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One potential application of magnetized RE-Ba-Cu-O (where RE = rare earth or Y) bulk superconductors is as a high-field alternative to conventional permanent magnets in desktop NMR and MRI systems. Pulsed field magnetization (PFM) is one of the most promising practical methods of magnetizing such bulks. However, the trapped fields obtained by PFM are much lower than those obtained using quasi-static methods like field-cooling magnetization (FCM) due to heating during PFM. Furthermore, bulk superconducting rings have proved more difficult to magnetize via PFM than discs. The reported trapped fields in single bulk superconducting rings magnetized by PFM are less than 0.35 T at the centre of the bore due to thermomagnetic instabilities. In this work, systematic PFM measurements on a bulk Gd-Ba-Cu-O ring were carried out and a trapped field of 1.3 T at 55 K was achieved using a multi-pulse, stepwise cooling (MPSC) method. In the MPSC method, a sequence of pulsed fields is used to magnetize the ring bulk. The pulsed field is increased in small increments and the sample temperature is decreased sequentially. Consequently, as some field is already trapped after the first pulse, the motion of the flux for subsequent pulses will be reduced, leading to less heat generated in the bulk sample. This greatly improves the thermomagnetic stability of the PFM process, enabling larger trapped fields.

Bulk high-temperature superconducting materials can trap magnetic fields up to an order of magnitude larger than conventional permanent magnets. Recent advances in pulsed field magnetization (PFM) techniques now provide a fast and cost-effective method to magnetize bulk superconductors to fields of up to 5 T. We have developed a portable, desktop bulk high-temperature superconducting magnet system by combining advanced PFM techniques with state-of-the-art cryocooler technology and single-grain, RE-Ba-Cu-O [(RE)BCO, where RE is a rare-earth element or yttrium] bulk superconducting materials. The base temperature of the system is 41 K and it takes about one hour for the system to cool down to 50 K from room temperature. A capacitor bank, combined with easily-interchangeable, solenoid- or split-type copper magnetizing coils and an insulated bipolar gate transistor acting as a high-speed switch, allows magnetic pulses to be generated with different pulse profiles. The system is capable of trapping magnetic fields of up to ~3 T. In this work, we report the results of the magnetization of a range of single-grain Y-Ba-Cu-O (YBCO), Eu-Ba-Cu-O (EuBCO) and Gd-Ba-Cu-O (GdBCO), bulk superconducting discs using this system. A higher trapped field was recorded using a split coil incorporating iron yokes at temperatures of 65 K and above, whereas at lower temperatures, a higher trapped field was obtained using the solenoid coil. The GdBCO sample achieved the highest trapped field for both single-pulse (SP) and two-stage-multi-pulse (TSMP) methods using the solenoid coil. Maximum trapped fields of 2.26 T at 55 K and 2.85 T at 49 K were recorded at the centre of the top surface of the GdBCO sample for the SP and TSMP methods, respectively. The PFM process is substantially an adiabatic process so, therefore, the thermal contact between the sample and sample holder is of critical importance for cooling the bulk sample during application of the pulse. The design of the sample holder can be modified easily to enhance the thermal stability of the sample in order to achieve a higher trapped field.

Funder: University of Cambridge; doi: http://dx.doi.org/10.13039/501100000735, Bulk superconductors can act as trapped-field magnets with the potential to be used for many applications such as portable medical magnet systems and rotating machines. Maximising the trapped field, particularly for practical magnetisation techniques such as pulsed field magnetisation (PFM), still remains a challenge. PFM is a dynamic process in which the magnetic field is driven into a superconducting bulk over milliseconds. This flux motion causes heating and a complex interplay between the magnetic and thermal properties. In this work, the local flux density during PFM in a MgB2 bulk superconductor has been studied. We find that improving the cooling architecture increases the flux trapping capabilities and alters the flux motion during PFM. These improvements lead to the largest trapped field (0.95 T) for a single MgB2 bulk sample magnetised by a solenoidal pulsed field magnet. The findings illustrate the fundamental role bulk cooling plays during PFM.

Objective To describe the demographic characteristics, clinical features, functional status and quality of life of elderly-onset (EORA) and young-onset (YORA) rheumatoid arthritis (RA) patients in an Asian cohort. Methods We studied all RA patients in our prospective disease registry, utilizing baseline data. EORA was defined as disease onset at 60 years or older. We collected data from January 2001 to December 2012. Results There were 1206 patients in our cohort, of which 178 (14.8%) had EORA, with a mean age of onset of 66.7 ± 5.6 years. There were more males in the EORA than YORA group (23.0% vs. 14.7%, P = 0.005). EORA patients were diagnosed sooner after symptom onset and had a higher number of comorbidities (median 2 [inter-quartile range 1–3] vs. 1 (0–2), P < 0.001). They were less likely to be rheumatoid factor positive, had higher erythrocyte sedimentation rate values and lower hemoglobin concentrations. There was no significant difference in joint counts, Disease Activity Score of 28 joints activity score and prevalence of radiographic erosions. Though EORA patients had worse Health Assessment Questionnaire scores and poorer functional status than YORA ones, they had lower pain scores and higher scores in the general health and mental component summary of the Short Form-36. EORA patients received significantly lower numbers of disease-modifying anti-rheumatic drugs. Conclusions EORA and YORA patients had different demographic characteristics. Although they had similar disease activities, EORA patients received less intensive treatment. EORA patients had a higher number of RA-related co-morbidities and poorer physical functioning but they coped better emotionally and mentally.