Search

We introduce the new idea of a nonlinear active plasma lens, as part of a larger transport lattice for achromatic electron beam transport. The proposed implementation is based on using the Hall effect in a plasma and is motivated by 1D-hydrodynamic simulations. The manufactured design is presented, including its undergoing experimental characterisation on the CLEAR beam-line at CERN., Comment: 16 pages, 10 figures, submitted to AAC 2024 conference proceedings

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., Comment: 9 pages, 4 figures, 11 supplementary figures

We discuss plans for the E302 instability-efficiency experiment, starting in 2024 at the recently upgraded FACET-II facility at SLAC National Accelerator Laboratory. The beam-breakup instability will be the main area of study for the E302 experiment. With the imaging spectrometer at FACET-II, we introduce a novel technique for observing and quantifying the amplitude growth of the trailing bunch due to the transverse instability. Using the transverse position on the spectrometer screen and the transfer matrix of the magnetic lattice used for the spectrometer, we aim to extract a $x'$-$E$ charge distribution that can be used to quantify the amplitude of the beam. By varying the trailing bunch's charge and, hence, the beam loading of the accelerating field, we aim to adjust the wake-to-beam power transfer efficiency in the E302 experiment. We plan to quantify the amplitude for different configurations of the beam charge and, hence, investigate the relationship between the beam-breakup instability and efficiency. We use a combination of particle-in-cell (PIC) codes to simulate a beam-driven plasma wakefield accelerator from start-to-end with a FACET-II-like spectrometer and demonstrate the methodology that will be used for the instability studies at the E302 experiment., Comment: 9 pages, 9 figures, conference proceeding for the 6th European Advanced Accelerator Concepts workshop (EAAC2023), 17-23 September 2023

This contribution outlines the HALHF concept, which combines the high gradients achievable in plasma-wakefield acceleration with conventional radio-frequency acceleration. In HALHF, beam-driven plasma-wakefield cells are used to accelerate electrons to high energy. Because plasma-based acceleration of positrons is problematic, conventional RF acceleration is used but to much lower energy. The HALHF concept utilises not only asymmetric energies but also asymmetric bunch charges and asymmetric transverse emittances, leading to comparable luminosity to conventional facilities but much lower capital cost. Possible upgrades to the HALHF facility are discussed, in particular to the $\rm{t\bar{t}}$ threshold and to 550 GeV, where the Higgs self-coupling and $\rm{t\bar{t}}H$ coupling can be measured. Other upgrades include the provision of two interaction points, to implement a $\gamma$$\unicode{x2013}$$\gamma$ collider of two possible types and finally a symmetric high-energy collider if the problem of plasma-based positron acceleration can be solved., Comment: 13 pages, 4 figures, conference proceeding for the 6th European Advanced Accelerator Concepts workshop (EAAC2023), 17-23 September 2023

Plasma acceleration has emerged as a promising technology for future particle accelerators, particularly linear colliders. Significant progress has been made in recent decades toward high-efficiency and high-quality acceleration of electrons in plasmas. However, this progress does not generalize to acceleration of positrons, as plasmas are inherently charge asymmetric. Here, we present a comprehensive review of historical and current efforts to accelerate positrons using plasma wakefields. Proposed schemes that aim to increase the energy efficiency and beam quality are summarised and quantitatively compared. A dimensionless metric that scales with the luminosity-per-beam power is introduced, indicating that positron-acceleration schemes are currently below the ultimate requirement for colliders. The primary issue is electron motion; the high mobility of plasma electrons compared to plasma ions, which leads to non-uniform accelerating and focusing fields that degrade the beam quality of the positron bunch, particularly for high efficiency acceleration. Finally, we discuss possible mitigation strategies and directions for future research., Comment: 24 pages (30 pages with references), 22 figures

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., Comment: Manuscript: 7 pages, 4 figures; Supplementary material: 3 pages, 1 figure

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., Comment: 6 pages, 4 figures

The interaction of intense particle bunches with plasma can give rise to plasma wakes capable of sustaining gigavolt-per-metre electric fields, which are orders of magnitude higher than provided by state-of-the-art radio-frequency technology. Plasma wakefields can, therefore, strongly accelerate charged particles and offer the opportunity to reach higher particle energies with smaller and hence more widely available accelerator facilities. However, the luminosity and brilliance demands of high-energy physics and photon science require particle bunches to be accelerated at repetition rates of thousands or even millions per second, which are orders of magnitude higher than demonstrated with plasma-wakefield technology. Here we investigate the upper limit on repetition rates of beam-driven plasma accelerators by measuring the time it takes for the plasma to recover to its initial state after perturbation by a wakefield. The many-nanosecond-level recovery time measured establishes the in-principle attainability of megahertz rates of acceleration in plasmas. The experimental signatures of the perturbation are well described by simulations of a temporally evolving parabolic ion channel, transferring energy from the collapsing wake to the surrounding media. This result establishes that plasma-wakefield modules could be developed as feasible high-repetition-rate energy boosters at current and future particle-physics and photon-science facilities.

