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 5+7 Joint Session: Session 1 of 2

Joint session between working groups 5 & 7:
WG5 - Beam Sources, Monitoring and Control
WG7 - Radiation Generation and Advanced Concepts

Conveners: John Palastro (University of Rochester, Laboratory for Laser Energetics) , Julia Mikhailova, Dr Samuel Barber (Lawrence Berkeley National Laboratory) , Yine Sun (Argonne National Laboratory)

08:30 High Flux Polarized Positron Production based on high efficiency FEL and high gradient IFEL

In this paper we discuss the design of polarized positron source for an e+e- linear collider based on polarization transfer from circularly polarized gamma-ray photons in a conversion target. A very high flux of gamma-ray photons can be obtained via inverse compton scattering a high current ultra-relativistic electron beam with an intense laser pulse circulating in an optical cavity. In order to sustain interactions at MHz-scale repetition rates, the electron beam is laser-accelerated to 1 GeV in a tapered helical undulator using the same laser which drives the ICS interaction and right after the ICS interaction is laser-decelerated to replenish the energy in the optical beam. The design of the tapered undulator system and the estimates for the gamma ray flux, spectrum and polarization are presented. The results suggest that positron beams with currents up to 30 uA (well in excess of the International Linear Collider requirements) and polarization of up to 70 \% could be obtained with this scheme.

Speaker: Pietro Musumeci

PolarizedPositrons_FASTGREENS_AAC22.pdf

08:50 A compact laser-plasma based setup for positron production and collection

Development of compact, Laser Plasma Acceleration (LPA)-based sources for positrons is a key step in the R&D effort towards development of a TeV collider. The conventional production and collection schemes of positron beams cannot be easily transferred to an LPA setup. This is mainly due to the large distance required to transport particles from the production to the acceleration point and the inherently small transverse acceptance of the LPA stage. For such reasons, positron production schemes compatible with a plasma-based accelerator are still lacking. In this work, we present a compact, laser-based scheme for the production of positron beams. Positrons are produced via pair decay of the Bremsstrahlung radiation generated when a multi-GeV, laser-plasma accelerated electron beam interacts with a high-Z solid target. We explore the possibility of using the back of the target itself as a plasma mirror for an incoming laser, in order to generate a plasma wave able to trap and accelerate positrons as soon as they leave the target. A realistic phase-space distribution for the positrons is obtained by modeling the electron beam interaction with the solid target using the Monte Carlo code Geant4. We then study the trapping and acceleration efficiency of the subsequent plasma stage in order to find an optimum working point.

Speaker: Davide Terzani (LBNL)

Terzani_AAC22_WG7.pptx

09:10 High intensity laser driven sources of gammas and positrons using BELLA PW Laser Dual Beamlines

Recent commissioning of the second laser pulse transport line at the BELLA PW facility enables strong-field quantum electrodynamics (SF-QED) experiments where an intense laser pulse collides with a GeV-class laser-wakefield-accelerated electron beam. An overview of the upgraded BELLA PW facility with a SF-QED experimental layout is presented. According to the simulation results these experiments can lead to the generation of an efficient source of high energy gammas and positrons via Compton and Breit-Wheeler processes as well as enable the study of the transition of the laser-particle interactions from the classical to the SF-QED regime.

Speaker: Stepan Bulanov (LBNL)

Bulanov_SFQED_AAC22.pdf

10:00 → 10:30 Coffee Break/Exhibits

10:30 → 12:00 WGs 5+7 Joint Session: Session 2 of 2

Joint session between working groups 5 & 7:
WG5 - Beam Sources, Monitoring and Control
WG7 - Radiation Generation and Advanced Concepts

Conveners: John Palastro (University of Rochester, Laboratory for Laser Energetics) , Julia Mikhailova, Dr Samuel Barber (Lawrence Berkeley National Laboratory) , Yine Sun (Argonne National Laboratory)

10:30 Plasma-accelerator-based linear beam cooling systems

Plasma-based accelerators enable compact acceleration of beams to high energy and are considered a potential technology for future linear colliders. Conventional linear colliders require damping rings to generate the required beam emittance for high-energy physics applications. We propose and discuss a plasma-based linear radiation damping system that allows cooling of ultrashort bunches compatible with plasma-based accelerators, potentially removing the need for bunch compression. The ultra-high plasma accelerating gradients enable relatively compact linear damping systems, and there is a trade-off between system length and the achievable emittance reduction. Final asymptotic normalized beam emittance is shown to be independent of beam energy.

