (704.76 KiB) Viewed 17 times

I am curious why there is such a significant difference.

Regards,

Shuo

[Didier]

image.png (21.19 KiB) Viewed 16 times