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Register a new userThe influence of the Al stabilizer layer thickness on the normal zone propagation velocity in high current superconductors
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The stability of high-current superconductors is challenging in the design of superconducting magnets. When the stability requirements are fulfilled, the protection against a quench must still be considered. A main factor in the design of quench protection systems is the resistance growth rate in the magnet following a quench. The usual method for determining the resistance growth in impregnated coils is to calculate the longitudinal velocity with which the normal zone propagates in the conductor along the coil windings. Here, we present a 2D numerical model for predicting the normal zone propagation velocity in Al stabilized Rutherford NbTi cables with large cross section. By solving two coupled differential equations under adiabatic conditions, the model takes into account the thermal diffusion and the current redistribution process following a quench. Both the temperature and magnetic field dependencies of the superconductor and the metal cladding materials properties are included. Unlike common normal zone propagation analyses, we study the influence of the thickness of the cladding on the propagation velocity for varying operating current and magnetic field. To assist in the comprehension of the numerical results, we also introduce an analytical formula for the longitudinal normal zone propagation. The analysis distinguishes between low-current and high-current regimes of normal zone propagation, depending on the ratio between the characteristic times of thermal and magnetic diffusion. We show that above a certain thickness, the cladding acts as a heat sink with a limited contribution to the acceleration of the propagation velocity with respect to the cladding geometry. Both numerical and analytical results show good agreement with experimental data.
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The MINOS experiment uses a beam of predominantly muon-type neutrinos generated using protons from the Main Injector at Fermilab in Batavia, IL, and travelling 735 km through the Earth to a disused iron mine in Soudan, MN. The 10{mu}s-long beam pulse contains fine time structure which allows a precise measurement of the neutrino time of flight to be made. The time structure of the parent proton pulse is measured in the beamline after extraction from the Main Injector, and neutrino interactions are timestamped at the Fermilab site in the Near Detector (ND), and at the Soudan site in the Far Detector (FD). Small, transportable auxiliary detectors, consisting of scintillator planes and associated readout electronics, are used to measure the relative latency between the two large detectors. Time at each location is measured with respect to HP5071A Cesium clocks, and time is transferred using GPS Precise Point Positioning (PPP) solutions for the clock offset at each location. We describe the timing calibration of the detectors and derive a measurement of the neutrino velocity, based on data from March and April 2012. We discuss the prospects for further improvements that would yield a still more accurate result.
A high-intensity hyperon beam was constructed at CERN to deliver Sigma- to experiment WA89 at the Omega facility and operated from 1989 to 1994. The setup allowed rapid changeover between hyperon and conventional hadron beam configurations. The beam provided a Sigma-flux of 1.4 x 10^5 per burst at mean momenta between 330 and 345 Gev/c, produced by about 3 x 10^10 protons of 450 GeV/c . At the experiment target the beam had a Sigma-/pi- ratio close to 0.4 and a size of 1.6 x 3.7 cm^2. The beam particle trajectories and their momenta were measured with a scintillating fibre hodoscope in the beam channel and a silicon microstrip detector at the exit of the channel. A fast transition radiation detector was used to identify the pion component of the beam.
The technique of current splitting is presented as part of an integrated circuit development for an X-ray imager. This method enables integration of charge signals of unprecedented magnitude in small pixels, achieving a dynamic range of ${10^5}$. Results from two front end prototypes are given and a final optimized design is proposed.
Surface acoustic waveguides are increasing in interest for (bio)chemical detection. The surface mass modification leads to measurable changes in the propagation properties of the waveguide. Among a wide variety of waveguides, Love mode has been investigated because of its high gravimetric sensitivity. The acoustic signal launched and detected in the waveguide by electrical transducers is accompanied by an electromagnetic wave; the interaction of the two signals, easily enhanced by the open structure of the sensor, creates interference patterns in the transfer function of the sensor. The influence of these interferences on the gravimetric sensitivity is presented, whereby the structure of the entire sensor is modelled. We show that electromagnetic interferences generate an error in the experimental value of the sensitivity. This error is different for the open and the closed loop configurations of the sensor. The theoretical approach is completed by the experimentation of an actual Love mode sensor operated under liquid in open loop configuration. The experiment indicates that the interaction depends on the frequency and the mass modifications.
Along with the protection of magnets and power converters, we have added a section on personnel protection because this is our highest priority in the design and operation of power systems. Thus, our topics are the protection of people, power converters, and magnet loads (protected from the powering equipment), including normal conducting magnets and superconducting magnets.
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