Measurements of crossed-field demagnetisation rate of trapped field magnets at high frequencies and below 77 K

Baškys, Algirdas; Patel, Anup; Glowacki, B.A.

doi:10.1088/1361-6668/aabf32

Cited by 31 publications

(27 citation statements)

References 15 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Once again, results show a significant reduction of the demagnetization effect when working with stacked tapes. This result is in qualitative agreement with previous experimental data obtained by measuring the trapped flux density by one or several Hall probes attached to the surface of the sample 63,64 . In this latter case, however, the signal is strongly dependent of the exact distance between the Hall sensor and the surface of the stacked tape.…”

Section: Resultssupporting

confidence: 92%

See 1 more Smart Citation

A simple torque magnetometer for magnetic moment measurement of large samples: Application to permanent magnets and bulk superconductors

Brialmont

Fagnard

Vanderbemden

2019

Review of Scientific Instruments

View full text Add to dashboard Cite

The development of large size magnetic materials requires non-destructive measurement techniques to characterize their magnetic moment. In this work we report the design and construction of a torque magnetometer able to accommodate sizable magnetic samples (> 1 cm 3) both at room and cryogenic temperature. This device has an intermediate sensitivity between miniature torque magnetometers designed to work at cryogenic temperature and industrial torquemeters poorly adapted to extreme conditions. We show that torque sensing in the range 10 −3-100 Nm can be achieved with piezoresistive metallic strain gages cemented on a cylindrical aluminum shaft with external temperature control. An absolute calibration of the device, carried out with a coil fed by a DC current, shows that magnetic moments down to 5 × 10 −3 Am 2 can be measured by this technique. The magnetometer is used to characterize a Nd-Fe-B permanent magnet and a permanently magnetized bulk, large grain superconductor at liquid nitrogen temperature (77 K). Results are in excellent agreement with data obtained with a flux extraction magnetometer for large samples. The device is able to measure magnetic moments in excess of 1.5 Am 2 , i.e. two orders of magnitude above the maximum magnetic moment of commercial magnetometers. The sample can be inserted in the air-gap of an electromagnet to measure the decrease of magnetic moment in the presence of a transverse applied field. The device was used to characterize the magnetic moment of 'quasi-bulk' superconductors made of stacked coated conductor tapes (12 mm width) in such 'crossed field' conditions.

show abstract

Section: Resultssupporting

confidence: 92%

“…As shown by recent work demonstrating the suitability of using stacked tapes in high power density electric motors, e.g. in the next generation of electric aircrafts, understanding their behavior under crossed fields is needed to assess their long time stability and the reliability of the device 63 .…”

Section: Resultsmentioning

confidence: 99%

A simple torque magnetometer for magnetic moment measurement of large samples: Application to permanent magnets and bulk superconductors

Brialmont

Fagnard

Vanderbemden

2019

Review of Scientific Instruments

View full text Add to dashboard Cite

show abstract

“…The demagnetization rate increases with the field ( figure 15). Rate per cycle at low frequencies depends on the frequency only slightly [26]. The reason is that the higher frequency of the applied field causes higher electric field, and hence the current density increases.…”

Section: G Cross-field Demagnetization: Measurements and Modellingmentioning

confidence: 98%

Cross-field demagnetization of stacks of tapes: 3D modelling and measurements

Kapolka¹,

Pardo

Grilli³

et al. 2019

Supercond. Sci. Technol.

