20th Advanced Accelerator Concepts Workshop

America/New_York
Hyatt Regency Long Island

Hyatt Regency Long Island

1717 Motor Parkway Hauppauge, New York 11788
Mark Palmer (Brookhaven National Laboratory), Navid Vafaei-Najafabadi (Stony Brook University)
Description

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/

 

Conference Coordinator
    • 6:00 PM 7:30 PM
      Welcome Reception 1h 30m Terrace Ballroom

      Terrace Ballroom

    • 10:20 AM 10:40 AM
      Coffee Break 20m Grand Ballroom Pre Function

      Grand Ballroom Pre Function

    • 12:10 PM 1:30 PM
      Lunch 1h 20m
    • 1:30 PM 3:00 PM
      WG4: Beam-Driven Acceleration: Session 1 Salon E

      Salon E

      Conveners: Jens Osterhoff (DESY), Spencer Gessner (SLAC)
      • 1:30 PM
        Progress towards high-repetition-rate operation of a beam-driven plasma wakefield accelerator 15m

        Beam-driven plasma-wakefield accelerators offer significant potential as compact, high-gradient, high-quality accelerators, either as the basis of a future plasma-based facility or as an ‘after-burner’ stage appended to conventional accelerators to boost their peak energy. To maximise applicability of such devices, plasma-based accelerators must be capable of operating at repetition-rates consistent with, or exceeding, existing state-of-the-art conventional accelerator facilities. This contribution discusses results obtained at the FLASHForward experiment at DESY: a plasma-wakefield-acceleration experiment driven by the FLASH accelerator, which is capable of providing nC-level, GeV-scale electron bunches to the plasma accelerator stage at up to 3 MHz repetition rates. Of these results, the definition of the maximum possible repetition rate of a plasma-wakefield accelerator, as dictated by the time it takes for the plasma to recover to its initial state after a wakefield has been driven, will be highlighted. This result—indicating that repetition rates at the level of O(10 MHz) are attainable in future—makes it worthwhile to consider a high-repetition-rate after-burner stage for FLASH. This contribution will conclude with further results and concepts of how to achieve this goal.

        Speaker: James Chappell (University of Oxford)
      • 1:45 PM
        Gigaelectronvolt Acceleration of Captured Electrons in a Positron Beam-Driven Plasma Wakefield Accelerator 15m

        Positron acceleration in plasma is a topic of interest for future applications of plasma-based linear colliders. At FACET, we investigated the acceleration of positrons in plasma under a variety of regimes including linear, non-linear, and hollow channel configurations. Over the course of these experiments, we observed the acceleration of plasma electrons captured in a positron beam-driven wake. The positron drive beam conditions were varied to determine the capture threshold of the plasma electrons. Simulations performed using OSIRIS 4.0 are in good agreement with the experiment which allows for a detailed analysis of the capture dynamics.

        Speaker: James Allen (SLAC National Accelerator Laboratory)
      • 2:00 PM
        Plasma heating and expansion in PWFA experiments FACET 15m

        In PWFA experiments, like at FACET, most of the beam energy can be transferred into the wake and trailing plasma oscillations. These oscillation in turn lead to intense plasma heating and expansion. As a practical matter, to reach high average current the heat must be removed between electron bunches. Interestingly, the rapid plasma expansion is unstable and can produce filamentary structures and corresponding large magnetic fields. These types of magnetic field structures are studied in astronomical phenomenon but difficult to produce in the laboratory. In our case, the magnetic filamentary structures are embedded in the plasma and last longer than the plasma recombination time. This allows the structures to be imaged along the beam axis by observing the hydrogen plasma recombination fluorescence at 656 nm. The images show helical structures consistent with radial expansion and plasma filamentation instability.

