arXiv subjects

E. Gschwendtner

Publications and source records attributed to E. Gschwendtner.

At least 19 recordsLinked to original sources

arXiv2026

Demonstration of a 10-metre-long discharge plasma source for plasma wakefield acceleration

The AWAKE experiment at CERN uses high-energy proton bunches to drive plasma wakefields capable of accelerating electron bunches up to hundreds of GeV in a single plasma. Realising this potential requires a plasma source that can extend to tens of metres while maintaining high longitudinal uniformity and reproducibility. Towards this goal, we report on the first experimental characterisation and beam-based validation of a 10-metre-long pulsed-DC discharge plasma source (DPS) used as an alternative to the laser-ionised rubidium vapour plasma source (VPS). The DPS reliably delivered plasma densities in three noble gases (He, Ar, Xe) at electron densities between 10$^{14}$ and 10$^{15}$ cm$^{-3}$. Proton bunch self-modulation was observed with all three gases, and the resulting modulation frequency was used as a beam-based diagnostic of the plasma density, showing good agreement with laboratory interferometry measurements. The event-to-event modulation frequency was demonstrated to be reproducible to within 0.63%, comparable to that of the VPS. These results establish the DPS as a valid alternative plasma source for beam-driven wakefield experiments, and support its further development towards longer plasma lengths. The present design is tailored to AWAKE requirements, but the underlying discharge concept provides a route to long, reproducible plasma sources with straightforward density control through discharge-beam timing for other beam-plasma experiments.

physics.plasm-ph↗

arXiv2026

Seeding of Self-Modulation using Truncated Seed Bunches as a Path to High Gradient Acceleration

This manuscript proposes a method to enable controlled high-gradient particle acceleration when requiring self-modulation of the drive bunch. While electron bunch seeding of self-modulation (eSSM) has been realised at a plasma electron density $n_\mathrm{pe}\cong10^{14}\mathrm{cm}^{-3}$, it has not been demonstrated at higher plasma densities due to limitations of available seed bunch properties. As experimentally shown in this manuscript, truncating available seed bunches with a relativistic ionisation front allows these limitations to be overcome. This seeding method is called truncated electron bunch seeding of self-modulation (teSSM) and experiments confirm that -- when using teSSM -- self-modulation becomes reproducible at $n_\mathrm{pe}=7\times10^{14}\mathrm{cm}^{-3}$. Additionally, the seed wakefield amplitude is also increased, which is known to be advantageous because it shortens the length needed to reach self-modulation saturation. The presented results establish teSSM as a method for achieving controlled, high-gradient particle acceleration with long drivers and available seed bunches.

physics.acc-ph↗

arXiv2025

Summary Report of the Physics Beyond Colliders Study at CERN

The Physics Beyond Collider (PBC) Study Group was initially mandated by the CERN Management to prepare the previous European Particle Physics Strategy Update for CERN projects other than the high-energy frontier colliders. The main findings were summarized in an PBC Summary Report submitted to the Strategy Update. Following the Update process, the PBC Study Group was confirmed on a permanent basis with an updated mandate taking into account the strategy recommendations. The Study Group is now in charge of supporting the proponents of new ideas to address the technical issues and physics motivation of the projects ahead of their review by the CERN Scientific Committees and decision by the Management. The present document updates the previous PBC summary report to inform the new ongoing European Particle Physics Strategy Update process, taking into account the evolution of the CERN and worldwide landscapes and the new projects under consideration within the Study Group.

hep-ex↗

arXiv2025

Contribution of ALEGRO to the Update of the European Strategy on Particle Physics

Advanced and novel accelerators (ANAs), driven a by laser pulse or a relativistic particle bunch, have made remarkable progress over the last decades. They accelerated electrons by 10GeV in 30cm (laser driven) and by 42GeV in 85cm (particle bunch driven). Rapid progress continues with lasers, plasma sources, computational methods, and more. In this document we highlight the main contributions made by the various major collaborations, facilities, and experiments that develop ANAs for applications to particle and high-energy physics. These include: ALiVE, ANL-AWA, AWAKE, BNL-ATF, CEPC Injector, DESY-KALDERA, ELI ERIC, EuPRAXIA, HALHF, LBNL-BELLA, LBNL-kBELLA, LCvison, PETRA IV Injector, 10TeV Collider design, SLAC-FACET II, as well as the development of structures, lasers and plasma sources, and sustainability, and demonstrate the intense activities in the field. ANAs can have, and already have, applications to particle and high-energy physics as subsystems, the so-called intermediate applications: injectors, lower energy experiments, beam dump experiments, test beds for detectors, etc. Additionally, an ANA could be an upgrade for any Higgs factory based on a linear accelerator, as proposed in the LCvison project. ANAs have advantages over other concepts for reaching multi-TeV energies: lower geographical and environmental footprints, higher luminosity to power ratio, and are thus more sustainable than other accelerators. However, ANAs must still meet a number of challenges before they can produce bunches with parameters and the luminosity required for a linear collider at the energy frontier. It is therefore extremely important to strongly support vigorous R&D of ANAs, because they are, at this time, the most sustainable acceleration scheme to reach very high energies with a linear accelerator.

