34037354
RF system for the elettra new full energy booster injector
The Elettra new full energy injector will be based on a 100 MeV linac and a 2.5 GeV booster synchrotron and it will replace the existing 1.2 linac injector. This paper presents the design, construction and the test results of the RF system for the booster synchrotron. The analysis of the foreseen operating scenario is also described. The system must be as simple and reliable as possible, taking into consideration the high availability required for the possible top-up mode of operation. It has also to be consistent with the other upgrades of the facility, as the upgrade of the storage ring RF system. The booster RF system will use a 500 MHz 5-cell copper cavity powered by a 60 kW klystron based power plant. The low level electronics has been in-house developed, starting from the system in operation in the storage ring, increasing the performances and developing the new features required by the use of a five-cell cavity, instead of a single cell one, and by the ramped operation. The commissioning of the new injector is scheduled to start in summer 2007, while the first Elettra operation for users with the new full energy injector is expected for the first quarter of 2008.
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.
209514446
OPERATIONAL EXPERIENCE WITH THE ELETTRA RF SYSTEM
The ELETTRA RF System has been in operation since October 1993 and has now exceeded 20000 running hours. With four 500 MHz cavities powered by four 60 kW transmitters, ELETTRA has successfully delivered synchrotron light to the users with 300 mA of stored current at 2 GeV in multibunch mode, which is 1.5 times the initial target value ( 200 mA at 2 GeV). The RF system has worked very satisfactorily. Apart from the usual problems of debugging a new system, the main problem encountered during the operation period came from the coaxial power transmission line. The global operational experience gained during these years of operation and the performances of the various elements making up the ELETTRA RF system will be reported.
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.
119288395
A new approach to non-commutative inflation
We propose an inflationary scenario inspired by a recent formulation, in terms of coherent states, of non-commutative quantum field theory. We consider the semiclassical Einstein equations, and exploit the ultraviolet finiteness of the non-commutative propagator to construct the expectation value of the energy–momentum tensor associated with a generic scalar field. It turns out that the latter is always finite and dominated by an effective cosmological constant. By combining this general feature with the intrinsic fuzziness of spacetime, we show that non-commutativity governs the energy density of the early Universe in such a way that the strong energy condition is violated. Thus, there might be a bounce and a subsequent inflationary phase, which does not need any ad hoc scalar field.
16251449
Brane world in a topological black hole bulk
We consider a static brane in the background of a topological black hole in arbitrary dimensions. For hyperbolic horizons, we find a solution only when the black hole mass assumes its minimum negative value. In this case, the tension of the brane vanishes, and the brane position coincides with the location of the horizon. For an elliptic horizon, we show that the massless mode of Randall–Sundrum is recovered in the limit of large black hole mass.
117924192
Generalized wess-zumino terms
119193598
Momentum-space representation of Green's functions with modified dispersion relations on general backgrounds
We consider the problem of calculating the Green's functions associated to a massive scalar field with modified dispersion relations. We analyze the case when dispersion is modified by higher derivative spatial operators acting on the field orthogonally to a preferred direction, determined by a unit timelike vector field. By assuming that the integral curves of the vector field are geodesics, we expand the modified Klein-Gordon equation in Fermi normal coordinates. By means of a Fourier transform, we find a series representation in momentum-space of the Green's functions. The coefficients of the series are geometrical terms containing combinations of the Ricci tensor and the vector field, as expected from previous calculations with different methods and for specific backgrounds.
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.