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[en] We are developing ultra-high energy resolution gamma-ray detectors based on superconducting transition edge sensors (TESs) for nuclear non-proliferation and fundamental science applications. They use bulk tin absorbers attached to molybdenum-copper multilayer TESs, and have achieved an energy resolution between 50 and 90 eV FWHM for gamma-ray energies below 122 keV. For increased user-friendliness, we have built a cryostat that attains the required detector operating temperature of 0.1 K at the push of a button without the use of cryogenic liquids. It uses a two-stage mechanical pulse tube refrigerator for precooling to ∼3 K, and a two-stage adiabatic demagnetization refrigerator for cooling to the base temperature. The cryostat is fully automated, attains a base temperature below 30 mK without the use of cryogenic liquids, and has a hold time of ∼2 days at 0.1 K between 1-hour demagnetization cycles. Here we discuss the performance of the cryostat for operation in a Gamma-spectrometer with 112-pixel arrays of superconducting TES detectors
[en] Adiabatic demagnetization refrigerators have been built and installed in small portable liquid helium cryostats to test the feasibility of this method of cooling infrared bolometric detectors to temperatures below 0.3 K. Performance has been achieved which suggests that bolometer temperatures of 0.2 K can be maintained for periods of approximately 60 hours. Applications to sensitive infrared detection from ground-based telescopes and space satellites are discussed. Design data are given which permit the evaluation of refrigerator performance for a variety of design parameters
[en] Complete text of publication follows. The Wai'anae Volcano is the older of two shield volcanoes that make up the island of O'ahu. Previous age determinations suggest that the subaerial portion of the edifice erupted between approximately 3.7 and 2.7 Ma. The eroded Wai'anae Volcano had a well-developed caldera centered near the back of its two most prominent valleys, and two major rift zones: a prominent north-west rift zone, well defined by a complex of sub-parallel dikes trending approximately N52W, and a more diffuse south rift zone, trending between S20W to due south. In order to investigate the volcanic evolution, the plumbing and the triggering mechanisms of the catastrophic mass wasting occurred in the volcano we have undertaken a paleomagnetic and AMS study of 7 dikes from the volcano. We drilled the dikes paying special attention to the chilled margins were we recovered a minimum of 8 and up to 23 samples per margin. The width of the dikes ranges between 0.5 to 4 m. In terms of the paleomagnetic results at least 20 samples per intrusive were stepwise demagnetized by a.f. from 5 to 100mT. Companion specimens from the same core were demagnetized at 15 temperature steps. In both cases demagnetization diagrams obtained with each technique showed a stable Characteristic direction of remanence (ChRM) determined with no ambiguity. The ChRM was calculated using principal component analysis for the demagnetization diagrams with a well-defined component trending to the origin. In addition, low field susceptibility vs temperature (k-T) and SIRM experiments were able to identify magnetite (575 degrees C) and a low temperature mineral phase at about 250-300 degrees C which probably reflects the presence of titanomagnetite. The determined directions of the intrusives resulted in normal and reversed polarities indicating that such dikes were emplaced at different periods of time covering a gap of 350 kyrs. Magnetic fabric studies of the dikes along a NW-SE section across the present southwestern part of the Waianae volcano have been conducted. The flow direction was studied using the imbrication angle between the dike walls and the magnetic foliation (e.g. Geoffroy et al., 2002). At the dike scale, the magnetic zone axis, which underlines the intersection of the magnetic foliation from the two borders of the dike (i.e. a direction perpendicular to flow), has yielded a precise orientation in three of the sites studied. The flow direction has been obtained in the seven studied dikes. For the majority of the cases, the maximum axis K1 appears to be perpendicular to the flow direction and in some cases with a partial axes permutation with respect to the intermediate axis K2 or even with respect to the minimum axis K3. In addition, in one of the sites studied, the minimum axis K3 is very close to the flow direction. In all the cases, the magma flowed along a direction with a moderate plunge. For six of the dikes, the interpreted flow was from the internal part of the volcano towards the volcano border and corresponds probably to the inflation phase of the volcano. In two cases (dikes located on the northwestern side of the volcano), the flow is slightly downwards, possibly related to the distal extension due to inflation of the central part of the volcano. The seventh dike is located closer to center of the volcano and is characterized by a slightly different orientation with respect to the other six dikes, and also revealed a downward flow that could correspond to another magma pulse that resulted from a flow-back during distension due to the collapsing of the Waianae volcano.
