Microwave Electrodynamics of the Antiferromagnetic Superconductor GdBa_2Cu_3O_{7-\delta}

The temperature dependence of the microwave surface impedance and conductivity are used to study the pairing symmetry and properties of cuprate superconductors. However, the superconducting properties can be hidden by the effects of paramagnetism and antiferromagnetic long-range order in the cuprates. To address this issue we have investigated the microwave electrodynamics of GdBa_2Cu_3O_{7-\delta}, a rare-earth cuprate superconductor which shows long-range ordered antiferromagnetism below T_N=2.2 K, the Neel temperature of the Gd ion subsystem. We measured the temperature dependence of the surface resistance and surface reactance of c-axis oriented epitaxial thin films at 10.4, 14.7 and 17.9 GHz with the parallel plate resonator technique down to 1.4 K. Both the resistance and the reactance data show an unusual upturn at low temperature and the resistance presents a strong peak around T_N mainly due to change in magnetic permeability.Comment: M2S-HTCS-VI Conference Paper, 2 pages, 2 eps figures, using Elsevier style espcrc2.st

Near-field scanning microwave microscope for interline capacitance characterization of nanoelectronics interconnect

We have developed a noncontact method for measurement of the interline capacitance in Cu/low-k interconnect. It is based on a miniature test vehicle with net capacitance of a few femto-Farads formed by two 20-\mu m-long parallel wires (lines) with widths and spacings the same as those of the interconnect wires of interest. Each line is connected to a small test pad. The vehicle impedance is measured at 4 GHz by a near-field microwave probe with 10 \mu m probe size via capacitive coupling of the probe to the vehicle's test pads. Full 3D finite element modeling at 4 GHz confirms that the microwave radiation is concentrated between the two wires forming the vehicle. An analytical lumped element model and a short/open calibration approach have been proposed to extract the interline capacitance value from the measured data. We have validated the technique on several test vehicles made with copper and low-k dielectric on a 300 mm wafer. The vehicles interline spacing ranges from 0.09 to 1 \mu m and a copper line width is 0.15 \mu m. This is the first time a near-field scanning microwave microscope has been applied to measure the lumped element impedance of a test vehicle

Study of Secondary Field Formation and Radiation Loads in the Central Region Detectors of the LHCb Experiment at LHC

The numerical study of secondary field formation for the central region of LHCb experiment at LHC has been carried out. The specific characteristics of radiation field, depending on the detectors location in the experimental region and on the accelerator vacuum chamber design are shown. The estimations of radiation loads which determine the detectors performance in the particular background environment are given

Solitons supported by singular spatial modulation of the Kerr nonlinearity

We introduce a setting based on the one-dimensional (1D) nonlinear Schroedinger equation (NLSE) with the self-focusing (SF) cubic term modulated by a singular function of the coordinate, |x|^{-a}. It may be additionally combined with the uniform self-defocusing (SDF) nonlinear background, and with a similar singular repulsive linear potential. The setting, which can be implemented in optics and BEC, aims to extend the general analysis of the existence and stability of solitons in NLSEs. Results for fundamental solitons are obtained analytically and verified numerically. The solitons feature a quasi-cuspon shape, with the second derivative diverging at the center, and are stable in the entire existence range, which is 0 < a < 1. Dipole (odd) solitons are found too. They are unstable in the infinite domain, but stable in the semi-infinite one. In the presence of the SDF background, there are two subfamilies of fundamental solitons, one stable and one unstable, which exist together above a threshold value of the norm (total power of the soliton). The system which additionally includes the singular repulsive linear potential emulates solitons in a uniform space of the fractional dimension, 0 < D < 1. A two-dimensional extension of the system, based on the quadratic nonlinearity, is formulated too.Comment: Physical Review A, in pres

On the accuracy of Monte Carlo based beam dynamics models for the degrader in proton therapy facilities

In a cyclotron-based proton therapy facility, the energy changes are performed by means of a degrader of variable thickness. The interaction of the proton beam with the degrader creates energy tails and increases the beam emittance. A precise model of the degraded beam properties is important not only to better understand the performance of a facility already in operation, but also to support the development of new proton therapy concepts. The exact knowledge of the degraded beam properties, in terms of energy spectrum and transverse phase space, depends on the model used to describe the proton interaction with the degrader material. In this work the model of a graphite degrader has been developed with four Monte Carlo codes: three conventional Monte Carlo codes (FLUKA, GEANT4 and MCNPX) and the multi-purpose particle tracking code OPAL equipped with a simplified Monte Carlo routine. From the comparison between the different codes, we can deduce how the accuracy of the degrader model influences the precision of the beam dynamics model of a possible transport line downstream of the degrader