Wakefield Damping Effects in the CLIC Power Extraction and Transfer Structure (PETS)

Wakefield Simulation of CLIC PETS Structure Using Parallel 3D Finite Element Time-Domain Solver T3P*

Arno Candel, Andreas Kabel, Zenghai Li, Cho Ng, Liequan Lee, Greg Schussman, Kwok Ko

Advanced Computations Department, SLAC

Igor Syratchev, CERN

Abstract

In recent years, SLAC's Advanced Computations Department (ACD) has developed the parallel 3D Finite Element electromagnetic time-domain code T3P. Higher-order Finite Element methods on conformal unstructured meshes and massively parallel processing allow unprecedented simulation accuracy for wakefield computations and simulations of transient effects in realistic accelerator structures. Applications include simulation of wakefield damping in the Compact Linear Collider (CLIC) Power Extraction and Transfer Structure (PETS).

Overview

*This work was supported by DOE Contract No. DE-AC02-76SF00515 and used resources of NERSC supported by DOE Contract No. DE-AC02-05CH11231, and of NCCS supported by DOE Contract No. DE-AC05-00OR22725.

Comparison to GdfidL results for simplified geometry (without outer tank & coupler):

Good agreement between T3P and GdfidL transverse impedance results

T3P PETS Model

Parallel Finite Element Time-Domain Code T3P

Summary

Dipole wakefields are shown in a cross-section view of the PETS structure as modeled with T3P. The beam is about to leave the structure (right side), and damping effects in the dielectric loads are visible (left side). The magnitude of the electric surface fields is indicated by colors. The vertical symmetry plane is added for visualization.

• SLAC is focusing on the modeling and simulation of DOE accelerators using high-performance computing

• The Advanced Computations Department has developed the parallel Finite Element time-domain code T3P for wakefield and transient calculations

• T3P has been extensively benchmarked and delivers state-of-the-art modeling accuracy for simulations of next-generation accelerator structures

• T3P has been applied to calculate wakefield damping effects in the CLIC PETS and convergence is shownGood agreement between T3P and GdfidL

transverse wake potential results

for lossy materials

N1

N2

For order p=2: 20 different Ni’sFor order p=6: 216 different Ni’s

curved tetrahedral element

r=2 cm

• Gaussian beam (=1cm, ±5) along z-axis

T3P: 10° 3Dvs

MAFIA T2: 2D

Absorber:=15, =1, =0.667(requires finer mesh)

The PETS dielectric loads are modeled with a finer mesh to accurately simulate the shorter wavelengths

Dielelectric loads:r=24, =1, f=12 GHz

= ftanr 0

• T3P uses conformal unstructured meshes of quadratic tetrahedral elements for unprecedented efficiency and accuracy

Interior view of the PETS model: Conformal curved quadratic elements enable high modeling accuracy

• T3P solves Maxwell’s lossy wave equation in time domain:

• T3P uses higher-order Finite Element methods with vector basis functions Ni for high field representation accuracy:

• SLAC is focusing on the modeling and simulation of DOE accelerators using high-performance computing

• In collaboration with CERN, SLAC is investigating wakefield damping effects in the CLIC PETS structure

Right: CLIC Module Layout (courtesy CERN)

T3P Validation for Lossy Materials: Simple Case

• T3P is supported by SciDAC and designed for massively parallel operation on leadership-class supercomputers

• Realistic 3D model of the PETS: 34 cells, 2 matching cells, dielectric loads, output coupler and outer tank

T3P transverse wake potential results converge when using higher-order basis functions

Difference in transverse wake potential without and with damping (dielectric losses turned off/on)