        Speaker: Kenneth Marsh (UCLA ECE)
      • 2:15 PM
        Observation of Skewed Electromagnetic Wakefields in an Asymmetric Structure Driven by Flat Electron Bunches 15m

        Relativistic charged-particle beams which generate intense longitudinal fields in accelerating structures also inherently couple to transverse modes. The effects of this coupling may lead to beam break-up instability, and thus must be countered to preserve beam quality in applications such as linear colliders. Beams with highly asymmetric transverse sizes (flat-beams) have been shown to suppress the initial instability in slab-symmetric structures. However, as the coupling to transverse modes remains, this solution serves only to delay instability. In order to understand the hazards of transverse coupling in such a case, we describe here an experiment characterizing the transverse effects on a flat-beam, traversing near a planar dielectric lined structure. The measurements reveal the emergence of a previously unobserved skew-quadrupole-like interaction when the beam is canted transversely, which is not present when the flat-beam travels parallel to the dielectric surface. We deploy a multipole field fitting algorithm to reconstruct the projected transverse wakefields from the data. We generate the effective kick vector map using a simple two-particle theoretical model, and particle-in-cell simulations provide further insight for realistic particle distributions.

        Speaker: Walter Lynn (UCLA)
      • 2:30 PM
        Transverse Stability in an Alternating Gradient Planar Dielectric Wakefield Structure 15m

        Dielectric Wakefield Acceleration (DWA) as a practical means of realizing next-generation accelerators is predicated on the ability to sustain the beam-structure interaction over experimentally meaningful length scales. This goal is complicated by the fact that the beams in question inherently couple to transverse modes in addition to the desired longitudinal modes which, if left unaccounted for, lead to a beam breakup instability. We attempt to, in part, address this issue by tackling the quadrupole mode excited in a planar-symmetry dielectric structure. We do so by periodically alternating the orientation of said structure in order to alternate the orientation of the excited quadrupole wake causing the tail of the beam to experience sequential focusing and defocusing fields, stabilizing the interaction. We examine this technique computationally and lay out a planned experiment at the Argonne Wakefield Accelerator to verify it experimentally.

        Speaker: Walter Lynn (UCLA)
      • 2:45 PM
        Wakefield Acceleration in Nanostructures: The E336 Experiment at FACET-II 15m

        When a high intensity electron beam is passed through a structured nano target, the solid-state density plasma created can support ultra-high accelerating gradients, on the order of 1-10 TeV/m. The similarly strong transverse focusing fields are expected to produce beams with small equilibrium emittance. Driving these extreme wakefields in the self-modulated regime requires high energy and high-density electron bunches. Such bunches are now within reach at the FACET-II facility at SLAC National Accelerator Laboratory. The E336 experiment at FACET-II is a proof of principle experiment that will utilize the high-density electron beams produced by the facility to demonstrate the unique processes expected to occur in structured solid targets. We discuss the motivation, status, and future plans for the experiment.

        Speaker: Robert Ariniello (SLAC National Accelerator Laboratory)
    • 3:00 PM 3:30 PM
      Coffee Break 30m Grand Ballroom Pre Function

      Grand Ballroom Pre Function

    • 10:00 AM 10:30 AM
      Coffee Break 30m Grand Ballroom Pre Function

      Grand Ballroom Pre Function

    • 12:00 PM 1:20 PM
      Lunch 1h 20m Terrace Ballroom

      Terrace Ballroom

    • 1:30 PM 3:00 PM
      WG4: Beam-Driven Acceleration: Session 3 Salon E

      Salon E

      Conveners: Jens Osterhoff (DESY), Spencer Gessner (SLAC)
      • 1:30 PM
        Progress towards Energy Doubling and Emittance Preservation through Beam Driven Plasma Wakefield Acceleration at FACET-II 15m

        The E300 experiment at FACET-II aims to demonstrate energy doubling of a witness bunch to 20 GeV through beam-driven plasma wakefield acceleration (PWFA) while preserving emittance and narrow energy spread. This talk will describe the status of the experimental setup including the current and expected accelerator parameters, the plasma source and associated differential pumping system, and post-interaction beam diagnostics. These diagnostics include single- and multi-shot emittance measurements using energy-dispersed beam profile measurements, energy resolved profile measurements to measure energy depletion and acceleration, and betatron gamma ray detectors that will be used to infer information about beam dynamics within the plasma. The first results will be discussed from the initial commissioning runs and from the first self-ionized PWFA interactions in helium and hydrogen gases.

