Energy recovery in filament-regime plasma wakefield acceleration of positron beams

Plasma wakefield acceleration using an electron filament offers stable, high-gradient, high-quality acceleration of positron beams analogous to the acceleration of electrons in the blowout regime. However, low energy-transfer efficiency is currently a limiting factor for future collider applications. We explore the addition of a secondary electron bunch in the electron filament plasma wakefield acceleration scheme to recover additional energy from the wake. Particle-in-cell simulations using HiPACE++ are used to demonstrate various energy recovery schemes. In addition to confirming the energy efficiency gains with a recovery electron beam, we also develop energy recovery schemes in the context of future plasma colliders

Emittance-preserving acceleration of high-quality positron beams using warm plasma filaments

Preserving the quality of positron beams in plasma-based accelerators, where wakefields are generated in electron filaments, is challenging. These wakefields are characterized by transversely non-linear focusing fields and non-uniform accelerating fields. However, a nonzero plasma temperature linearizes the transverse wakefield within the central region of the electron filament. In this study, we employ 3D particle-in-cell simulations with mesh refinement to demonstrate that beams with emittances on the order of tens of nanometers are contained within the linearized region of the transverse wakefield. This enables emittance preservation to one percent, while positron beams with the same charge and micrometer emittances, which sample the non-linear part of the transverse wakefield, experience a relative emittance growth of ten percent. Additionally, we observe a significant reduction in the growth rate of the slice energy spread for the tens of nanometers emittance beams in comparison to the micrometer emittance beams. The utilization of warm plasmas in conjunction with low-emittance beams opens up new avenues for enhancing the beam quality across various plasma-based positron acceleration approaches.Comment: To be submitted as a proceedings for the 6th European Advanced Accelerator Concepts worksho

From Compact Plasma Particle Sources to Advanced Accelerators with Modeling at Exascale

Developing complex, reliable advanced accelerators requires a coordinated, extensible, and comprehensive approach in modeling, from source to the end of beam lifetime. We present highlights in Exascale Computing to scale accelerator modeling software to the requirements set for contemporary science drivers. In particular, we present the first laser-plasma modeling on an exaflop supercomputer using the US DOE Exascale Computing Project WarpX. Leveraging developments for Exascale, the new DOE SCIDAC-5 Consortium for Advanced Modeling of Particle Accelerators (CAMPA) will advance numerical algorithms and accelerate community modeling codes in a cohesive manner: from beam source, over energy boost, transport, injection, storage, to application or interaction. Such start-to-end modeling will enable the exploration of hybrid accelerators, with conventional and advanced elements, as the next step for advanced accelerator modeling. Following open community standards, we seed an open ecosystem of codes that can be readily combined with each other and machine learning frameworks. These will cover ultrafast to ultraprecise modeling for future hybrid accelerator design, even enabling virtual test stands and twins of accelerators that can be used in operations.Comment: 4 pages, 3 figures, submitted to the 20th Advanced Accelerator Concepts Workshop (AAC22

Controlled density-downramp injection in a beam-driven plasma wakefield accelerator

This paper describes the utilization of beam-driven plasma wakefield acceleration to implement a high-quality plasma cathode via density-downramp injection in a short injector stage at the FLASHForward facility at DESY. Electron beams with charge of up to 105 pC and energy spread of a few percent were accelerated by a tunable effective accelerating field of up to 2.7 GV/m. The plasma cathode was operated drift-free with very high injection efficiency. Sources of jitter, the emittance and divergence of the resulting beam were investigated and modeled, as were strategies for performance improvements that would further increase the wide-ranging applications for a plasma cathode with the demonstrated operational stabilityComment: 11 pages, 9 figure

Positron acceleration in a plasma column

The particle physics community has expressed significant interest in a 10 TeV-class electron-positron collider to advance our understanding of matter. However, the costs associated with such a collider usingconventional radio-frequency technology seem to be prohibitive. Thus,significant research and development is needed on the accelerator sideto reduce both construction and power consumption costs.Plasma-based accelerators, due to their extremely high acceleratinggradients, are a potential solution to reduce construction costs.Although significant progress has been made in plasma-based electronacceleration in recent years, positron acceleration still poses anotorious challenge and has been identified as a critical point in therealization of a plasma-based electron-positron collider. Additionally,plasma-based positron acceleration, while preserving the requiredhigh beam quality for a collider, is challenging even conceptually anddifficult to model with currently available simulation tools.Positron acceleration in a plasma column is a promising new conceptowing to its high accelerating gradient and the ability to preservepositron beam emittance, a fundamental requirement for a collider.In this scheme, a relativistic electron beam travels along the axis of aplasma column, driving a plasma wake in the blowout regime. Dueto the finite radius of the plasma, the restoring force acting on theplasma electrons is reduced and the plasma electrons return in a long,high-density electron filament to the axis some distance behind thedriver. This electron filament generates high-gradient accelerating andfocusing fields for positrons. However, questions regarding stabilityand beam quality remain.In this thesis, positron acceleration in a plasma column is put tothe test. Beyond proof of concept, the acceleration of high-qualitypositron beams and its resilience to realistic conditions, such as misalignmentis demonstrated. Realistic plasma profiles and temperatureeffects are also considered and found to be beneficial to the scheme.The results show that positron acceleration in a plasma column isindeed a viable concept for a possible collider application, althoughadditional research is needed to optimize efficiency. Furthermore, theGPU-accelerated, quasi-static Particle-in-Cell code HiPACE++ has beendeveloped. The new code allows for modeling plasma-based positronacceleration scenarios in full 3D with previously unattainable precisionwhile drastically reducing computational costs, enabling thestudies presented. An outlook for the next possible steps towards aplasma-based collider is given

