Generation, Acceleration and Measurement of Attosecond Electron Beams from Laser-Plasma Accelerators

Accelerator-based light sources are extremely useful machines for investigating matter on a microscopic level, yet their capability for time-resolved research is limited by the femtosecond-scale duration of their radiation pulses. Attosecond beams could enhance these capacities enabling the measurement of most outer shell electron dynamics in molecular and atomic systems. However, one of the main challenges in this direction remains the generation of attosecond-scale electron bunches which can be used for ultrashort radiation generation or as probes themselves. The research presented in this thesis tackles this issue from two angles. First, mechanisms for ultrashort electron beam generation and acceleration in laser wakefield accelerators - as promising, compact accelerator systems - are investigated through particle-in-cell simulations. Both an optimised electron plasma injector, using upramp-assisted self-injection, and an external injection setup with the plasma stage as an energy booster to a conventionally accelerated beam are capable of providing electron bunches of few hundred attoseconds duration. The externally injected beams are found to be limited in duration, but preserve well the initial high beam quality for energies up to gigaelectronvolts, while in self-injection high beam currents and ultrashort duration can be achieved, yet at some cost to beam quality and stability. As a second research branch, longitudinal beam profile diagnostics with sub-femtosecond resolution are examined as possible means for measuring such ultrashort electron beams. A first proof-of-principle experiment of a novel streaking device is presented and compared with measurements with an X-band radiofrequency deflecting cavity. Additional computational and theoretical studies provide insights into the possibilities and challenges to apply this new diagnostic technique to sub-femtosecond electron beams from conventional and novel accelerators

Generation, acceleration and measurement of attosecond electron beams from laser-plasma accelerators

Strathclyde theses - ask staff. Thesis no. : T14888Accelerator-based light sources are extremely useful machines for investigating matter on a microscopic level, yet their capability for time-resolved research is limited by the femtosecond-scale duration of their radiation pulses. Attosecond beams could enhance these capacities enabling the measurement of most outer shell electron dynamics in molecular and atomic systems. However,one of the main challenges in this direction remains the generation of attosecond-scale electron bunches which can be used for ultrashort radiation generation or as probes themselves.The research presented in this thesis tackles this issue from two angles. First, mechanisms for ultrashort electron beam generation and acceleration in laser wakefield accelerators - as promising,compact accelerator systems - are investigated through particle-in-cell simulations. Bothan optimised electron plasma injector, using upramp-assisted self-injection, and an external injection setup with the plasma stage as an energy booster to a conventionally accelerated beam are capable of providing electron bunches of few hundred attoseconds duration. The externally injected beams are found to be limited in duration, but preserve well the initial high beam quality for energies up to gigaelectronvolts, while in self-injection high beam currents and ultrashort duration can be achieved, yet at some cost to beam quality and stability. As a second research branch, longitudinal beam profile diagnostics with sub-femtosecond resolution are examined as possible means for measuring such ultrashort electron beams. A first proof-of-principle experiment of a novel streaking device is presented and compared with measurements with anX-band radiofrequency deflecting cavity. Additional computational and theoretical studies provide insights into the possibilities and challenges to apply this new diagnostic technique to sub-femtosecond electron beams from conventional and novel accelerators.Accelerator-based light sources are extremely useful machines for investigating matter on a microscopic level, yet their capability for time-resolved research is limited by the femtosecond-scale duration of their radiation pulses. Attosecond beams could enhance these capacities enabling the measurement of most outer shell electron dynamics in molecular and atomic systems. However,one of the main challenges in this direction remains the generation of attosecond-scale electron bunches which can be used for ultrashort radiation generation or as probes themselves.The research presented in this thesis tackles this issue from two angles. First, mechanisms for ultrashort electron beam generation and acceleration in laser wakefield accelerators - as promising,compact accelerator systems - are investigated through particle-in-cell simulations. Bothan optimised electron plasma injector, using upramp-assisted self-injection, and an external injection setup with the plasma stage as an energy booster to a conventionally accelerated beam are capable of providing electron bunches of few hundred attoseconds duration. The externally injected beams are found to be limited in duration, but preserve well the initial high beam quality for energies up to gigaelectronvolts, while in self-injection high beam currents and ultrashort duration can be achieved, yet at some cost to beam quality and stability. As a second research branch, longitudinal beam profile diagnostics with sub-femtosecond resolution are examined as possible means for measuring such ultrashort electron beams. A first proof-of-principle experiment of a novel streaking device is presented and compared with measurements with anX-band radiofrequency deflecting cavity. Additional computational and theoretical studies provide insights into the possibilities and challenges to apply this new diagnostic technique to sub-femtosecond electron beams from conventional and novel accelerators

