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RFQ Development for FETS. Simon Jolly Imperial College 16 th December 2009. FETS RFQ Development. FETS will utilise a 4m-long, 324 MHz four-vane RFQ channel, consisting of four resonantly coupled sections. RFQ focuses beam from LEBT and accelerates it to 3MeV, ready for Chopper/MEBT. - PowerPoint PPT Presentation
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RFQ Development for FETS
Simon Jolly
Imperial College
16th December 2009
FETS RFQ Development
• FETS will utilise a 4m-long, 324 MHz four-vane RFQ channel, consisting of four resonantly coupled sections.
• RFQ focuses beam from LEBT and accelerates it to 3MeV, ready for Chopper/MEBT.
• 4-vane cold model showed agreement between CST simulations and bulk RF properties.
• Previous beam dynamics simulations, based on field maps produced with a field approximation code, provide a baseline for the new design.
• Novel design method currently under development to combine CAD and electromagnetic modeling with beam dynamics simulations in GPT.
16/12/09 2Simon Jolly, Imperial College
Previous RFQ Design Method
• RFQ parameterised by a and m parameters for modulations, for vane radius and L for cell length (see following slide).
• These parameters optimised by iteratively solving Kapchinsky-Teplyakov (K-T) equations.
• Alan wrote custom code (RFQSIM) to generate RFQ parameters for both 4-rod and 4-vane RFQ’s: results compare favourably to other codes (eg. PARMTEQM).
• RFQSIM used to successfully design ISIS 665 keV RFQ.
• These parameters handed directly to Frankfurt for RFQ manufacture.
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RFQ Design Parameters• RFQ parameterised by 3 (+ 1)
parameters:– a and m parameters define
modulation depth.– r0 defines the mean vane
distance from the beam axis and is derived from a and m.
gives the radius of curvature (vane) or mean radius (rod).
– L defines the length of each cell (half sinusoidal period).
• For field approximation method, these values generated for idealised RFQ field.
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L
a
r0 (mm)ma
0 (mm)
L/2
rod axis
beam axis
FETS Integrated RFQ Design
• Would like to have a method of designing RFQ where all steps are integrated:– Engineering design.– EM modelling.– Beam dynamics simulations.
• Integrating design steps allows us to characterise effects of:– Fringe fields and higher order modes.– Particular CNC machining techniques and
options on beam dynamics.
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RFQ Design Stages
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RFQ Parameters (from TUP066, LINAC06)
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CAD Modelling• Autodesk Inventor CAD
package used to model RFQ cold model (and a lot more besides…).
• RFQ parameters stored in Excel spreadsheet.
• Inventor can dynamically link to parameters in Excel spreadsheet:– Change spreadsheet
parameters and model updates automatically.
– Use spline to approximate sinusoidal vane shape: only 2% difference.
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CAD Sketches With Vane Modulations
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Vane Modulation Sketch
Vane Profile Sketch
RFQ CAD Modelling
• Autodesk Inventor CAD package used to model RFQ cold model (and a lot more besides…).
• Inventor can dynamically link to parameters in Excel spreadsheet:– Change spreadsheet
parameters and model updates automatically.
– Use spline to approximate sinusoidal vane shape: only 2% difference.
16/12/09 Simon Jolly, Imperial College 10
CST MicroWave Studio E-field Modelling
• Four vanes from inventor imported by a macro.
• Model cut into 6 sections (5 plus matching section) for ease of modelling and to increase CST mesh density.
• Potentials and boundary conditions defined in the macro.
• Run solver to produce electrostatic field map.
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Beam Dynamics Simulations
• GPT used for beam dynamics simulations.
• Import electrostatic field map from text file produced by CST.
• Integration algorithm traces particle movements through time-varying field.
• Compare results to field map from optimised RFQ field expansion.
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Full RFQ Simulation: Z-Y, 5 bunches
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Full RFQ Simulation: Z-E, full beam
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CST Mesh Density
• A lot of effort on optimising meshing in CST.• Need a field map that gives transmission results
similar to RFQSIM.• Important to quantify whether we can model
Electrostatic field of vanes with enough accuracy in CST to measure beam dynamics.
• Non-trivial: modelling 30mm x 30mm x 4m volume with micron accuracy.
• Changes in beam dynamics MUST be unaffected by coarseness of CST field meshing so we can compare to optimised field.
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Varying CST Mesh (640 points)
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Varying CST Mesh (4700 points)
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Particle Tracking For High/Low Mesh
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First CST Field Map
• Produced with CST, tracked with GPT:– Transmission = 99%
– Mean energy = 1.31 MeV
– Energy rms = 261 keV
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Best CST Field Map• Five sections reconstructed
into whole RFQ, high mesh density, tangential boundary:– Transmission = 100%– Mean energy = 3.03 MeV– Energy rms = 12 keV
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Varying Mesh Density Results
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Transverse Field Map Comparison
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Transverse Field Map Comparison
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Conclusions• CAD modelling process now pretty mature: can model vane, rod
and “vod” with parameter adjustment on-the-fly (everything except no. of cells).
• Models import into CST and output to GPT: beam dynamics simulations well understood.
• Need to ensure we’re not re-inventing the wheel: RFQ’s have been designed before without this process.
• Next steps:– Output CAD model to Comsol, repeat process from CST to
produce more easily adaptable field map (tighter integration with Inventor and Matlab).
– Compare CST coarse, fine, Comsol and RFQSIM field maps point-by-point to determine whether discrepancies are a result of poor field mapping or more accurate modelling of vane tips.
• Need to ensure CAM systems will understand our CAD models so we can manufacture what we’re designing (this is the point…).
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