        Speaker: Doug Storey (SLAC National Accelerator Laboratory)
      • 1:45 PM
        High-efficiency wake excitation in beam-ionized plasmas at FACET-II 15m

        FACET-II is a new 10 GeV electron beam facility hosted by the SLAC National Accelerator Laboratory and E300 is the flagship experiment aiming at demonstrating high-quality two-bunch PWFA [1, 2]. An important goal of E300 is to demonstrate efficient (40%) energy transfer from the drive to the trailing bunch [1]. This number in turn is the product of the drive beam to the wake (80%) and from the wake to the trailing bunch (50%) efficiencies. In order to obtain such a high drive beam to the wake energy transfer, the bulk of the particles must be nearly fully depleted of their energy. In this talk, we will present experimental results on high-efficiency wake excitation which is an important stepping stone for achieving overall high energy transfer efficiency. We show that up to 70% of the charge contained in the FACET-II beam can self-ionize static fill (up to 2 Torr) of hydrogen gas over greater than one meter and lose significant amount of its energy in driving a wake. Correlation measurements on the integrated plasma emission and the energy spectrum of the beam after interaction suggest a beam-to-wake energy transfer efficiency up to ~70%. The measurements also show evidence for that a portion of the 10 GeV drive beam has lost all its 10 GeV energy (pump depletion), which is necessary for achieving high beam-to-wake energy transfer efficiency.

        References
        [1] Joshi C. et al., "Plasma wakefield acceleration experiments at FACET II." Plasma Physics and Controlled Fusion 60, no. 3 (2018): 034001.
        [2] Yakimenko V. et al., "FACET-II facility for advanced accelerator experimental tests." Physical Review Accelerators and Beams 22, no. 10 (2019).

        Speaker: Chaojie Zhang (UCLA)
      • 2:00 PM
        QPAD modeling of wake excitation and acceleration in meter-long beam-ionized plasma at FACET-II 15m

        FACET-II, a new 10 GeV electron beam facility at SLAC National Accelerator Laboratory for R&D on beam physics and novel acceleration techniques [1, 2], has been commissioned this year. One major research effort is on further development of the Plasma Wakefield Acceleration scheme (E300). The experimental results from the first run of the E300 experiment at FACET-II has shown evidence of high-efficiency wake excitation and energy depletion of the drive beam in beam-ionized hydrogen or helium gases. This self-ionization of both hydrogen and helium came as somewhat of a surprise since the calculated peak current in the beam was not high enough to field ionize these atoms. Fortunately, multiple diagnostics showed that the drive beam frequently had much narrower, higher current peaks. We therefore model the drive beam as having an ~80 fs Gaussian temporal shape with a peak current of 4.7 kA that has a much higher current spike (>50 kA, ~4 fs). To explain these results, a quasi-3D quasi-static particle-in-cell code QPAD [3] was used. We find that such a beam with a high current spike can indeed ionize both gases via ADK (He) or MO-ADK (H2) ionization model. The current spike was placed such that up to 30 to 40% of the drive beam charges did not lose any energy to agree with experimental observations. Once the plasma was formed by the spike, the rest of the beam with nb>np, rapidly forms a wake and transfers up to ~70% of the remaining beam energy to the wake. The model qualitatively reproduced the maximum energy loss as a function of gas pressure, energy gain seen at high pressures, pump depletion and betatron oscillations seen in the experiment.

        References
        [1] C. Joshi, et al., "Plasma wakefield acceleration experiments at FACET II." Plasma Phys. Control. Fusion 60, 034001 (2018).
        [2] V. Yakimenko, et al., "FACET-II facility for advanced accelerator experimental tests." Phys. Rev. Accel. Beams 22, 101301 (2019).
        [3] F. Li, et al., “A quasi-static particle-in-cell algorithm based on an azimuthal Fourier decomposition for highly efficient simulations of plasma-based acceleration: QPAD” Comput. Phys. Commun. 261, 107784 (2021).

