Collimation Wakefield Simulations

Carl Beard

ASTeC

Daresbury Laboratory

Computer Simulations of Spoiler designs

1mm

1m

•Codes being developed to measure the impedance of vessels

•ECHO2D, MWStudio, HFSS, GDFIDL

•Calculation errors due to small angle of taper

•Off axis measurements

user defined pulse possibleThe length of the structure and the frequency make

simulation time very long

MAFIA

MAFIA 3D Time domain simulations allow

the possibility of TDR simulations Many benchmarks with measurement

and code have validated results (SNS, CEBAF).

Limited to below 30 GHz due to memory constraints.

Particle-in-cell Diagonal filled cells (though mesh

Many benchmarks have also unvalidated the code

Meshing solutions

Quadratic mesh yields fast results but poor resolution

Diagonal mesh cells do allow tapers to be accurately meshed, however shallow angles lead to poor aspect ratios

Time V’s accuracy

Coarse mesh

Fast run-time

Low accuracy

Fine mesh

Slow run-time

Good accuracy

Finding the

balance

Microwave Studio

Same solver as MAFIA Improved meshing (PBA) Still limited to below 30 GHz Early days…

GDFIDL

3D Finite difference time domain code Lossy materials are allowed for calculations of resistive

wall wakefield. Particle-in-cell Capability

Bunch lengths could lead to lengthy simulation time Some verifiaction with “Real” tests up to 120 GHz

Synergy with LC-ABD Cavity BPM Energy Spectrometry GDFIDL Simulations Bench tests with Impedance Test Apparatus Beam tests

Cluster license purchased, to be hosted at UCL.

Other codes

HFSS Frequency domain solver

Over large bandwidths sharp resonance's could be overlooked. Tetrahedral meshing

MAGIC MAFIA-esque

No diagonal cells, so stepped geometry guaranteed ECHO-2D 3D??

Only 2D FDTD version working Initial discussions suggested that bunch lengths were too

demanding Unproven CST Solver (again) Availability ?????

Bench Test TDR and Transmission impedance measurements

Current apparatus provides ~ 25ps pulse waveform analysis provides loss parameter Critical issue:

Pulse speed! Time ~ LC bunch z

~1 ps 10 ps fastest pulse time available VNA ~6GHz Above 10 GHz Signal-to-noise ratio is

too low

~1.7m

Test Rig

Test Rig 2

Matching Parts

Launch cone

Test Vessels

Impedance Rig 3

Tektronics 7854

TDR Scope

6 GHz NA –

S-parameter test set

Purpose of the test

Following the last meeting in February there was a recommendation that the test gear should NOT be used for spoiler design

Benefits Experimental expertise Benchmarking Low frequency verification

of designs Improve the understanding

of the physics By scaling at 100ps, 50ps, 25ps

and 10ps, extrapolate for 1psTimescale

Impe

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