20th Advanced Accelerator Concepts Workshop

6 Nov 2022, 15:00 → 11 Nov 2022, 17:10 America/New_York

Hyatt Regency Long Island

Mark Palmer (Brookhaven National Laboratory) , Navid Vafaei-Najafabadi (Stony Brook University)

The AAC’22 workshop is the 20th in a series of by-invitation biennial fora for intensive discussions on long-term research in advanced accelerator physics and technology. This research supports the development of capabilities for the basic sciences, from photon science to high energy physics, as well as the development of compact accelerators for industrial, medical and security applications.

AAC'22 will be organized into eight working groups covering the following topical areas:

1. Laser-Plasma Wakefield Acceleration 
2. Computation for Accelerator Physics
3. Laser and High-Gradient Structure-Based Acceleration
4. Beam-Driven Acceleration
5. Beam Sources, Monitoring, and Control
6. Laser-Plasma Acceleration of Ions
7. Radiation Generation and Advanced Concepts
8. Advanced Laser and Beam Technology and Facilities

Conference Home:  https://www.aac2022.org/

 

Sunday, 6 November

18:00 → 19:30 Welcome Reception

Monday, 7 November

10:20 → 10:40 Coffee Break

12:10 → 13:30 Lunch

15:00 → 15:30 Coffee Break

15:30 → 17:00 WGs 1+2 Joint Session: Session 1 of 2

Joint session between Working Groups 1 & 2:
WG1 - Laser-Plasma Wakefield Acceleration
WG2 - Computation for Accelerator Physics

Conveners: Yong Ma (University of Michigan) , Marlene Turner (LBNL) , Irina Petrushina (Stony Brook University) , David Bruhwiler (RadiaSoft LLC) , Alexey Arefiev (UC San Diego)

15:30 GPU accelerated simulations of channel formation via laser gas interaction for LWFA

Lasers of sufficient intensity passing through a neutral gas will ionize the gas creating a plasma channel in its wake. A shock can propagate from this locally heated region through the created plasma and background gas, however the density of the plasma will determine the dynamics of the plasma. For collisional (high density) plasmas this can be modeled with a fluid code, however a kinetic simulation is required for low collisionality. The Vorpal code [1] allows for self-consistent modeling of the laser pulse, plasma formation via field ionization, laser-plasma interaction, and subsequent plasma dynamics via particle-in-cell and EM simulation. It also includes a reaction framework that enables the simulation of collisional dynamics such as elastic collisions, impact ionizations, and charge exchange reactions. Because of the computational expense of kinetic (particle-in-cell) codes, we have made use of modern hardware through GPU acceleration of the field and particle dynamics as well as the reactions. We will show results for these laser-plasma interactions in low density regimes, and we will also present the performance we see in moving to GPU simulations.

Speaker: Jarrod Leddy (Tech-X Corporation)

LeddyGPUAcceleratedSimulations.pdf

15:45 Magnetohydrodynamic Modeling of Plasma Channels for Acceleration and Beam Transport

Structured plasmas present myriad opportunities for acceleration and control of electron and positron beams for advanced concepts accelerators. Modeling these systems is challenging, owing to the orders of magnitude disparities in the spatiotemporal scale lengths between beam or laser and background plasma evolution. We discuss the application of the FLASH code, a publicly available MHD software, to model capillary discharges for use as laser plasma acceleration stages and as active plasma lenses. We discuss system sensitivities to the use of varying initial conidtions, boundary conditions, and transport models. We also consider system scalings for different inputs, including the use of a laser heater. Lastly, we discuss the application of FLASH for modeling a different class of plasma channels known as hydrodynamic optical-field ionized plasmas, which show promise for future meter-scale plasma accelerator sources.

Speaker: Nathan Cook (RadiaSoft LLC)

Cook_AAC_FLASH.pdf

16:00 Simulations of Hydrodynamic Optical-Field-Ionised Plasma Channels

Recent results have demonstrated hydrodynamic optical-field-ionised plasma channels as being a promising plasma source for efficient, high-repetition-rate laser plasma accelerators.

Understanding the dynamics of these plasma waveguides is critical to improving their performance and for tailoring their modal properties to fit a given experimental setup. This can be challenging as the important physical processes span multiple orders of magnitude with ionisation/heating on femtosecond timescales, thermalisation on picosecond timescales, and expansion/waveguide formation on nanosecond timescales.

Here, we present simulation results capturing the key dynamics of these plasma structures from ionisation to waveguide formation and benchmark the results against experimental data. Further, we explore how key experimental parameters can be used to tune the waveguides properties.

