An intense laser pulse in a plasma can accelerate electrons [1][2][3][4] to GeV energies in centimetres [5][6][7] . Transverse betatron motion 8,9 in the plasma wake results in X-ray photons with an energy that depends on the electron energy, oscillation amplitude and frequency of the betatron motion [10][11][12] . Betatron X-rays from laser-accelerator electrons have hitherto been limited to spectra peaking between 1 and 10 keV (ref. 13). Here we show that the betatron amplitude is resonantly enhanced when electrons interact with the rear of the laser pulse 14,15 . At high electron energy, resonance occurs when the laser frequency is a harmonic of the betatron frequency, leading to a significant increase in the photon energy. 10 X-ray pulses from synchrotron sources have become immensely useful tools for investigating the structure of matter 17 , which has led to a huge international effort to construct light sources for many different scientific and technological applications. Synchrotrons are usually based on radio-frequency (RF) accelerating cavities that are limited to fields of 10-100 MV m −1 because of electrical breakdown, which results in very large and expensive devices.High-power lasers, on the other hand, have led to the development of many new areas of science, as diverse as inertial confinement fusion and laboratory astrophysics to the study of warm dense matter. However, they now have the potential to transform accelerator and light source technology. In the late 1970s, Tajima and Dawson 1 proposed harnessing the ponderomotive force associated with intense laser fields to excite plasma waves and form wake-like structures 18 (as behind a boat) that travel with a velocity close to the speed of light, c. The electrostatic forces of these charge density structures can rapidly accelerate particles to very high energies 6 ; where momentum is gained analogous to a surfer riding an ocean wave. Recent progress in the development of laser wakefield accelerators (LWFAs) has enabled electron beams to be accelerated with unprecedented acceleration gradients 2-4 , three orders of magnitude higher than in RF cavities, thus reducing a 100 m long GeV accelerator to centimetres in length 6 . The LWFA can now produce high-quality electron beams with low emittance, ε n , of the order 1π mm mrad 19 , small energy spread 20 , δγ /γ 1%, where γ is the Lorenz factor, and high charge 4 , Q = 10-100 pC. At high laser intensities, in the so-called blowout regime 21 , the LWFA structure has an approximately spherical bubble shape with a radius of R ≈ 2 √ a 0 c/ω p , which is primarily determined by the normalized laser vector potential, a 0 = eA/m e c 2 and the plasma frequency, ω p = √ 4π n p e 2 /m e , where n p is the plasma density, e, the electron charge and m e , the electron mass 22 . The plasma wave is efficiently driven when the laser pulse duration is approximately a plasma period. Micrometre-long electron bunches that extend only a fraction of the plasma wavelength, λ p = 2πc/ω p , are self-injected and accelerate...

Progress in laser wakefield accelerators indicates their suitability as a driver of compact free-electron lasers (FELs). High brightness is defined by the normalized transverse emittance, which should be less than 1π mm mrad for an x-ray FEL. We report high-resolution measurements of the emittance of 125 MeV, monoenergetic beams from a wakefield accelerator. An emittance as low as 1.1±0.1π mm mrad is measured using a pepper-pot mask. This sets an upper limit on the emittance, which is comparable with conventional linear accelerators. A peak transverse brightness of 5×10¹⁵ A m⁻¹ rad⁻¹ makes it suitable for compact XUV FELs.

This report describes the conceptual steps in reaching the design of the AWAKE experiment currently under construction at CERN. We start with an introduction to plasma wakefield acceleration and the motivation for using proton drivers. We then describe the self-modulation instability -a key to an early realization of the concept. This is then followed by the historical development of the experimental design, where the critical issues that arose and their solutions are described. We conclude with the design of the experiment as it is being realized at CERN and some words on the future outlook. A summary of the AWAKE design and construction status as presented in this conference is given in [1].

Abstract. New acceleration technology is mandatory for the future elucidation of fundamental particles and their interactions. A promising approach is to exploit the properties of plasmas. Past research has focused on creating large-amplitude plasma waves by injecting an intense laser pulse or an electron bunch into the plasma. However, the maximum energy gain of electrons accelerated in a single plasma stage is limited by the energy of the driver. Proton bunches are the most promising drivers of wakefields to accelerate electrons to the TeV energy scale in a single stage. An experimental program at CERN -the AWAKE experiment -has been launched to study in detail the important physical processes and to demonstrate the power of proton-driven plasma wakefield acceleration. Here we review the physical principles and some experimental considerations for a future proton-driven plasma wakefield accelerator.