[en] Highlights: • We have fabricated superconducting shifted strip arrays (SSAs) up to 4 layers. • Flux penetrations into SSAs are observed by using magneto-optical imaging. • Linear flux avalanches are observed in a wider range of overlap in the 4-layer SSAs than in the 2- or 3-layer SSAs. - Abstract: We have fabricated multi-layer superconducting shifted strip arrays (SSAs) of Nb up to 4 layers and systematically studied the vortex penetrations into these structures. We observed the vortex penetration as a function of the number of layers and the ratio of overlap between neighboring layers by using magneto-optical (MO) imaging. In the case of 2- and 3-layer SSAs, spot-like avalanches occur when the overlap is small, while linear avalanches occur when the overlap is large, consistent with our previous reports. In the 4-layer SSAs, the smallest limit of the overlap between the neighboring layers for the linear avalanche is lower. Flux penetrations parallel to the strip which were observed in the 3-layer SSA were also observed in the 4-layer SSAs with smaller ratio of overlap. Larger demagnetization effects in the middle two layers in 4-layer SSA help to make avalanches larger and more extended.
[en] The inner demagnetization factor Ni of polymer-bonded soft magnetic composites (PBSMC) varying in filler material and filler content C was measured, using a computer-controlled measurement system. For all materials the results show a decrease from an inner demagnetization factor close to the demagnetization factor of a single particle to Ni∼0 on increasing the magnetic content C. Measurement data of a selected material were compared with a model derived from an effective medium theory using the composite's effective susceptibility and show superb accordance
[en] Complete text of publication follows. Experimental data indicate that the elegant multiple-specimen technique of Dekkers and Boehnel (2006) tends to systematically overestimate paleointensity for intermediate pseudo-single domain to multi-domain (MD) particle sizes. By analyzing the relevant properties of thermoremanence acquisition, it is possible to design an extended version of the multiple-specimen technique, which is more reliable in the critical domain state range. The improved measurement scheme regards for the fraction of demagnetized remanence, estimates the MD contribution, and corrects MD overestimates. Furthermore, it removes viscous overprints, and uses an alteration check for determining error bars on the final paleointensity result. Experimental results on synthetic samples show the effectiveness of the improved technique.
[en] The intrinsic angular-dependent hysteresis loops in perpendicular recording media have been measured by iteratively correcting the demagnetization effect in order to maintain the internal total field at a fixed angle. Both the angle and the magnitude of the applied field are adjusted simultaneously to compensate for the demagnetization field change. Significant differences have been observed between the conventional angular-dependent hysteresis loop with a constant applied field angle and the intrinsic angular-dependent hysteresis loop with a fixed total field angle. Without demagnetization corrections, the field range in which irreversible magnetization occurs changes as a function of the field angle, whereas it remains constant if proper demagnetization field corrections are applied
[en] Complete text of publication follows. We have automated a 2G Enterprises superconducting magnetometer to measure and demagnetize standard paleomagnetic samples. After loading a sample and setting the desired demagnetization steps, the operation is performed automatically. All three axes are measured in both directions multiple times. A single solenoid performs three-axis static demagnetization by rotating the specimen 120 degrees about an oblique axis to each orthogonal position, eliminating potential errors resulting from differences between the fields generated when using two orthogonal coils with different geometry. Each sample is handled only once, minimizing angular alignment errors. For natural remament magnetizations greater than 10-3 A/m, high quality AF demagnetization results can be obtained. 10-to-20-step demagnetization takes between 20 and 70 minutes, depending on the sample's moment. 160-step demagnetizations have been run overnight. This automated system is complemented by a custom program that controls all system elements. In addition, the controlling software includes tools for 1) sample parameter input and instant results recalculation upon parameter adjustment, 2) real time results visualization, 3) integrated sun compass correction software, and 4) several demagnetization routines optimized for different magnitudes of magnetization. The software uses a very general and flexible, XML-based file structure capable of storing an entire field study in one hierarchical file format, with levels for locality, site, sample, and demagnetization step. It serves as an electronic field notebook for recording many more parameters and comments than those strictly needed to measure the direction of the core. For more information, please see http://es.ucsc.edu/~emorris/cryoslug.