The behaviour of copper in view of radiation damage in the LHC luminosity upgrade

In view of the safe operation of the quadrupoles in the luminosity upgrade of the LHC accelerator, the response of the copper stabilizer at low temperatures to the various high energy radiation sources is of primary importance. The present study takes into account the expected high energy spectrum of the simultaneous radiation by neutrons, protons, pions, electrons and photons, calculated using the FLUKA code by F. Cerutti (CERN) as well as on literature values. It was found that proton irradiation causes a considerably higher damage than neutron irradiation: in spite of a 3.8% proton fraction, the measured damage is of the order of 20%, which fits with the calculations of N. Mokhov (Fermilab) on the contribution of protons to the dpa. The same calculations indicate that the total effect of protons, pions and electrons is at least as high as that of neutrons. Since recent neutron experiments of Nakamoto et al. show that the RRR of Cu is reduced from 200 to 50-120 for a fluence of 10^{21} n/cm^{2}, it follows that the inclusion of all high energy sources would lead to RRR values well below 50, thus endangering stability and protection. This result confirms the necessity of including a tungsten shield inside the quadrupoles.Comment: 7 pages, Contribution to WAMSDO 2013: Workshop on Accelerator Magnet, Superconductor, Design and Optimization; 15 - 16 Jan 2013, CERN, Geneva, Switzerlan

Mechanism of Enhancement in Electromagnetic Properties of MgB2 by Nano SiC Doping

A comparative study of pure, SiC, and C doped MgB2 wires has revealed that the SiC doping allowed C substitution and MgB2 formation to take place simultaneously at low temperatures. C substitution enhances Hc2, while the defects, small grain size, and nanoinclusions induced by C incorporation and low-temperature processing are responsible for the improvement in Jc. The irreversibility field (Hirr) for the SiC doped sample reached the benchmarking value of 10 T at 20 K, exceeding that of NbTi at 4.2 K. This dual reaction model also enables us to predict desirable dopants for enhancing the performance properties of MgB2

New features in the microwave response of YBCO crystals: Evidence for a multi-component order parameter

New features are reported in precision measurements of the complex microwave conductivity of high quality $YBa_{2}Cu_{3}O_{6.95}$ crystals grown in $BaZrO_{3}$ crucibles. A third peak in the normal conductivity, $\sigma_{1}(T)$, at around $80K$, and enhanced pair conductivity $\sigma_{2}(T)$ below $\sim 65K$ are observed. The data are inconsistent with a single order parameter, and instead are indicative of multi-component superconductivity. Overall, these results point to the presence of multiple pairing interactions in $YBa_{2}Cu_{3}O_{6.95}$ and also provide a natural explanation to account for the low temperature $35K$ conductivity peak observed in all $YBa_{2}Cu_{3}O_{6.95}$ crystals.Comment: 4 pages 4 figures, Revtex, multicols [to appear in Phys. Rev. B (Rapid Comm)]. Our preprints also available at http://sagar.physics.neu.edu/preprints.htm