E-J Characteristic of 2G YBCO Coated Conductor Tapes at Different Temperatures

AbstractThe E-J characteristics of High temperature superconducting (HTS) composite are not only fundamental to the understanding of flux dynamics and flux pinning but also the quench behaviour of HTS at an extended temperature range. The present work present the E-J characteristics of state-of-the-art 2G YBCO Tapes of SuperPowerTM measured at different temperatures between 40K and 80K. The results revealed a appreciable deviation from the power-law E-J characteristics, an established framework for 1G 2223 conductors. In contrast, the equivalent power exponent n was found to decrease with increasing current, resulting in a reduced rate for the non-linear increase of voltage at higher current. The softening of E-J characteristic remain unchanged as the temperature is lowered. Furthermore the power exponent n at the critical current appears to be constant increasing at lower temperatures. Analysis presented in the work shows that the collective pinning of vortex glass gives a satisfactory quantitative description of the E-J characteristics of 2G YBCO tapes. A constant collective pinning potential U/kBT ∼ 15 and vortex glass exponent μ ∼ 2 were found for temperatures between 45K and 80K

Quench characteristics of a Cu-Stabilized 2G HTS conductor

The prospect of medium/high field superconducting magnets using 2G HTS tapes is approaching to reality with continued enhancement in the performance of these conductors. Direct measurements of 1d adiabatic quench initiation and propagation of a Cu-stabilized 2G conductor have been carried out with spatial-temporal recording of temperature and voltage following the deposition of various local heat pulses to the conductor at different temperatures between 40K and 64K carrying different transport currents. It was found that the stabilizer-free 2G tape maintains the unique characteristics previously measured in non-stabilized tape of increasing MPZ with transport current and higher quench energy at lower temperatures. The minimum quench energy, minimum propagation zone (MPZ) length are determined as a function of temperature and transport current. The change in MPZ size is investigated with measured temperature dependent E-J characteristics. The results add more detail to help understand the unique characteristics of increasing MPZ with transport current and lower temperatures

Fertility in female survivors of hodgkin's lymphoma.

Currently, Hodgkin's lymphoma is one of the most curable types of cancer. Patients are often young and so the long-term morbidities of treatment have become of increasing concern. Among these, infertility is one of the most challenging consequences for patients in reproductive age. Premature ovarian failure in premenopausal women is a serious long-term sequel of the toxicity of chemotherapy. The main consequence of this syndrome is infertility, but women also present other symptoms related to estrogen deprivation. Different rates of impaired gonadal function are reported, depending on the patient's age, stage of disease, dose and intensity of chemotherapy and the use of radiation therapy. The most established strategy in female infertility is cryopreservation of embryos after in vitro fertilization. Additionally, the use of oral contraceptives or gonadotropin-releasing hormone analogs (GnRH-a) during treatment is under study. This review will provide a general overview of the main studies conducted to evaluate the infertility rate among female Hodgkin's lymphoma survivors and risk factors associated to treatment, different end-pointg definitions for evaluating fertility and also a brief description of the available strategies for fertility preservation

Flux pinning distribution and E-J characteristics of 2G YBCO Tapes

E-J characteristics of SuperPower YBCO 2G tapes have been measured in the temperature range 15K-80K. It was found that the E-J characteristics deviate significantly from the standard power-law behaviour with apparent power exponent decreasing continuously at high voltage with increasing current. The deviation of E-J characteristic from the standard power-law was found to be consistent with a Weibull distribution of critical current. The identical scaling of E-J characteristics above 40K suggests a common critical current distribution. At lower temperature the critical current distribution becomes narrower to give higher apparent power exponent at lower temperature. With the critical current distribution model it is shown that the dissipation can be correlated directly to the flux flow resistance of Bardeen. The distribution of the critical current can be associated with a distribution of pinning potential of collective pinning and the headline pinning range is obtained as function of temperatur

Transport IV characterisation of MgB2 conductor at a bend radius of 50mm

Performance of state of the art MgB2 multifilamentary conductor at a required bend radius is essential for many applications including but not limited to magnets and motors. The characterisation is generally done with benchmark transport Ic but further detail can be seen in IV characteristics which are undertaken in this paper. Two conductors with the same architecture but different diameters, 0.89 and 0.45 mm were measured from 32 K to 20 K in self-field in conditions of as received and deformed to a 50 mm bend diameter, corresponding to strains of 1.4 % and 0.7 % respectively. The qualifying 0.45mm conductor was further measured in background fields up to 3 T. The smaller diameter wire was found to have no signs of degradation of critical behaviour in Ic or IV characteristic

