High Quality Electron Bunches up to 1 GeV from Laser Wakefield Acceleration at LBNL

Experiments at the LOASIS laboratory of LBNL havedemonstrated production of 100 MeV to 1 GeV electron bunches with lowenergy spread and low divergence from laser wakefield acceleration. Theradiation pressure of a 10 TW laser pulse, guided over 10 diffractionranges by a few-mm long plasma density channel, was used to drive anintense plasma wave (wakefield), producing electron bunches with energieson the order of 100 MeV and acceleration gradients on the order of 100GV/m. Beam energy was increased from 100 MeV to 1 GeV by using a few-cmlong guiding channel at lower density, driven by a 40 TW laser,demonstrating the anticipated scaling to higher beam energies. Particlesimulations indicate that the low energy spread beams were produced fromself-trapped electrons through the interplay of trapping, loading, anddephasing. Other experiments and simulations are also underway to controlinjection of particles into the wake, and hence improve beam quality andstability further

Study of Anthocyanin Content, Antioxidant Property, UV Absorbance & SPF Analysis of A Few Petals

Herbal medicine has been commonly used over the years for treatment and prevention of diseases and health promotion as well as for enhancement of the life span and quality of life. It is a well-known fact that Traditional Systems of medicine always played an important role in meeting the global health care needs. Herbal cosmetics use phytochemicals from variety of plants. The botanical ingredients present influence biological functions of skin and provides nutrients necessary for healthy skin. Skin care is major problem faced by many people due to increase in pollution and other factors. The aim of this study was to determine the Anthocyanin content, Antioxidant property, UV Absorbance & Sun Protection Factor (SPF) of few petals namely, Rose, Bougainvillea, Chrysanthemum, Dahlia, Marigold and Ixora. It was found that dry ethanolic and aqueous extracts of Dahlia, Chrysanthemum and Rose has high anthocyanin content and SPF value above 30 compared to other flower petals. Skin cream was prepared using aqueous extract of these three petals. Lavender oil was used for fragrance. Survey was conducted through questionnaire. Though many plants are known to cure various diseases, knowledge of traditional medicine used by communities in India has been lost due to lack of documentation. Hence efforts were made to visit villages in Karnataka & Mumbai to collect data of plants used for primary health care

Diagnostics and controls for spatiotemporal couplings for laser-plasma accelerator drivers

International audienceDiagnostic and control of spatiotemporal couplings for laser-plasma acceleration drive lasers are discussed. Near-field angular dispersion and spatial chirp were measured by GRENOUILLE. The calculation of the pulse front tilt evolution is presented, and it is shown that the pulse front angle near focus can be controlled within 5 mrad, and finely tuned through temporal chirp

Modeling of a square pulsed capillary discharge waveguide for interferometry measurements

Slow pulsed capillary discharges in round capillaries are currently under investigation for use as plasma channel laser waveguides in laser-wakefield acceleration, x-ray lasers, and higher-harmonic generation. In this study, a capillary discharge with a square cross section is presented. The electron d., which dets. the laser guiding properties, can be measured by means of transverse interferometry in this device. Using a numerical model of the plasma and the capillary wall, an anal. of the discharge is made. The results predict that the square channel is capable of guiding circular laser pulses. The guiding properties are quite similar to those of a round channel with nearly the same diam. as the channel width. This suggests the results obtained by measuring the square capillary discharge are applicable for round channels as well. It was found that the wall heating was inhomogeneous, which makes the wall more susceptible to ablation. The heating of the wall changes the transverse optical pathlength in the interferometry expts. [on SciFinder (R)