View full text Add to dashboard Cite

Stacks of superconducting tapes can trap much higher magnetic fields than conventional magnets. This makes them very promising for motors and generators.However, ripple magnetic fields in these machines present a cross-field component that demagnetizes the stacks. At present, there is no quantitative agreement between measurements and modeling of cross-field demagnetization, mainly due to the need of a 3D model that takes the end effects and real micron-thick superconducting layer into account. This article presents 3D modeling and measurements of cross-field demagnetization in stacks of up to 5 tapes and initial magnetization modeling of stacks of up to 15 tapes. 3D modeling of the cross-field demagnetization explicitly shows that the critical current density, J c , in the direction perpendicular to the tape surface does not play a role in cross-field demagnetization. When taking the measured anisotropic magnetic field dependence of J c into account, 3D calculations agree with measurements with less than 4 % deviation, while the error of 2D modeling is much higher. Then, our 3D numerical methods can realistically predict cross-field demaga This article has been published in Supercond. Sci. Technol. with netization. Due to the force-free configuration of part of the current density, J, in the stack, better agreement with experiments will probably require measuring the J c anisotropy for the whole solid angle range, including J parallel to the magnetic field.the probe is at least 10 mV/T. Cross-field demagnetization consists on the following three main steps: magnetization by field cooling (FC) method, relaxation time and cross-field demagnetization. The detailed process is the following:• The sample is placed into the electromagnet at room temperature.• The electromagnet is ramped up to 1 T.• The sample is cooled down in liquid nitrogen bath at 77 K.• The electromagnet is ramped down with ramp rate 10 mT/s. 400 405 410 415 420 425 B t /B 0 [-] t [s] cal 50 mT cal 100 mT cal 150 mT cal 50 mT n(B,θ) cal 100 mT n(B,θ) cal 150 mT n(B,θ) (b) FIG. 19: (a) The n(B, θ) measured data on a 4 mm wide SuperOx tape, measured in Bratislava by the set-up in [46]. (b) The comparison of calculation with constant n=30 and n(B, θ) dependence, both cases use J c (B, θ) dependence. Using n(B, θ) slightly reduces the demagnetization rate for a few number of cycles, but later on it is increased slightly.

show abstract

“…This effect is more sensitive to the amplitude of the cross-field and only proportional to its frequency (constant for the same number of cycles). Therefore, it is expected that demagnetization increases more with a rising torque rather than with the speed of the machine [24]. Figure 11 shows the results of laboratory tests that used an actual rotating electric machine with a 9-layer insulated AMSC stack (<1 mm) fixed to the rotor surface, which is magnetized and rotated in a liquid nitrogen environment (77 K) at 10 Hz.…”

Section: Demagnetizationmentioning

confidence: 99%

Magnetization and Losses for an Improved Architecture of Trapped-Flux Superconducting Rotor

Climente-Alarcón

Smara

Patel

et al. 2020

Journal of Propulsion and Power

View full text Add to dashboard Cite

A hybrid electric configuration for aircraft propulsion yields several advantages, such as reducing the fuel consumption and takeoff distance, improving control, and decreasing emissions. For such a scenario to occur, advances designed to increase the power-to-weight ratio of actual electric motors must be developed. Superconducting technologies offer the prospect of achieving such performances but at a cost of increased design and construction complexities. In that sense, stacks of high temperature superconductors have proven to trap high-current vortexes that provide a source of magnetic flux density for torque production without the need of current leads or other equipment in the rotor. However, these macroscopic currents must be induced prior to operation and remain undisturbed by variations in the magnetic flux density of the airgap, such as the ones caused by heating and demagnetization. This work presents the results of numerical computations on a new rotor architecture designed to facilitate the magnetization of stacks from a superconducting stator and prevent their demagnetization during torque production. The machine performance is assessed, and the expected survivability of the trapped-flux in stacks is compared to laboratory measurements.

show abstract

Measurements of crossed-field demagnetisation rate of trapped field magnets at high frequencies and below 77 K

Cited by 31 publications

References 15 publications

A simple torque magnetometer for magnetic moment measurement of large samples: Application to permanent magnets and bulk superconductors

A simple torque magnetometer for magnetic moment measurement of large samples: Application to permanent magnets and bulk superconductors

Cross-field demagnetization of stacks of tapes: 3D modelling and measurements

Magnetization and Losses for an Improved Architecture of Trapped-Flux Superconducting Rotor

Contact Info

Product

Resources

About