Studies of Decay and Snapback Effects on LHC Dipole Magnets

LHC model magnets have dynamic field imperfections of various nature. Two effects of particular importance are field component decay during injection and ''snapback'' during the first few seconds of acceleration, which happens over typically 15 to 20 mT. The dynamic behaviour of the model magnets was measured as a function of several parameters in the operation cycle and powering history. We demonstrate how the systematic variation of only one single operation cycle parameter can affect the behaviour of the sextupole component

Interaction between current imbalance and magnetization in LHC cables

The quality of the magnetic field in superconducting accelerator magnets is associated with the properties of the superconducting cable. Current imbalances due to coupling currents ¿I, as large as 100 A, are induced by spatial variations of the field sweep rate and contact resistances. During injection at a constant field all magnetic field components show a decay behavior. The decay is caused by a diffusion of coupling currents into the whole magnet. This results in a redistribution of the transport current among the strands and causes a demagnetization of the superconducting cable. As soon as the field is ramped up again after the end of injection, the magnetization rapidly recovers from the decay and follows the course of the original hysteresis curve. In order to clarify the interactions between the changes in current and magnetization during injection the authors performed a number of experiments. A magnetic field with a spatially periodic pattern was applied to a superconducting wire in order to simulate the coupling behavior in a magnet. This model system was placed into a stand for magnetization measurements and the influence of different powering conditions was analyze

Degaussing and Decay Reduction in the Short Superconducting Dipole Models for the LHC

The time decay of field harmonics during current plateaus is a known drawback of superconducting accelerator magnets. The present understanding of this phenomenon refers to a combination of flux creep and of the interaction between the redistribution of currents in Rutherford cables and the filament magnetization. Current cycles of decreasing amplitude, called here degaussing, were found to reduce significantly the decay observed in accelerator magnets. This paper reports on the measured reduction of decay obtained in short dipole models for the LHC and on one experiment with a single LHC strand

Anatomical and physiological development of the Xenopus embryonic motor system in the absence of neural activity

Embryos of Xenopus laevis were continually immobilized by immersion in solutions of either chloretone or lidocaine, from the late neural-fold stage to the approximate time of hatching. Such treatment has been shown to result in only transient quantitative effects on swimming behavior. Chronic immobilization was without either immediate or long- term effect on the ventral root output exhibited during “fictive” swimming episodes. Development under these conditions of diminished or absent neural activity similarly had no effects on a number of measures of the size and complexity of motoneuron dendritic arborizations. These results support the premise that the early development of specific neuronal morphology and connectivity may be largely independent of functional activity

Immunocytochemical and electrophysiological characterization of GABA receptors in the frog and turtle retina

AbstractThe expression of GABA receptors (GABARs) was studied in frog and turtle retinae. Using immunocytochemical methods, GABAARs and GABACRs were preferentially localized to the inner plexiform layer (IPL). Label in the IPL was punctate indicating a synaptic clustering of GABARs. Distinct, but weaker label was also present in the outer plexiform layer. GABAAR and GABACR mediated effects were studied by recording electroretinograms (ERGs) and by the application of specific antagonists. Bicuculline, the GABAAR antagonist, produced a significant increase of the ERG. Picrotoxin, when co-applied with saturating doses of bicuculline, caused a further increase of the ERG due to blocking of GABACRs. The putative GABACR antagonist Imidazole-4-acidic acid (I4AA) failed to antagonize GABACR mediated inhibition and, in contrast, appeared rather as an agonist of GABARs

Relative timing jitter measurements with an indirect phase comparison method

We propose and demonstrate experimentally a method for the sensitive measurement of the relative timing jitter of two mode-locked lasers, which can be either free-running or timing-synchronized to a common reference oscillator. The method is based on the indirect comparison of the phases of two photodetector outputs, using a microwave oscillator, the noise of which does not affect the results, electronic mixers, and a sampling oscilloscope. We carefully analyze and experimentally demonstrate the potential of this method. Compared to phase detector methods, it has a broader scope of applications and a lower sensitivity to intensity noise. We also obtained data on the coupling of intensity to timing noise in photodetector