Visualization of the Field Penetration at the Shielding Current Break and Its Restoration in the Pulse Magnetized YBCO Ring

Brazhnik, P. A.; Krasnoperov, E. P.

doi:10.1007/s10948-021-05826-w

Cited by 6 publications

(7 citation statements)

References 13 publications

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“…In Figure 7 we plot the time dependence of the trapped field in the ring bulk at 73 K after applying magnetizing pulses with different rise times. When the IGBT was in the default state only a small amount of flux could penetrate into the sample for an applied field of 2.40 T. More flux could be forced to penetrate into the sample by increasing the applied field, but this would also increase the amount of heating and might trigger a flux jump, leading to a lower final trapped field (and possibly a negative trapped field if the circulating magnetizing current is broken) [18,19]. As shown in Figure 7, when the IGBT was in the default state for an applied field of 2.44 T, the peak field in the bore of the sample was 2.23 T, which is very close to the applied field, suggesting there was very little shielding current in the bulk superconducting ring.…”

Section: Resultsmentioning

confidence: 99%

Waveform Control Pulsed Field Magnetization of RE-Ba-Cu-O Bulk Superconducting Rings

Tsui¹,

Moseley

Dennis³

et al. 2022

IEEE Trans. Appl. Supercond.

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One of the potential applications of ring-shaped, single grain RE-Ba-Cu-O bulk superconductors is in desktop magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) systems as an alternative to conventional permanent magnets. The higher magnetic field available from magnetized bulk superconductors could significantly improve the performance of such systems, as well as reduce their size and increase portability. The pulsed field magnetization (PFM) method provides a fast, compact and cost-effective method for magnetizing these materials as trapped field magnets. However, bulk superconducting rings are very susceptible to thermomagnetic instabilities during the PFM process, and thus, to date, the reported trapped fields in ring bulks magnetized by PFM are less than 0.35 T at the centre of single rings.In this work, we demonstrate that the trapped field in a superconducting ring bulk can be enhanced significantly by optimizing the waveform of the magnetizing pulse used in the PFM method. This optimization can be achieved easily by using an Insulated Gate Bipolar Transistor as a fast-switching device with a controllable switching frequency in the pulse-generating electric circuit. Our findings represent a key step forward in utilizing bulk, singlegrain superconducting rings magnetized by PFM in portable magnet systems.

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Section: Resultsmentioning

confidence: 99%

Waveform Control Pulsed Field Magnetization of RE-Ba-Cu-O Bulk Superconducting Rings

Tsui¹,

Moseley

Dennis³

et al. 2022

IEEE Trans. Appl. Supercond.

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“…For the 2.19 T applied field, the field at the inner surface then rapidly increases to 2.5 T at a time t = 37.5 ms. The measured central field at this time exceeds the applied field, indicating that the circulating supercurrent has been broken within the ring [47], causing the ring essentially to act as a magnetic lens for the applied field [48,49]. As the flux density measured at H1 has not similarly increased, the flux penetration has occurred elsewhere within the ring due to the non-uniformity of the critical current density throughout the sample [50]thus the probed axis is not likely to be the weakest region of the ring [51].…”

Section: Measuring Flux Propagation Into a Bulk Superconducting Ring ...mentioning

confidence: 90%

Dynamics of magnetic flux propagation in bulk, single grain superconducting rings during pulsed field magnetisation

Beck

Tsui

Shi

et al. 2022

Supercond. Sci. Technol.

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When used as trapped field magnets (TFMs), single grain, bulk high-temperature superconducting (HTS) rings are promising candidates for the generation of strong, uniform magnetic fields for nuclear magnetic resonance (NMR). The pulsed field magnetisation (PFM) technique provides a low cost, compact and portable method to magnetise these samples as TFMs; however it has proven difficult to achieve high trapped fields in HTS rings using PFM. To date, a record field of only 0.60 T has been achieved for rings magnetised by single-pulse PFM – compared with over 4 T for disc-shaped HTS – and the reasons for this discrepancy are poorly understood. In this work, we use the finite element method (FEM) to model the propagation of magnetic flux into HTS rings under quasi-static zero field cooled (ZFC) magnetisation and PFM, and validate the results analytically and experimentally. Magnetic flux is found to penetrate finite HTS rings from both the inner and outer surfaces, inducing a negative field at the inner face of the ring. This field is reversed as the applied field increases past the point of full penetration, locally dissipating magnetic energy and heating the sample. HTS rings are therefore more susceptible to local instabilities that severely limit their ability to trap a useful magnetic field. Consequently, thermomagnetic stability of HTS rings during single-pulse PFM can only be ensured by taking careful consideration about reducing flux movement through the bulk around the point at which the field is reversed. This may require more advanced PFM techniques like waveform control or multi-pulse stepwise-cooling to reduce local heating and increase the trapped field.

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“…Applied fields higher than 3 T triggered large flux jumps resulting in a small negative trapped field. This is likely due to breaking of the circulating supercurrent because of the large heating generated due to flux jumps [12]. For disc bulks, flux jumps during PFM can greatly enhance the trapped field and magnetization efficiency as flux jumps could lead to magnetic flux suddenly penetrating into the centre of the disc bulks [21].…”

Section: A Single-pulse Pfm Measurementsmentioning

confidence: 99%

“…The heating problem is worse in the case of bulk superconducting rings during PFM because the magnetic flux penetrates from both the inner and outer edges of the sample [9], [10]. This can result in significant heating [11], causing the magnetization current to be disrupted and the trapped field to reduce significantly [12], [13]. As a result, it has been very challenging to magnetize bulk superconducting rings with high trapped fields.…”

Section: Introductionmentioning

confidence: 99%

Trapped Fields >1 T in a Bulk Superconducting Ring by Pulsed Field Magnetization

Tsui¹,

Moseley

Dennis³

et al. 2022

IEEE Trans. Appl. Supercond.

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One potential application of magnetized RE-Ba-Cu-O (where RE = rare earth or Y) bulk superconductors is as a highfield 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.

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Visualization of the Field Penetration at the Shielding Current Break and Its Restoration in the Pulse Magnetized YBCO Ring

Cited by 6 publications

References 13 publications

Waveform Control Pulsed Field Magnetization of RE-Ba-Cu-O Bulk Superconducting Rings

Waveform Control Pulsed Field Magnetization of RE-Ba-Cu-O Bulk Superconducting Rings

Dynamics of magnetic flux propagation in bulk, single grain superconducting rings during pulsed field magnetisation

Trapped Fields >1 T in a Bulk Superconducting Ring by Pulsed Field Magnetization

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