        Speaker: Zan Nie (UCLA)
      • 2:15 PM
        Focusing of a Long Relativistic Proton Bunch in Underdense Plasma 15m

        In this contribution we show, with experimental and numerical simulation results, that a long, relativistic proton bunch can be focused to an equilibrium transverse size, when traveling in underdense plasma.
        In the presence of the space-charge field of the bunch, the plasma electrons move towards the axis of propagation of the beam, generating a focusing force for the protons.
        We observe that the transverse size of the bunch, measured downstream of the plasma exit, decreases when increasing the plasma electrons density, until it reaches a saturation value.
        Moreover, the transverse size does not oscillate along the bunch, further suggesting that no transverse oscillation of the plasma electrons nor of the protons occurs, and that the plasma does not sustain wakefields.
        When the plasma electron density becomes comparable to the peak density of the bunch, the effect of the self-modulation instability becomes observable on the proton bunch charge distribution.
        This indicates the transition to collective motion of the plasma electrons and to the presence of wakefields, that can be used for high-gradient particle acceleration, as in the AWAKE experiment at CERN.

        Speaker: Livio Verra (CERN)
      • 2:30 PM
        Large Energy Depletion of a Beam Driver in a Plasma-Wakefield Accelerator 15m

        Beam-driven plasma-wakefield acceleration has the potential to reduce the size and construction cost of large-scale accelerator facilities, by providing accelerating fields orders of magnitude greater than that of conventional accelerating structures. To keep the running costs affordable, high energy-transfer efficiency from the wall-plug to the accelerated bunch has to be demonstrated. For this, drive bunches must be efficiently produced, strong decelerating fields must be sustained for the drive bunches until their energy is depleted, and the resulting accelerating fields must be strongly beam loaded by the trailing bunches. Here we address the second of these points, showing measurements performed at FLASHForward using a 500 MeV drive bunch where approximately half of its total energy is deposited into a 20 cm long plasma. This level of energy-transfer efficiency demonstrates that plasma accelerators hold the potential to become competitive with conventional accelerators. An experimental outlook of how to achieve this goal will conclude the talk.

        Speaker: Felipe Peña (DESY/UHH)
      • 2:45 PM
        Plasma-based longitudinal phase space manipulation 15m

        High-brightness electron beams are crucial for tremendous scientific applications, such as linear colliders, free-electron lasers (FEL) and accelerator-based coherent terahertz (THz) radiation sources. For these applications, precise manipulation of the beam longitudinal phase space (LPS), namely shaping the beam temporal and energy profiles, is of great importance. Here we present a novel method for tailoring the beam LPS by means of self-generated plasma wakefields. Physically, the passage of the beam through a plasma section excites a strong longitudinal wakefield that acts to remove or imprint any time-energy correlation. Based on this solution, we experimentally demonstrate that a plasma-based passive “dechirper” can be utilized to remove the beam’s linear energy chirp, leading to a tenfold reduction in the beam energy spread. Additionally, we demonstrate that by properly adjusting the density, the plasma can also act as a tunable “linearizer” to significantly compensate for the nonlinear energy chirp imprinted on the beam, resulting in a fourfold reduction in energy spread. Furthermore, we propose that a plasma-based “modulator” can also imprint a sawtooth periodic energy modulation on the beam. Such energy modulation is then effectively converted into the beam density modulation by means of magnetic optics, forming micro-bunches with tunable picosecond spacing and a bunching factor as high as 0.8, which can be used to produce narrowband THz radiation with energies ranging from mJ to 10 mJ. These plasma-based advanced LPS manipulation techniques will significantly improve the performance of accelerator-based scientific facilities.

