Vorsitzende der Sitzung
Laser-driven electron acceleration
- Chandrashekhar Joshi (UCLA)
Laser-driven electron acceleration: Recent progress in LWFA
- Olle Lundh (Lund university)
Laser-driven electron acceleration
- Victor Malka (Weizmann Institute of Science and CNRS)
Laser-driven electron acceleration
- Laszlo Veisz (Umea University)
Laser-driven electron acceleration
- Alec Thomas
Laser-driven electron acceleration
- Hyung Taek Kim
The BELLA petawatt (PW) laser facility at Lawrence Berkeley National Laboratory is pursuing development of 10-GeV-class laser plasma accelerators. In this presentation, we show recent progress toward this goal: guiding of 0.85 PW peak power laser pulses over 200 mm in plasma channels and electron acceleration up to 8 GeV. This was achieved by increasing the focusing strength of a capillary...
We will review our recent research activities on high-repetition rate laser-wakefield acceleration. In a recent series of experiments, we have used millijoule near-single-cycle laser pulses of 3.5 fs duration at kHz repetition rate to accelerate electrons to 5 MeV energies [1]. The single-cycle laser pulses were able to excite nonlinear plasma wakefields and accelerate electrons to MeV...
Controlling the parameters of a laser plasma accelerated electron beam is a topic of intense research with a particular focus placed on controlling the injection phase of electrons into the accelerating structure from the background plasma. An essential prerequisite for high-quality beams is dark-current free acceleration (i.e., no electrons accelerated beyond those deliberately injected). We...
We report on the generation of quasi-monoenergetic electron beams with up to 1.2nC charge, 18 pC/MeV spectral charge density and 1mrad rms divergence using shock-front injection in a 100-TW-class laser wakefield accelerator. These high charge densities result in significant beam loading which affects both the final energy and the spectral shape of the electron beam. We confirm and explain the...
Laser wakefield acceleration (LWFA) is a candidate to build next generation of electron accelerators due to its huge acceleration field in a plasma medium. Progresses of intense laser technologies contributed to developments of multi-GeV [1,2] and high repetition-rate electron beams [3] by LWFA. Recently, we accomplished upgrading one of our PW beamlines to 4 PW peak power [4] and started...
The advent of chirped-pulse-amplified CO2 lasers [1] has yielded picosecond, long-wavelength infrared (λ=10 μm) laser pulses of terawatt (TW) peak power suitable for driving laser wakefield accelerators (LWFAs) with high ponderomotive force (∼Iλ2) in low-density (1016 cm-3 < ne <1018 cm-3) plasma [2]. Such pulses...
Laser Plasma Acceleration (LPA) enables to generate up to several GeV electron beam with short bunch length and high peak current within centimeters scale. However, the generated beam quality (energy spread, divergence) is not sufficient for numerous applications. In view of a Free Electron Laser application, the energy spread has to be adapted to reach the required small slice value while the...
Focusing petawatt-level laser beams to a variety of spot sizes for different applications is expensive in cost, labor and space. In this talk, we present a plasma lens, similar to an adjustable eyepiece in a telescope, to flexibly resize the laser beam by utilizing the laser self-focusing effect. Using a fixed conventional focusing system to focus the laser a short distance in front of the...
Plasma beam dump has been recently proposed to absorb the kinetic energy of the spent beam from particle accelerators. In this presentation a passive beam dump with multiple stage plasma cells are investigated. In this new scheme, the stepped plasma densities are required after the first stage so as to maintain a high decelerating gradient compared to a uniform plasma. Particle-in-cell...
Experiments were conducted using a high:repetition rate (500 Hz) Ti:sapphire laser to measure the scaling of laser wakefield acceleration at low energy (< 20 mJ) and high repetition rate. Electron spectra were measured and the effect of feedback control of the laser pulse phase front and the laser temporal phase were investigated. The development of liquid targets for high rep rate ion and...
