RFQ CAD Model Beam Dynamics

StudiesSimon Jolly

3rd August 2011

The State Of Play…

• Comsol/Matlab code to create field maps from Inventor SAT-files is complete:– Inventor model now models arbitrary number of

cells (up to 1000) and changes dynamically based on spreadsheet.

– Code dynamically identifies end flanges and grounds them if they’re present.

– For some reason, native Inventor files won’t import properly: end flanges are missing…

• Inventor models have been built for 6 models, featuring combinations of:– Standard and final FETS matching section.– With/without lead out section.– Full model with lead out and end flanges.

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CAD Models: Matching Sections

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CAD Models: Lead Out/End Flanges

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Comsol Meshing• Import CAD model and

select single quadrant: take advantage of RFQ symmetry.

• Optimum meshes different for different regions:– Vane tips: triangular

(extremely fine auto).– “Inner Beam Box”: 2mm x

2mm, swept rectangular (0.25mm x 0.25mm x 32 slices).

– “Outer Beam Box”: 10mm x 10mm, tetrahedral (extremely fine auto).

– “Air Bag”: 15mm x 15mm, tetrahedral (normal auto).

• Model vanes as “terminals”: only interested in surface fields.

• If end flange is present, model as ground plane.

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Vane tips

Air Bag

Inner Beam Box

Outer Beam Box

Nov’10 UKNF Results

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Scott’s Matching Section, No Lead-Out

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Scott’s Matching Section, Lead-Out

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Standard Matching Section, Lead-Out

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Scott’s Matching Section, End Flanges

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Standard Matching Section, End Flanges

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Preliminary Conclusions

• Well, some good, some very bad…• Good:

– No significant difference between beam transmission with/without lead-out section.

– Scott’s matching section shows slightly better transmission than the standard! Not yet sure why…

• Bad:– Significant beam losses when end flanges are

included!– This is not as bad as is seems: turns out I

started the beam in the wrong place…• Reran simulations using Alan’s setWBemittance

function and correctly aligned field map.03/08/11 Simon Jolly, Imperial College

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Scott’s Matching Section, Lead-Out

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Scott’s Matching Section, Lead-Out (New)

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Scott’s Matching Section, End Flanges

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Scott’s Matching Section, End Flanges (New)

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Standard Matching Section, Lead-Out

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Standard Matching Section, Lead-Out (New)

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Standard Matching Section, End Flanges

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Standard Matching Section, End Flanges (New)

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Scott’s Matching Section, End Flanges (New)

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Results• Hurrah! Proper transmission for full field map using

final matching section, lead out section and end flanges.

• Virtually no difference between with/without end flanges.

• Current seems to be lower for “Lead-Out” models:– > 92% for previous, 91.7% for newer.– Turns out using “setWBemittance” gives slightly

bigger beam than 10,000 particle input file I was using before.

– Obviously sensitive to input conditions!• Also measured effect of 10 micron and 100 micron

tolerance on “Lead-Out” model:– Fixes transverse parameters to nearest 10/100

microns in spreadsheet.– Can we set the machining tolerance?

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Standard Matching Section, Lead-Out (New)

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Lead-Out Section, 10 micron Tolerance

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Lead-Out Section, 100 micron Tolerance

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Conclusions• Possible to generate “arbitrary” models in Inventor: takes a

few minutes to update model (but need to test in 2012…).• Nice to be able to generate models in Comsol very easily

without any “coaxing”: full run takes 6 hours, but can model individual cells if only a few change.

• Lots of interesting results from simulations:– Virtually no difference in transmission or energy spread when

we change model.– Slight increase in emittance:

• Input: eps_x = 0.257 pi mm mrad; eps_y = 0.255 pi mm mrad.• Without end flanges or lead out section: eps_x = 0.305 pi mm

mrad; eps_y = 0.301 pi mm mrad.• With half cell but no lead out section: eps_x = 0.302 pi mm mrad;

eps_y = 0.309 pi mm mrad.• With lead out but no end flanges: eps_x = 0.300 pi mm mrad;

eps_y = 0.321 pi mm mrad.• With lead out but no end flanges: eps_x = 0.309 pi mm mrad;

eps_y = 0.317 pi mm mrad.• Looks like tolerance is less than 100 microns, but 10 microns

is okay. Not yet sure how realistic the model is…

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For Next Time…

• Jürgen’s results show that the field leaks out into the end flange: need to start beam 1-2cm back from matching section to include these effects (should be small).

• Run beam backwards from matching section using 2D space charge and 60mA current, calculate trajectories and produce 3D bunch with correct londitudinal distribution that can be started at any point (use Matlab interpolation).

• Check acceptance for all models using zero beam current: not perfect but gives upper limit.

• Include “map3D_remove” GPT element and particle removal map using CAD model.

• No need for Stephen Brooks to repeat RFQ transmission simulations…

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