RFQ .vane file modification

[smorard]

Dear Didier,

I modified the .vane file of my RFQ to simulate a deformation. It seems that the file is being read correctly by TraceWin. I then wanted to investigate the impact of this deformation in order to evaluate its effect on the transmission.

The files toutatis_0.61_mm.vane and toutatis_0.62_mm.vane appear to show no degradation of the RFQ transmission compared with toutatis_nominal.vane, which corresponds to the ideal geometry.

However, with the file toutatis_0.63_mm.vane, which contains a slightly larger deformation, the transmission suddenly drops by about 40%. Then, for much larger deformations such as toutatis_0.7_mm.vane and toutatis_0.8_mm.vane, the transmission remains almost unchanged from 0.63 mm. This behaviour seems somewhat unusual to me. In addition, I noticed that starting from 0.63 mm and above, I obtain a warning message related to the mesh generation when the particle tracking starts.

error_message.png (11.27 KiB) Viewed 351 times

This raises two questions for me:

- Am I applying the deformation correctly ? I am applying it both to the vane coordinate columns and to the centroid columns. By modifying both, could I actually be cancelling out the deformation ? If so, would that explain why I do not observe any significant difference in transmission for the 0.61 mm and 0.62 mm cases ?

- Can the mesh warning message be safely ignored, or is it indicative of a real issue that could affect the transmission calculation ? Given that the sudden drop in transmission appears exactly when this warning starts to occur, I am wondering whether the observed loss of transmission might be related to a numerical or meshing problem rather than a physical effect of the deformation.



On another topic, I have the impression that I can no longer modify the particle mass to an arbitrary value, nor can I select a negative charge when clicking on the yellow arrow next to the particle type name.

Thank you in advance for your help.

[Didier]

Dear Sophie,

Negative charge issue has been fixed.
For Toutatis problem, I'm still working about it

Regards,

Didier

[Didier]

Dear Sophie,

Sorry, Romuald, who looked into the problem, is very busy. So the issue is that the cell mesh is built from data taken from the INP file. The VANE file shouldn’t alter the initial geometry so much that the mesh ends up inside the copper. Those are the errors you see appearing in the messages. As a result, the calculation of the electric fields is completely incorrect, and therefore most of the beam is lost. This is what you’re seeing starting at 0.63.
So this is really a much too significant error that you’re introducing into the VANE file, particularly at the beginning of the RFQ. In my opinion, it doesn’t correspond to anything physically realistic. Either you modify the INP file to better match what you’re going to put in the VANE file, and the mesher should be able to handle it.

Regards,

Didier

[smorard]

Dear Didier,

Thank you for your feedback. I will look into how to modify the INP file in this case and whether it is straightforward to achieve what I want using that file.

That said, I agree that such deformations are significant. This is precisely why I initially started with much smaller modifications. I therefore expected to observe beam losses or at least a noticeable impact on the beam well before reaching the limits of the code. However, what I am seeing is a transition from virtually no effect at all to a deformation that is too large for the code to handle properly.

Regards,
Sophie