Speaker: Dr Rob Shalloo (DESY)

Shalloo_PlasmaChannels_AAC.pdf

16:15 Accompanying the hybrid LPWFA experiment campaign with a computer simulation campaign: What we model, what we learn, and where we need to become better

The Hybrid Collaboration, a joint undertaking by HZDR, DESY, University of Strathclyde, LMU, and LOA, performed hybrid LPWFA experiments which utilize electron bunches from a laser wakefield accelerator (LWFA) as drivers of a plasma wakefield stage (PWFA) to demonstrate the feasibility of compact PWFAs serving as a test bed for the efficient investigation and optimization of PWFAs and their development into brightness boosters. To better understand the microscopic, nonlinear dynamic of these accelerators, the experiments were accompanied by 3D3V particle-in-cell simulations using PIConGPU.

Here, we present insights into the dynamics of the hybrid LPWFA that we gained from start-to-end simulations of the experimental setup at HZDR.
These regard electron injections due to hydrodynamic shocks, beam self-modulation and breakup, and cavity elongation - all backed-up by synthetic diagnostics that allow direct comparison with experimental measurements.
We discuss our approach to model these synthetic diagnostics directly within the PIConGPU simulation as well as modelling certain aspects of the experimental setup, such as the drive laser. Continuing this, the talk highlights a few recent technical advances in PIConGPU that enable better modelling of the micro-physics, experiment conditions, or signals of experiment diagnostics.

Speaker: Klaus Steiniger (Helmholtz-Zentrum Dresden-Rossendorf)

Steiniger_LPWFA.pdf

16:30 Acceleration of positrons generated via photon-photon collisions in a dense laser-irradiated plasma

In a typical laboratory plasma, there are no native positrons, which complicates attempts to develop a laser-driven positron accelerator. High-power high-intensity lasers provide an attractive opportunity to create positrons directly from light. While most attention has been focused on the multi-photon process, the process that involves two gamma-rays, the linear Breit-Wheeler (BW) process, has been overlooked due to a misconception that it is more difficult to realize. To objectively assess the linear BW process, we have developed a first-ever fully kinetic code for predictive simulations of the electron-positron pair production via this process in high-intensity laser-matter interactions and the subsequent positron acceleration. Using this new tool, we have discovered several regimes where one or two laser pulses propagating through a dense plasma form an effective self-organized collider of gamma-rays and an adjoining accelerator for the generated positrons. In contrast to the regimes proposed for the multi-photon process, our regimes only require a peak intensity that is already accessible at most flagship laser facilities to produce from tens of millions to billions of electron-positron pairs. The created positrons are emitted from the plasma as ultra-relativistic beams with a narrow divergence angle, which is likely to facilitate their use for applications.

Speaker: Alexey Arefiev (UC San Diego)

16:45 Discussion

Tuesday, 8 November

10:00 → 10:30 Coffee Break

12:00 → 13:20 Lunch

15:00 → 15:30 Coffee Break/Exhibits

Wednesday, 9 November

10:00 → 10:30 Coffee Break/Exhibits

12:00 → 13:20 Lunch

Thursday, 10 November

10:00 → 10:30 Coffee Break/Exhibits

10:30 → 12:00 WGs 1+2 Joint Session: Session 2 of 2

Joint session between Working Groups 1 & 2:
WG1 - Laser-Plasma Wakefield Acceleration
WG2 - Computation for Accelerator Physics

Conveners: Yong Ma (University of Michigan) , Marlene Turner (LBNL) , Irina Petrushina (Stony Brook University) , David Bruhwiler (RadiaSoft LLC) , Alexey Arefiev (UC San Diego)

10:30 PIConGPU + X – Building blocks for successful Exascale accelerator simulations

Exascale computing is close to becoming a reality. As technology progresses, it has become clear that heterogeneous computing is going to stay and adapting to new hardware is an ongoing challenge. Since 2015 PIConGPU has paved the way to accelerating plasma simulations across compute platforms using the Alpaka framework. This has enabled early adaption to new compute hardware and readiness for Exascale compute capabilities.
However, experience has shown that the real challenges are of a different nature. The first is in detailed analysis of the data produced in simulations. Here, we present our current work on I/O, code coupling, visual analytics and large-scale data analytics.
The second, and more pressing challenge, is comparison to experiment. Here, not only has the increasing quality of experiments put more demand on simulation quality, but more and more the damnd for fast, close to real time analysis has grown. This puts high quality simulations to the test, as runs on supercomputers tend to be costly. We present workflows to match experiment and simulations and a future look on how feedback loops between experiment and simulation can be optimized.

Speaker: Dr Alexander Debus (Helmholtz-Zentrum Dresden - Rossendorf, Bautzner Landstrasse 400, 01328 Dresden, Germany)

10:45 HiPACE++: GPU-accelerated modeling of plasma wakefield accelerators

Modeling plasma wakefield accelerators is computationally challenging. Using the quasi-static approximation allows for efficient modeling of demanding plasma wakefield accelerator scenarios. Here, the latest highlights of the performance-portable, 3D quasi-static particle-in-cell (PIC) code HiPACE++ are presented. HiPACE++ demonstrates orders of magnitude speed-up on modern GPU-equipped supercomputers in comparison to its CPU-only predecessor HiPACE. Thus, HiPACE++ enables fast and accurate modeling of challenging simulation settings, including the proton-beam-driven accelerator AWAKE or low-emittance positron acceleration schemes at unprecedented resolution.

