arXiv subjects

J. Björklund Svensson

Publications and source records attributed to J. Björklund Svensson.

9 recordsLinked to original sources

arXiv2026

Slice Emittance Preservation and Focus Control in a Passive Plasma Lens

Strong, symmetrically focusing plasma lenses are promising for accommodating the small beams associated with plasma-based accelerators and collider final foci. However, while focusing with active and passive plasma lenses has been experimentally demonstrated, compatibility with high-brightness beams relevant for applications has not. In this work, we show experimentally that passive plasma lenses can preserve free-electron-laser-quality slice emittance while focusing two orders of magnitude more strongly than quadrupole magnets, and that the focal parameters can be controlled.

physics.acc-ph↗

arXiv2025

The Linear Collider Facility (LCF) at CERN

In this paper we outline a proposal for a Linear Collider Facility as the next flagship project for CERN. It offers the opportunity for a timely, cost-effective and staged construction of a new collider that will be able to comprehensively map the Higgs boson's properties, including the Higgs field potential, thanks to a large span in centre-of-mass energies and polarised beams. A comprehensive programme to study the Higgs boson and its closest relatives with high precision requires data at centre-of-mass energies from the Z pole to at least 1 TeV. It should include measurements of the Higgs boson in both major production mechanisms, ee -> ZH and ee -> vvH, precision measurements of gauge boson interactions as well as of the W boson, Higgs boson and top-quark masses, measurement of the top-quark Yukawa coupling through ee ->ttH, measurement of the Higgs boson self-coupling through HH production, and precision measurements of the electroweak couplings of the top quark. In addition, ee collisions offer discovery potential for new particles complementary to HL-LHC.

hep-ex↗

arXiv2025

Ion-motion simulations of a plasma-wakefield experiment at FLASHForward

In plasma-based acceleration, an ultra-relativistic particle bunch$\unicode{x2014}$or an intense laser beam$\unicode{x2014}$is used to expel electrons from its propagation path, forming a wake that is devoid of electrons. The ions, being significantly more massive, are often assumed to be stationary. However, both theory and simulations suggest that any sufficiently dense electron bunch can trigger ion motion, and its effect must be taken into account. We simulate beam-driven plasma wakefields to identify key features$\unicode{x2014}$such as longitudinally dependent emittance growth$\unicode{x2014}$that could be observed in an experiment using plasma and beam parameters from the FLASHForward facility at DESY.

physics.acc-ph↗

arXiv2025

Experimental demonstration of a tomographic 5D phase-space reconstruction

Detailed knowledge of particle-beam properties is of great importance to understand and push the performance of existing and next-generation particle accelerators. We recently proposed a new phase-space tomography method to reconstruct the five-dimensional (5D) phase space, i.e., the charge density distribution in all three spatial directions and the two transverse momenta. Here, we present the first experimental demonstration of the method at the FLASHForward facility at DESY. This includes the reconstruction of the 5D phase-space distribution of a GeV-class electron bunch, the use of this measured phase space to create a particle distribution for simulations, and the extraction of the transverse 4D slice emittance.

physics.acc-ph↗

arXiv2024

Energy Depletion and Re-Acceleration of Driver Electrons in a Plasma-Wakefield Accelerator

For plasma-wakefield accelerators to fulfil their potential for cost effectiveness, it is essential that their energy-transfer efficiency be maximized. A key aspect of this efficiency is the near-complete transfer of energy, or depletion, from the driver electrons to the plasma wake. Achieving full depletion is limited by the process of re-acceleration, which occurs when the driver electrons decelerate to non-relativistic energies, slipping backwards into the accelerating phase of the wakefield and being subsequently re-accelerated. Such re-acceleration is unambiguously observed here for the first time. At this re-acceleration limit, we measure a beam driver depositing (57 $\pm$ 3)\% of its energy into a 195-mm-long plasma. Combining this driver-to-plasma efficiency with previously measured plasma-to-beam and expected wall-plug-to-driver efficiencies, our result suggests that plasma-wakefield accelerators can in principle reach or even exceed the energy-transfer efficiency of conventional accelerators.

physics.acc-ph↗

arXiv2024

Emittance preservation in a plasma-wakefield accelerator

Radio-frequency particle accelerators are engines of discovery, powering high-energy physics and photon science, but are also large and expensive due to their limited accelerating fields. Plasma-wakefield accelerators (PWFAs) provide orders-of-magnitude stronger fields in the charge-density wave behind a particle bunch travelling in a plasma, promising particle accelerators of greatly reduced size and cost. However, PWFAs can easily degrade the beam quality of the bunches they accelerate. Emittance, which determines how tightly beams can be focused, is a critical beam quality in for instance colliders and free-electron lasers, but is particularly prone to degradation. We demonstrate, for the first time, emittance preservation in a high-gradient and high-efficiency PWFA while simultaneously preserving charge and energy spread. This establishes that PWFAs can accelerate without degradation$\unicode{x2014}$essential for energy boosters in photon science and multistage facilities for compact high-energy particle colliders.

physics.acc-ph↗

arXiv2022

Longitudinally resolved measurement of energy-transfer efficiency in a plasma-wakefield accelerator

Energy-transfer efficiency is an important quantity in plasma-wakefield acceleration, especially for applications that demand high average power. Conventionally, the efficiency is measured using an electron spectrometer; an invasive method that provides an energy-transfer efficiency averaged over the full length of the plasma accelerator. Here, we experimentally demonstrate a novel diagnostic utilizing the excess light emitted by the plasma after a beam-plasma interaction, which yields noninvasive, longitudinally resolved measurements of the local energy-transfer efficiency from the wake to the accelerated bunch; here, as high as (58 $\pm$ 3)%. This method is suitable for online optimization of individual stages in a future multistage plasma accelerator, and enables experimental studies of the relation between efficiency and transverse instability in the acceleration process.

physics.acc-ph↗

arXiv2022

Mechanisms to control laser-plasma coupling in laser wakefield electron acceleration

Experimental results, supported by precise modelling, demonstrate optimisation of a plasma-based injector with intermediate laser pulse energy ($<1$ J), corresponding to a normalised vector potential $a_0 = 2.15$, using ionisation injection in a tailored plasma density profile. An increase in electron bunch quality and energy is achieved experimentally with the extension of the density downramp at the plasma exit. Optimisation of the focal position of the laser pulse in the tailored plasma density profile is shown to efficiently reduce electron bunch angular deviation, leading to a better alignment of the electron bunch with the laser axis. Single peak electron spectra are produced in a previously unexplored regime by combining an early focal position and adaptive optic control of the laser wavefront through optimising the symmetry of the pre-focal laser energy distribution. Experimental results have been validated through particle-in-cell simulations using realistic laser energy, phase distribution, and temporal envelope, allowing for accurate predictions of difficult to model parameters, such as total charge and spatial properties of the electron bunches, opening the way for more accurate modelling for the design of plasma-based accelerators.

physics.plasm-ph↗

arXiv2021

Progress of the FLASHForward X-2 high-beam-quality, high-efficiency plasma-accelerator experiment

FLASHForward is an experimental facility at DESY dedicated to beam-driven plasma-accelerator research. The X-2 experiment aims to demonstrate acceleration with simultaneous beam-quality preservation and high energy efficiency in a compact plasma stage. We report on the completed commissioning, first experimental results, ongoing research topics, as well as plans for future upgrades.

physics.acc-ph↗