Graphene doping to enhance flux pinning and supercurrent carrying ability in magnesium diboride superconductor

It has been shown that graphene doping is sufficient to lead to an improvement in the critical current density - field performance (Jc(B)), with little change in the transition temperature in MgB2. At 3.7 at% graphene doping of MgB2 an optimal enhancement in Jc(B) was reached by a factor of 30 at 5 K and 10 T, compared to the un-doped sample. The results suggested that effective carbon substitutions by grapheme, 2D nature of grapheme and the strain effect induced by difference thermal coefficient between single grapheme sheet and MgB2 superconductor may play an important role in flux pinning enhancement

Experimental research of high field pinning centers in 2% C doped MgB2 wires at 20K and 25K

High field pinning centers in MgB doped with 2 at. % carbon under a low and a high hot isostatic pressures have been investigated by transport measurements. The field dependence of the transport critical current density was analyzed within the different pinning mechanisms: surface pinning, point pinning, and pinning due to spatial variation in the Ginzburg-Landau parameter (Δκ pinning). Research indicates that a pressure of 1 GPa allows similar pinning centers to Δκ pinning centers to be obtained. This pinning is very important, because it makes it possible to increase the critical current density in high magnetic fields at 20 K and 25 K. Our results indicate that the δT and δl pinning mechanisms, which are due to a spatial variation in the critical temperature (T) and the mean free path, l, respectively, create dislocations. The high density of dislocations with inhomogeneous distribution in the structure of the superconducting material creates the δl pinning mechanism. The low density of dislocations with inhomogeneous distribution creates the δT pinning mechanism. Research indicates that the hot isostatic pressure process makes it possible to obtain a high dislocation density with a homogeneous distribution. This allows us to obtain the δT pinning mechanism in MgB wires. In addition, a high pressure increases the crossover field from the single vortex to the small vortex bundle regime (B) and improves the δT pinning mechanism. Our research has proved that a high pressure significantly increases the crossover field from the small bundle to the thermal regime (B), with only a modest decrease in T of 1.5 K, decreases the thermal fluctuations, increases the irreversibility magnetic field (B) and the upper critical field (B) in the temperature range from 4.2 K to 25 K, and reduces B and B above 25 K

The design, construction, and commissioning of the KATRIN experiment

The KArlsruhe TRItium Neutrino (KATRIN) experiment, which aims to make a direct and model-independent determination of the absolute neutrino mass scale, is a complex experiment with many components. More than 15 years ago, we published a technical design report (TDR) [1] to describe the hardware design and requirements to achieve our sensitivity goal of 0.2 eV at 90% C.L. on the neutrino mass. Since then there has been considerable progress, culminating in the publication of first neutrino mass results with the entire beamline operating [2]. In this paper, we document the current state of all completed beamline components (as of the first neutrino mass measurement campaign), demonstrate our ability to reliably and stably control them over long times, and present details on their respective commissioning campaigns

Evaluating workflow definition language revisions with graph-based tools

In industry, there are many workflow management systems (wfms) which have been incrementally developed over a long time. The workflow definition languages that come along with these wfms are mostly graph oriented. These incrementally developed definition languages sometimes lack important modeling constructs as well as a clear conceptual foundation. Any workflow definition language revision has to be evaluated against end user's acceptance before implementation in the respective wfms. In this paper, we report about an industrial application of graph-based techniques in the workflow domain. We present an evaluation environment which has been developed in a graph-based rapid prototyping approach. The evaluation environment comprises editing support for workflow definitions conforming to the language's revision. Furthermore, it provides a translator that maps definitions from the revised to the original language. Thus, the wfms can be used to enact definitions of the revised language without modifying its implementation

High-quality MgB2 nanocrystals synthesized by using modified amorphous nano-boron powders: Study of defect structures and superconductivity properties

Nano sized magnesium diboride (MgB2) samples were synthesized using various high-quality nano-B precursor powders. The microscopic defect structures of MgB2 samples were systematically investigated using X-ray powder diffraction, Raman, resistivity measurements and electron paramagnetic resonance spectroscopy. A significant deviation in the critical temperature Tc was observed due to defects and crystal distortion. The symmetry effect of the latter is also reflected on the vibrational modes in the Raman spectra. Scanning electron microscopy analysis demonstrate uniform and ultrafine morphology for the modified MgB2. Defect center in particular Mg vacancies influence the connectivity and the conductivity properties which are crucial for the superconductivity applications