GeV electron beams from a cm-scale accelerator

GeV electron accelerators are essential to synchrotron radiation facilities and free electron lasers, and as modules for high-energy particle physics. Radio frequency based accelerators are limited to relatively low accelerating fields (10-50 MV/m) and hence require tens to hundreds of metres to reach the multi-GeV beam energies needed to drive radiation sources, and many kilometres to generate particle energies of interest to the frontiers of high-energy physics. Laser wakefield accelerators (LWFA) in which particles are accelerated by the field of a plasma wave driven by an intense laser pulse produce electric fields several orders of magnitude stronger (10-100 GV/m) and so offer the potential of very compact devices. However, until now it has not been possible to maintain the required laser intensity, and hence acceleration, over the several centimetres needed to reach GeV energies. For this reason laser-driven accelerators have to date been limited to the 100 MeV scale. Contrary to predictions that PW-class lasers would be needed to reach GeV energies, here we demonstrate production of a high-quality electron beam with 1 GeV energy by channelling a 40 TW peak power laser pulse in a 3.3 cm long gas-filled capillary discharge waveguide. We anticipate that laser-plasma accelerators based on capillary discharge waveguides will have a major impact on the development of future femtosecond radiation sources such as x-ray free electron lasers and become a standard building block for next generation high-energy accelerators

GeV electron beams from cm-scale channel guided laser wakefield accelerator

Laser-wakefield accelerators (LWFA) can produce electric fields of order 10-100 GV/m suitable for acceleration of electrons to relativistic energies. The wakefields are excited by a relativistically intense laser pulse propagating through a plasma and have a phase velocity determined by the group velocity of the light pulse. Two important effects that can limit the acceleration distanceand hence the net energy gain obtained by an electron are diffraction of the drive laser pulse and particle-wake dephasing. Diffraction of a focused ultra-short laser pulse can be overcome by using preformed plasma channels. The dephasing limit can be increased by operating at a lower plasma density, since this results in an increase in the laser group velocity. Here we present detailed results on the generation of GeV-class electron beams using an intense femtosecond laser beamand a 3.3 cm long preformed discharge-based plasma channel [W.P. Leemans et al., Nature Physics 2, 696-699 (2006)]. The use of a discharge-based waveguide permitted operation at an order ofmagnitude lower density and 15 times longer distance than in previous experiments that relied on laser preformed plasma channels. Laser pulses with peak power ranging from 10-50 TW were guided over more than 20 Rayleigh ranges and high-quality electron beams with energy up to 1 GeV were obtained by channelling a 40 TW peak power laser pulse. The dependence of the electron beam characteristics on capillary properties, plasma density, and laser parameters are discussed

GeV electron beams from a laser-plasma accelerator

High-quality electron beams with up to 1 GeV energy have been generated by a laser-driven plasma-based accelerator by guiding a 40 TW peak power laser pulse in a 3.3 cm long gas-filled capillary discharge waveguide

GeV electron beams from cm-scale channel guided laser wakefield accelerator

Laser-wakefield accelerators (LWFA) can produce electric fields of order 10-100 GV/m suitable for acceleration of electrons to relativistic energies. The wakefields are excited by a relativistically intense laser pulse propagating through a plasma and have a phase velocity determined by the group velocity of the light pulse. Two important effects that can limit the acceleration distanceand hence the net energy gain obtained by an electron are diffraction of the drive laser pulse and particle-wake dephasing. Diffraction of a focused ultra-short laser pulse can be overcome by using preformed plasma channels. The dephasing limit can be increased by operating at a lower plasma density, since this results in an increase in the laser group velocity. Here we present detailed results on the generation of GeV-class electron beams using an intense femtosecond laser beamand a 3.3 cm long preformed discharge-based plasma channel [W.P. Leemans et al., Nature Physics 2, 696-699 (2006)]. The use of a discharge-based waveguide permitted operation at an order ofmagnitude lower density and 15 times longer distance than in previous experiments that relied on laser preformed plasma channels. Laser pulses with peak power ranging from 10-50 TW were guided over more than 20 Rayleigh ranges and high-quality electron beams with energy up to 1 GeV were obtained by channelling a 40 TW peak power laser pulse. The dependence of the electron beam characteristics on capillary properties, plasma density, and laser parameters are discussed