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., Comment: 5 pages, 2 figures; proceeding of the EPS-HEP2021 conference (Hamburg, July 26-30 2021) submitted to Proceedings of Science

Active plasma lenses are compact devices developed as a promising beam-focusing alternative for charged particle beams, capable of short focal lengths for high-energy beams. We have previously shown that linear magnetic fields with gradients of around 0.3 kT/m can be achieved in argon-filled plasma lenses that preserve beam emittance [C.A. Lindstr{\o}m et al., Phys. Rev. Lett. 121, 194801 (2018)]. Here we show that with argon in a 500 {\mu}m diameter capillary, the fields are still linear with a focusing gradient of 3.6 kT/m, which is an order of magnitude higher than the gradients of quadrupole magnets. The current pulses that generate the magnetic field are provided by compact Marx banks, and are highly repeatable. These results establish active plasma lenses as an ideal device for pulsed particle beam applications requiring very high focusing gradients that are uniform throughout the lens aperture., Comment: 8 pages, 6 figures. Submitted to Physical Review Applied

Accelerating particles to high energies with a high-gradient wakefield accelerator may require use of multiple stages. Coupling beams from one stage to another can be difficult due to high divergence and non-negligible energy spreads. We review the challenges, technical requirements and currently proposed methods for solving the staging problem., Comment: 24 pages, contribution to the CAS - CERN Accelerator School: High Gradient Wakefield Accelerators, 11-22 March 2019, Sesimbra, Portugal

Beam-driven plasma-wakefield acceleration based on external injection has the potential to significantly reduce the size of future accelerators. Stability and quality of the acceleration process substantially depends on the incoming bunch parameters. Precise control of the current profile is essential for optimising energy-transfer efficiency and preserving energy spread. At the FLASHForward facility, driver--witness bunch pairs of adjustable bunch length and separation are generated by a set of collimators in a dispersive section, which enables fs-level control of the longitudinal bunch profile. The design of the collimator apparatus and its commissioning is presented., Comment: 7 pages, 5 figures, to be published in the proceedings of the 4th European Advanced Accelerator Concepts Workshop, 15-21 September 2019, La Biodola Bay, Isola d'Elba, Italy

Matching to small beta functions is required to preserve emittance in plasma accelerators. The plasma wake provides strong focusing fields, which typically require beta functions on the mm-scale, comparable to those found in the final focusing of a linear collider. Such beams can be time consuming to experimentally produce and diagnose. We present a simple, fast, and noninvasive method to measure Twiss parameters in a linac using two beam position monitors only, relying on the similarity of the beam phase space and the jitter phase space. By benchmarking against conventional quadrupole scans, the viability of this technique was experimentally demonstrated at the FLASHForward plasma-accelerator facility., Comment: 8 pages, 7 figures

The Compact Linear Collider (CLIC) is a TeV-scale high-luminosity linear $e^+e^-$ collider under development at CERN. Following the CLIC conceptual design published in 2012, this report provides an overview of the CLIC project, its current status, and future developments. It presents the CLIC physics potential and reports on design, technology, and implementation aspects of the accelerator and the detector. CLIC is foreseen to be built and operated in stages, at centre-of-mass energies of 380 GeV, 1.5 TeV and 3 TeV, respectively. CLIC uses a two-beam acceleration scheme, in which 12 GHz accelerating structures are powered via a high-current drive beam. For the first stage, an alternative with X-band klystron powering is also considered. CLIC accelerator optimisation, technical developments and system tests have resulted in an increased energy efficiency (power around 170 MW) for the 380 GeV stage, together with a reduced cost estimate at the level of 6 billion CHF. The detector concept has been refined using improved software tools. Significant progress has been made on detector technology developments for the tracking and calorimetry systems. A wide range of CLIC physics studies has been conducted, both through full detector simulations and parametric studies, together providing a broad overview of the CLIC physics potential. Each of the three energy stages adds cornerstones of the full CLIC physics programme, such as Higgs width and couplings, top-quark properties, Higgs self-coupling, direct searches, and many precision electroweak measurements. The interpretation of the combined results gives crucial and accurate insight into new physics, largely complementary to LHC and HL-LHC. The construction of the first CLIC energy stage could start by 2026. First beams would be available by 2035, marking the beginning of a broad CLIC physics programme spanning 25-30 years., Comment: 112 pages, 59 figures; published as CERN Yellow Report Monograph Vol. 2/2018; corresponding editors: Philip N. Burrows, Nuria Catalan Lasheras, Lucie Linssen, Marko Petri\v{c}, Aidan Robson, Daniel Schulte, Eva Sicking, Steinar Stapnes

