Characterization of transverse beam emittance of electrons from a laser-plasma wakefield accelerator in the bubble regime using betatron x-ray radiation (original) (raw)
Related papers
2011
We propose and use a technique to measure the transverse emittance of a laser-wakefield accelerated beam of relativistic electrons. The technique is based on the simultaneous measurements of the electron beam divergence given by vperp/vparallelv_{\perp}/v_{\parallel}vperp/vparallel, the measured longitudinal spectrum gammaparallel\gamma_\parallelgammaparallel and the transverse electron bunch size in the bubble rperpr_{\perp}rperp. The latter is obtained via the measurement of the source size of the x-rays emitted by the accelerating electron bunch in the bubble. We measure a \textit{normalised} RMS beam transverse emittance <0.5<0.5<0.5 pi\pipi mm$\:$mrad as an upper limit for a spatially gaussian, spectrally quasi-monoenergetic electron beam with 230 MeV energy in agreement with numerical modeling and analytic theory in the bubble regime.
Emittance Measurements of a Laser-Wakefield-Accelerated Electron Beam
Physical Review Letters, 2004
The transverse emittance of a relativistic electron beam generated by the interaction of a highintensity laser with an underdense plasma has been measured with the ''pepper-pot'' method. For parameters pertaining to the forced laser wakefield regime, we have measured an emittance as low as 2:7 0:9 mm mrad for 55 2 MeV electrons. These measurements are consistent with 3D particle-in-cell simulations of the experiment, which additionally show the existence of a relatively large halo around the beam core.
Experimental study of energy spread in a space-charge dominated electron beam
Proceedings of the 2003 Bipolar/BiCMOS Circuits and Technology Meeting (IEEE Cat. No.03CH37440), 2003
Characterization of beam energy spread in a spacecharge dominated beam is very important to understand the physics of intense beams. It is believed that coupling between transverse and longitudinal direction via Coulomb collisions will cause an increase of the beam longitudinal energy spread. At the University of Maryland, experiments have been carried out to study the energy evolution in such intense beams. To measure the energy spread, a high-resolution retarding field energy analyzer has been developed. In this paper, we present the initial experimental results using this energy analyzer. The temporal beam energy profile along the beam pulse has been characterized at the exit of the electron gun. It is the first time that we measure the energy profile of the head and tail of the bunched beams in the experiment. The measured mean energy variation along the beam pulse is in excellent agreement with direct measurement of the cathode-grid pulse waveform. The measured rms energy spread is very close to the theoretical prediction of Coulomb scattering.
Laser-wakefield acceleration of electron beams in a low density plasma channel
2010
The generation of quasimonoenergetic electron beams, with energies greater than 500 MeV, in a laserplasma accelerator driven by 2.5 J, 80 fs laser pulses guided in a low density plasma channel, is investigated. The laser energy required to achieve electron injection is found to depend strongly on the quality of the input laser focal spot. Simulations show that, although the matched spot size of the plasma channel is greater than the self-focused spot size, the channel assists relativistic self-focusing and enables electron injection to occur at lower plasma densities and laser powers than would be possible without a waveguide.
Characterisation of the transverse emittance of laser-wakefield-accelerated electrons
2018
Die Experimente dieser Doktorarbeit befassen sich mit Aspekten der Strahlenlenkung und der Charakterisierung von Laser-Plasma beschleunigten Elektronen. Ein fokusierter Hochleistungslaser kann Plasmawellen treiben, die elektrische Felder von ca. 100 GV/m aufweisen. Solche elektrischen Felder sind drei bis vier Gröÿenordnungen stärker als solche, die von Hochfrequenzresonatoren (rf-cavities) wie zum Beispiel am Large Hadron Collider am CERN eingesetzt werden. Ein Plasmabeschleuniger kann daher in entsprechend kürzeren Strecken Teilchen zu hohen Energien beschleunigen. Üblicherweise werden Plasmazellen mit einer Länge von ∼1 cm verwendet, mit denen Elektronen mit Energien von mehreren hundert MeV bis einige GeV und ∼10 pC erzeugt werden können. Weitere Vorteile dieser Technologie folgen aus der kleinen Gröÿe der Plasmawelle: Diese führt zu einer kurzen Pulsdauer (<10 fs) und zu einer geringen transversalen Emittanz der Elektronen. Das Ziel dieser Arbeit war die Vermessung der Emittanz von Laser-Plasma beschleunigten Elektronen. Durch Messungen mit Quadrupollinsen konnte eine normalisierte Emittanz von 0.21 +0.01 −0.02 π•mm•mrad für Elektronen mit einer Energie von 245 MeV erechnet werden. Zusätzlich zur bekannten quadrupole scan-Methode wurde in dieser Arbeit eine Variante entwickelt, welche die Berechnung der Emittanz auch für einzelne Elektronenstrahle errechnen lässt. Die Ergebnisse beider Methoden stimmen überein. Die normalisierte Emittanz bleibt relativ konstant für Energien zwischen 245 und 300 MeV. Dies entspricht der Erwartung von linearen Fokussierfeldern innerhalb der Plasmawelle, eine vorteilhafte Eigenschaft solcher Beschleuniger. In den Experimenten wurde eine auällig geringe Divergenz der Elektronenstrahlen von 0.5 mrad gemessen. Mithilfe eines einfachen Modells des Übergangs zwischen Plasma und Vakuum können die Divergenz und die Quellgrösse der Elektronen nachgebildet werden. Im Experiment konnte die Beschleunigungslänge und die Elektronendichte variiert werden. Somit konnte die Wechselwirkung zwischen Elektronen und dem Laserpuls innerhalb der Plasmawelle untersucht werden. Die hoch-relativistischen Elektronen holen den Laserpuls ein, werden gestreut, und zeigen eine messbare Vergrösserung der Emittanz auf. In dieser Arbeit wurden magnetische Quadrupollinsen mit einem Feldgradienten von ∼500 T/m verwendet um den Elektronenstrahl zu führen. Indem die Elektronenquelle mit den Quadrupollinsen entsprechend in einem Spektrometer abgebildet wurde, konnte die Auösung des Spektrometers signikant erhöht werden. Diese Methode ermöglichte die Messung der Energieverteilung eines Elektronenstrahls von vi Zusammenfassung 1% rms bei 190 MeV. Die Strahlenführung kann durch entsprechende Positionierung der Quadrupollinsen für verschiedene Energien angepasst werden. Indem die Linsen den Elektronenstrahl kollimierten, konnte das integrierte Strahlprol einen Meter nach der Quelle um einen Faktor fünf reduziert werden. Durch einen transversalen Versatz der Quadrupollinsen kann der Elektronenstrahl um einige mrad abgelenkt werden. Die oben genannten Methoden können ohne wesentliche zeitliche Verlängerung, ohne Vergröÿerung der transversalen Emittanz und ohne wesentlichen Verlust der Ladung des Elektronenstrahls implementiert werden. Diese kompakte und zuverlässige Methode um plasmabeschleunigte Elektronen zu führen, ist unabhangig vom Beschleuniger selbst und erweist sich als nützliches Werkzeug.
