7289726
Installation and commissioning of the new 150 KW plant for the elettra RF system upgrade
Elettra is the Italian third generation light source in operation in Trieste since 1993. The project of upgrade of the Elettra RF system has become necessary to provide the needed operating margins when all the insertion devices are operational and in view of possible increases in beam current and energy. The first phase of the project regards one of the four plants, which has been upgraded from 60 to 150 kW cw. The power amplifier has been built combining two 80 kW IOTs (inductive output tubes) by means of a switchless combiner. The amplifier and the power plant components have been installed in the second half of year 2006. A coaxial to waveguide transition has been specially designed to interface the coaxial coupler of the cavity to the waveguide power transmission system, taking into account the risks connected to power from the higher order modes excited by the beam in the cavity. After giving an overview of the project, this paper discusses the technical choices adopted, the tests performed during the installation phase and the commissioning of the new system with beam during machine operation.
49385697
INSTALLATION AND COMMISSIONING OF THE RF SYSTEM FOR THE NEW ELETTRA BOOSTER
The commissioning of the new booster of the Elettra synchrotron radiation storage ring started in Fall 2007. The RF system of the booster is made of a five cells accelerating cavity fed by a 60 kW 500 MHz power plant. The accelerating cavity voltage is ramped along with the booster energy at repetition rate 3 Hz. The cavity field is controlled by analog feedback loops on amplitude, phase and the resonant frequency. This paper describes the setting into operation of the system and its performances during the commissioning phase of the machine.
117021213
Studying the neutron orbital structure by coherent hard exclusive processes off 3He
Hard exclusive processes, such as Deeply Virtual Compton Scattering (DVCS), allow to access generalized parton distributions (GPDs). By means of an Impulse Approximation (IA) calculation, it is shown here how, in the low momentum transfer region, the sum of the GPDs H and E is dominated by the neutron contribution. Thanks to this property, 3He could open a new way to access the neutron structure information. In this work, a simple and efficient extraction procedure of the neutron GPDs, able to take into account the nuclear effects included in IA analysis, is proposed.
1328077
Spinning Q-balls in Abelian Gauge Theories with positive potentials: existence and non existence
We study the existence of cylindrically symmetric electro-magneto-static solitary waves for a system of a nonlinear Klein–Gordon equation coupled with Maxwell’s equations in presence of a positive mass and of a nonnegative nonlinear potential. Nonexistence results are provided as well.
118790490
Observational signatures of pre-inflationary and lower-dimensional effective gravity
Several alternative ways to quantize gravitational interactions seem to indicate that gravity at short distances is effectively two-dimensional. If this were true, and the energy scale at which the dimensional transition occurs is of the order of the inflationary one, it is reasonable to investigate eventual signatures in the primordial perturbation spectra. In this paper we look at this possibility by assuming that the inflationary era was preceded by an effectively two-dimensional evolution of the Universe. We model the transition with a mode matching and we show that, in this case, no observational signatures are expected in the tensor and scalar power spectra nor in their ratio. We also show that assuming modified dispersion relations before the matching between two sets of four-dimensional modes leads to similar results.
119943646
Relation between representations of KN and virasoro algebras
Abstract Some aspects of conformal field theory over Riemann surfaces are examined. We study, in particular, on simple systems (b−c systems) the relation between representations of the Virasoro and the KN algebras. KN algebra representations decompose into an infinite sum of the Virasoro algebra representations. We argue that the KN algebra representations are the right tool in order to classify conformal field theories over higher genus Riemann surfaces.
15231170
Momentum-space representation of Green’s functions with modified dispersion on ultrastatic space-time
We consider Green's functions associated to a scalar field propagating on a curved, ultrastatic background, in the presence of modified dispersion relations. The usual proper-time DeWitt-Schwinger procedure to obtain a series representation of Green's functions is doomed to failure because of higher order spatial derivatives in the Klein-Gordon operator. We show how to overcome this difficulty by considering a preferred frame, associated to a unit timelike vector. With respect to this frame, we can express Green's functions as an integral over all frequencies of a space-dependent function. The latter can be expanded in momentum space, as a series with geometric coefficients similar to the DeWitt-Schwinger ones. By integrating over all frequencies, we finally find the expansion of Green's function up to four derivatives of the metric tensor. The relation with the proper-time formalism is also discussed.