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 possible The length of the structure and the frequency make simulation time very long

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 1ps Timescale Impedance