Active plasma lensing is a compact technology for strong focusing of charged particle beams, which has gained considerable interest for use in novel accelerator schemes. While providing kT/m focusing gradients, active plasma lenses can have aberrations caused by a radially nonuniform plasma temperature profile, leading to degradation of the beam quality. We present the first direct measurement of this aberration, consistent with theory, and show that it can be fully suppressed by changing from a light gas species (helium) to a heavier gas species (argon). Based on this result, we demonstrate emittance preservation for an electron beam focused by an argon-filled active plasma lens., Comment: 6 pages, 3 figures

Hollow channel plasma wakefield acceleration is a proposed method to provide high acceleration gradients for electrons and positrons alike: a key to future lepton colliders. However, beams which are misaligned from the channel axis induce strong transverse wakefields, deflecting beams and reducing the collider luminosity. This undesirable consequence sets a tight constraint on the alignment accuracy of the beam propagating through the channel. Direct measurements of beam misalignment-induced transverse wakefields are therefore essential for designing mitigation strategies. We present the first quantitative measurements of transverse wakefields in a hollow plasma channel, induced by an off-axis 20 GeV positron bunch, and measured with another 20 GeV lower charge trailing positron probe bunch. The measurements are largely consistent with theory., Comment: 5 pages, 4 figures. Submitted to Physical Review Letters

Discharge capillary-based active plasma lenses are a promising new technology for strongly focusing charged particle beams, especially when combined with novel high gradient acceleration methods. Still, many questions remain concerning such lenses, including their transverse field uniformity, limitations due to plasma wakefields and whether they can be combined in multi-lens lattices in a way to cancel chromaticity. These questions will be addressed in a new plasma lens experiment at the CLEAR User Facility at CERN. All the subsystems have been constructed, tested and integrated into the CLEAR beam line, and are ready for experiments starting late 2017., Comment: Conference proceeding for the European Advanced Accelerator Concepts (EAAC) Workshop 2017, submitted to NIMA Proceedings

We present our first results for a sample of southern high-amplitude delta Scuti stars (HADS), based on a spectrophotometric survey started in 2003. For CY Aqr and AD CMi, we found very stable light and radial velocity curves; we confirmed the double-mode nature of ZZ Mic, BQ Ind and RY Lep. Finally, we detected gamma-velocity changes in RS Gru and RY Lep, Comment: 2 pages, conference proceedings, Workshop on Stellar Pulsation and Evolution, Rome, June 2005

We present spectroscopic observations of the black-hole binary V4641 Sagittarii, obtained between 4th July 2004 and 28th March 2005, which cover the minor outburst of the star in early July 2004 and quiescence variations on 19 nights scattered over six months. During the outburst, the star peaked approximately 3 magnitudes brighter than usual, and our spectra were dominated by broad hydrogen, helium and iron emission lines. The very first spectra showed P Cygni profiles, which disappeared within a few hours, indicating rapid changes in matter ejection. The H-alpha line had multiple components, one being a broad blue-shifted wing exceeding 5000 km/s. During a simultaneously observed 10-min photometric flare-up, the equivalent width of the H-alpha line temporarily decreased, implying that it was a flare of the continuum. The overall spectral appearance was similar to that observed in the 1999 September active phase, which suggests that similar mass-ejection processes were associated with both eruptions. In quiescence, the spectra were those of the early-type secondary star showing its orbital motion around the primary. By measuring cross-correlation radial velocities, we give an improved set of spectroscopic elements. Whereas we measure the same velocity amplitude (K_2=211.3+/-1.0 km/s), within errors, as Orosz et al. (2001), our centre-of-mass velocity (v_gamma=72.7+/-3.3 km/s) differs significantly from the previously published value (107.4+/-m2.9 km/s). However, we find evidence that the difference is caused by a systematic error in data reduction in the previous study, rather than by gravitational effects of an invisible third component., Comment: 9 pages, 8 figures, accepted for publication in MNRAS

The spectral properties of ridge-waveguide graded-index separate-confinement heterostructure single-quantum-well (SQW) GaAs/AlGaAs lasers are measured. Long-cavity lasers (800 microns) exhibit remarkably pure CW single-longitudinal-mode spectra in spite of the short cavity mode spacing. At output power 5 mW, the sidemode suppression exceeds 24 dB and the linewidth is 1.5 MHz. The linewidth-power product (LPP) is 6.4 MHz mW. Measurements of LPP as a function of cavity length L gives a 1/L-squared dependence, in agreement with theory. The results are used to deduce the linewidth enhancement factor alpha at the gain peak wavelength and its dependence on the excitation level. The sublinear gain-carrier density relation in the SQW results in an increase in alpha with increasing carrier density (decreasing cavity length). A decrease in alpha was observed for lasers operating at the second quantized state due to a recovery of the differential gain.