        Speaker: Yipeng Wu (UCLA)
    • 3:00 PM 3:30 PM
      Coffee Break/Exhibits 30m Grand Ballroom Pre Function

      Grand Ballroom Pre Function

    • 10:00 AM 10:30 AM
      Coffee Break/Exhibits 30m Grand Ballroom Pre-Function

      Grand Ballroom Pre-Function

    • 12:00 PM 1:20 PM
      Lunch 1h 20m Terrace Ballroom

      Terrace Ballroom

    • 10:00 AM 10:30 AM
      Coffee Break/Exhibits 30m Grand Ballroom Pre-Function

      Grand Ballroom Pre-Function

    • 10:30 AM 12:00 PM
      WG4: Beam-Driven Acceleration: Session 7 Salon E

      Salon E

      Conveners: Jens Osterhoff (DESY), Spencer Gessner (SLAC)
      • 10:30 AM
        An Analytic Theory of Chromatic Emittance Growth in a Plasma Wakefield Accelerator 15m

        Preserving the emittance of an electron bunch as it is accelerated by a plasma wakefield accelerator is one of the major challenges that needs to be overcome for these accelerators to replace conventional techniques. Energy spread in the bunch primarily drives the emittance growth through the process of chromatic phase spreading. The chromatic effects are complicated by the acceleration process; the different particles in the bunch are accelerated at different rates depending on how well the witness beam loads the wake. We present an analytic theory describing this evolution that includes the effects of nonuniformity in the accelerating field, the witness beam’s initial energy spread, and mismatch between the beam and the plasma. We discuss some of the interesting features that emerge including the evolution of the longitudinal and energy slices.

        Speaker: Robert Ariniello (SLAC National Accelerator Laboratory)
      • 10:45 AM
        Dominance of the seed from a tightly-focused electron bunch over the self-modulation of a long proton bunch in an over-dense plasma 15m

        The phase and growth rate of the self-modulation of a long proton bunch in over-dense plasma can be controlled by a preceding charged particle bunch. In order to selectively seed the growth of the proton bunch self-field, the dominance of seed over any undesired imperfections of the proton bunch is important. In this work, we investigate analytically and numerically the phase and growth rate of the long proton bunch self-modulation, including the effects of its gently rising current profile and of the wakefields of the tightly focused low energy electron seed at the early stage of the self-modulation. We also show that the low energy electron bunch simultaneously drives a single mode modulation along the entire long proton bunch, mitigating mode polarization with the anomalous phase shift of the long proton bunch self-modulation.

        Speaker: Kook-Jin Moon (Ulsan National Institute of Science and Technology)
      • 11:00 AM
        Beam-Driven Dielectric Wakefield Acceleration with a plasma photocathode at the AWA 15m

        The Trojan Horse experiment has recently demonstrated the plasma photocathode concept at SLAC FACET, with a two-gas mixture where on species is ionized for wakefield generation and the other for precision witness beam generation within the plasma bubble. In an experimentally similar approach called the 'Dielectric Trojan Horse', the plasma accelerator component is replaced with a solid-state dielectric structure for the wakefield medium. The dielectric structure is filled with a gas that is ionized by an injection laser to generate the witness beam for the plasma photocathode process. While the peak accelerating field if sacrificed compared to the plasma accelerator, the hybrid method may provide low emittance beam generation that is maintained through transport. Here, we described the design and implementation of this experimental scenario at the Argonne Wakefield Accelerator (AWA) where the concept of a bunch brightness transformer can be realized. In the AWA experiment, a bunch train resonantly excites the fundamental mode in the dielectric wakefield accelerator and a precision laser ionizes Xe-gas, filled into the structure, to generate the witness beam. Proposed experimental methods and diagnostic capabilities and are discussed.

        Speaker: Gerard Andonian (UCLA/Radiabeam)
      • 11:15 AM
        Proof of principle experiments of PV/m plasmonics using structured semiconductors 15m

        A new paradigm of extreme plasmonics unearthed by our work opens the unprecedented possibility of PetaVolts per meter fields that make it possible to access 1,000,000 times the acceleration gradient in RF accelerators. Plasmonic accelerators and light-sources put forth in our work rely on these extreme plasmons over timescales where the ionic-lattice remains largely unperturbed. A specific realization of this concept uses ultrashort particle beams propagating inside tubes made of conductive walls. Beam fields excite the conduction band electrons and sustain a large-amplitude surface crunch-in plasmon which is critical to mitigate collision of the beam with the ionic lattice but at the same time access strong focusing fields along with acceleration gradient. We elucidate our proof-of-principle experiments based on “tunable semiconductor plasmons” excited in n-type doped Silicon tube to match with currently accessible beams from linacs such as FACET-II or laser wakefield accelerators. Experimental verification of principles underlying extreme plasmons will pave the way towards PV/m plasmonics.