Novel method for characterizing relativistic electron beams in a harsh laser-plasma environment
Review of Scientific Instruments, 2007
Particle pulses generated by laser-plasma interaction are characterized by ultrashort duration, high particle density, and sometimes a very strong accompanying electromagnetic pulse ͑EMP͒. Therefore, beam diagnostics different from those known from classical particle accelerators such as synchrotrons or linacs are required. Easy to use single-shot techniques are favored, which must be insensitive towards the EMP and associated stray light of all frequencies, taking into account the comparably low repetition rates and which, at the same time, allow for usage in very space-limited environments. Various measurement techniques are discussed here, and a space-saving method to determine several important properties of laser-generated electron bunches simultaneously is presented. The method is based on experimental results of electron-sensitive imaging plate stacks and combines these with Monte Carlo-type ray-tracing calculations, yielding a comprehensive picture of the properties of particle beams. The total charge, the energy spectrum, and the divergence can be derived simultaneously for a single bunch.
Ion Motion Induced Emittance Growth of Matched Electron Beams in Plasma Wakefields
Physical review letters, 2017
Plasma-based acceleration is being considered as the basis for building a future linear collider. Nonlinear plasma wakefields have ideal properties for accelerating and focusing electron beams. Preservation of the emittance of nano-Coulomb beams with nanometer scale matched spot sizes in these wakefields remains a critical issue due to ion motion caused by their large space charge forces. We use fully resolved quasistatic particle-in-cell simulations of electron beams in hydrogen and lithium plasmas, including when the accelerated beam has different emittances in the two transverse planes. The projected emittance initially grows and rapidly saturates with a maximum emittance growth of less than 80% in hydrogen and 20% in lithium. The use of overfocused beams is found to dramatically reduce the emittance growth. The underlying physics that leads to the lower than expected emittance growth is elucidated.
Laser-Wakefield Acceleration of Monoenergetic Electron Beams in the First Plasma-Wave Period
Physical Review Letters, 2006
Beam profile measurements of laser-wakefield accelerated electron bunches reveal that in the monoenergetic regime the electrons are injected and accelerated at the back of the first period of the plasma wave. With pulse durations c p , we observe an elliptical beam profile with the axis of the ellipse parallel to the axis of the laser polarization. This increase in divergence in the laser polarization direction indicates that the electrons are accelerated within the laser pulse. Reducing the plasma density (decreasing c= p ) leads to a beam profile with less ellipticity, implying that the self-injection occurs at the rear of the first period of the plasma wave. This also demonstrates that the electron bunches are less than a plasma wavelength long, i.e., have a duration <25 fs. This interpretation is supported by 3D particle-in-cell simulations.
Radius Measurements from Time-Resolved Images of a Relativistic Electronbeam
Ninth IEEE International Pulsed Power Conference
Images of the cross-section of au intense relativistic electron beam are obtained using a fast framing camera called a Gated Optical Imager (GO!). Cherenkov radiation generated by the beam passing through a thin quartz plate is viewed by the GOI, which provides 2-ns resolution of the beam current density profile at three times during the beam pulse on each shot. These images have been characterized quantitatively to provide measurements of the electron beam radius and position, without assuming a particular form of the profile. Using a direct, pixel-by-pixel approach rather t.han an iterative technique to evaluate the image, the beam ~centroid and various measures of the radius are found, including for example finding all the contours and choosing one, such as the one tha.t contains half the beam current. The algorithms that have been developed will be described, as well as the physical significance of the results, in terms of both a general profile and the electron beam in the experiment. These techniques may be applicable to quantitative measurements of the profile of any beam, such as a laser beam or an ion beam, and to the analysis of any two-dimensional image, such as the cross-section of a plasma. These algorithms have been implemented for an experiment that studies beam propagation through the atmosphere. 1 Intense relativistic electron beams prC!pagating through gas are subject to the resistive hose instability. The GO! is being used to study various "beam conditioning" techniques to reduce the effect of the hose instability and extend the propagation distance of the beam. The 5-MeV, 2.5-kA, 40-ns beam from SuperiBEX is injected into a 1-atm gas cell. Preliminary experimental results will be presented.