physics.acc-ph↗

arXiv2025

AWAKE Input to the European Strategy for Particle Physics Update on behalf of the AWAKE Collaboration

The Advanced Wakefield Experiment, AWAKE, is a well-established international collaboration and aims to develop the proton-driven plasma wakefield acceleration of electron bunches to energies and qualities suitable for first particle physics applications, such as strong-field QED and fixed target experiments ($\sim$50-200GeV). Numerical simulations show that these energies can be reached with an average accelerating gradient of $\sim1$GeV/m in a single proton-driven plasma wakefield stage. This is enabled by the high energy per particle and per bunch of the CERN SPS 19kJ, 400GeV and LHC ($\sim$120kJ, 7TeV) proton bunches. Bunches produced by synchrotrons are long, and AWAKE takes advantage of the self-modulation process to drive wakefields with GV/m amplitude. By the end of 2025, all physics concepts related to self-modulation will have been experimentally established as part of the AWAKE ongoing program that started in 2016. Key achievements include: direct observation of self-modulation, stabilization and control by two seeding methods, acceleration of externally injected electrons from 19MeV to more than 2GeV, and sustained high wakefield amplitudes beyond self-modulation saturation using a plasma density step. In addition to a brief summary of achievements reached so far, this document outlines the AWAKE roadmap as a demonstrator facility for producing beams with quality sufficient for first applications. The plan includes: 1) Accelerating a quality-controlled electron bunch to multi-GeV energies in a 10m plasma by 2031; 2) Demonstrating scalability to even higher energies by LS4. Synergies of the R&D performed in AWAKE that are relevant for advancing plasma wakefield acceleration in general are highlighted. We argue that AWAKE and similar advanced accelerator R&D be strongly supported by the European Strategy for Particle Physics Update.

physics.acc-ph↗

arXiv2025

Experimental Observation of Motion of Ions in a Resonantly Driven Plasma Wakefield Accelerator

We show experimentally that an effect of motion of ions, observed in a plasma-based accelerator, depends inversely on the plasma ion mass. The effect appears within a single wakefield event and manifests itself as a bunch tail, occurring only when sufficient motion of ions suppresses wakefields. Wakefields are driven resonantly by multiple bunches, and simulation results indicate that the ponderomotive force causes the motion of ions. In this case, the effect is also expected to depend on the amplitude of the wakefields, experimentally confirmed through variations in the drive bunch charge.

physics.plasm-ph↗

arXiv2024

Measurement of the emittance of accelerated electron bunches at the AWAKE experiment

The vertical plane transverse emittance of accelerated electron bunches at the AWAKE experiment at CERN has been determined, using three different methods of data analysis. This is a proof-of-principle measurement using the existing AWAKE electron spectrometer to validate the measurement technique. Large values of the geometric emittance, compared to that of the injection beam, are observed ($\sim \SI{0.5}{\milli\metre\milli\radian}$ compared with $\sim \SI{0.08}{\milli\metre\milli\radian}$), which is in line with expectations of emittance growth arising from plasma density ramps and large injection beam bunch size. Future iterations of AWAKE are anticipated to operate in conditions where emittance growth is better controlled, and the effects of the imaging systems of the existing and future spectrometer designs on the ability to measure the emittance are discussed. Good performance of the instrument down to geometric emittances of approximately $\SI{1e-4}{\milli\metre\milli\radian}$ is required, which may be possible with improved electron optics and imaging.

physics.acc-ph↗

arXiv2023

Filamentation of a Relativistic Proton Bunch in Plasma

We show in experiments that a long, underdense, relativistic proton bunch propagating in plasma undergoes the oblique instability, that we observe as filamentation. We determine a threshold value for the ratio between the bunch transverse size and plasma skin depth for the instability to occur. At the threshold, the outcome of the experiment alternates between filamentation and self-modulation instability (evidenced by longitudinal modulation into microbunches). Time-resolved images of the bunch density distribution reveal that filamentation grows to an observable level late along the bunch, confirming the spatio-temporal nature of the instability. We calculate the amplitude of the magnetic field generated in the plasma by the instability and show that the associated magnetic energy increases with plasma density.