The laser-plasma wakefield accelerator is a compact source of high brightness, ultra-short duration electron bunches. Self-injection occurs when electrons from the background plasma gain sufficient momentum at the back of the bubble-shaped accelerating structure to experience sustained acceleration. The shortest duration and highest brightness electron bunches result from self-injection close to the threshold for injection. Here we show that in this case injection is due to the localized charge density build-up in the sheath crossing region at the rear of the bubble, which has the effect of increasing the accelerating potential to above a critical value. Bunch duration is determined by the dwell time above this critical value, which explains why single or multiple ultra-short electron bunches with little dark current are formed in the first bubble. We confirm experimentally, using coherent optical transition radiation measurements, that single or multiple bunches with femtosecond duration and peak currents of several kiloAmpere, and femtosecond intervals between bunches, emerge from the accelerator.

The Advanced Proton Driven Plasma Wakefield Acceleration Experiment (AWAKE) aims at studying plasma wakefield generation and electron acceleration driven by proton bunches. It is a proof-of-principle R&D experiment at CERN and the world's first proton driven plasma wakefield acceleration experiment. The AWAKE experiment will be installed in the former CNGS facility and uses the 400 GeV/c proton beam bunches from the SPS. The first experiments will focus on the self-modulation instability of the long (rms ∼ 12 cm) proton bunch in the plasma. These experiments are planned for the end of 2016. Later, in 2017/2018, low energy (∼ 15 MeV) electrons will be externally injected to sample the wakefields and be accelerated beyond 1 GeV. The main goals of the experiment will be summarized. A summary of the AWAKE design and construction status will be presented.

CO2 methanation is often performed on Ni/Al2O3 catalysts, which can suffer from mass transport limitations and, therefore, decreased efficiency. Here we show the application of a hierarchically porous Ni/Al2O3 catalyst for methanation of CO2. The material has a well-defined and connected meso- and macropore structure with a total porosity of 78%. The pore structure was thoroughly studied with conventional methods, i.e., N2 sorption, Hg porosimetry, and He pycnometry, and advanced imaging techniques, i.e., electron tomography and ptychographic X-ray computed tomography. Tomography can quantify the pore system in a manner that is not possible using conventional porosimetry. Macrokinetic simulations were performed based on the measures obtained by porosity analysis. These show the potential benefit of enhanced mass-transfer properties of the hierarchical pore system compared to a pure mesoporous catalyst at industrially relevant conditions. Besides the investigation of the pore system, the catalyst was studied by Rietveld refinement, diffuse reflectance ultraviolet-visible (DRUV/vis) spectroscopy, and H2-temperature programmed reduction (TPR), showing a high reduction temperature required for activation due to structural incorporation of Ni into the transition alumina. The reduced hierarchically porous Ni/Al2O3 catalyst is highly active in CO2 methanation, showing comparable conversion and selectivity for CH4 to an industrial reference catalyst.

Very high energy electrons (VHEE) in the range from 100-250 MeV have the potential of becoming an alternative modality in radiotherapy because of their improved dosimetry properties compared with MV photons from contemporary medical linear accelerators. Due to the need for accurate dosimetry of small field size VHEE beams we have performed dose measurements using EBT2 Gafchromic® film. Calibration of the film has been carried out for beams of two different energy ranges: 20 MeV and 165 MeV from conventional radio frequency linear accelerators. In addition, EBT2 film has been used for dose measurements with 135 MeV electron beams produced by a laser-plasma wakefield accelerator. The dose response measurements and percentage depth dose profiles have been compared with calculations carried out using the general-purpose FLUKA Monte Carlo (MC) radiation transport code. The impact of induced radioactivity on film response for VHEEs has been evaluated using the MC simulations. A neutron yield of the order of 10 −5 neutrons cm −2 per incident electron has been estimated and induced activity due to radionuclide production is found to have a negligible effect on total dose deposition and film response. Neutron and proton contribution to the equivalent doses are negligible for VHEE. The study demonstrates that EBT2 Gafchromic film is a reliable dosimeter that can be used for dosimetry of VHEE. The results indicate an energy-independent response of the dosimeter for 20 MeV and 165 MeV electron beams and has been found to be suitable for dosimetry of VHEE.