An Improved Method using RBF Neural Networks to Speed up Optimization Algorithms

The paper presents a method using Radial Basis Function (RBF) neural networks to speed up deterministic search algorithms used for the optimization of superconducting magnets for the LHC accelerator project at CERN. The optimization of the iron yoke of the main LHC dipoles requires a number of numerical field computations per trial solution as the field quality depends on the excitation and local iron saturation in the yoke. This results in computation times of about 30 minutes for each objective function evaluation (on DEC-Alpha 600/333). In this paper we present a method for constructing an RBF neural network for a local approximation of the objective function. The computational time required for such a construction is negligible compared to the deterministic function evaluation, and thus yields a speed-up of the overall search process. The effectiveness of this method is demonstrated by means of two- and three-parametric optimization examples. The achieved speed-up of the search routine is up to 30 %

The correlation of processes of crystallization and changes of free electron density amorphous alloy powder Co80Ni20

Great attention is being given today to investigations on the capabilities and structural changes of amorphous and nanocrystal materials. Structural changes of the amorphous cobalt and nickel alloy powder obtained by electrochemical deposition were investigated in this paper. The crystallization process, as determined by the DSC method, occurred in two steps. The temperature dependence of electrical resistively and magnetic susceptibility in isothermal and non-isothermal conditions within the temperature range of room temperature to 700ºC was determined for the powder samples pressed under pressure of 800 MPa. The X-ray structural examinations results correlate with those of the DSC analysis and the electrical resistively measuring

Integrated Design of Superconducting Magnets with the CERN Field Computation Program ROXIE

The program package ROXIE has been developed at CERN for the field computation of superconducting accelerator magnets and is used as an approach towards the integrated design of such magnets. It is also an example of fruitful international collaborations in software development.The integrated design of magnets includes feature based geometry generation, conceptual design using genetic optimization algorithms, optimization of the iron yoke (both in 2d and 3d) using deterministic methods, end-spacer design and inverse field calculation.The paper describes the version 8.0 of ROXIE which comprises an automatic mesh generator, an hysteresis model for the magnetization in superconducting filaments, the BEM-FEM coupling method for the 3d field calculation, a routine for the calculation of the peak temperature during a quench and neural network approximations of the objective function for the speed-up of optimization algorithms, amongst others.New results of the magnet design work for the LHC are given as examples

Rate effects in high-resolution drift chambers

The impact of high counting rates on the spatial resolution of cylindrical drift tubes is investigated in detail and the results are compared with simulations. Electronics effects and space-charge effects are quantitatively analysed. A spatial resolution of $\sigma < 80\,\mu\mathrm{m}$ can be achieved even at rates as high as 1500\,Hz/cm wire length (300\,kHz per wire)

Measurement of the solenoid magnetic field

We describe the machine used to map the solenoid field and the data sets that were collected. The bulk of the note describes the analysis of this data. A series of small corrections are made; some taken from surveys and some derived from the data itself. Two fitting methods are defined and applied to all data sets. The final result is that the field map at normal operating current can be fitted to a function that obeys Maxwell with an r.m.s. residual of less than 5 Gauss. Systematic errors on the measurement of track sagitta due to the field uncertainty are estimated to be in the range 2.3E-4 to 12E-4, depending on the track rapidity. Finally, the representation of the map in Athena is briefly described

Front-end electronics for drift tubes in a high-rate environment

A front-end electronics readout for drift tubes in a high-rate environment is presented. This system allows us to encode several pieces of information (leading edge time, trailing edge time, signal charge and piled-up hits from multiple tracks) into a single readout channel that is presented to the TDC. The advantage of active baseline restoration compared to bipolar signal shaping is discussed

Measurement of the ATLAS solenoid magnetic field

ATLAS is a general purpose detector designed to explore a wide range of physics at the Large Hadron Collider. At the centre of ATLAS is a tracking detector in a 2 T solenoidal magnetic field. This paper describes the machine built to map the field, the data analysis methods, the final results, and their estimated uncertainties. The remotely controlled mapping machine used pneumatic motors with feedback from optical encoders to scan an array of Hall probes over the field volume and log data at more than 20 000 points in a few hours. The data were analysed, making full use of the physical constraints on the field and of our knowledge of the solenoid coil geometry. After a series of small corrections derived from the data itself, the resulting maps were fitted with a function obeying Maxwell's equations. The fit residuals had an r.m.s. less than 0.5 mT and the systematic error on the measurement of track sagitta due to the field uncertainty was estimated to be in the range 0.02 % to 0.12 % depending on the track rapidity

Measurement and Analysis of the Field Quality of LHC Prototype and Pre-series Superconducting Dipoles

We report the main results of the magnetic field measurements performed on the full-size LHC superconducting dipoles tested at CERN since summer 1998. Main field strength and field errors are summarised. We discuss in detail the contributions related to the geometry of the collared coil, the assembled cold mass, cool-down effects, magnetisation of the superconducting cable and saturation effects at high field. Dynamic effects on field harmonics, such as the field decay during injection and field errors during current ramps, are assessed statistically

Space charge in drift chambers operated with the Xe,CO2(15%) mixture

Using prototype modules of the ALICE Transition Radiation Detector we investigate space charge effects and the dependence of the pion rejection performance on the incident angle of the ionizing particle. The average pulse height distributions in the drift chambers operated with the Xe,CO2(15%) mixture provide quantitative information on the gas gain reduction due to space charge accumulating during the drift of the primary ionization. Our results demonstrate that the pion rejection performance of a TRD is better for tracks which are not at normal incidence to the anode wires. We present detailed simulations of detector signals, which reproduce the measurements and lend strong support to our interpretation of the measurements in terms of space charge effects.Comment: 18 pages, 10 figures, accepted for publication in Nucl.Instrum.Meth. A. Data files available at http://www-alice.gsi.de/tr