Stable Operation of a Free-Electron Laser Driven by a Plasma Accelerator.

The breakthrough provided by plasma-based accelerators enabled unprecedented accelerating fields by boosting electron beams to gigaelectronvolt energies within a few centimeters [1-4]. This, in turn, allows the realization of ultracompact light sources based on free-electron lasers (FELs) [5], as demonstrated by two pioneering experiments that reported the observation of self-amplified spontaneous emission (SASE) driven by plasma-accelerated beams [6,7]. However, the lack of stability and reproducibility due to the intrinsic nature of the SASE process (whose amplification starts from the shot noise of the electron beam) may hinder their effective implementation for user purposes. Here, we report a proof-of-principle experiment using plasma-accelerated beams to generate stable and reproducible FEL light seeded by an external laser. FEL radiation is emitted in the infrared range, showing the typical exponential growth of its energy over six consecutive undulators. Compared to SASE, the seeded FEL pulses have energies 2 orders of magnitude larger and stability that is 3 times higher.

Free-electron lasing with compact beam-driven plasma wakefield accelerator.

The possibility to accelerate electron beams to ultra-relativistic velocities over short distances by using plasma-based technology holds the potential for a revolution in the field of particle accelerators1-4. The compact nature of plasma-based accelerators would allow the realization of table-top machines capable of driving a free-electron laser (FEL)5, a formidable tool to investigate matter at the sub-atomic level by generating coherent light pulses with sub-ångström wavelengths and sub-femtosecond durations6,7. So far, however, the high-energy electron beams required to operate FELs had to be obtained through the use of conventional large-size radio-frequency (RF) accelerators, bound to a sizeable footprint as a result of their limited accelerating fields. Here we report the experimental evidence of FEL lasing by a compact (3-cm) particle-beam-driven plasma accelerator. The accelerated beams are completely characterized in the six-dimensional phase space and have high quality, comparable with state-of-the-art accelerators8. This allowed the observation of narrow-band amplified radiation in the infrared range with typical exponential growth of its intensity over six consecutive undulators. This proof-of-principle experiment represents a fundamental milestone in the use of plasma-based accelerators, contributing to the development of next-generation compact facilities for user-oriented applications9.

A SINGLE-EXPOSURE, MULTIDETECTOR NEUTRON SPECTROMETER FOR WORKPLACE MONITORING.

This communication describes a recently developed single-exposure neutron spectrometer, based on multiple active thermal neutron detectors located within a moderating sphere, which have been developed jointly by CIEMAT (Spain), INFN (Italy) and Politecnico di Milano (Italy) in the framework of Italian and Spanish collaboration projects. The fabricated prototypes permit to achieve spectrometric resolution with nearly isotropic response for neutron with energies from thermal to 100-200 MeV, thus being able to characterise the complete neutron spectrum in only one exposure by unfolding the measured responses of the detectors. This makes it especially advantageous for characterising neutron fields and workplace monitoring purposes in neutron-producing facilities.

ETHERNES: A new design of radionuclide source-based thermal neutron facility with large homogeneity area.

A new thermal neutron irradiation facility based on an (241)Am-Be source embedded in a polyethylene moderator has been designed, and is called ETHERNES (Extended THERmal NEutron Source). The facility shows a large irradiation cavity (45 cm × 45 cm square section, 63 cm in height), which is separated from the source by means of a polyethylene sphere acting as shadowing object. Taking advantage of multiple scattering of neutrons with the walls of this cavity, the moderation process is especially effective and allows obtaining useful thermal fluence rates from 550 to 800 cm(-2) s(-1) with a source having nominal emission rate 5.7×10(6) s(-1). Irradiation planes parallel to the cavity bottom have been identified. The fluence rate across a given plane is as uniform as 3% (or better) in a disk with 30 cm (or higher) diameter. In practice, the value of thermal fluence rate simply depends on the height from the cavity bottom. The thermal neutron spectral fraction ranges from 77% up to 89%, depending on the irradiation plane. The angular distribution of thermal neutrons is roughly isotropic, with a slight prevalence of directions from bottom to top of the cavity. The mentioned characteristics are expected to be attractive for the scientific community involved in neutron metrology, neutron dosimetry and neutron detector testing.

Development of single-exposure, multidetector neutron spectrometers: the NESCOFI@BTF project.

NESCOFI@BTF is a 3-y project (2011-13) supported by the Scientific Commission 5 of INFN (Italy). The target is the development of neutron spectrometers similar to the Bonner spheres, in terms of response energy interval and accuracy, but able to determine the neutron spectrum in only one exposure. These devices embed multiple (10 to 30) thermal neutron detectors (TNDs) within a single moderator. Two prototypes, called SPherical SPectrometer (SP(2)) and cylindrical spectrometer (CYSP), have been set up. Whilst SP(2) has spherical geometry and nearly isotropic response, the CYSP has cylindrical geometry and is intended to be used as a directional spectrometer. Suitable active TNDs will be embedded in the final version of the devices. The resulting instruments could be used as real-time neutron spectrometers in neutron-producing facilities. This communication describes the design criteria, numerical analysis, experimental issues, state-of-the-art and future developments connected with the development of these instruments.

Estrogens and neuropeptides in postmenopausal women: un update.

Menopause is characterized by depletion of ovarian follicles, a reduction of ovarian hormones to castrate levels and elevated levels of serum gonadotropins from the anterior pituitary gland. Although this process has significant repercussions throughout the body and affects a large proportion of our society, the neuroendocrine control mechanisms that accompany menopause are poorly understood. This review aims to examine rigorously the most accredited literature to provide an update about our current understanding of the role of the hypothalamic-pituitary axis in the onset of and transition into female reproductive senescence, focusing on the role of some specific neuropeptides in regulating the HPG axis and on their effects on several menopausal symptoms, especially referring to the cardiovascular risk, to open up new horizons for new therapeutic strategies.

A new long-term reversible contraception method: sexual and metabolic impact.

BACKGROUND: Data relating to the influence of hormonal contraception on sexual life are conflicting and mostly they refer to oral contraceptives. In this study we evaluated the effect of a long-acting contraceptive on sexual function, metabolism and bleeding pattern variations. METHODS: 23 women with a permanent partner and an active sexual life completed a specific questionnaire at the start of the study and after cycles 3 and 6 of contraceptive use; a blood sample was performed or metabolic evaluation and a "bleeding calendar" was compiled by the patients. CONCLUSION: There is an increase of quality and frequency of sexual function after 6 month of contraception; there aren't significant change in metabolic parameters and is detectable a modification of bleeding patterns.

Test of "crab-waist" collisions at the DAPhiNE Phi factory.

The electron-positron collider DAPhiNE, the Italian Phi factory, has been recently upgraded in order to implement an innovative collision scheme based on large crossing angle, small beam sizes at the crossing point, and compensation of beam-beam interaction by means of sextupole pairs creating a "crab-waist" configuration in the interaction region. Experimental tests of the novel scheme exhibited an increase by a factor of 3 in the peak luminosity of the collider with respect to the performances reached before the upgrade. In this Letter we present the new collision scheme, discuss its advantages, describe the hardware modifications realized for the upgrade, and report the results of the experimental tests carried out during commissioning of the machine in the new configuration and standard operation for the users.

A diffusive-convective model for the dynamics of population-toxicant interactions: some analytical and numerical results.

In this paper we consider a diffusive-convective model for the dynamics of a population living in a polluted environment. Threshold results are given concerning the effect of the toxicant on the living population. Some analytic results are proved and numerical experiments give suggestions in more general cases.