We will give an overview of the latest commissioning status of the ATLAS-3000 laser system at CALA, before reviewing the main results from the laser-wakefield related campaigns with the predecessor 100-TW system. Quasi-monoenergetic shock-front accelerated electron bunches with energies up to 300 MeV and charge figures of >250 pC were routinely produced. The scaling of their spectral shape...
I will present an overview the research being undertaken in my group at the Clarendon Laboratory, University of Oxford and with colleagues at the Rutherford Appleton Laboratory. We are particularly interested in exploring how laser energy is absorbed in the laser-QED regime for the 10 PW laser pulses that will shortly be available with the ELI facilities. We have found that there is a regime...
Subluminal and superluminal light pulses have attracted a considerable attention in the past decades opening perspectives in telecommunications, optical storage, and fundamental physics. Usually achieved in matter, superluminal propagation has also been demonstrated in vacuum with quasi-Bessel beams or Spatio-Temporal Couplings (STCs). While in the first case the propagation was...
We present Traveling-Wave Electron Acceleration (TWEAC), a novel compact electron accelerator scheme based on laser-plasma acceleration. While laser-plasma accelerators provide multi-GeV electron beams today, the acceleration to higher energies is limited. The sub-luminal group-velocity of plasma waves let electrons outrun the accelerating field.
In order to control the speed of the...
The capture and acceleration of short electron bunches externally injected into wakefields generated by an intense femtosecond laser pulse in the plasma channel are studied. The injection of low-energy bunches is analyzed, which allows to obtain a substantial longitudinal bunch compression, and also to obtain the bunch energy gain to the GeV range with a small energy spread at an acceleration...
It is generally believed [1] that the matched laser profile provides the optimal regime of electron acceleration. The laser spot size and the pulse duration evolve a little during laser propagation when the laser intensity, the plasma density and the laser profile are matched. The scaling laws predicted the electron energy as a function of the laser-plasma parameters have been formulated for...
We study both experimentally and numerically the emission of energetic electrons during the reflection of a relativistic few-cycle laser pulse ($1.4 \times 10^{19} \mathrm{~W/cm}^2$, 3.5 fs) on an overdense plasma. Two distinct acceleration regimes are identified (see Fig. 1), for which the electron ejection mechanisms are radically different. On the one hand, when the plasma-vacuum interface...
Experiments were performed to study electron acceleration by intense sub-picosecond laser pulses propagating in sub-mm long plasmas of near critical electron density (NCD). Production of hydrodynamically stable NCD-plasmas remains an important issue for such type of experiments. For these purposes we used low density CHO-foam layers of 300-500 m thickness. In foams, the NCD-plasma was...
Generation of high energy electrons using laser plasma interactions have been of immense interest over the past few decades, owing to their application in various fields like ion acceleration and fast ignition for ICF. Till date relativistic electrons (> 1 MeV) are mostly obtained at intensities of 〖10〗^18 W/cm^2 and above. Such high intensities are generally achieved by using either high...
The low transverse emittance of electron bunches from laser wakefield accelerators (LWFAs) makes these advanced accelerators attractive for compact FELs and colliders. Single-shot, direct, non-intercepting diagnostics of this emittance outside the LWFA are, however, needed. Here we present single-shot coherent transition radiation (CTR) imaging and interferometry data from electron bunches...
Here we report on optimization of both energy spread and beam divergence in a laser wakefield accelerator (LWFA) operating in the beam loading regime. The self-truncated ionization injection scheme is employed, enabling a precise control over the amount of injected electrons with charges up to 0.5 nC (FWHM) at a quasi-monoenergetic peak.
By employing the optimal beam loading condition, the...
Plasma based electron acceleration is widely considered as a promising concept for a compact electron accelerator with broad range of future applications from high energy particle colliders to photon science. These accelerators can be powered by either ultra-intense laser beams (LWFA) or relativistic high-current particle beams (PWFA).
Here, we report on a novel approach to combine both...
AWAKE is a proton-driven plasma wakefield experiment under way at CERN that recently demonstrated the successful acceleration of injected electrons [1]. Underpinning the experiment is the fact that the long proton bunches (~6-12 cm) used to drive the wakefields undergo a self-modulation process, which in practice corresponds to a seeded instability [2]. The resulting train of microbunches...
