Optimisation of the FETS RFQ

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Optimisation of the FETS RFQ

• Simon Jolly
• Imperial College
• 16th September 2008

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FETS RFQ Optimisation

• RFQ development progressing on a number of
  fronts.
• Bead-pull and resonance measurements of cold
  model.
• Beam dynamics simulations in General Particle
  Tracer (GPT).
• New integrated design method using Autodesk,
  Microwave Studio and GPT.

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Bead-Pull Field Flatness Measurements
Ø6mm dielectric bead
EPAC08 THPP024
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Cold Model End Flange Inserts
2 new types of end flange were designed to alter
the inductance and capacitance of the RFQ end
regions a cone-shaped flange insert and a flat
insert with 4 removable fingers (copper or iron).
GUIDE
CONE
HUB
FINGER HUB
SPACER
FINGERS
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Cold Model Frequency and Q-value
EPAC08 THPP024
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GPT RFQ Simulations

• General Particle Tracer is a particle tracking
  package sophisticated particle tracking but only
  simple beamline components.
• Need to model RFQ as time-varying E and B field
  map track particles through field map and
  measure beam properties.
• Field map produced using RFQ optimisation code
  (Alan) for full 4m FETS
• 11 x 11 x 3110 mesh points.
• x/y -3.5 to 3.5mm (fixed mesh).
• z 0 to 4.1m (variable mesh).
• Includes transverse and longitudinal field
  modulations.
• Input conditions
• Input beam 60mA, 65keV, x/y 2mm, x/y
  100mrad, ex/ey 0.2p mm mrad, beam converging.
• 10,000 particles, 0.3ns timestep (freq/10), 100
  3Dtree space charge.
• Single bunch at injection with 3D space charge.
• Measure beam transmission, bunching and energy.

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RFQ Transverse Field Map
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RFQ On-Axis Ez Field
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RFQ Parameters (from TUP066, LINAC06)
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Initial Conditions Z-Y, 5 bunches
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Full FETS Simulation Z-Y, 5 bunches
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Initial Conditions Z-E, full beam
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Full FETS Simulation Z-E, full beam
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Final Beam Energy (60mA)
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RFQ Beam Transmission
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RFQ Transmitted Current
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RFQ Integrated Design

• RFQ parameterised by a and m parameters for
  modulations and L for cell length.
• These parameters generated using optimisation
  code, then handed to Frankfurt for RFQ
  manufacture.
• Would like to have a method of designing RFQ
  where all steps are integrated
• Engineering design.
• EM modelling.
• Beam dynamics simulations.

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RFQ Integrated Design Step 1

• Most FETS CAD modelling done using Autodesk
  Inventor, including the cold model.
• Possible to draw vane modulations using spline
  interpolation.
• Parameters read out from Excel spreadsheet can
  change modulations on the fly...

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RFQ Integrated Design Step 2

• EM modelling already carried out for cold model
  using CST Microwave Studio.
• Export .sat file to MWS from Autodesk of 3D
  vane model only central 1cm x 1cm section.
• Cut into 4 sections
• Mirrors real assembly.
• Easier for MWS meshing.
• Output as E B field map.

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RFQ Integrated Design Step 3

• Import field map of central field region into GPT
  for particle tracking.
• Optimise design based on RFQ transmission and
  feed back into engineering design.
• We now have a method of producing a field map and
  carrying out simulations for the thing were
  going to build!

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Conclusions

• Incremental progress on field flatness and
  resonant properties see EPAC08 paper THPP024,
  S. Jolly et al.
• RFQ beam dynamics simulations in GPT very
  promising see bunching, acceleration,
  current-dependent transmission.
• gt90 transmission for ideal beam, only 50 for
  real parameters.
• Can (almost) run end-to-end simulations in GPT
  using pepperpot measurements from ion source,
  optimised LEBT parameters and field map for RFQ.
• Integrating Autodesk, MWS and GPT design steps
  will reduce bifurcation of design.
• Need to ensure CAM systems will understand our
  CAD models so we can manufacture what were
  designing (this is the point...).