physics.plasm-ph↗

arXiv2023

Development of the Self-Modulation Instability of a Relativistic Proton Bunch in Plasma

Self-modulation is a beam-plasma instability that is useful to drive large-amplitude wakefields with bunches much longer than the plasma skin depth. We present experimental results showing that, when increasing the ratio between the initial transverse size of the bunch and the plasma skin depth, the instability occurs later along the bunch, or not at all, over a fixed plasma length, because the amplitude of the initial wakefields decreases. We show cases for which self-modulation does not develop and we introduce a simple model discussing the conditions for which it would not occur after any plasma length. Changing bunch size and plasma electron density also changes the growth rate of the instability. We discuss the impact of these results on the design of a particle accelerator based on the self-modulation instability seeded by a relativistic ionization front, such as the future upgrade of the AWAKE experiment.

physics.plasm-ph↗

arXiv2023

Techniques to seed the self-modulation instability of a long proton bunch in plasma

The Advanced Wakefield Experiment (AWAKE) at CERN relies on the seeded Self-Modulation (SM) of a long relativistic proton bunch in plasma to accelerate an externally injected MeV witness electron bunch to GeV energies. During AWAKE Run 1 (2016-2018) and Run 2a (2021-2022), two seeding methods were investigated experimentally: relativistic ionization front seeding and electron bunch seeding. In the first one, a short laser pulse copropagates within the proton bunch and ionizes the rubidium vapor, generating the plasma. In the second, a short electron bunch propagates in plasma ahead of the proton bunch and drives the seed wakefields. Both seeding methods will be further employed during AWAKE Run 2b (2023-2024) to study their effect on the SM evolution in the presence of a plasma density step. In this contribution, we will show the main experimental results and discuss their impact for the future design of the experiment, in particular for Run 2c (starting in 2028), where the plasma will be split in two sections: one dedicated to SM of the proton bunch, and the other to the electron acceleration process.

physics.acc-ph↗

arXiv2022

Adiabatic Focusing of a Long Proton Bunch in Plasma

We show in experiments that a long, relativistic proton bunch is focused by the plasma adiabatic response. The free plasma electrons migrate so as to neutralize the space charge field of the bunch, and the bunch is therefore focused by the azimuthal magnetic field generated by its own current, that is not balanced by the radial electric field. Since the length of the bunch is much longer than the plasma electron wavelength, the bunch also undergoes the self-modulation instability. Thus, the amplitude of the wakefields grows along the bunch and along the plasma, and the defocusing effect of the self-modulation can become dominant over the adiabatic focusing effect. We show that, when seeding the self-modulation with a preceding electron bunch, the transition between the effect of the adiabatic response and that of the self-modulation depends on the amplitude of the seed wakefields.

physics.acc-ph↗

arXiv2022

Mapping charge capture and acceleration in a plasma wakefield of a proton bunch using variable emittance electron beam injection

In the Phase 2 of the AWAKE first experimental run (from May to November 2018), an electron beam was used to probe and test proton-driven wakefield acceleration in a rubidium plasma column. In this work, we analyze the overall charge capture and shot-to-shot reproducibility of the proton-driven plasma wakefield accelerator with various electron bunch injection parameters. The witness electron bunches were produced using an RF-gun equipped with a Cs2Te photocathode illuminated by a tailorable ultrafast deep ultraviolet (UV) laser pulse. The construction of the UV beam optical system enabled appropriate transverse beam shaping and control of its pulse duration, size, and position on the photocathode, as well as time delay with respect to the ionizing laser pulse that seeds the plasma wakefields in the proton bunches. Variable photocathode illumination provided the required flexibility to produce electron bunches with variable charge, emittance, and injection trajectory into the plasma column. We demonstrate charge capture rates exceeding 15% (40 pC of GeV accelerated charge for a 385 pC injected electron bunch) under optimized electron injection conditions.

physics.acc-ph↗

arXiv2022

European Strategy for Particle Physics -- Accelerator R&D Roadmap

The 2020 update of the European Strategy for Particle Physics emphasised the importance of an intensified and well-coordinated programme of accelerator R&D, supporting the design and delivery of future particle accelerators in a timely, affordable and sustainable way. This report sets out a roadmap for European accelerator R&D for the next five to ten years, covering five topical areas identified in the Strategy update. The R&D objectives include: improvement of the performance and cost-performance of magnet and radio-frequency acceleration systems; investigations of the potential of laser / plasma acceleration and energy-recovery linac techniques; and development of new concepts for muon beams and muon colliders. The goal of the roadmap is to document the collective view of the field on the next steps for the R&D programme, and to provide the evidence base to support subsequent decisions on prioritisation, resourcing and implementation.