Positron Acceleration with Beam-Driven Plasma Wakefield Accelerators

The transport and acceleration of positron beams is a crucial challengeon the path towards plasma-based particle colliders. This work pro-poses to use a finite radius plasma in a plasma wakefield acceleratoras a way to reduce the restoring force acting on the plasma electrons,resulting in an elongation of their on-axis return point and, hence,creating a long, high-density electron filament. This leads to a regionwith accelerating and focusing fields for positrons, allowing for theacceleration and quality-preserving transport of high current positronbeams. The generation of the finite radius plasma targets as well astheir associated wakefields are investigated, before quality-preservingpositron acceleration is demonstrated

Inverse Regulation of Cartilage Neogenesis at Physiologically Relevant Calcium Conditions by Human Articular Chondrocytes and Mesenchymal Stromal Cells

Elaborate bioreactor cultivation or expensive growth factor supplementation can enhance extracellular matrix production in engineered neocartilage to provide sufficient mechanical resistance. We here investigated whether raising extracellular calcium levels in chondrogenic cultures to physiologically relevant levels would provide a simple and inexpensive alternative to enhance cartilage neogenesis from human articular chondrocytes (AC) or bone marrow-derived mesenchymal stromal cells (BMSC). Interestingly, AC and BMSC-derived chondrocytes showed an opposite response to a calcium increase from 1.8 mM to 8 mM by which glycosaminoglycan (GAG) and collagen type II production were elevated during BMSC chondrogenesis but depressed in AC, leading to two-fold higher GAG/DNA values in BMSC-based neocartilage compared to the AC group. According to control treatments with Mg2+ or sucrose, these effects were specific for CaCl2 rather than divalent cations or osmolarity. Importantly, undesired pro-hypertrophic traits were not stimulated by calcium treatment. Specific induction of PTHrP mRNA and protein by 8.0mM calcium only in AC, along with negative effects of recombinant PTHrP1-34 on cartilage matrix production, suggested that the PTHrP pathway contributed to the detrimental effects in AC-based neocartilage. Altogether, raising extracellular calcium levels was discovered as a novel, simple and inexpensive stimulator for BMSC-based cartilage neogenesis without the need for special bioreactors, whereas such conditions should be avoided for AC

High-Quality Positron Beams in Beam-Driven Plasma Wakefield Accelerators using a Plasma Column

Acceleration of positron beams in a plasma-based accelerator is a highly-challenging task. However, in order to realize a plasma-based linear collider, accelerating a positron bunch with high charge and efficiency, while maintaining a low emittance and a sub-percent-level energy spread, is required. Recently, a plasma-based positron acceleration scheme was proposed in which a wake suitable for the acceleration and transport of positrons is produced in a plasma column by means of an electron drive beam [Diederichs et al., PRAB 22, 081301 (2019)]. In this talk, we present a study of beamloading for a positron beam in this type of wake. We demonstrate via particle-in-cell simulations that acceleration of high-quality positron beams is possible, and we discuss a possible path to achieve collider-relevant parameters

Stable Electron Beam Propagation in a Plasma Column

The stability of plasma-based accelerators against transverse misalignments and asymmetries of the drive beam is crucial for their applicability. Without stabilizing mechanisms, even small initial offsets of the drive beam centroid can couple coherently to the plasma wake, grow, and ultimately lead to emittance degradation or beam loss for a trailing witness beam. In this work, we demonstrate the intrinsic stability of a beam propagating in a plasma column. This result is relevant in the context of plasma-based positron acceleration, where a wakefield suitable for the transport and acceleration of a positron witness beam is generated in a plasma column by means of an electron drive beam. The stable propagation of the drive beam is a necessary condition for the experimental implementation of this scheme. The differences and similarities of stabilizing mechanisms in a plasma column compared to a homogeneous plasma are identified via theory and particle-in-cell simulations. Experimental tolerances are given, demonstrating the experimental feasibility of the scheme

Self-Stabilizing Positron Acceleration in a Plasma Column

Plasma accelerators sustain extreme  eld gradients and potentially enable future compact linear colliders. Although tremendous progress has been achieved in accelerating electron beams in a plasma accelerator, positron acceleration with collider-relevant parameters is challenging. The wake generated by an electron drive beam in a plasma column represents a promising candidate for positron acceleration owing to the ability to accelerate positron beams with low emittance and low energy spread. However, since this scheme relies on cylindrical symmetry, it is possibly prone to beam-break-up instabilities. In this Letter, we show that both the drive and the witness beams are subject to various damping mechanisms and therefore, this positron acceleration con guration is inherently stable. This enables stable, high-quality positron acceleration