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 4+5 Joint Session: Session 1 of 2

Joint session between Working Groups 4 & 5:
WG4 - Beam-Driven Acceleration
WG5 - Beam Sources, Monitoring and Control

Conveners: Jens Osterhoff (DESY) , Dr Samuel Barber (Lawrence Berkeley National Laboratory) , Spencer Gessner (SLAC) , Yine Sun (Argonne National Laboratory)

15:30 Highly spin-polarized multi-GeV sub-femtosecond electron beams generated from single-species plasma photocathodes

High-gradient and high-efficiency acceleration in plasma-based accelerators has been demonstrated, showing its potential as the building block for a future collider operating at the energy frontier of particle physics. However, generating and accelerating the required spin-polarized beams in such a collider using plasma-based accelerators has been a long-standing challenge. Here we show that the passage of a highly relativistic, high-current electron beam through a single-species (ytterbium) vapor excites a nonlinear plasma wake by primarily ionizing the two outer 6s electrons [1, 2]. Further photoionization of the resultant Yb2+ ions by a circularly polarized laser injects the 4f14 electrons into this wake generating a highly spin-polarized beam. Combining time-dependent Schrodinger equation simulations with particle-in-cell simulations, we show that a sub-femtosecond, high-current (4 kA) electron beam with up to 56% net spin polarization can be generated and accelerated to 15 GeV in just 41 cm. This relatively simple scheme solves the perplexing problem of producing spin-polarized relativistic electrons in plasma-based accelerators.

References:
[1] Z. Nie, et. al., Phys. Rev. Lett. 126, 054801 (2021).
[2] Z. Nie, et. al., Phys. Rev. Res. 4, 033015 (2022).

Speaker: Zan Nie (UCLA)

AAC2022_spin_ZanNie.pptx

15:48 A scheme for generation and measurement of spin polarized GeV electrons from a PWFA

The generation and acceleration of an electron beam with a high degree of spin polarization is desirable for future plasma-based high-energy colliders. Our recent theoretical and simulations work [1,2] has shown that spin polarized electrons can be produced from photoionization of 4f14 electrons of Yb III ions by a circularly polarized laser, and then accelerated to multi-GeV energies while maintaining their spin polarization in a beam-driven plasma wakefield accelerator (PWFA). An experimental realization of this scheme would require a method of measuring the spin polarization of the accelerated electrons. In our proposed scheme, Møller scattering polarimetry is used to measure the spin polarization of the beam, which involves scattering the beam off of a magnetized target and observing the yield of scattered electrons at specific angles. Measuring the spin polarization of a beam produced from a PWFA presents additional challenges due to the unpolarised drive beam that typically contains nC of charge and a lack of stability from shot to shot. Our spectrometer design addresses these challenges and provides a scheme for both producing and detecting high-energy spin polarized electrons accelerated in a beam-driven plasma-based accelerator.

References:
[1] Z. Nie, et. al., Phys. Rev. Lett. 126, 054801 (2021).
[2] Z. Nie, et. al., arXiv:2206.09017.

Speaker: Nainoa Nambu (UCLA)

16:06 Investigating the Transverse Trapping Condition in Beam-Induced-Ionization-Injection in Plasma Wakefield Accelerators

Plasma wakefield accelerators (PWFA) have demonstrated acceleration gradients of tens of GeV per meter. For injecting high-quality electron beams, a method called beam-induced ionization injection (B-III) is proposed. In this method, the drive beam field increases as its slice envelope oscillates to its minimum value due to the betatron oscillations and releases impurity plasma electrons that are then injected. Controlling the trailing beam qualities requires an understanding of a transverse trapping mechanism. In this poster, we will present our research based on the injection of the ultrashort, femtosecond electron beams using B-III.
To investigate the formation of a trailing beam, we will track ionized electron motions in the Particle-In-Cell(PIC) simulation field maps using our eTracks code. The trailing beam quality will be shown based on the simulation results. We will also present that a critical Hamiltonian has to be satisfied for the trapped electrons. This critical condition can also be noticed as a transverse trapping condition in the transverse phase space. We are investigating the formalism for the threshold Hamiltonian value or the critical condition in transverse phase space.

Speaker: Jiayang Yan (Stony Brook University)

AAC22_JiayangYan.pdf

16:24 Trojan Horse-II at FACET-II: prospects and experimental plans.

Plasma photocathodes aim for the tunable production of compact electron beams with normalized emittance and brightness many orders of magnitude better than conventional sources. Experimental realization of such beams would open numerous prospects for transformative plasma wakefield accelerator applications based on ultrahigh-brightness beams. Developing a plasma capable of high-gradient acceleration but also as a source of practical electron bunches is paramount. Here, we present details of the upcoming E-310: Trojan Horse-II program at FACET-II specifically reporting on the development of a preionized plasma channel suitable for optimizing charge injection and stable energy gain.