Speaker: Carl Schroeder (LBNL)

10:50 Application of Optical Stochastic Cooling Mechanism to Beam Shaping

Stochastic Cooling is a feedback system for cooling particle beams in storage rings which uses radiation produced by the beam to correct the average deviation of temporal slices with a duration inversely proportional to the bandwidth. Optical Stochastic Cooling (OSC) uses optical wavelengths which decreases the duration of each slice and, therefore, reduces the incoherent noise each individual particle observes. Particles pass through an undulator (the pickup) where they emit radiation which is amplified and reintroduced downstream in another undulator (the kicker). The optical delay and amplification system, in combination with the relatively short sample slices, provides a potential tool to shape the phase-space of a beam. We outline and simulate two potential methods for shaping the longitudinal phase-space (LPS) of a beam using the OSC mechanism. The first modulates the amplification of the undulator radiation each turn which can be used to focus the cooling into a specific degree of freedom and produce flat beams in LPS. The second non-uniformly amplifies longitudinal sections of the undulator radiation pulse. This may target cooling to specific regions of the beam. Using the two techniques together we demonstrate how the OSC setup can be used to produce micro-bunches with arbitrary separation.

Speaker: Austin Dick (Northern Illinois University)

AAC_Slides.pdf

11:10 Coherent 3D microstructure of laser-wakefield-accelerated electron bunches

Recent breakthroughs in laser wakefield accelerator (LWFA) technology have allowed them to drive free-electron lasers (FELs) [1]. This is made more impressive by the relative lack of phase-space control in plasma accelerators when compared to conventional linear accelerators. However, the complicated phase spaces and microstructures in LWFA beams could be harnessed to accelerate the self-amplified spontaneous emission (SASE) process. Pre-bunched beams have been shown to achieve gain with shorter saturation length than conventional beams [2]. Because of the nature of the LWFA process, electron beams from LWFAs emerge from the plasma with preformed microstructures. The parameters of the accelerator dictate the shape, size, and coherence of these features. There is interest in creating and harnessing such substructures for the next generation of X-ray FEL [3]. However, to use these structures they must be measured and characterized. Coherent optical transition radiation (COTR) can diagnose such microfeatures in electron beams. We present experimental results across three different LWFA injection regimes demonstrating regime dependent levels of visible COTR. In each regime, we examined near field COTR images at eight different wavelengths from a foil directly after the end of the accelerator. Depending on the injection regime, we observe different levels of bunch substructure. How this structure evolves across optical wavelengths is also regime dependent. Wavelength-dependent variations in the size and radial distribution of the TR images can be correlated with features in the bunch longitudinal profile. Observed multispectral COTR images corroborate injection-regime-dependent beam substructures predicted by three-dimensional particle in cell (PIC) simulations. Moreover, with the aid of physically reasonable assumptions about the bunch profile, we present reconstructions of the three-dimensional electron bunch density distribution.

[1] Wang, et al. Free-electron lasing at 27 nanometres based on a laser wakefield accelerator. Nature 595, 516–520 (2021).
[2] A. H. Lumpkin et al., Evidence for Microbunching “Sidebands” in a Saturated Free-Electron Laser Using Coherent Optical Transition Radiation, Phys. Rev. Lett. 88, 234801 (2002).
[3] Xu, Xinlu, et al. "Generation of ultrahigh-brightness pre-bunched beams from a plasma cathode for X-ray free-electron lasers." Nature communications 13.1 (2022): 1-8.

Speaker: Maxwell LaBerge

11:30 Electron source bunch length characterization based on chicane-decompressed coherent transition radiation emission

Laser plasma accelerators (LPAs) are capable of producing electron bunches as short as a few femtoseconds at percent-level energy spread. However, measuring the bunch length is not straightforward, let alone unraveling source correlations between the longitudinal position and momentum distribution. Here we present the theoretical framework and preliminary experimental demonstration of a multi-shot technique that applies a chicane decompression scan and records the emitted Coherent Transition Radiation (CTR) pulse energy. Comparing the measurement of CTR energy vs chicane R56 to accurate modeling of CTR generation allows us to diagnose the longitudinal emittance in a manner that is analogous to retrieving the transverse emittance from a quadrupole scan. The combination of chicane-decompressed CTR emission and chromatic transport of energy-spread electron beams yields CTR emission in a regime where the longitudinal and transverse coherent radiation form factors are not separable, thus forcing a more rigorous treatment to match experimental data to the theory and simulations. Analytic expressions in a simplified scenario are presented, highlighting the diagnostic sensitivity to position-momentum source correlations. The experimental demonstration was performed at the BELLA Center 100 TW HTU laser plasma accelerator, producing electron beams at 100 MeV, coupled into a beam line consisting of a quadrupole triplet, chiance, CTR screen, and CTR energy detector.

Speaker: Mr Jeroen Van Tilborg (Lawrence Berkeley National Laboratory)

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