1. PARALLEL FINITE ELEMENT MODELING TOOLS FOR ERL DESIGN AND ANALYSIS
Liling Xiao, Volkan Akcelik, Arno Candel, Lixin Ge, Andreas Kabel, Kwok Ko, Lie-Quan Lee, Zenghai Li, Cho Ng, Greg Schussman
SLAC, Menlo Park, CA 94025, USA
With support from SLAC’s accelerator program and the DOE SciDAC project, the Advanced Computations Department has developed a suite of 3D parallel finite element electromagnetic codes aimed at high-accuracy, high-fidelity simulations that can help address the design issues and analysis challenges in ERLs which include SRF gun design, cavity HOM damping, beam heating, and multipacting.
SLAC Parallel Finite Element Codes
HOM Damping Evaluation with Omega3P (Eigensolver)
TESLA TDR Cavity
Omega3P results based on an ideal
cavity (in black);
Measurements from 8 cavities in TTF
module 5 (in color), showing cavity
imperfections;
Cavity imperfection is studied to
identify critical dimensions affecting Qe.
For accelerator modeling requiring
Complexity – Disparate length scales (unstructured mesh for model fidelity)
Problem size – Multiple cavities (large memory of supercomputers needed)
Accuracy – Resolve close mode spacing (higher order curved elements)
Speed – Fast turn around time to impact design (code scalability important)
0.5 mm
gap .
Beam Heating Study with T3P (Transients & wakefields)
SRF Gun Simulation with Pic3P (Particle-in-Cell)
High current and short bunch will generate large amount of HOM heating;
Broadband power spectrum computed for realistic 3D structure and bunch
size to study the beamline absorber efficiency.
BNL Polarized SRF Gun (Design by J. Kewisch)
½ cell, 350 MHz, 24.5 MV/m, 5 MeV, solenoid (18 Gauss), recessed GaAs cathode at T=70K inserted via choke joint, cathode spot size 6.5 mm, Q=3.2 nC, 0.4eV initial energy
Mode Spectrum in 2-cavity Structure
XFEL (DESY)
ERL (Cornell)
Multipacting Analysis with Track3P
Scattered self-fields as calculated with Pic3P - retardation and wakefields are included from first principles
SNS SRF cavity HOM coupler
RF heating observed at HOM coupler
3D simulations showed MP barriers close to measurements
Expt. MP bands
Track3P
Mesh model near cathode
Pic3P shows fast convergence of transverse emittance (DOFs: field degrees of freedom)
Bunch at gun exit, colored by energy
* Work supported by the US DOE under contract DE-AC02-76SF This research used resources of the National Energy Research Scientific Computing Center and the National Center for Computational Sciences at Oak Ridge National Laboratory, which are supported by the Office of science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 and DE-AC05-00OR22725, respectively.