17 research outputs found
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
Multi-system neurological disease is common in patients with OPA1 mutations
Additional neurological features have recently been described in seven families transmitting pathogenic mutations in OPA1, the most common cause of autosomal dominant optic atrophy. However, the frequency of these syndromal âdominant optic atrophy plusâ variants and the extent of neurological involvement have not been established. In this large multi-centre study of 104 patients from 45 independent families, including 60 new cases, we show that extra-ocular neurological complications are common in OPA1 disease, and affect up to 20% of all mutational carriers. Bilateral sensorineural deafness beginning in late childhood and early adulthood was a prominent manifestation, followed by a combination of ataxia, myopathy, peripheral neuropathy and progressive external ophthalmoplegia from the third decade of life onwards. We also identified novel clinical presentations with spastic paraparesis mimicking hereditary spastic paraplegia, and a multiple sclerosis-like illness. In contrast to initial reports, multi-system neurological disease was associated with all mutational subtypes, although there was an increased risk with missense mutations [odds ratio = 3.06, 95% confidence interval = 1.44â6.49; P = 0.0027], and mutations located within the guanosine triphosphate-ase region (odds ratio = 2.29, 95% confidence interval = 1.08â4.82; P = 0.0271). Histochemical and molecular characterization of skeletal muscle biopsies revealed the presence of cytochrome c oxidase-deficient fibres and multiple mitochondrial DNA deletions in the majority of patients harbouring OPA1 mutations, even in those with isolated optic nerve involvement. However, the cytochrome c oxidase-deficient load was over four times higher in the dominant optic atrophy + group compared to the pure optic neuropathy group, implicating a causal role for these secondary mitochondrial DNA defects in disease pathophysiology. Individuals with dominant optic atrophy plus phenotypes also had significantly worse visual outcomes, and careful surveillance is therefore mandatory to optimize the detection and management of neurological disability in a group of patients who already have significant visual impairment
ANTARES: the first undersea neutrino telescope
The ANTARES Neutrino Telescope was completed in May 2008 and is the first
operational Neutrino Telescope in the Mediterranean Sea. The main purpose of
the detector is to perform neutrino astronomy and the apparatus also offers
facilities for marine and Earth sciences. This paper describes the design, the
construction and the installation of the telescope in the deep sea, offshore
from Toulon in France. An illustration of the detector performance is given
Design of a plasma discharge circuit for particle wakefield acceleration
Plasma wakefield acceleration is the most promising acceleration technique known nowadays, able to provide very high accelerating Fields (10-100 GV m(-1)), to enabling acceleration of electrons to GeV energy in few centimetres. However, the quality of the electron bunches accelerated with this technique is still not comparable with that of conventional accelerators; radiofrequency-based accelerators, in fact, are limited in the accelerating field (10-100 MV m(-1)) requiring therefore kilometric distances to reach the GeV energies, but can provide very bright electron bunches. Combining high brightness electron bunches from conventional accelerators and high accelerating fields reachable with plasmas could be a good compromise allowing to further accelerate high brightness electron bunches coming from LINAC while preserving electron beam quality. Following the idea of plasma wave resonant excitation driven by a train of short bunches, we have started to study the requirements in terms of plasma for SPARC-LAB [1,2]. In particular, here we focus on the ionization process; we show a simplified model to study the evolution of plasma induced by discharge, very useful to design the discharge circuit able to fully ionize the gas and bring the plasma at the needed temperature and density