Downramp-assisted underdense photocathode electron bunch generation in plasma wakefield accelerators

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 figure

Plasma accelerator-based ultrabright x-ray beams from ultrabright electron beams

We provide a pathway to compact ultrabright light sources, based on ultrabright, high energy electron beams emerging from a combination of plasma Wakefield acceleration and plasma photocathodes. While plasma acceleration is known to produce accelerating fields three or four orders of magnitude larger than conventional accelerators, the plasma photocathode allows production of electron beams three or four orders of magnitude brighter than conventional, and thus is suitable to unleash the full potential of plasma accelerators. In particular, this is the case for various types of light sources, which profit enormously from an increased electron beam brightness. Building on the recent first experimental demonstration of the plasma photocathode, in this work we discuss the prospects of plasma photocathodes for key photon source approaches such as x-ray free-electron lasers, betatron radiation, ion-channel lasers and inverse Compton scattering

Electron bunch generation from a plasma photocathode

Plasma waves generated in the wake of intense, relativistic laser or particle beams can accelerate electron bunches to giga-electronvolt (GeV) energies in centimetre-scale distances. This allows the realization of compact accelerators having emerging applications, ranging from modern light sources such as the free-electron laser (FEL) to energy frontier lepton colliders. In a plasma wakefield accelerator, such multi-gigavolt-per-metre (GV m$^{-1}$) wakefields can accelerate witness electron bunches that are either externally injected or captured from the background plasma. Here we demonstrate optically triggered injection and acceleration of electron bunches, generated in a multi-component hydrogen and helium plasma employing a spatially aligned and synchronized laser pulse. This ''plasma photocathode'' decouples injection from wake excitation by liberating tunnel-ionized helium electrons directly inside the plasma cavity, where these cold electrons are then rapidly boosted to relativistic velocities. The injection regime can be accessed via optical density down-ramp injection, is highly tunable and paves the way to generation of electron beams with unprecedented low transverse emittance, high current and 6D-brightness. This experimental path opens numerous prospects for transformative plasma wakefield accelerator applications based on ultra-high brightness beams

Studies of transverse properties of relativistic electrons from laser wakefield accelerator

Laser wakefield acceleration (LWFA) can occur when the ponderomotive force of high power ultra short laser pulses produce wakefields in underdense plasma. The structure of these wakefields are similar to those in rf cavities of conventional linear accelerators, but are characterised by large fields that can accelerate particles to high energies over much shorter distances. Compactness and inherent short bunch duration make LWFAs potential candidates for laboratory-scale coherent radiation sources. Currently, theoretical and experimental studies are being pursued to obtain in-depth understanding of LWFAs, in particular the injection mechanisms, as these will lead to better control and improved quality of the electron beams. Experimental effort is being directed towards the design of suitable diagnostics to measure the most important properties of the electron beam, one of which is the emittance. Emittance is a good figure of merit as it describes the beam distribution in phase space and provides information on the beam focusability. This work presents a numerical and experimental study of the potential of LWFA as a next generation table-top accelerator. The first part of the thesis investigates the transport of LWFA produced electron beams using conventional devices. To provide a "usable" beam, the transport system should be capable of preserving the transverse emittance. Possible sources of emittance growth are examined, focusing on the effects of energy spread, divergence and pointing stability on the emittance. The second part of the thesis presents direct single shot measurements of the transverse emittance using the pepper-pot technique. This method is also used to quantify the performance of high-gradient miniature permanent quadrupoles.Laser wakefield acceleration (LWFA) can occur when the ponderomotive force of high power ultra short laser pulses produce wakefields in underdense plasma. The structure of these wakefields are similar to those in rf cavities of conventional linear accelerators, but are characterised by large fields that can accelerate particles to high energies over much shorter distances. Compactness and inherent short bunch duration make LWFAs potential candidates for laboratory-scale coherent radiation sources. Currently, theoretical and experimental studies are being pursued to obtain in-depth understanding of LWFAs, in particular the injection mechanisms, as these will lead to better control and improved quality of the electron beams. Experimental effort is being directed towards the design of suitable diagnostics to measure the most important properties of the electron beam, one of which is the emittance. Emittance is a good figure of merit as it describes the beam distribution in phase space and provides information on the beam focusability. This work presents a numerical and experimental study of the potential of LWFA as a next generation table-top accelerator. The first part of the thesis investigates the transport of LWFA produced electron beams using conventional devices. To provide a "usable" beam, the transport system should be capable of preserving the transverse emittance. Possible sources of emittance growth are examined, focusing on the effects of energy spread, divergence and pointing stability on the emittance. The second part of the thesis presents direct single shot measurements of the transverse emittance using the pepper-pot technique. This method is also used to quantify the performance of high-gradient miniature permanent quadrupoles

Downramp-assisted underdense photocathode electron bunch generation in plasma wakefield accelerators

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

Fundamentals and Applications of Hybrid LWFA-PWFA

International audienceFundamental similarities and differences between laser-driven plasma wakefield acceleration (LWFA) Plasma Wakefield Acceleration (PWFA)  and particle-driven plasma wakefield acceleration (PWFA) Plasma Wakefield Acceleration (PWFA)  are discussed. The complementary features enable the conception and development of novel hybrid plasma acceleratorsLaser-plasma accelerator, which allow previously not accessible compact solutions for high quality electron bunchElectron bunch generation and arising applications. Very high energy gains can be realized by electron beam drivers even in single stages because PWFA is practically dephasing-free and not diffraction-limited. These electron driver beams for PWFA in turn can be produced in compact LWFA stages. In various hybrid approaches, these PWFA systems can be spiked with ionizing laser pulses to realize tunable and high-quality electron sources via optical density downramp injectionDownramp injection (also known as plasma torch) Plasma torch  or plasma photocathodesPlasma photocathode (also known as Trojan Horse) and via wakefield-induced injection (also known as WII). These hybrids can act as beam energy, brightness and quality transformers, and partially have built-in stabilizing features. They thus offer compact pathways towards beams with unprecedented emittanceEmittance and brightness, which may have transformative impact for light sources and photon science applications. Furthermore, they allow the study of PWFA-specific challenges in compact setups in addition to large linac-based facilities, such as fundamental beam–plasma interaction physics, to develop novel diagnostics, and to develop contributions such as ultralow emittanceEmittance test beams or other building blocks and schemes which support futurePlasma-based collider plasma-based collider concepts