Speaker: Andrew Sutherland (University of Strathclyde)

AAC22_THII_Final.pptx

16:42 Towards a soft x-ray PWFA-FEL via Trojan Horse single bunch injection

A barrier to realizing a plasma-based XFEL is the energy chirp of the accelerated electron bunch. If such a chirp is not removed prior to extraction it is difficult to maintain bunch qualities during transport to the undulator stage, and the FEL performance will be degraded or inhibited entirely. The Trojan Horse (TH) injection method uses a plasma photocathode approach to release and trap electrons directly inside the blowout of a PWFA stage [1], as demonstrated during the FACET-I campaign at SLAC [2]. The E310 experiment at FACET-II will aim to demonstrate ultrahigh brightness beam production via the efforts of multiple UK and US collaborators [3]. TH injection may produce low-charge electron beams with kA peak current and unprecedented emittance as low as 20 nm rad. Maintaining such ultralow emittance through a transport line may be possible via the multi-bunch dechirping scheme, which has already been developed [4]. Here, we present simulation-based efforts towards an alternative chirp-suppression scheme using a single injected electron bunch of higher charge. Exploiting the tunable nature of TH injection, we attempt to optimize an electron bunch for optimum beam-loading to remove projected energy spread while producing a multi-kA peak current, maintaining low emittance of a few hundred nm rad and few 0.1 % slice energy spread. Such a beam would have the potential to produce soft XFEL radiation using existing undulator technology.

[1] B. Hidding, G. Pretzler, J. B. Rosenzweig, T. Königstein, D. Schiller, and D. L. Bruhwiler, ‘Ultracold Electron Bunch Generation via Plasma Photocathode Emission and Acceleration in a Beam-Driven Plasma Blowout’, Phys. Rev. Lett, Jan. 2012

[2] A. Deng et al., ‘Generation and acceleration of electron bunches from a plasma photocathode’, Nat. Phys, Nov. 2019

[3] A. F. Habib et al., ‘Ultrahigh brightness beams from plasma photoguns’, ArXiv211101502 Phys., Nov. 2021

[4] G. G. Manahan, A. F. Habib et al., ‘Single-stage plasma-based correlated energy spread compensation for ultrahigh 6D brightness electron beams’, Nat. Commun, Aug. 2017

Speaker: Lily Berman (University of Strathclyde)

AAC talk Lily Berman.pdf

Tuesday, 8 November

10:00 → 10:30 Coffee Break

12:00 → 13:20 Lunch

15:00 → 15:30 Coffee Break/Exhibits

15:30 → 17:00 WGs 4+5 Joint Session: Session 2 of 2

Joint session between Working Groups 4 & 5:
WG4 - Beam-Driven Acceleration
WG5 - Beam Sources, Monitoring and Control

Conveners: Jens Osterhoff (DESY) , Dr Samuel Barber (Lawrence Berkeley National Laboratory) , Spencer Gessner (SLAC) , Yine Sun (Argonne National Laboratory)

15:30 Direct measurements of emittance growth from Coulomb scattering on neutral gas atoms in a plasma lens

Plasma lenses are of much interest to the plasma-accelerator community as their cylindrically symmetric and large focusing gradients facilitate beam-optics control of the highly divergent beams usually associated with plasma accelerators. However, a fundamental difference between plasma-based and conventional accelerators/focusing devices is that in the former the beams propagate through matter rather than a vacuum. This invariably leads to interactions such as Coulomb scattering between the beam and plasma particles, which in turn likely leads to emittance growth. Whereas the beam sizes inside plasma accelerators are comparatively small, limiting the induced emittance growth, the situation in plasma lenses is quite different as the beam size must be larger in these devices than in the accelerators to allow collimation or focusing. In particular, in active plasma lenses beam sizes must be large to avoid driving a wake, which in turn increases the induced emittance growth from scattering. This is further exacerbated by the fact that using gases of heavier elements, which scatter more strongly than their lighter counterparts, are preferable as they produce linear focusing gradients. However, direct measurements of the induced emittance growth from Coulomb scattering has hitherto not been shown for beam and lens parameters relevant for plasma-based focusing devices. In this work we show the measurements of emittance growth from scattering in neutral (i.e. un-ionized) argon, nitrogen and hydrogen over a range of pressures. Results from a corresponding set of simulations in GEANT4 and Ocelot, which represent the experimental environment, are also outlined.

Speaker: Jonas Björklund Svensson (DESY)

AAC_emittance_growth_scattering_v3.pdf

15:48 Longitudinal bunch shaping using transverse deflecting cavities at Argonne Wakefield Accelerator Facility

Longitudinal bunch shaping based on transverse deflecting cavities (TDCs) was first proposed in Tech. Rep. No. LBNL-2670E, 2009 and further elaborated in Phys. Rev. Accel. Beams 23, 072803, 2020. Bunch shaping takes place in a straight beamline configuration of TDCs and a shaping mask. Two potential advantages of TDC-based shaping, over other shaping methods, is that it does not use dipole magnets so it is CSR-free and it shapes an ultra-relativistic beam so space charge is minimized. In this paper, we will show a variety of longitudinal bunch shapes, and discuss the possible applications for high-gradient, beam-driven wakefield accelerators such as high-transformer ratio and quality preservation of the accelerated beam.