A novel approach for positron injection and acceleration in laser driven plasma wakefield is proposed. A three-staged theoretical model is developed and confirmed through simulations. The proposal using two co-axis propagating beams, a Laguerre-Gaussian beam and a Gaussian beam, to drive wakefields in a preformed plasma volume filled with both electrons and positrons. The bremsstrahlung force...
The Advanced Wakefield Experiment (AWAKE) recently demonstrated that: 1) a 400 GeV/c proton bunch (with a bunch length 30-100 times longer than the plasma electron wavelength) self-modulates over 10m of plasma; 2) externally injected ~20 MeV electrons can be accelerated to GeV energies in the resonantly excited wakefield. In this contribution, we show the results of an AWAKE experimental...
Hollow plasma channels are promising candidates for the acceleration of electron and positron beams, as the transverse forces are nearly vanishing inside the hollow channel, as long as the accelerated bunches are perfectly cylindrically symmetric and injected on the axis of the hollow channel structure. Furthermore, the accelerating fields can also be nearly constant provided that the...
Schemes for generating ultra-low emittance beams have been developed in the last years with applications, for example, in high-energy physics and free-electron laser science. Current methods for the characterization of low emittance beams such as pepperpot measurements or quadrupole scans are limit to about $e_n\approx0.2\pi$ $mm$ $mrad$. Here we propose a novel method for the characterization...
We present the development and experimental testing of a permanent magnet system to detect electron positron pairs on high intensity laser experiments at Astra Gemini. These experiments where designed to measure fundamental QED phenomena, like the Linear Breit-Wheeler effect as an example for $e^+ e^-$-pair production from quantum vacuum, or strong field effects like the Nonlinear...
In Laser-Plasma Accelerators (LPA), an ultra-short laser pulse is focused in a plasma to generate a plasma wave. The electromagnetic fields amplitude generated by this plasma wave are 3 orders of magnitudes higher than those created in classical accelerators. However, for reaching higher energies, the electron beam has to experience these fields on large distances. This remains an issue in LPA...
Laser-wakefield acceleration experiments performed at the Hercules laser show a lowering of the self-injection threshold by circular polarized laser pulses, similar to the threshold lowering in wakfields driven in a warm plasma. In addition to the lower injection threshold, a significantly higher charge was observed for CP compared to LP for a wide range of parameters. We performed...
The ESCULAP project aims at studying the capture and acceleration of relativistic electron bunches in a laser plasma wave. A configuration has been proposed where the interaction between the electron bunch and the plasma wave starts few Rayleigh lengths before the laser focal plane. In that configuration, a 100fs 10MeV electron bunch can be compressed up to ~ 4fs during the laser focusing....
Because the proof of principle of operation of plasma-based accelerators is firmly established, much effort is currently been put in demonstrating the generation of relativistic electron bunches with the required quality for various scientific and technological applications. In addition to high-quality beams, several applications also demand very high repetition rates. Here, the long-term...
The non-linear bubble regime of laser-wakefield acceleration (LWFA) is studied for a laser beam with a spatial super-Gaussian profile. Contrarily to the Gaussian beam, the intensity profile of the super-Gaussian beam is flat over almost all the covered area, which alters the bubble shape in a different way. Moreover, diffraction rings are induced during the formation of the super-Gaussian...
A laser wakefield accelerator(LWFA)[1], which can be used to accelerate electrons by interaction between high-intensity laser pulse and plasmas, has the advantage to miniaturize the system size as it can obtain in a narrow region compared with conventional systems. The characteristics of the Very High Energy Electron(VHEE) beam in LWFA has attracted much interest because of its potential...
We report the first observation of large amplitude Langmuir waves in a plasma of nanometer-scale clusters. The shape of these wakefields is captured by a single-shot frequency-domain holography diagnostic at an oblique angle of incidence. The wavefronts are observed to curve backwards, in contrast to the forwards curvature of wakefields in uniform plasma. The first wakefield period is longer...
