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Since the initial identification of the iron-based superconductors (IBS) in 2008, numerous studies had focused on how to improve critical current density. However, the research of quench behaviors for iron-based multi-filamentary tapes was rarely reported. It is important to understand quench behaviors, and two main parameters should be examined carefully, i.e., normal zone propagation velocity (NZPV) and minimum quench energy (MQE). In this paper, a two-dimensional quench model integrating the stationary electrodynamics equations and heat conduction equation was proposed to study the quench propagation of iron-based Sr/Ba0.6K0.4Fe2As2 (Sr/Ba122) tape in different transport currents and temperatures. MQEs and NPZVs of IBS tape were calculated by the quench model, and the results were well complied with experimentally results which verified the correctness of the proposed quench model. In addition, since iron-based superconducting coils for high magnetic field application were operating in liquid helium mostly, an experiment was performed to study the quench behaviors of Ba122 tape in liquid helium, for the purpose of understanding the stability of the iron-based superconductor and designing quench protection systems of IBS coils reliably.

The local thermal disturbance will produce a joule heat. When the joule heat is larger than the minimum quench energy (MQE), it will lead to the phenomenon of a quench. The same problem exists in stacked superconducting tapes. In this article, the defects in REBCO tapes were created using the bending method. The voltage and temperature traces were measured during the quench process. The quench characteristics of the MQE and normal zone propagation velocity (NZPV) of the stacked REBCO tapes were investigated of different stacked REBCO tapes in the following configurations: two defects-free tapes; one defect-free tape and one tape with a defect; and both tapes with defects. The MQE of the stacked tapes with the defect is smaller than that of the tapes without defects, while the NZPV of the stacked tapes with the defect is larger than that of the tapes without defects.

In the present study, attempts have been made to evaluate the geotechnical characteristics of Quaternary sediments of the Nubra Valley located in high-altitude Ladakh Himalaya to demarcate the active sediment (soil) zones and their bearing on natural hazards susceptibility and mitigation measures. The experimental works have been carried out on collected sediment (soils) samples from different locations and depths to determine their grain-size-sensitive parameters and geotechnical responses. The results reveal that the majority of uniformly graded sediments (soils) of size 0.02–2.0 mm fall in wide range of values of shear strengths, cohesions (c) and angle of internal frictions, which may be due to distinct variations in their bulk and dry densities, void ratios, and liquid and plastic limits. In view of evaluated geotechnical parameters, the sediment sequences of the valley are classified in normal and active sediment zones. The sediment layers of active zone exhibit a high rate of reduction in shear strengths and cohesions in comparison with normal zone due to higher liquid and plastic limits of sediments subjected to temperature-sensitive freezing and thawing actions and may responsible for slope instabilities, differential settlements and mass flow hazards. Hence, such sediment layers require serious and careful investigations for safe settlements and mitigation measures of natural hazards.

Normal zone propagation velocity (NZPV) and minimum quench energy (MQE) are the important parameters for quench protection of superconducting magnets. In this research, a series of experiments were conducted on single-length conductor, small coils, and parallel double conductors made of YBCO and BSCCO high-temperature superconducting (HTS) tapes at the liquid nitrogen temperature, and their normal zone propagation velocities and minimum quench energies were tested and analyzed. The experimental results show that the NZPVs of HTS single-length tape, parallel double tapes, and coils are closely related to the critical current ratio i of HTS tapes. When i is in a certain range, the NZPV is approximately proportional to i, and similarly, MQE is inversely proportional to i.

Quench detection in a rare-earth barium copper oxide (REBCO) coil is difficult due to the slow normal zone propagation in it. To address this issue, we have proposed a quench detection method using a low temperature superconducting (LTS) wire as a quench detector. A demonstration experiment in our previous research using a REBCO tape showed that the quench detector was able to detect quench in the tape before it burned out. Therefore, to verify the applicability of this method to a real magnet system, we first numerically evaluated the quench detectability of Nb-Ti and Nb 3 Al detectors attached on stacked REBCO tapes at 4.2 K under magnetic fields up to 20 T assuming the coil excitation process. The results indicated that the detectors were not needed to be placed in each layer of the REBCO coil. Furthermore, we have conducted an experiment using a REBCO single pancake coil with the Nb-Ti quench detector at 4.2 K and self-field. As the results of the experiment, we demonstrated that one Nb-Ti detector was able to detect the quench in the REBCO coil even if there were at least three REBCO tapes and the polyimide tapes between the detector and the hot-spot in the REBCO coil.

