Showing papers by "F. J. Bermejo published in 2012"

Solid para-hydrogen as the paradigmatic quantum crystal: Three observables probed by ultrahigh-resolution neutron spectroscopy

Abstract: Quantum crystals are characterized by zero-point-energy motions large enough to explore the details of the interaction potential beyond the harmonic approximation even at zero temperature. By making recourse to ultrahigh-resolution neutron spectroscopy, we have probed simultaneously three observables sensitive to anharmonic effects in solid para-H${}_{2}$ over a wide temperature range, namely, Bragg scattering, molecular root-mean-square displacements, and the spectral linewidth of the $J=0\ensuremath{\rightarrow}$ 1 rotational transition which, on average, amounts to a half-width at half-maximum of $1.8\ifmmode\pm\else\textpm\fi{}0.2$ $\ensuremath{\mu}$eV. These three quantities show no measurable variation with temperature, thus signaling the existence of a fully expanded crystal across the entire solid phase. Our results provide unambiguous experimental evidence for the intrinsic quantum character of this fundamental molecular solid.

Differences in first neighbor orientation behind the anomalies in the low and high density trans-1,2-dichloroethene liquid.

Abstract: Trans-1,2-dichloroethene (HClC=CClH) has several structural and dynamic anomalies between its low- and high-density liquid, previously found through neutron scattering experiments. To explain the microscopic origin of the differences found in those experiments, a series of molecular dynamics simulations were performed. The analysis of molecular short-range order shows that the number of molecules in the first neighbor shell is 12 for the high-density liquid and 11 for the low-density one. It also shows that the angular position of the center of mass of the first neighbor is roughly the same although the molecular orientation is not. In both liquids the first neighbor and its reference molecule arrange mainly in two configurations, each being the most probable in one of the liquids. First neighbors in the configuration that predominates in the high-density liquid tend to locate themselves closer to the reference molecule, an evidence that they are more strongly bonded. This arrangement facilitates a better packing of the rest of molecules in the first neighbor shell so that on average an additional molecule can be included, and is proposed to be the key in the explanation of all the observed anomalies in the characteristics of both liquids.

Design and fabrication of the ess-bilbao rfq prototype models

Abstract: As part of the development of the ESS-Bilbao Accelerator in Spain, two different sets of radio frequency quadrupole (RFQ) models have been developed. A set of four oxygen free high conductivity copper weld test models has been designed and manufactured, in order to test different welding methods as well as other mechanical aspects involved in the fabrication of the RFQ. A 352.2MHz four vane RFQ cold model, 1 meter in length, has also been designed and built in Aluminum. These models serve as a good test bench to investigate the validity of different finite element analysis (FEA) software packages. This is a critical part, since the design of the final RFQ will be based on such simulations. The cold model also includes 16 slug tunersand8 coupler/pick-upports,whichwill allowthe use of the bead-pull perturbation method to measure the electric field profile, Q-value and resonant modes. In order to investigate fabrication tolerances, the cold model also includes a longitudinal test modulation in the vanes, which is similar to the one intended for the final RFQ. In addition, it represents a useful tool to explore the influence of the modulations in the electromagnetic design.

Design and measurements of the stripline bpm system of the ess-bilbao

Abstract: A new design for the Beam Position Monitors (BPMs) diagnostics of ESS-Bilbao, consisting of a whole block of stripline sensors, has been designed and manufactured. The design is based on travelling wave principles to detect the position of the beam in the vacuum chamber. The length of the stripline is 200 mm and the coverage angle is 0.952 rad. The position of the internal tube simulating the beam can be changed with respect to the outer tube within a range of 20 mm approximately for both X and Y axis, with a resolution less than 10 μm. The characteristics of the block with and without beam are measured and evaluated at frequencies of 175 and 352 MHz, using the electronics system developed for the BPM capacitive pick-ups. This electronics system is divided in an Analog Front-End (AFE) unit, where the signals are conditioned and converted to baseband, and a Digital Unit (DU) to sample them and calculate the position and phase of the beam. In this contribution, the performed tests will be fully described and the results also discussed.

Status of the ion sources at ess-bilbao

Abstract: Currently there are two types of ion sources under development and testing at ESS-Bilbao, the first one is a Penning type source based on the ISIS/RAL source, modified to use permanent magnets to generate the Penning field. The second source is an off-resonance ECR source that is being developed in-house. The Penning source is in the late stages of commissioning, and a beam has been extracted from it. Currently the main work on that source is in the optimization of the operating parameters. The ECR source on the other hand is in the early stages of the commissioning, all parts have been fabricated, and Vacuum tests are underway. Testing of the RF and control systems will follow, and finally the whole system will be tested. The control system for both ion sources was developed under LabView, and runs on a real time system. While for testing the timing sequences run locally, the system is being developed so that it can run using a central timing system.