        Speaker: Prof. Aakash Sahai (University of Colorado Denver)
      • 11:30 AM
        Wakefield-based afterburner for increasing the spectral range of X-FELs 15m

        Advanced accelerator techniques based on collinear wakefield accelerations have demonstrated the capability of achieving very high accelerating fields. These schemes are based on passing a high charge driver electron beam in a plasma or near field structure which results in high rate energy extraction. In this process a strong wakefield is left behind that can be used for high gradient acceleration of a properly injected trailing electron bunch. Generation of tunably spaced high energy bunches is in fact common in modern XFEL beamlines which strive to provide pump and probe and multi-color capabilities to the most advanced X-ray users. In this paper, we propose to leverage some of these developments and take advantage of the many shaping techniques developed at FEL beamlines to generate a bunch pair suitable to be injected into a collinear wakefield-based high gradient acceleration section. This will result in a significant boost in the beam energy of the trailing beam which can be used to ease lasing (and increase the radiated power) at very short wavelengths or even to extend the spectral reach of current XFELs.

        Speaker: Pietro Musumeci
      • 11:45 AM
        Experimental Opportunities for the Plasma Wakefield Acceleration in a Narrow Plasma Channel 15m

        The stability of the drive electron beam in plasma wakefield acceleration (PWFA) is critical for the realization of many applications. The growing instability of a drive electron beam can couple into the plasma wake and further impact the transverse dynamics of the witness beam, rendering the emittance and energy spread to grow. Applications like positron acceleration in an electron-driven blowout wake require a stable drive beam to produce an experimentally usable accelerating phase for the positrons at the tail of the wake.
        Recent theoretical developments show that finite radius plasma columns suppress the hosing instability introduced by a tilted drive beam or by a transversely misaligned drive beam. This theoretical work motivates our experimental study. We present experimental opportunities at the Facility for Advanced Accelerator Experimental Tests II (FACET-II) E333 experiment to study the longitudinal dynamics of an electron beam propagating in a laser-ionized plasma column with a finite radius smaller than its blowout radius. Various widths of the plasma column will be formed in the experiment to study the acceleration gradient and energy transformer ratio of a narrow plasma column PWFA and further understand the relationship between beam stability and acceleration efficiency in a finite plasma channel.

        Speaker: Valentina Lee (University of Colorado, Boulder)
    • 12:00 PM 1:20 PM
      Lunch 1h 20m Terrace Ballroom

      Terrace Ballroom

    • 1:30 PM 3:00 PM
      WG4: Beam-Driven Acceleration: Session 8 Salon E

      Salon E

      • 1:30 PM
        High average gradient in a laser-gated multistage plasma wakefield accelerator 18m

        Owing to the provision of GV/m accelerating fields, beam-driven plasma accelerators are a promising technology for the miniaturization of particle accelerators. Energy gains of GeV or even tens of GeV are already achievable so to extend this range to 0.1 - 1 TeV, a sequence of multiple plasma stages is being considered.
        While plasma-accelerator stages itself are sufficiently small, beam-transport components and distances between stages can be among the biggest contributors to the total accelerator length and therefore decrease the average accelerating gradient of a plasma-accelerator linac.
        A new concept to design beam lattices in beam-driven plasma accelerators will be presented. By taking advantage of the fs-ionization front, typical for laser-ionized plasmas, plasma wakefields are gated in, thereby allowing for different lattices - separated in the temporal domain.
        When applying this method to staged beam-driven plasma accelerators, drive beams can propagate as a bunch train with a small spacing and in-and out-coupling is possible with compact magnetic chicanes. As a consequence, the total stage size can remain sufficiently short to maintain an accelerating gradient of about 1 GV/m, scalable to TeV energy gains.

