A $\hbox{Nb}_{3}\hbox{Sn}$ -Based, Model Superconducting Helical Undulator Fabricated Using a Wind and React Process
A model helical undulator 250 mm in length, with a period of 14 mm, was designed, fabricated and tested. The helical coil was wound with multifilamentary, internal-Sn type Nba3Sn strand. The 0.7 mm OD strand was insulated with S-glass, wound onto the former, and reacted, after which the coil underwent vacuum epoxy impregnation. The beam aperture was 7 mm, the winding bore diameter was 8 mm, and the OD of the complete winding was 18 mm. The helical poles were made from 1016 low carbon steel, and projected slightly above the coil pack, with an OD of 19.06 mm. The coil Ic and the magnetic field in the bore were measured at 4.2 K in a liquid helium bath. The bore field was also measured as a function of position along the length of the undulator.
A model superconducting helical undulator fabricated using a small filament, tube-type, multifilamentary Nb3Sn wire
A model helical undulator 250 mm in length, designed and fabricated with a period of 14 mm, was tested in a liquid helium bath. The helical coil was wound with a multifilamentary, tube-type Nb3Sn strand with 217 sub-elements. The coil Ic and the magnetic field in the bore were measured at 4.2 K in a liquid helium bath using a Hall probe. Ic was found to be 842 A, and the bore field reached the design specification of 0.8 T. The transverse bore field was also measured as a function of position along the length of the undulator axis and was seen to exhibit the expected sinusoidal behavior. The measured Ic was compared with that obtained from a crossing of a load line (determined from FEM modeling) with the Ic(B) curve of a short sample Nb3Sn strand. The coil exhibited the same critical current as the short sample.
Climatology of the cusp-related thermospheric mass density anomaly, as derived from CHAMP observations
We report on the thermospheric mass density anomaly in the vicinity of the ionospheric cusp. A systematic survey of the anomalies is presented, based on a statistical analysis of 4 years of data (2002–2005) obtained by the accelerometer onboard CHAMP. The anomalies are detected during all years and seasons in both hemispheres but with stronger signatures in the Northern Hemisphere. For the same geophysical conditions, solar flux and geomagnetic activity the anomalies in the north are larger by a factor of about 1.35. Over the course of the survey period the amplitude decreases by more than a factor of 5 while the level of solar flux reduces by a factor of 2. The anomaly strength also depends on the solar wind input. The merging electric field, E merg , is generally enhanced for about an hour before the anomaly detection. There is a quadratic response of the anomaly amplitude to E merg . For geophysical conditions of P10.7 E merg E merg , where the weight of E merg , in mV/m, is by about 50 times higher than that of the solar flux level. The solar zenith angle and the influence of particle precipitation are found to play a minor role as a controlling parameter of seasonal variation. The well-known annual variation of the thermospheric density with a minimum around June also influences the formation of the cusp anomalies. This leads to a clear hemispheric asymmetry with very weak anomalies in the south during June solstice, which is supposed to be a combined effect of the minimum in annual variation and the seasonal decrease of solar insolation in this region.