Paper  Title  Page 

SUPAF07  HighFidelity ThreeDimensional Simulations of Thermionic Energy Converters  59 


Funding: This work is supported the US DOE Office of Science, Office of High Energy Physics: DESC0017162. Thermionic energy converters (TEC) are a class of thermoelectric devices, which promise improvements to the efficiency and cost of both small and largescale electricity generation. A TEC is comprised of a narrowlyseparated thermionic emitter and an anode. Simple structures are often spacecharge limited as operating temperatures produce currents exceeding the ChildLangmuir limit. We present results from 3D simulations of these devices using the particleincell code Warp, developed at Lawrence Berkeley National Lab. We demonstrate improvements to the Warp code permitting high fidelity simulations of complex device geometries. These improvements include modeling of nonconformal geometries using mesh refinement and cutcells with a dielectric solver. We also consider selfconsistent effects to model Schottky emission near the spacecharge limit for arrays of shaped emitters. The efficiency of these devices is computed by modeling distinct loss channels, including kinetic losses, radiative losses, and dielectric charging. We demonstrate many of these features within an opensource, browserbased interface for running 3D electrostatic simulations with Warp, including design and analysis tools, as well as streamlined submission to HPC centers. 

Slides SUPAF07 [6.097 MB]  
DOI •  reference for this paper ※ https://doi.org/10.18429/JACoWICAP2018SUPAF07  
About •  paper received ※ 01 November 2018 paper accepted ※ 19 November 2018 issue date ※ 26 January 2019  
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WEPLG03  Theoretical and Computational Modeling of a Plasma Wakefield BBU Instability  341 


Funding: This work was supported in part by the Department of Energy, Office of Science, Office of High Energy Physics, under contract number DESC0018718. Plasma wakefield accelerators achieve accelerating gradients on the order of the wavebreaking limit, m c^{2} k_{p}/e, so that higher accelerating gradients correspond to shorter plasma wavelengths. Smallscale accelerating structures, such as plasma and dielectric wakefields, are susceptible to the beam breakup instability (BBU), which can be understood from the PanofskyWenzel theorem: if the fundamental accelerating mode scales as b^{1} for a structure radius b, then the dipole mode must scale as b^{3}, meaning that high accelerating gradients necessarily come with strong dipole wake fields. Because of this relationship, any plasmaacceleratorbased future collider will require detailed study of the tradeoffs between extracting the maximum energy from the driver and mitigating the beam breakup instability. Recent theoretical work* predicts the tradeoff between the witness bunch stability and the amount of energy that can be extracted from the drive bunch, a socalled efficiencyinstability relation . We will discuss the beam breakup instability and the efficiencyinstability relation and the theoretical assumptions made in reaching this conclusion. We will also present preliminary particleincell simulations of a beamdriven plasma wakefield accelerator used to test the domain of validity for the assumptions made in this model. * V. Lebedev, A. Burov, and S. Nagaitsev, "Efficiency versus instability in plasma accelerators", Phys. Rev. Acc. Beams 20, 121301 (2017). 

Slides WEPLG03 [2.234 MB]  
DOI •  reference for this paper ※ https://doi.org/10.18429/JACoWICAP2018WEPLG03  
About •  paper received ※ 01 November 2018 paper accepted ※ 28 January 2019 issue date ※ 26 January 2019  
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