The development of coils that can survive a quench is crucial for demonstrating the viability of MgB(2)-based main magnet coils used in MRI systems. Here we have studied the performance and quench properties of a large (outer diameter: 901 mm; winding pack: 44 mm thick × 50.6 mm high) conduction-cooled, react-and-wind (R&W), MgB(2) superconducting coil. Minimum quench energy (MQE) values were measured at several coil operating currents (I(op)), and distinguished from the minimum energy needed to generate a normal zone (MGE). During these measurements, normal zone propagation velocities (NZPV) were also determined using multiple voltage taps placed around the heater zone. The conduction cooled coil obtained a critical current (I(c)) of 186 A at 15 K. As the operating currents (I(op)) varied from 80 A to 175 A, MQE ranged from 152 J to 10 J, and NZPV increased from 1.3 to 5.5 cm/s. Two kinds of heater were involved in this study: (1) a localized heater (“test heater”) used to initiate the quench, and (2) a larger “protection heater” used to protect the coil by distributing the normal zone after a quench was detected. The protection heater was placed on the outside surface of the coil winding. The test heater was also placed on the outside surface of the coil at a small opening made in the protection heater. As part of this work, we also developed and tested an active protection scheme for the coil. Such active protection schemes are of great interest for MgB(2)-based MRIs because they permit exploitation of the relatively large MQE values of MgB(2) to enable the use of higher J(e) values which in turn lead to competitive MgB(2) MRI designs. Finally, the ability to use a quench detection voltage to fire a protection heater as part of an active protection scheme was also demonstrated.

Local recurrences in early gastric cancers (EGCs) after complete endoscopic submucosal dissection (ESD) remain problematic. Here, we investigated the spatially sequential molecular changes in various cancer-related proteins along the axis of the histologically clear but recurrent resection margins (TRM) to determine the appropriate tumor-free margin distance and potential molecular risk markers related to local recurrence. Five eligible patients with recurrent EGCs after complete ESD were selected from 548 EGC patients. The specimens, including recurrent resection margin axis, were divided into 5 zones. Digital spatial profiling assay was performed to quantify the expression level of 31 cancer-related proteins along each zone. p-Chk1 level was significantly reduced in TRM zone than non-recurrent resection margin. The expression of p44/42 ERK and p-Chk1 were significantly decreased along the lateral axis of the recurrent resection margin, with no significance toward the normal zone, which may suggest that p44/42 ERK and p-Chk1 may be involved in the recurrent side compared to non-recurrent margin. Although we could not evaluate more than 5.5 mm, the significant linear decreases in p44/42 ERK and p-Chk1 were maintained until at least 5.5 mm from the tumor zone in the TRM direction. We estimated the possible margin distance using scatterplots and linear regression analyses, which also showed the estimated distance more than 5.5 mm. In conclusion, the p-Chk1 and p44/42 ERK may be potential candidates of molecular risk markers that may be related to the local recurrence after complete ESD, and a tumor-free distance of 5.5 mm is not enough for safety margin.

The effect of local defects on the quench properties for YBCO tapes after applying bending strain was investigated at self-field in 77 K. The minimum quench energy (MQE) was related to the position of defects in the tape and the smallest MQE appears where the region of the defects existed in the position of the heater at the same transport current. The normal zone propagation velocity (NZPV) was related to the size and quantity of the regions of defects. The more defects were in the tape, the faster the normal-zone propagation velocity.