Speaker: Severin Diederichs (DESY / LBNL)

AAC_2022_HiPACE_Severin.pdf

11:00 Latest advances in the Particle - In - Cell code WarpX for efficient modeling of plasma accelerators at Exascale

The electromagnetic Particle-In-Cell (PIC) code WarpX has been developed within the the U.S. Department of Energy’s Exascale Computing Project toward the modeling of plasma accelerators for future high-energy physics colliders on Exascale Supercomputers. We will present the latest multi-GPU capable physics features, such as a Coulomb collision module and a QED module. We will also report on the latest algorithmic advances that enable full PIC modeling of plasma accelerators with higher efficiency: a time-averaged pseudo-spectral PIC solver that enables larger timesteps, a hybrid nodal-staggered PIC loop that provides improved stability, an algorithm to handle particles crossing Perfectly Matched Layers, application of mesh refinement to the modeling of ion motion in a plasma accelerator. All presented features are fully CPU and GPU (Nvidia/AMD/Intel) capable. The status, examples of applications and future developments will be discussed, and thoughts toward the establishment of a 10-year roadmap for advanced accelerator concepts computation will be given.

Speaker: Jean-Luc Vay (Lawrence Berkeley National Laboratory)

AAC22_Vay.pptx

11:15 Mesh refinement in QuickPIC

The PWFA has emerged as a promising candidate for the accelerator technology used to build a future linear collider and/or light source. In this scheme witness beams are accelerated in the plasma wakefield created by a driver beam. The three-dimensional (3D) quasi-static (QS) particle-in-cell (PIC) approach, e.g., using QuickPIC, has been shown to provide high fidelity simulation capability and 2-4 orders of magnitude speedup over 3D fully explicit PIC codes. In some linear collider designs for the electron arm, the witness beam is accelerated in a wake excited in the blowout regime. In this regime the matched spot size of the witness beam can be 2 to 3 orders of magnitude smaller that spot size of the wakefield. To efficiently simulate such a disparity in length scales requires some mesh refinement capability. We describe a mesh refinement scheme that has been implemented into the 3D QS PIC code, QuickPIC. We use very fine (high) resolution in a small spatial region that includes the witness beam and a progressively coarser resolution in the rest of the simulation domain. A fast multigrid Poisson solver has been implemented for the field solve on the fine mesh. The code has been parallelized with both MPI and OpenMP, and the scalability has also been improved by using pipelining. The effects of the boundary between a course and fine mesh has been studied. We have also developed a preliminary adaptive mesh refinement algorithm for an evolving beam size. Several benchmark cases have been tested and it is found that the mesh refinement algorithm provides good agreement with previously published results and with simulations using a new quasi-3d QS PIC code called QPAD. For round beams QPAD operates as an 2D r-z code and we can use fine resolution throughout the entire simulation domain. Details of the algorithm and results on PWFA simulations will be presented.

Speaker: Qianqian Su

Mesh refinement in QuickPIC_2022.pdf

11:30 A preliminary analysis for efficient laser wakefield acceleration

Adopting a recently developed simplified model of the impact of a very short and intense laser pulse onto an inhomogeneous diluted plasma, we analitycally derive preliminary conditions on the input data (initial plasma density $\widetilde{n_0}$ and pulse profile) allowing to control the wave-breaking of the laser-driven plasma wakefield and to maximize the energy transfer to small bunches of self-injected electrons. The model is a fully relativistic plane hydrodynamic one: The pulse is a plane wave propagating in the $z$-direction hitting a cold plasma at rest with $\widetilde{n_0}=\widetilde{n_0}(z)$; as long as the depletion of the laser pulse is small the system of the Lorentz-Maxwell and continuity PDEs is reduced to a family (parametrized by $Z>0$) of decoupled systems of non-autonomous Hamilton equations with 1 degree of freedom 1 and the light-like coordinate $\xi=ct\!-\!z$ (instead of time $t$) as an independent variable; each $Z$ is the initial $z$-coordinate of a layer of electrons, whose motion is ruled by the corresponding system. Wave-breaking (and self-injection) start when the Jacobian $J=\partial z/\partial Z$ vanishes. In the more realistic situation of a finite, but not too small, laser spot radius $R$, the results will approximately hold for the part of the plasma close to the axis $\vec{z}$ of cylindrical symmetry of the spot, and may be used to preselect interesting regions in the input parameter space where to perform, by PIC simulations, more accurate analysis of the wakefield acceleration.

Speaker: Prof. Gaetano Fiore (INFN, Sezione di Napoli, and Università Federico II, Napoli)

Presentation_AAC2022.pdf

11:45 Discussion

12:00 → 13:20 Lunch

15:00 → 18:00 Afternoon at Leisure

Friday, 11 November

10:00 → 10:30 Coffee Break

12:00 → 13:00 Lunch

14:40 → 15:00 Coffee Break