Near-threshold electron injection in the laser-plasma wakefield accelerator leading to femtosecond bunches

We gratefully acknowledge the support of the UK EPSRC (grant no. EP/J018171/1), the EU FP7 programmes: the Extreme Light Infrastructure (ELI) project, the Laserlab-Europe (no. 284464), and the EUCARD-2 project (no. 312453).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.Publisher PDFPeer reviewe

numerical studies on capillary discharges as focusing elements for electron beams

Abstract Active plasma lenses are promising technologies for the focusing of high brightness electron beams due to their radially symmetric focusing and their high field gradients (up to several kT/m). However, in a number of experimental situations, the transverse non-uniformity of the current density flowing in the lens causes beam emittance growth and increases the minimum achievable spot size. To study the physics of the capillary discharge processes employed as active plasma lenses, we developed a 2-D hydrodynamic computational model. Here, we present preliminary simulation results and we compare the computed magnetic field profile with one from literature, which has been experimentally inferred. The result of the comparison is discussed

Overview of Plasma Lens Experiments and Recent Results at SPARC_LAB

Beam injection and extraction from a plasma module is still one of the crucial aspects to solve in order to produce high quality electron beams with a plasma accelerator. Proper matching conditions require to focus the incoming high brightness beam down to few microns size and to capture a high divergent beam at the exit without loss of beam quality. Plasma-based lenses have proven to provide focusing gradients of the order of kT/m with radially symmetric focusing thus promising compact and affordable alternative to permanent magnets in the design of transport lines. In this paper an overview of recent experiments and future perspectives of plasma lenses is reported

Observation of Time-Domain Modulation of Free-Electron-Laser Pulses by Multipeaked Electron-Energy Spectrum

We present the experimental demonstration of a new scheme for the generation of ultrashort pulse trains based on free-electron-laser (FEL) emission from a multipeaked electron energy distribution. Two electron beamlets with energy difference larger than the FEL parameter have been generated by illuminating the cathode with two ps-spaced laser pulses, followed by a rotation of the longitudinal phase space by velocity bunching in the linac. The resulting self-amplified spontaneous emission FEL radiation, measured through frequency-resolved optical gating diagnostics, reveals a double-peaked spectrum and a temporally modulated pulse structure

Self-amplified spontaneous emission free electron laser devices and nonideal electron beam transport

We have developed, at the SPARC test facility, a procedure for a real time self-amplified spontaneous emission free electron laser (FEL) device performance control. We describe an actual FEL, including electron and optical beam transport, through a set of analytical formulas, allowing a fast and reliable on-line "simulation" of the experiment. The system is designed in such a way that the characteristics of the transport elements and the laser intensity are measured and adjusted, via a real time computation, during the experimental run, to obtain an on-line feedback of the laser performances. The detail of the procedure and the relevant experimental results are discussed

Diuretic agents related to indapamide

A series of N-(4-chloro-3-sulfamoylbenzamido)-1,2,3,4-tetrahydroquinoline (IV-1) and isoquinoline (IV-2) have been synthesized and their diuretic and antihypertensive activities evaluated. While none of the test compounds was found to be provided with antihypertensive properties, most of them displayed a diuretic activity comparable to (IV-2 a) or higher (IV-1 a,b) (IV-2 c) than those of indapamide and clopamide, taken as reference drugs

High energy electrons from interaction with a 10 mm gas-jet at FLAME

In this paper we discuss the spectra of the electrons produced in the laser-plasma acceleration experiment at FLAME. Here a < 30 fs laser pulse is focused via an f/10 parabola in a focal spot of 10 μm diameter into a 1.2 mm by 10 mm rectangular Helium gas-jets at a backing pressure ranging from 5 to 15 bar. The intensity achieved exceeds 1019 Wcm-2. In our experiment the laser is set to propagate in the gas-jet along the longitudinal axis to use the 10 mm gas-jet length and to evaluate the role of density gradients. The propagation of the laser pulse in the gas is monitored by means of a Thomson scattering optical imaging. Accelerated electrons are set to propagate for 47,5 cm before being detected by a scintillating screen to evaluate bunch divergence and pointing. Alternatively, electrons are set to propagate in the field of a magnetic dipole before reaching the scintillating screen in order to evaluate their energy spectrum. Our experimental data show highly collimated bunches (< 1 mrad) with a relatively stable pointing direction (< 10 mrad). Typical bunch electron energy ranges between 50 and 200 MeV with occasional exceptional events of higher energy up to 1GeV. © 2013 SPIE

High energy electrons from interaction with a structured gas-jet at FLAME

In this paper we analyze the properties of the electron bunches produced in a laser-plasma acceleration experiment using a 10 mm helium gas-jet with a longitudinal density profile characterized by a double peak structure. Data were taken at three different gas-jet backing pressures of 5, 8 and 15 bars, corresponding to plasma densities of 1.2–3.6 1019 cm 3 in the peaks and 3.5–10 1018 cm 3 in the central plateau. The highest energy peak is recorded at more than 450 MeV, with average energies between 80 and 180 MeV. Bunch divergence and pointing stability have been measured and are found to be very sensitive to the density. Fully 3D PIC numerical simulations confirm that laser intensity and plasma density of our set up are in the range where electron acceleration takes place by self-injection in a bubble-like structure. Analysis shows that after the first density peak, accelerated electrons propagate through the plateau and the second density peak without the driver, undergoing non-linear interaction with the background plasma