Generation of Attosecond Electron Bunches in a laser-plasma Accelerator Using a Plasma Density Upramp

Attosecond electron bunches and attosecond radiation pulses enable the study of ultrafast dynamics of matter in an unprecedented regime. In this paper, the suitability for the experimental realization of a novel scheme producing sub-femtosecond duration electron bunches from laser-wakefield acceleration in plasma with self-injection in a plasma upramp profile has been investigated. While it has previously been predicted that this requires laser power above a few hundred terawatts typically, here we show that the scheme can be extended with reduced driving laser powers down to tens of terawatts, generating accelerated electron pulses with minimum length of around 166 as and picocoulombs charge. Using particle-in-cell simulations and theoretical models, the evolution of the accelerated electron bunch within the plasma as well as simple scalings of the bunch properties with initial laser and plasma parameters are presented

Potential Applications of the Dielectric Wakefield Accelerators in the SINBAD Facility at DESY

Short, high-brightness relativistic electron bunches can drive ultra-high wakefields in the dielectric wakefield accelerators (DWFAs). This effect can be used to generate high power THz coherent Cherenkov radiation, accelerate a witness bunch with gradient two or three orders of magnitude larger than that in the conventional RF linear accelerators, and introduce energy modulation within the driving bunch itself, etc. The paper studies potential applications of the DWFAs in the SINBAD facility at DESY. The simulations show that the ultra-short relativistic bunches from the SINBAD injector ARES can excite accelerating wakefields with peak amplitudes as high as GV/m at THz frequencies in proper DWFA structures. In addition, it illustrates that the DWFA structure can serve as a dechirper to compensate the correlated energy spread of the bunches accelerated by the laser plasma wakefield accelerator

Facility Considerations for a European Plasma Accelerator Infrastructure (EuPRAXIA)

International audienceEuPRAXIA (European Plasma Research Accelerator with eXcellence In Applications) is a conceptual design study for a compact European infrastructure with multi-GeV electron beams based on plasma accelerators. The concept foresees two main experimental sites, one at INFN in Frascati and one at DESY in Hamburg. In Frascati, an RF injector based on S-band and X-band technology (electron energy up to 1 GeV) will be constructed and used as a drive beam for beam driven plasma acceleration (PWFA) with final electron beam energies up to 5 GeV. At DESY, the focus will be on laser driven plasma acceleration (LWFA) and an RF injector based on S-band technology (electron energy up to 240 MeV) or alternatively a plasma injector (electron energy up to 150 MeV) can be used before the beam is injected into the plasma accelerator for external LWFA and acceleration up to 5 GeV. A single stage approach based on LWFA with internal injection will also be pursued in a second beamline. User areas at both sites will provide access to FEL pilot experiments, positron generation, compact radiation sources, and test beams for HEP detector development. This contribution discusses facility space considerations for the future plasma accelerator research infrastructure of EuPRAXIA

Query-log based Authority Analysis for Web Information Search

The ongoing explosion of web information calls for more intelligent and personalied methods towards better search result quality for advanced queries. Query log and click streams obtained from web browsers or search engines can contribute to better quality by exploiting the collaborative recommendations that are implicitly embedded in this information. This paper presents a new method that incorporates the notion of query nodes into PageRank model and integrates the implicite relevance feedback given by click streams into the automated process of authority analysis. This approach generalizes the well-known random-surfer model into a random-expert model that mimics the behavior of an expert user in an extended session consisting of queries, query refinements, and result-navigation steps. The enhanced PageRank scores, coined QRank scores, can be computed offline; at query-time they are combined with query-specific relevance measures with virtually no overhead. Our preliminary experiments, based on real-life query-log and click-stream traces from eight different trial users indicate significant improvements in the precision of search results

