A. Specka

Mapping the X-Ray Emission Region in a Laser-Plasma Accelerator

The x-ray emission in laser-plasma accelerators can be a powerful tool to understand the physics of relativistic laser-plasma interaction. It is shown here that the mapping of betatron x-ray radiation can be obtained from the x-ray beam profile when an aperture mask is positioned just beyond the end of the emission region. The influence of the plasma density on the position and the longitudinal profile of the x-ray emission is investigated and compared to particle-in-cell simulations. The measurement of the x-ray emission position and length provides insight on the dynamics of the interaction, including the electron self-injection region, possible multiple injection, and the role of the electron beam driven wakefield.

Coupling between electron and ion waves in Nd‐laser beat‐wave experiments

The beating between two colinear Nd‐YLF and Nd‐YAG lasers in a homogeneous plasma generates intense relativistic plasma waves associated with a high longitudinal electric field of the order of 1 GV/m. It is shown that these electron waves couple with ion waves in the regime of modulational instability. Electric field amplitude and saturation time obtained by Thomson scattering are in agreement with theoretical predictions taking this mechanism into account.

The plasma beat-wave acceleration experiment at Ecole Polytechnique

Abstract We present an experiment for demonstrating the principle of plasma beat-wave acceleration. The beating of two Nd-laser pulses creates a relativistic plasma wave in a deuterium plasma. Electrons at an energy of 3 MeV are injected into the plasma. We observe several hundred electrons accelerated up to 3.7 MeV. This paper is mainly devoted to the description of the experimental apparatus. In the design of the apparatus, we gave particular attention to efficient electron injection and to background noise suppression. We present also some preliminary results of electron acceleration experiments.

Laser particle acceleration: beat-wave and wakefield experiments

In a plasma, some of the energy of a high-power laser beam can be transferred to a longitudinal plasma wave with a high phase velocity. This wave can in turn accelerate relativistic charged particles to very high energies. Several mechanisms have been proposed to generate these intense electric fields and some of them have already been tested experimentally. Using the beat wave method, electric fields of 1 - 10 have been produced and electrons have been accelerated with an energy gain from 1 MeV to more than 30 MeV. Some preliminary experiments have shown that electrons can be accelerated in plasma waves generated by the wakefield method. In the case of self-modulated wakefield, electric fields larger than 100 trap electrons and eject them from the plasma with an energy up to 100 MeV. The perspectives in the near future are the production of intense and short electron beams of a few MeV and the acceleration of electrons up to 1 GeV. To reach an energy of 1 TeV and get closer to the parameters required by the high-energy physicists, one will have to test some new methods to be able to guide the laser beam over large distances.

The new H1 luminosity system for HERA II

Abstract At HERA, luminosity is determined on-line and bunch by bunch by measuring the bremsstrahlung spectrum from e–p collisions. The H1 collaboration has built a completely new luminosity system in order to sustain the harsh running conditions after the four-fold luminosity increase. Namely, the higher synchrotron radiation doses and the increased event pile-up have governed the design of the two major components, a radiation-resistant quartz-fiber electro-magnetic calorimeter, and a fast readout electronics with on-line energy histogramming at a rate of 500 kHz . An overview of the different components of the new luminosity system is given, and the commissioning status is reported.

Electron acceleration in the plasma beat‐wave experiment at Ecole Polytechnique

Recent results of a plasma Beat‐Wave acceleration experiment are presented. A plasma wave is created in a D2 plasma by the beating of a Nd‐YAG and a Nd‐YLF laser pulse. Electrons at energies of 3 MeV are injected into the plasma. Several hundred electrons accelerated up to 3.7 MeV are observed in correlation with a Thomson scattering signal. The dependence of the electron acceleration on the plasma density demonstrates the beat‐wave origin of the acceleration mechanism. This paper is mainly devoted to the description of the experimental set‐up. A particular attention was paid to efficient electron injection and to background noise suppression. A preliminary analysis of the results is also presented.

Experimental study of electron acceleration by plasma beat-waves with Nd lasers

We have observed the acceleration of electrons by a beat-wave generated in a deuterium plasma by two Nd-YAG and Nd-YLF laser wavelengths. Electrons injected at an energy of 3.3 MeV are observed to be accelerated up to 4.7 MeV after the plasma. The energy gain is compatible with a peak electric field of the order of 1.2 GV/m. The experiment has been performed with different injection energies, from 2.5 to 3.3 MeV, with different plasma dimensions, and with different laser intensities.

On triple focusing dipole magnets

Abstract We present a general, paraxial study of triple focusing (i.e., stigmatic and non-dispersive) index-free dipole magnets. The transcendental equations which describe such magnets lead to a second-degree polynomial equation which we solve analytically. The two solutions of this equation correspond to magnets having either one or no intermediate focal points in the vertical direction. The first-order optical properties of the physical solutions are studied.

Electron acceleration in Nd-laser plasma beat-wave experiments

The beating between two colinear Nd-YLF (λ = 1.053 μm, τ = 90 ps) and Nd-YAG (λ = 1.064 μm, τ = 160 ps) lasers in a homogeneous plasma (ne = 1017 cm−3) generates intense relativistic plasma waves associated with a high longitudinal electric field of the order of 1 GVm−1. In the conditions of the experiment, these electron plasma waves couple with ion waves in the regime of modulational instability as it has been demonstrated by electric field amplitude and saturation time measurements by Thomson scattering. When 3 MeV energy electrons are injected into the plasma, several hundreds of electrons accelerated up to 3.7 MeV are observed in correlation with the Thomson scattering signal associated to the plasma waves. This result is in agreement with a numerical simulation which takes into account the relative focussing geometry of electron and laser beams.