Paper  Title  Page 

SUPAF11 
Computer Architecture Independent Adaptive Geometric Multigrid Solver for AMRPIC  


Funding: SNSF project 200021_{1}59936 The accurate and efficient simulation of neighboring bunch effects in high intensity cyclotrons requires to solve largescale Nbody problems of O(10^{9}…10^{z}EhNZeHn) particles coupled with Maxwell’s equations. In order to capture the effects of halo creation and evolution of such simulations with standard particleincell models an extremely fine mesh with O(10^{8}…10^{9}) grid points is necessary to meet the condition of high resolution. This requirement represents a waste of memory in regions of void, therefore, the usage of blockstructured adaptive mesh refinement algorithms is more suitable. The Nbody problem is then solved on a hierarchy of levels and grids using geometric multigrid algorithms. We show benchmarks of a new implementation of an adaptive geometric multigrid algorithm using 2nd generation Trilinos packages that ran on Piz Daint with O(10^{4}…10^{5}) cores. 

Slides SUPAF11 [6.094 MB]  
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SUPAF12 
Surrogate Models for Beam Dynamics in Charged Particle Accelerators  


Highfidelity, PICbased beam dynamics simulations are time and resource intensive. Consider a high dimensional search space, that is far too large to probe with such a high resolution simulation model. We demonstrate that a coarse sampling of the search space can produce surrogate models, which are accurate and fast to evaluate. In constructing the surrogate models, we use artificial neural networks [1] and multivariate polynomial chaos expansion [2]. The performance of both methods are demonstrated in a comparison with highfidelity simulations, using OPAL, of the Argonne Wakefield Accelerator [3]. We claim that such surrogate models are good candidates for accurate online modeling of large, complex accelerator systems. We also address how to estimate the accuracy of the surrogate model and how to refine the surrogate model under changing machine conditions. [1] A. L. Edelen et al., arXiv:1610.06151[physics.acc ph] [2] A. Adelmann, arXiv:1509.08130v6[physics.acc ph] [3] N. Neveu et al., 2017 J. Phys.: Conf. Ser. 874 012062  
Slides SUPAF12 [11.505 MB]  
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MOPLG01  Challenges in Simulating Beam Dynamics of Dielectric Laser Acceleration  120 


Funding: ACHIP is funded by the Gordon and Betty Moore Foundation (Grant No. GBMF4744). U.N. acknowledges German BMBF Grant No. FKZ:05K16RDB. B.C. acknowledges NERSC, Contract No. DEAC0205CH11231. Dielectric Laser Acceleration (DLA) achieves the high est gradients among structurebased electron accelerators. The use of dielectrics increases the breakdown field limit, and thus the achievable gradient, by a factor of at least 10 in comparison to metals. Experimental demonstrations of DLA in 2013 led to the Accelerator on a Chip International Program (ACHIP), funded by the Gordon and Betty Moore Foundation. In ACHIP, our main goal is to build an acceler ator on a silicon chip, which can accelerate electrons from below 100keV to above 1MeV with a gradient of at least 100MeV/m. For stable acceleration on the chip, magnet only focusing techniques are insufficient to compensate the strong acceleration defocusing. Thus spatial harmonic and Alternating Phase Focusing (APF) laserbased focusing tech niques have been developed. We have also developed the simplified symplectic tracking code DLAtrack6D, which makes use of the periodicity and applies only one kick per DLA cell, which is calculated by the Fourier coefficient of the synchronous spatial harmonic. Due to coupling, the Fourier coefficients of neighboring cells are not entirely independent and a field flatness optimization (similarly as in multicell cavities) needs to be performed. The simu lation of the entire accelerator on a chip by a Particle In Cell (PIC) code is possible, but impractical for optimization purposes. Finally, we have also outlined the treatment of wake field effects in attosecond bunches in the grating within DLAtrack6D, where the wake function is computed by an external solver. 

Slides MOPLG01 [3.947 MB]  
DOI •  reference for this paper ※ https://doi.org/10.18429/JACoWICAP2018MOPLG01  
About •  paper received ※ 20 October 2018 paper accepted ※ 24 October 2018 issue date ※ 26 January 2019  
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TUPAF07 
Recent Developments of the Open Source Code OPAL  


After a general introduction of OPAL, I will introduce a set of new features available with version 2.0 released in July 2018. All new features will be presented together with examples of ongoing research projects. In the OPALt flavour, elements can now be placed in 3D, without restriction. Overlapping fringe fields are handled, and offmomentum beams as occurring in tolerance studies can be tracked. Furthermore, survey plots of placed elements are a valuable diagnostic when dealing with complex designs. A new element, a flexibly configurable collimator, will be presented. In the OPALcyc flavour, a robust way of generating matched distributions with linear space charge is introduced. A new method for describing fixed field accelerators (FFAs) in a very general way will be shown. A new element TRIMCOIL can be used to correct for fielderrors in cyclotrons and FFAs. The OPAL language (a derivative of the MAD language) was extended to allow the specification of multi objective optimisation problems, which are then solved with a built in NGSAII genetic algorithm. A new feature SAMPLER allows you to setup and run random or sequential parameter studies and seamless utilisation of a vast number of computing cores. Finally, a set of Python tools (pyOPALTools) was created for post processing. The manual is now available on the OPALwiki as well as in pdf format.  
Slides TUPAF07 [2.778 MB]  
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TUPAG05 
Trimcoil Optimisation Using MultiObjective Optimisation Techniques and HPC  


Funding: SNSF project 200021_{1}59936 Uncertainties in the bunch injection (i.e. energy, radius, radial momentum and angle) as well as magnet inaccuracies harm the isochronicity of the PSI 590 MeV Ring Cyclotron. An additional magnetic field provided by trim coils is an effective solution to restore this condition. Therefore, an accurate description of trim coils is essential to match the turn pattern of the machine in simulations. However, due to the highdimensional search space consisting of 21 design variables and more than 180 objectives the turns cannot be matched in a straightforward manner and without sufficient HPC resources. In this talk we present a realistic trim coil model for the PSI 590 MeV Ring Cyclotron implemented in OPAL that was used together with its builtin multiobjective optimisation algorithm to find the 4 injection parameters and the magnetic field strengths of 17 trim coils. The optimisations were performed on Piz Daint (currently 3rd fastest supercomputer worldwide) with more than 1000 cores per job. 

Slides TUPAG05 [6.765 MB]  
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TUPAG14  Constrained MultiObjective Shape Optimization of Superconducting RF Cavities to Counteract Dangerous Higher Order Modes  293 


High current storage rings, such as the Z operating mode of the FCCee, require superconducting radio frequency (RF) cavities that are optimized with respect to both the fundamental mode and the dangerous higher order modes. In order to optimize the shape of the RF cavity, a constrained multiobjective optimization problem is solved using a massively parallel implementation of an evolutionary algorithm. Additionally, a frequencyfixing scheme is employed to deal with the constraint on the frequency of the fundamental mode. Finally, the computed Pareto front approximation and an RF cavity shape with desired properties are shown.  
Slides TUPAG14 [3.001 MB]  
DOI •  reference for this paper ※ https://doi.org/10.18429/JACoWICAP2018TUPAG14  
About •  paper received ※ 19 October 2018 paper accepted ※ 10 December 2018 issue date ※ 26 January 2019  
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