Speaker: Seongyeol Kim (Argonne National Laboratory)

2022_11_08_AAC_JointW45_TDCshaping_SeongyeolKim.pdf

16:06 Progress Toward a Laser-Ionized, Unconfined Gas PWFA at FACET-II

We present the progress made toward a plasma wakefield accelerator using a laser-ionized, unconfined gas plasma source for the E301 experiment at FACET-II. One advantage of this plasma source is that the density profile can be semi-arbitrarily defined via controlled focusing of a terawatt class laser pulse, allowing for the creation of entrance and exit ramps that can match the beam into and out of the PWFA, preserving its emittance. Another advantage is the rapid tunability of the plasma density and length, permitting parameter scans for detailed studies of PWFA physics. In addition, this type of plasma source permits the introduction of multiple localized gas species via the placement of gas jets along the length of the primary plasma filament. This is useful for many high-brightness injection schemes. The plasma is also highly accessible to diagnostics due to being unconfined inside a large vacuum chamber. Finally, this type of plasma source is a stepping-stone toward a laser ionized, meter-scale gas jet with supersonic transverse flow. Such a plasma source may be the only means of efficiently dealing with residual heat left in the plasma/gas from the PWFA when operating at high repetition rates.

Speaker: Michael Litos (University of Colorado Boulder)

AAC 2022 WG4 - Litos.pdf

16:24 Underdense Plasma Lens Commissioning at FACET II and Future Experimental Plans

With the commissioning of the 10 GeV FACET-II accelerator underway, early experimental shifts of the plasma lens have been taken. These shifts use a single electron bunch propagating through a laser-ionized elongated gas jet, with an electron beam imaging spectrometer set up to disperse the beam in energy for one transverse axis and image the beam directly in the other. Currently, a laser co-propagating to the electron beam axis is used to ionize the gas jet at the focus of an axilens. Here we discuss the early findings of these plasma/electron beam interactions and state future experimental upgrades and plans. The most important of these upgrades are modifications of the laser in order to ionize a small thickness plasma lens, the upgrading of FACET-II to accommodate a drive and witness bunch, and investigating the effects of a transverse plasma density gradient due to the gas jet density profile.

Speaker: Christopher Doss (University of Colorado Boulder)

16:42 Optical visualization of e-beam-driven plasma wakes at FACET-II

The goal of the E-324 experiment ("Optical visualization of e-beam-driven wakes") at SLAC's 2nd-generation Facility for Advanced Accelerator Science and Experimental Tests (FACET-II) is to observe and understand electron- and ion-density structures that arise during, and at delays up to ~ms after, e-beam-driven production of strongly nonlinear plasma wakefields. The current set-up interrogates the plasma with a probe pulse (𝜆 = 0.8 µm, 50 fs) that is temporally synchronized with the 10 GeV e-beam driver and impinges on the wake at grazing angle 𝜃 < 1˚ to its propagation direction, thereby achieving high-sensitivity to structures of density $n_e \leq 10^{16}$ cm$^{-3}$. Recent time-resolved diffractometry measurements with this setup have identified the principal physical mechanisms, and quantified the dominant dynamical pathways, by which nonlinear wakes release their stored electrostatic energy into the surrounding plasma on ps to ns time scales [1], and have bench-marked large-scale simulations of these dynamics [2]. Clear optical signatures of residual plasma heat at tens of µs delays have been observed [1], well beyond the ~60 ns "lower limit" plasma recovery time determined by 2-pulse wake excitation measurements alone [3]. Full understanding of this recovery time is essential to designing future high-luminosity plasma-based accelerators. We will also discuss current efforts to simulate and detect warm hollow-channel ion-density structures that form within tens of ps following nonlinear wake excitation, and that are promising for plasma-based positron acceleration [4].

[1] R. Zgadzaj et al., “Dissipation of electron-beam-driven plasma wakes,” Nature Commun. 11, 4753 (2020).

[2] V. K. Khudyakov, K. V. Lotov and M. C. Downer, "Ion dynamics driven by strongly nonlinear plasma wake," Plasma Phys. Control. Fusion 64, 045003 (2022).

[3] R. D'Arcy et al., "Recovery time of a plasma-wakefield accelerator," Nature 603, 58 (2022).

[4] T. Silva et al., "Stable positron acceleration in thin, warm, hollow plasma channels," Phys. Rev. Lett. 127, 104801 (2021).

Speaker: Rafal Zgadzaj (UT at Austin)

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

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