physics.acc-ph↗

arXiv2021

Analysis of Proton Bunch Parameters in the AWAKE Experiment

A precise characterization of the incoming proton bunch parameters is required to accurately simulate the self-modulation process in the Advanced Wakefield Experiment (AWAKE). This paper presents an analysis of the parameters of the incoming proton bunches used in the later stages of the AWAKE Run 1 data-taking period. The transverse structure of the bunch is observed at multiple positions along the beamline using scintillating or optical transition radiation screens. The parameters of a model that describes the bunch transverse dimensions and divergence are fitted to represent the observed data using Bayesian inference. The analysis is tested on simulated data and then applied to the experimental data.

physics.acc-ph↗

arXiv2021

Simulation and Experimental Study of Proton Bunch Self-Modulation in Plasma with Linear Density Gradients

We present numerical simulations and experimental results of the self-modulation of a long proton bunch in a plasma with linear density gradients along the beam path. Simulation results agree with the experimental results reported in arXiv:2007.14894v2: with negative gradients, the charge of the modulated bunch is lower than with positive gradients. In addition, the bunch modulation frequency varies with gradient. Simulation results show that dephasing of the wakefields with respect to the relativistic protons along the plasma is the main cause for the loss of charge. The study of the modulation frequency reveals details about the evolution of the self-modulation process along the plasma. In particular for negative gradients, the modulation frequency across time-resolved images of the bunch indicates the position along the plasma where protons leave the wakefields. Simulations and experimental results are in excellent agreement.

physics.plasm-ph↗

arXiv2021

Seeding of proton bunch self-modulation by an electron bunch in plasma

The AWAKE experiment relies on the self-modulation instability of a long proton bunch to effectively drive wakefields and accelerate an electron bunch to GeV-level energies. During the first experimental run (2016-2018) the instability was made phase reproducible by means of a seeding process: a short laser pulse co-propagates within the proton bunch in a rubidium vapor. Thus, the fast creation of plasma and the onset of beam-plasma interaction within the bunch drives seed wakefields. However, this seeding method leaves the front of the bunch not modulated. The bunch front could self-modulate in a second, preformed plasma and drive wakefields that would interfere with those driven by the (already self-modulated) back of the bunch and with the acceleration process. We present studies of the seeded the self-modulation (SSM) of a long proton bunch using a short electron bunch. The short seed bunch is placed ahead of the proton bunch leading to self-modulation of the entire bunch. Numerical simulations show that this method have other advantages when compared to the ionization front method. We discuss the requirements for the electron bunch parameters (charge, emittance, transverse size at the focal point, length), to effectively seed the self-modulation process. We also present preliminary experimental studies on the electron bunch seed wakefields generation.

physics.acc-ph↗

arXiv2020

A primary electron beam facility at CERN -- eSPS Conceptual design report

The design of a primary electron beam facility at CERN is described. The study has been carried out within the framework of the wider Physics Beyond Colliders study. It re-enables the Super Proton Synchrotron (SPS) as an electron accelerator, and leverages the development invested in Compact Linear Collider (CLIC) technology for its injector and as an accelerator research and development infrastructure. The facility would be relevant for several of the key priorities in the 2020 update of the European Strategy for Particle Physics, such as an electron-positron Higgs factory, accelerator R\&D, dark sector physics, and neutrino physics. In addition, it could serve experiments in nuclear physics. The electron beam delivered by this facility would provide access to light dark matter production significantly beyond the targets predicted by a thermal dark matter origin, and for natures of dark matter particles that are not accessible by direct detection experiments. It would also enable electro-nuclear measurements crucial for precise modelling the energy dependence of neutrino-nucleus interactions, which is needed to precisely measure neutrino oscillations as a function of energy. The implementation of the facility is the natural next step in the development of X-band high-gradient acceleration technology, a key technology for compact and cost-effective electron/positron linacs. It would also become the only facility with multi-GeV drive bunches and truly independent electron witness bunches for plasma wakefield acceleration. A second phase capable to deliver positron witness bunches would make it a complete facility for plasma wakefield collider studies. [...]

physics.acc-ph↗

arXiv2020

Transition between Instability and Seeded Self-Modulation of a Relativistic Particle Bunch in Plasma

We use a relativistic ionization front to provide various initial transverse wakefield amplitudes for the self-modulation of a long proton bunch in plasma. We show experimentally that, with sufficient initial amplitude ($\ge(4.1\pm0.4)$ MV/m), the phase of the modulation along the bunch is reproducible from event to event, with 3 to 7% (of 2$π$) rms variations all along the bunch. The phase is not reproducible for lower initial amplitudes. We observe the transition between these two regimes. Phase reproducibility is essential for deterministic external injection of particles to be accelerated.

physics.plasm-ph↗