Quench characteristic and minimum quench energy of 2G YBCO tapes

Due to a much extended current sharing regime and to the power law like E-J characteristics instead of the critical state, the quench characteristics of high temperature superconductors (HTSs) potentially differs from LTS. The understanding of thermal stability is therefore of crucial importance to meet the performance requirements set up by applications. In this work the quench characteristic and MQE measurements were carried out on 2G YBCO tape in self-field and field (0.1 T) scenario, in a wide range of temperature (40-80 K), where the conductors have a modest power exponent n ~ 20-30. The study focuses in particular on high current in the vicinity of Ic (j = I/Ic ~ 1), where power law current sharing dominates. Instead of vanishing with (1 - j), as expected for the critical state, the measured MQE is much higher near Ic. The high MQE and the heat generation of a non-(1 - j) scaling were constantly found in the temperature range 40 K-80 K of measurements. Such an enhanced MQE in the high current regime could be significant for HTS applications and suggests the possibility of sufficient stability very close to Ic. We show that the results can be explained by approximating the non-linear current sharing power-law heat generation with temperature by an equivalent critical state at a higher current sharing temperature. While the power-law and critical state converge at low j regions, the non-linear temperature dependence of thermal properties needs to be considered due to elevated quench/current sharing temperatures

Temperature and background field dependence of a compact react and wind MgB2 solenoid coil

The manufacture of react and wind MgB2 coils with bend diameters suitable for compact applications, such as narrow bore magnets, or demonstrators, such as generators, remains a challenge due to the finite strain tolerance of the MgB2 filaments. One solution is to improve the conductor strain tolerance under bending by reducing the wire diameter and increasing the number of filaments. A 243-m single length of 36-filament, 0.55-mm-diameter conductor with 50-?m-thick s-glass insulation, manufactured by Hyper Tech, is continuously wound onto a 100-mm-inside-diameter, 100-mm-long, 770-turn, 5-layer solenoid coil. As a preliminary verification of short-length conductor properties, transport critical current was measured on samples as reeled. Using both dc and pulsed currents, the solenoid coil is characterized in a background field of up to 5 T, and from 4.2 K to Tc, in both liquid and vapor. Layer-by-layer instrumentation of the coil, together with short-length test data, enables voltage characteristics to be spatially determined. Dissipation in the coil was evenly distributed across all layers with a joint contact resistance of ~20 n?. With an inductance of 0.37 H, the coil achieved a magnetic field of 0.82 T at 22.5 K at 100 A, 415 A/mm2, with no background field, and 0.32 T in a background field of 5 T at 4.2 K. The injected current values correlated with short-length critical current to within 10%

Quench Property of Twisted-Pair MgB2_2 Superconducting Cables in Helium Gas

CERN's twisted-pair superconducting cable is a novel design which offers filament transposition, low cable inductance and is particularly suited for tape conductors such as 2G YBCO coated conductors, Ag-sheathed Bi2223 tapes and Ni/Monel-sheathed MgB2 tapes. A typical design of such twistedpair cables consists of multiple superconducting tapes intercalated with thin copper tapes as additional stabilizers. The copper tapes are typically not soldered to the superconducting tapes so that sufficient flexibility is retained for the twisting of the tape assembly. The electrical and thermal contacts between the copper and superconducting tapes are an important parameter for current sharing, cryogenic stability and quench propagation. Using an MgB2 twisted-pair cable assembly manufactured at CERN, we have carried out minimum quench energy (MQE) and propagation velocity (vp) measurements with point-like heat deposition localized within a tape. Furthermore, different contacts between the copper and superconductor around the hot spot have also been studied, including the co-twisted assembly in Kapton wrapping and locally separated tapes. The measurements have been performed in cooling helium gas at temperatures between 20 K and 35 K, with different current fractions with respect to the thermal runaway current. The results suggest a potential optimization strategy, compromising between: a higher stabilization with better contact between the copper and superconducting layers; and a faster propagation velocity and easier quench detection with a higher contact resistance

Quench property of twisted-pair MgB2 superconducting cables in helium gas

CERN's twisted-pair superconducting cable is a novel design which offers filament transposition, low cable inductance and is particularly suited for tape conductors such as 2G YBCO coated conductors, Ag-sheathed Bi2223 tapes and Ni/Monel-sheathed MgB2 tapes. A typical design of such twistedpair cables consists of multiple superconducting tapes intercalated with thin copper tapes as additional stabilizers. The copper tapes are typically not soldered to the superconducting tapes so that sufficient flexibility is retained for the twisting of the tape assembly. The electrical and thermal contacts between the copper and superconducting tapes are an important parameter for current sharing, cryogenic stability and quench propagation. Using an MgB2 twisted-pair cable assembly manufactured at CERN, we have carried out minimum quench energy (MQE) and propagation velocity (vp) measurements with point-like heat deposition localized within a tape. Furthermore, different contacts between the copper and superconductor around the hot spot have also been studied, including the co-twisted assembly in Kapton wrapping and locally separated tapes. The measurements have been performed in cooling helium gas at temperatures between 20 K and 35 K, with different current fractions with respect to the thermal runaway current. The results suggest a potential optimization strategy, compromising between: a higher stabilization with better contact between the copper and superconducting layers; and a faster propagation velocity and easier quench detection with a higher contact resistance