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Laser wakefield accelerators (LWFAs) can produce high-energy electron bunches in short distances. Successfully coupling these sources with undulators has the potential to form an LWFA-driven free-electron laser (FEL), providing high-intensity short-wavelength radiation. Electron bunches produced from LWFAs have a correlated distribution in longitudinal phase space: a chirp. However, both LWFAs and FELs have strict parameter requirements. The bunch chirp created using ideal LWFA parameters may not suit the FEL; for example, a chirp can reduce the high peak current required for free-electron lasing. We, therefore, design a flexible beamline that can accept either positively or negatively chirped LWFA bunches and adjust the chirp during transport to an undulator. We have used the accelerator design program MAD8 to design a beamline in stages, and to track particle bunches. The final beamline design can produce ambidirectional values of longitudinal dispersion ($$R_{56}$$ R 56 ): we demonstrate values of + 0.20 mm, 0.00 mm and − 0.22 mm. Positive or negative values of $$R_{56}$$ R 56 apply a shear forward or backward in the longitudinal phase space of the electron bunch, which provides control of the bunch chirp. This chirp control during the bunch transport gives an additional free parameter and marks a new approach to matching future LWFA-driven FELs.

We propose a new method for laser pulse compression that uses the spatially varying dispersion of a plasma plume with a density gradient. This novel scheme can be used to compress ultrahigh power lasers. A long, negatively frequency-chirped, laser pulse reflects off the plasma ramp of an over-dense plasma. As the density increases longitudinally the high frequency photons at the leading part of the laser pulse propagates more deeply than low frequency photons, the pulse is compressed in a similar way to compression off a chirped mirror. Proof-of-principle simulations, using a one-dimensional (1-D) particle-in-cell (PIC) simulation code demonstrates the compression of 2.35 ps laser pulse to 10.3 fs, with a compression ratio of 225. As plasmas is robust and resistant to high intensities, unlike gratings in a chirped-pulse amplification (CPA) technique [1], the method could be used as a compressor to reach exawatt or zettawatt peak power lasers.

In an electron wakefield accelerator, an intense laser pulse or charged particle beam excites plasma waves. Under proper conditions, electrons from the background plasma are trapped in the plasma wave and accelerated to ultra-relativistic velocities. We present recent results from a proof-of-principle wakefield acceleration experiment that reveal a unique synergy between a laser-driven and particle-driven accelerator: a high-charge laser-wakefield accelerated electron bunch can drive its own wakefield while simultaneously drawing energy from the laser pulse via direct laser acceleration. This process continues to accelerate electrons beyond the usual decelerating phase of the wakefield, thus reaching much higher energies. We find that the 10-centimeter-long nanoparticle-assisted wakefield accelerator can generate 340 pC, 10.4+-0.6 GeV electron bunches with 3.4 GeV RMS convolved energy spread and 0.9 mrad RMS divergence. It can also produce bunches with lower energy, a few percent energy spread, and a higher charge. This synergistic mechanism and the simplicity of the experimental setup represent a step closer to compact tabletop particle accelerators suitable for applications requiring high charge at high energies, such as free electron lasers or radiation sources producing muon beams.

Data produced using the FBPIC particle-in-cell code https://github.com/fbpic/fbpic and used in the corresponding publication "Controlling the group velocity of an intense laser pulse using a pre-pulse". Data details available in the README file.

We propose an innovative beam cooling scheme based on laser driven plasma wakefields to address the challenge of high luminosity generation for a future linear collider. For linear colliders, beam cooling is realised by means of damping rings equipped with wiggler magnets and accelerating cavities. This scheme ensures systematic reduction of phase space volume through synchrotron radiation emission whilst compensating for longitudinal momentum loss via an accelerating cavity. In this paper, the concept of a plasma wiggler and its effective model analogous to a magnetic wiggler are introduced; relation of plasma wiggler characteristics with damping properties are demonstrated; underpinning particle-in-cell simulations for laser propagation optimisation are presented. The oscillation of transverse wakefields and resulting sinusoidal probe beam trajectory are numerically demonstrated. The formation of an order of magnitude larger effective wiggler field compared to conventional wigglers is successfully illustrated. Potential damping ring designs on the basis of this novel plasma-based technology are presented and performance in terms of damping times and footprint was compared to an existing conventional damping ring design.

