High-performance computing in accelerating structure design and analysis

Abstract

Future high-energy accelerators such as the Next Linear Collider (NLC) will accelerate multi-bunch beams of high current and low emittance to obtain high luminosity, which put stringent requirements on the accelerating structures for efficiency and beam stability. While numerical modeling has been quite standard in accelerator R&D, designing the NLC accelerating structure required a new simulation capability because of the geometric complexity and level of accuracy involved. Under the US DOE Advanced Computing initiatives (first the Grand Challenge and now SciDAC), SLAC has developed a suite of electromagnetic codes based on unstructured grids and utilizing high performance computing to provide an advanced tool for modeling structures at accuracies and scales previously not possible. This paper will discuss the code development and computational science research (e.g. domain decomposition, scalable eigensolvers, adaptive mesh refinement) that have enabled the large-scale simulations needed for meeting the computational challenges posed by the NLC as well as projects such as the PEP-II and RIA. Numerical results will be presented to show how high performance computing has made a qualitative improvement in accelerator structure modeling for these accelerators, either at the component level (single cell optimization), or on the scale of an entire structure (beam heating and long range wakefields).

Exact cancellation of emittance growth due to coupled transverse dynamics in solenoids and rf couplers

“…The transverse coupling due to rf fields can be eliminated by canceling the on-axis dipole and quadrupole fields with a dual rf feed and a racetracklike cavity shape [7]. Such designs have been implemented into modern rf guns [8] and upgraded rf couplers for room temperature linacs [9].…”

Omega3P: A Parallel Finite-Element Eigenmode Analysis Code for Accelerator Cavities

“…We compute both wall loss quality factor for a cavity with perfectly conducting surfaces and the quality factor from Eq (17) for a cavity with impedance boundary condition (18). The results from the former has been validated by microwave QC of the fabricated cells showing measured frequencies within 0.01% of target value [22], [23]. Table II lists the results of the frequencies and quality factors computed from both ways.…”

Calculation of wakefields in a 17 GHz beam-driven photonic band-gap accelerator structure

“…Many innovative methods have been proposed to provide sufficient wakefield damping for high-energy accelerators. These methods include HOM damping couplers [1], choke-mode structures [2,3], damped, detuned structures (DDS) [4,5], Compact Linear Collider structure with waveguide HOM damping [6], square [7] and triangular lattice metallic photonic band-gap (PBG) structures [8,9], and dielectric PBG structures [10][11][12][13].…”