著者の誤記: Inatani, Yoshihiro, Accepted: 2019-01-14, 資料番号: SA1180364000

Based on a fully two-dimensional (2D) electrothermal model, the quench propagation characteristics of short superconducting YBa2Cu3O7-x conductors (AMSC and SuperPower), including the minimum quench energy (MQE), normal zone propagation velocity (NZPV) and hot spot temperature rising rate, are studied by numerical simulations in this paper. It is found that different heater configurations, such as the size of heater and the duration of heat pulse, can result variations of the MQEs and NZPVs. During the quench propagation processes, the NZPV and the normal zone length (LNZ), when viewed as functions of the hot spot temperature Tpeak, i.e., NZPV(Tpeak) and LNZ(Tpeak), are not sensitive to the heater configurations for relatively higher operating temperature from 50 K – 70 K. For both AMSC and SuperPower's YBCO conductor, the simulation results show that the hot spot temperature rising rate dTpeak/dt, as a nearly-linear function of Tpeak, is almost not affected by heater configurations for a given fixed operating temperature in the regime 30 – 70 K. For a fixed operating temperature in the regime 30 – 50 K, the temperature rising rate of SuperPower's conductor can reach 1000 K/s ~ 6000 K/s as Tpeak rising from ~110 K to 300 K, which makes it challenging to experimentally determine the NZPV prior the moment Tpeak reaches the temperature limit 300 K. The relations LNZ(Tpeak) obtained for SuperPower's conductor can provide information for the selection of reference voltage employed to determine the NZPV.

Copper-stabilized second generation high-temperature superconductor (HTS) coated conductors were modified to enhance their normal zone propagation velocity (NZPV). Experimental results, supported by numerical simulations, indicate that adding copper on the substrate side instead of adding it on the HTS side increases the NZPV by a factor of 2–3. Furthermore, a novel tape architecture, called hybrid-current flow diverter (CFD), was investigated. This hybrid-CFD tape was designed with the goal of having a very long current transfer length, which is the key to enhance the NZPV. Results show that it is possible to fabricate an HTS tape with double stabilizer thickness in comparison to a bare tape, while accelerating the NZPV by a factor of three. With the same approach, a ten-fold increase of the NZPV can be expected for a tape with a 40 µm thick copper-stabilizer.

For practical application, stability investigations of Sr 0.6 K 0.4 Fe 2 As 2 conductors are of great importance. In this paper, quench development and propagation in Ag sheath are experimentally and numerically investigated. Measurements are performed as a function of transport current for several operating temperatures between 19 and 35 K. This work focuses on the evaluation of quench development and the estimation of normal zone propagation velocity (NZPV) and minimum quench energy (MQE). The experimentally obtained temperature dependence of NZPV is compared with a simplified adiabatic model. In addition, the NZPV and the MQE of the sample are compared with those of a low-temperature superconductor (LTS) and a high-temperature superconductor (HTS). According to the results, the basic quench characteristics fit between those of LTS and HTS materials.

In applications, superconducting wires may carry AC or DC transport current. Thus, it is important to understand the behavior of normal zone propagation in conductors and magnets under different current conditions in order to develop an effective quench protection system. In this paper, quench behavior of Ag sheathed Sr 0.6 K 0.4 Fe 2 As 2 (Sr-122 in the family of iron-based superconductor) tapes with AC and DC transport current is reported. The measurements are performed as a function of different temperature (20 K–30 K), varying transport current and operating frequency (50 Hz–250 Hz). The focus of the research is the minimum quench energy (MQE), the normal zone propagation velocity (NZPV) and the comparison of the related results with AC and DC transport current.

In this paper, normal zone in a REBCO single-pancake coil induced by quenches in a low-temperature superconducting outsert coil is investigated in both experimental and numerical methods to discuss the quench protection of REBCO coils. The normal zone is experimentally clarified by measuring a partial voltage in the REBCO coil at temperatures from 30 K to 50 K during quenches of the outsert coil charging 5 T. Using practical fittings for the physical properties of the components of the REBCO coil in ranges of 0-5 T and 10-77 K, the numerical results have good agreement with the experimental results. The simulation reveals the heating distribution with initial temperatures from 10 K to 65 K, which indicates that the maximum temperature in a hot spot becomes higher for the lower initial temperature. Unexpectedly, the temperature distribution becomes rather homogeneous with an initial temperature of 65 K. It suggests that the hot spot at higher temperature has a lower risk of burning out. Finally, possible coil protections are discussed as the operation at the high temperature or the quench heater method to keep the REBCO coil at high temperature when a hot spot appears.