Transcript LEBT and RFQ Simulations in GPT

Optimisation of the FETS RFQ
Simon Jolly
Imperial College
16th September 2008
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
EPAC’08
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
HUB
SPACER
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CONE
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FINGER
HUB
FINGERS
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Cold Model Frequency and Q-value
Frequency (MHz)
Q-value
CST Simulation
319.7
9306
Brazed RFQ
318.954±0.1
5616±50
Flat end plates
319.145±0.1
7773±30
EPAC’08
THPP024
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GPT RFQ Simulations
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•
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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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rod axis
r0 (mm)
ma
r0 (mm)
a
L/2
beam axis
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L
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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
we’re going to build!
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Conclusions
• Incremental progress on field flatness and resonant properties
– see EPAC’08 paper THPP024, S. Jolly et al.
• RFQ beam dynamics simulations in GPT very promising: see
bunching, acceleration, current-dependent transmission.
• >90% 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 we’re designing (this is
the point...).
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