Modern particle accelerators and their applications increasingly rely on precisely coordinated interactions of intense charged particle and laser beams. Femtosecond-scale synchronization alongside micrometre-scale spatial precision are essential e.g. for pump-probe experiments, seeding and diagnostics of advanced light sources and for plasma-based accelerators. State-of-the-art temporal or spatial diagnostics typically operate with low-intensity beams to avoid material damage at high intensity. As such, we present a plasma-based approach, which allows measurement of both temporal and spatial overlap of high-intensity beams directly at their interaction point. It exploits amplification of plasma afterglow arising from the passage of an electron beam through a laser-generated plasma filament. The corresponding photon yield carries the spatiotemporal signature of the femtosecond-scale dynamics, yet can be observed as a visible light signal on microsecond-millimetre scales.

Longitudinal beam cooling due to radiation reaction in the interaction of a high-intensity laser pulse and a high-relativistic electron beam. Comparison of a stochastic model based on single photon emission probabilities calculated from strong-field QED to classical and quasi-classical theories. Measurement of the emitted radiation spectrum with positively- and negatively-chirped laser pulses

It is shown that the requirements for high quality electron bunch generation and trapping from an underdense photocathode in plasma wakefield accelerators can be substantially relaxed through localizing it on a plasma density downramp. This depresses the phase velocity of the accelerating electric field until the generated electrons are in phase, allowing for trapping in shallow trapping potentials. As a consequence the underdense photocathode technique is applicable by a much larger number of accelerator facilities. Furthermore, dark current generation is effectively suppressed., Comment: 4 pages, 3 figures

Accelerators driven by 10s TW-class lasers can produce electron bunches with femtosecond-scale duration and energy of 100s of MeV. A potential application of such short bunches is high-dose rate radiotherapy, which could transition to FLASH radiotherapy if a sufficiently large dose is delivered in a single shot. Here we present Monte Carlo simulations to study the bunch length evolution of an electron beam propagating in a water phantom. We show that for electron energies above 100 MeV the bunch lengthens to 1--10 ps duration after interaction with a 30 cm long water phantom, both for a collimated and weakly focused geometry. The corresponding dose rates are on the order of 200 Gy/s per primary electron, much higher than in conventional radiotherapy.

The Scottish Centre for the Application of Plasma-based Accelerators (SCAPA) is a research centre dedicated to providing high energy particle beams and high peak brightness radiation pulses for users across all scientific and engineering disciplines. A pair of Ti:Sapphire femtosecond laser systems (40 TW peak power at 10 Hz pulse repetition rate and 350 TW at 5 Hz, respectively) are the drivers for a suite of laser-plasma accelerator beamlines housed across a series of radiation shielded areas. The petawatt-scale laser delivers 45 W of average power that establishes it as the world leader in its class. The University of Strathclyde has had an operational laser wakefield accelerator since 2007 as the centrepiece of the ongoing Advanced Laser Plasma High-energy Accelerators towards X-rays (ALPHA-X) project. SCAPA, which is a multipartner venture under the auspices of the Scottish Universities Physics Alliance, continues the dedicated beamline approach pioneered by ALPHA-X and represents a significant expansion in the UK's experimental capability at the university level in laser-driven acceleration. The new centre supports seven radiation beamlines across three concrete shielded bunkers that each nominally specialise in a different aspect of fundamental laser-plasma interaction physics and radiation sources: GeVscale electron beams, MeV/c proton and ion beams, X-rays, gamma rays and so on. Development of application programmes based on these sources cover a wide range of fields including nuclear physics, radiotherapy, space radiation reproduction, warm dense matter, high field physics and radioisotope generation.

The laser wake-field accelerator (LWFA) traditionally produces high brightness, quasi-monoenergetic electron beams with Gaussian-like spatial and angular distributions. In the present work we investigate the generation of ultra-relativistic beams with ring-like structures in the blowout regime of the LWFA using a dual stage accelerator. A density down-ramp triggers injection after the first stage and is used to produce ring-like electron spectra in the 300 – 600 MeV energy range. These well defined, annular beams are observed simultaneously with the on-axis, high energy electron beams, with a divergence of a few milliradians. The rings have quasi-monoenergetic energy spectra with an RMS spread estimated to be less than 5%. Particle-in-cell simulations confirm that off-axis injection provides the electrons with the initial transverse momentum necessary to undertake distinct betatron oscillations within the plasma bubble during their acceleration process.