Improved Electron Beam Quality from External Injection in Laser-Driven Plasma Acceleration at SINBAD

External injection into laser wakefield accelerators is one of the possible routes towards high energy, high quality electron beams through plasma acceleration. Among other reasons this is due to the increased control over the electron beam parameters and overall experimental setup when compared to other plasma schemes, such as controlled self-injection. At the future SINBAD (Short INnovative Bunches and Accelerators at DESY) facility at DESY this technique is planned to be tested experimentally through injection and acceleration of a sub-femtosecond electron beam, produced from a conventional RF-injector, with a charge of around 0.7 pC and initial mean energy of 100 MeV at the plasma entrance. A summary of optimisation steps for the potential experimental setup is presented in this paper, including considerations regarding effects of electron beam self-fields and matching of the beam into the plasma stage. The discussion is complemented by first start-to-end simulations of the plasma accelerator setup based on these findings

Preliminary Measurements for a Sub-Femtosecond Electron Bunch Length Diagnostic

With electron beam durations down to femtoseconds and sub-femtoseconds achievable in current state-of-the-artaccelerators, longitudinal bunch length diagnostics with resolution at the attosecond level are required. In thispaper, we present such a novel measurement device which combines a high-power laser modulator with an RFdeflecting cavity in the orthogonal direction. While the laser applies a strong correlated angular modulation to abeam, the RF deflector ensures the full resolution of this streaking effect across the bunch hence recovering thetemporal beam profile with sub-femtosecond resolution. Preliminary measurements to test the key components ofthis concept were carried out at the Accelerator Test Facility (ATF) at Brookhaven National Laboratory recently,the results of which are presented and discussed here. Moreover, a possible application of the technique fornovel accelerator schemes is examined based on simulations with the particle-tracking code elegant and ourbeam profile reconstruction tool

Polarization-resolved photoluminescence study of an atom probe tip containing a ZnO-(Mg,Zn)O heterostructure

SPIE OPTO 2022, San Francisco, California, United StatesInternational audienceWe studied polarization-resolved photoluminescence originating from a ZnO-(Mg,Zn)O quantum well heterostucture embedded within an atom probe tip, i.e. a nanoscale needle-shaped sample with apex radius of several tens of nm, prepared by focused ion beam. The study was carried out within a photonic atom probe before the atom probe analysis of the sample. This setup allows for the analysis of the polarization of the photoluminescence emitted by the tip and for its orientation around its axis. While the photoluminescence emitted by bulk ZnO and by the (Mg,Zn)O alloy is strongly polarized along the tip axis, coinciding with the crystal [1-100] axis, the ZnO/(Mg,Zn)O quantum well luminescence appears to be strongly polarized along its in-plane direction, perpendicular to the crystal [1-100] axis. Finite-difference time domain calculations provide a key for the interpretation of these results in terms of selection rules and of effects related to the waveguide effect of the tip

Polarization-resolved photoluminescence study of an atom probe tip containing a ZnO-(Mg,Zn)O heterostructure

SPIE OPTO 2022, San Francisco, California, United StatesInternational audienceWe studied polarization-resolved photoluminescence originating from a ZnO-(Mg,Zn)O quantum well heterostucture embedded within an atom probe tip, i.e. a nanoscale needle-shaped sample with apex radius of several tens of nm, prepared by focused ion beam. The study was carried out within a photonic atom probe before the atom probe analysis of the sample. This setup allows for the analysis of the polarization of the photoluminescence emitted by the tip and for its orientation around its axis. While the photoluminescence emitted by bulk ZnO and by the (Mg,Zn)O alloy is strongly polarized along the tip axis, coinciding with the crystal [1-100] axis, the ZnO/(Mg,Zn)O quantum well luminescence appears to be strongly polarized along its in-plane direction, perpendicular to the crystal [1-100] axis. Finite-difference time domain calculations provide a key for the interpretation of these results in terms of selection rules and of effects related to the waveguide effect of the tip