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

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

08:30 → 10:00 WGs 2+4 Joint Session: Session 1 of 1

Joint session between working groups 2 & 4:
WG2 - Computation for Accelerator Physics
WG4 - Beam-Driven Acceleration

08:30 Relativistically induced ballistic transport and novel effects underlying PV/m plasmonics

PV/m plasmonics model pioneers extreme plasmons where the free electron Fermi gas constituted by the conduction band electrons in condensed matter is excited to its ultimate limits. Here we discuss novel physical mechanisms that begin to dominate the physics of extreme plasmons. For instance, relativistically induced ballistic electron transport helps explain earlier beam-metal interaction experiments where damage and solid-plasma formation were not observed when the SLAC electron beam was compressed to <100fs. Furthermore, as the conduction band electrons attain relativistic velocities, they are capable of freely tunneling across the surface especially when excited in a direction perpendicular to the surface giving rise to relativistic tunneling. Besides these prominent novel effects, we differentiate and describe several foundational principles that underlie the physics of extreme plasmons.

Speaker: Prof. Aakash Sahai (University of Colorado Denver)

08:45 Spatiotemporal dynamics of beam-plasma instabilities in the ultra-relativistic regime

Relativistic beam-plasma instabilities play a crucial role in high-energy astrophysical sources, such as gamma-ray bursts or blazars, in particular to create the electromagnetic turbulence responsible for the synchrotron emission of accelerated particles in these sources. These instabilities are also important in certain experimental concepts of particle accelerators or ultra-intense photonic sources based on beam-plasma or laser-plasma interaction [A. Benedetti et al., Nat. Photon. 12, 319 (2018)].

In order to characterize, for the first time in the laboratory, their dynamics in the ultra-relativistic regime and their potential as sources of gamma radiation, a series of experiments (named E-305) is planned on the new accelerator FACET-II of the SLAC National Accelerator Laboratory. As part of this project, we will present a theoretical study of the evolution of the instabilities in the presence of a finite size beam as produced by an accelerator. A novel theory describing the spatiotemporal dynamics of electrostatic oblique modes will be presented [P. San Miguel Claveria et al., Phys. Rev. Research 4, 023085 (2022)]. For an ultra-relativistic beam, this model reveals, in good agreement with particle-in-cell simulations, the intrinsic spatiotemporal character of the instability, thus disproving the usual theories which suppose a purely temporal growth. Finally, we will determine the conditions for the instabilities to dominate over the beam self-focusing dynamics due to plasma wakefield excitation.

Speaker: Pablo San Miguel (Laboratoire d'Optique Appliquée / Instituto Superior Técnico)

AAC_2022_E305_Spatiotemp_PSanMiguel.pdf

09:00 Optimal beam loading to 20 GeV through wakefield slope rotation using an evolving electron driver

The goals of plasma-based acceleration (PBA) are high gradient, high efficient acceleration and high quality beam generation. Various synchronized injection schemes utilizing PBA have been proposed and investigated to generate beams capable of driving a compact x-ray free electron laser (XFEL). In each of these ideas, the main challenge is how to maximize the energy transfer to the injected bunch and minimize its projected energy spread. Using particle-in-cell (PIC) simulations, we demonstrate a new approach to optimal beam loading that relies on wakefield slope rotation triggered by an evolving electron driver. Injection is triggered by self-focusing an electron driver in the nonlinear blowout regime. As the driver loses energy following injection, its evolution alters the shape of the wake and accelerating field loaded by the injected bunch. For high current injected bunches, the slope of the accelerating field can fully rotate from negative to positive over the course of pump depletion so that the average acceleration field has near-zero slope. We also examine beam loading effects at different stages of the acceleration and explain the results using nonlinear theory. PIC simulations using OSIRIS indicate that injection and optimal beam loading can be achieved until the drive beam fully pump depletes. Based on simulation results, the injected beams can be efficiently accelerated with energies up to 20 GeV, projected energy spreads of $0.5\%$, and peak normalized brightness of $10^{20} \text{A}/\text{m}^2/\text{rad}^2$.

Speaker: Thamine Dalichaouch (UCLA)

09:15 Optimization of transformer ratio and beam loading in plasma wakefield accelerator with a structure-exploiting algorithm

Plasma-based acceleration has emerged as a promising candidate as an accelerator technology for a future linear collider or a next-generation light source. We consider the plasma wakefield accelerator (PWFA) concept where a plasma wave wake is excited by a particle beam and a trailing beam surfs on the wake. For a linear collider, the energy transfer from the drive beam to the wake and from the wake to the trailing beam must be large, while the emittance and energy spread of the trailing bunch must be preserved. One way to simultaneously achieve this for accelerating electrons is to use longitudinally shaped bunches and nonlinear wakes. In the linear regime, there is an analytical formalism to obtain the optimal shapes. In the nonlinear regime, however, the optimum shape of the driver to maximize the energy transfer efficiency cannot be precisely obtained as there is at present no theory that describes the wake structure and excitation process for all degrees of nonlinearity, and because the plasma electron response at the beginning of the drive beam transitions from a linear to a nonlinear behavior. We present results using a novel optimization method to effectively determine a current profile for the drive and trailing beam in PWFA that provides low energy spread, low emittance, and high acceleration efficiency. We parameterize the longitudinal beam current profile as a piecewise linear function and define optimization objectives. For the trailing beam the algorithm converges quickly to a nearly inverse trapezoidal trailing beam current profile similar to that predicted by the ultra-relativistic limit of the nonlinear wakefield theory. For the drive beam, the algorithm-searched optimal beam profile in the nonlinear regime that maximizes the transformer ratio also resembles that predicted by linear theory. The current profiles found from the optimization method provide a higher transformer ratio compared with the linear ramp predicted by the relativistic limit of the nonlinear theory. We will present details of the optimization procedure and results on obtaining high energy transfer efficiency in a PWFA two bunch accelerator stage.

Speaker: Qianqian Su

optimization_aac_qianqian.pdf

09:30 Witness beam realignment in plasma wakefi eld accelerators in the linear collider regime

Beam driven plasma wakefield acceleration (PWFA) has shown the ability to accelerate electron beams with high acceleration gradients ~50 GeV/m, high efficiency, and low energy spread. This has inspired future linear collider (LC) designs where witness beams are accelerated over a series of plasma stages. In the LC regime, the witness beam emittance is ~100 nm and the charge is ~1 nC. With these parameters, the ion collapse will be drastic and lead to emittance growth. An et al. (2017) [1] showed this emittance growth is tolerable when using a wide driver and assuming no witness beam offset. Mehrling et al. (2018) [2] showed hosing of the witness beam is suppressed in this regime, due to the non-linear focusing created by the ion motion caused by the witness beam itself. Hildebrand et al. (2018) [3] showed that the on-axis ion density formed by a high density
(small spot size) drive beam can fully eliminate the witness beam hosing and realign it with the drive beam at the cost of emittance growth. We will show that using adiabatic density ramps can match the beam with the presence of ion motion and realign an offset witness beam with tolerable emittance growth. We do this by running self-consistent simulations of a full lithium plasma stage in the LC regime using the code QPAD, a quasi-static PIC code with azimuthal decomposition.

Speaker: Lance Hildebrand (University of California, Los Angeles)

Hildebrand_AAC_2022.pptx

09:45 Discussion

10:00 → 10:30 Coffee Break/Exhibits

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