        Speaker: Alexander Knetsch
      • 1:48 PM
        Emittance preservation in a single PWFA-LC stage using adiabatic plasma density ramp matching sections in the presence of ion motion 18m

        Plasma based acceleration (PBA) is being considered as a building block for a future linear collider (LC). In PBA a short pulse laser or particle beam creates a wakefield and a witness particle beam is accelerated in the wakefield. As the witness beam is accelerated its energy spread must be small and its emittance must be preserved. In some designs the witness beam parameters required by a linear collider are expected to trigger background ion motion which can lead to nonlinear focusing forces which vary along the witness beam. This can lead to emittance growth of the witness beam. To mitigate this, we propose to use an adiabatic plasma density ramp as a matching section. We match the witness beam to the low density plasma entrance, where the beam initially has a large matched spot size so the ion motion effects are relatively small. As the beam propagates in the plasma upramp (downramp), it is adiabatically focused (defocused) and its distribution evolves slowly towards an equilibrium distribution including the effects of the adiabatically changing ion motion. We present simulation results using QPAD which is a quasi-3D quasi-static PIC code based on the workflow of QuickPIC. Simulation results show that this method can reduce the projected emittance growth of a 25GeV, 0.1um emittance witness beam to only ~3% within a single stage, which includes adiabatic matching sections at both the entrance and exit. The trade-off among the length of the plasma density ramp, the adiabaticity of the plasma density ramp, and the plasma density at the entrance is also discussed. This is an important issue for later accelerating stages when the witness beam has an even higher energy.

        Speaker: Yujian Zhao
      • 2:06 PM
        Flat beam plasma wakefield accelerator 18m

        Particle beams with highly asymmetric emittance ratios are employed at accelerator facilities and are expected at the interaction point of high energy colliders. These asymmetric beams can be used to drive wakefields in dielectric structures and can be used to drive high gradient wakefields in plasmas. In plasma, the high aspect ratio of the drive beam can create a transversely elliptical blowout cavity and the asymmetry in the ion column creates asymmetric focusing in the two transverse planes. The ellipticity of the blowout depends on the ellipticity and normalized charge density of the beam. Simulations are performed to investigate the ellipticity of the wakefield based on the initial driver beam parameters and the parameter space for the two cases at the AWA and FACET facilities.

        Speaker: Pratik Manwani (University of California, Los Angeles)
      • 2:24 PM
        Acceleration and Focusing of Positrons Using Elongated Bubbles in Warm Plasmas 18m

        Plasma wakefields produced by high-charge electron bunches are attractive for lepton colliders because they combine high-gradient acceleration and, in the regime of full electron blowout, emittance preserving linear focusing of the accelerated electrons by the remaining positively charged ions. Achieving the same for positrons is more challenging because it requires producing a uniform high-density filament of plasma electrons. I will discuss a novel approach to creating such filaments behind the driver-generated plasma "bubble" by adding a trailing escort bunch. Initial plasma temperature, as well as the electric charge and time delay of the escort bunch, determine the size of the filament region favorable to simultaneous focusing/acceleration of witness positrons. I will further discuss how efficient energy transfer from the driver to the positrons, combined with emittance preservation, can be achieved for such elongated bubbles in warm plasmas.

        Speaker: Prof. Gennady Shvets (Cornell University)
      • 2:42 PM
        Beam-Beam Considerations for Highest-Energy Linear Colliders 18m

        The AAC community proposed linear collider concepts with energies extending to 15 TeV center-of-mass and luminosities up to 50E34 cm^-2 s^-1 as part of the Snowmass process. The beam power required to reach these energies and luminosities is prohibitive. We discuss the results of initial investigations of strategies to increase luminosity per beam power, a key figure-of-merit for linear colliders.

        Speaker: Spencer Gessner (SLAC)
    • 3:00 PM 6:00 PM
      Afternoon at Leisure 3h
    • 10:00 AM 10:30 AM
      Coffee Break 30m
    • 12:00 PM 1:00 PM
      Lunch 1h Terrace Ballroom

      Terrace Ballroom

    • 2:40 PM 3:00 PM
      Coffee Break 20m Grand Ballroom Pre-Function

      Grand Ballroom Pre-Function