High energy attosecond electron bunches from the laser-plasma wakefield accelerator (LWFA) are potentially useful sources of ultra-short duration X-rays pulses, which can be used for ultrafast imaging of electron motion in biological and physical systems. Electron injection in the LWFA depends on the plasma density and gradient, and the laser intensity. Recent research has shown that injection of attosecond electron bunches is possible using a short plasma density ramp. For controlled injection it is necessary to keep both the laser intensity and background plasma density constant, but set to just below the threshold for injection. This ensures that injection is only triggered by an imposed density perturbation; the peak density should also not exceed the threshold for injection. A density gradient that only persists over a short range can lead to the injection of femtosecond duration bunches, which are then Lorentz contracted to attoseconds on injection. We consider an example of a sin^2 shaped modulation where the gradient varies until the downward slope exceeds the threshold for injection and then reduces subsequently to prevent any further injection. The persistence above the threshold determines the injected bunch length, which can be varied. We consider several designs of plasma media including density perturbations formed by shaped Laval nozzles and present an experimental and theoretical study of the modulated media suitable for producing attosecond-duration electron bunches.

In the coming years, a new generation of high-power laser facilities (such as the Extreme Light Infrastructure) will become operational, for which it is important to understand how the interaction with intense laser pulses affects the bulk properties of relativistic electron bunches. At such high field intensities, we expect both radiation reaction and quantum effects to have a dominant role to play in determining the dynamics. The reduction in relative energy spread (beam cooling) at the expense of mean beam energy predicted by classical theories of radiation reaction has been shown to occur equally in the longitudinal and transverse directions, whereas this symmetry is broken when the theory is extended to approximate certain quantum effects. The reduction in longitudinal cooling suggests that the effects of radiation reaction could be better observed in measurements of the transverse distribution, which for real-world laser pulses motivates the investigation of the angular dependence of the interaction. Using a stochastic single-photon emission model with a (Gaussian beam) focussed pulse, we find strong angular dependence of the stochastic heating.

The ponderomotive force is an important concept in plasma physics and, in particular, plays an important role in many aspects of the theory of laser plasma interactions including current concerns like wakefield acceleration and Raman amplification. The most familiar form of this gives a force on a charged particle that is proportional to the slowly varying gradient of the intensity of a high frequency electromagnetic field and directed down the intensity gradiant. For a field amplitude simply oscillating in time there is a simple derivation of this formula, but in the more general case of a travelling wave the problem is more difficult. Over the years there has been much work on this using Hamiltonian or Lagrangian averaging techniques, but little or no investigation of how well these theories work. Here we look at the very basic problem of a particle entering a region with a monotonically increasing electrostatic field amplitude and being reflected. We show that the equation of motion derived from a widely quoted ponderomotive potential only agrees with the numerically computed orbit within a restricted parameter range and that outside this range it shows features which are inconsistent with any ponderomotive potential quadratic in the field amplitude. Since the ponderomotive force plays a fundamental role in a variety of problems in plasma physics we think that it is important to point out that even in the simplest of configurations standard theories may not be accurate.

The ion-channel laser (ICL) has been proposed as an alternative to the free-electron laser (FEL), replacing the deflection of electrons by the periodic magnetic field of an undulator with the periodic betatron motion in an ion channel. Ion channels can be generated by passing dense energetic electron bunches or intense laser pulses through plasma. The ICL has potential to replace FELs based on magnetic undulators, leading to very compact coherent X-ray sources. In particular, coupling the ICL with a laser plasma wakefield accelerator would reduce the size of a coherent light source by several orders of magnitude. An important difference between FEL and ICL is the wavelength of transverse oscillations: In the former it is fixed by the undulator period, whereas in the latter it depends on the betatron amplitude, which therefore has to be treated as variable. Even so, the resulting equations for the ICL are formally similar to those for the FEL with space charge taken into account, so that the well-developed formalism for the FEL can be applied. The amplitude dependence leads to additional requirements compared to the FEL, e.g. a small spread of betatron amplitudes. We shall address these requirements and the resulting practical considerations for realizing an ICL, and give parameters for operation at UV fundamental wavelength, with harmonics extending into X-rays.