Multipacting Analysis with Track3P

Expt. MP bands

Track3P

SNS SRF cavity HOM coupler

• RF heating observed at HOM coupler

• 3D simulations showed MP barriers close to measurements

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

* Work supported by the US DOE under contract DE-AC02-76SF00515. 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. 

SLAC Parallel Finite Element Codes HOM Damping Evaluation with Omega3P (Eigensolver)

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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.

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.

ERL (Cornell)

Mode spectrum in the first cavity

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Mode spectrum in between 2 cavities

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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

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

Mesh model near cathode

Scattered self-fields as calculated with Pic3P - retardation and wakefields are included from first principles

Pic3P shows fast convergence of transverse emittance (DOFs: field degrees of freedom)Bunch at gun exit, colored by energy

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.

Mode Spectrum in 2-cavity Structure

XFEL (DESY)