Flux Pinning Force Density Research Articles

Enhanced trapped magnetic field in bulk (Gd, Y, Er) Ba2Cu3O7-y via varied liquid sources in top-seeded infiltration growth process

The practical applications of the bulk superconductors are determined by the trapped field (TF) and its overall performance. This study aims to demonstrate the effect of various compositions of liquid sources on the trapped field performance of bulk superconductors fabricated using the Top-Seeded Infiltration Growth process (TSIG) in air. We utilized a combination of different liquid sources, Ba3Cu5O8, Yb2O3: BaCuO2: CuO (1:10:6) and ErBa2Cu3Oy + Ba3Cu5O8 (1:1) to fabricate the ternary bulk (Gd, Y, Er) Ba2Cu3O7-y (Gd, Y, Er)-123. The use of these liquid sources demonstrated a pivotal role in fabricating single-domain bulks, showcasing significant variation in the trapped field performance. Specifically, the bulk fabricated using ErBa2Cu3Oy + Ba3Cu5O8 (1:1) as a liquid source exhibited the best-trapped field performance, showcasing an improvement of 42.92 % compared to the bulk obtained using conventional Ba3Cu5O8 as the liquid source. An enhancement in the critical current density below 77 K was observed in the bulk material produced utilizing Ba3Cu5O8 as the liquid source, with a Jc (3T, 50 K) value reaching 244 kA/cm2. The flux pinning force density (Fp) was analyzed for all samples to understand the pinning mechanisms in ternary (Gd, Y, Er)-123 bulk materials. Furthermore, the maximum trapped field for a 30 mm bulk sample fabricated using a mixture of ErBa2Cu3Oy + Ba3Cu5O8 (1:1) was measured at 0.336T. These results emphasize the potential for enhancing or controlling the trapped field performance of the TSIG-processed RE-123 bulks by optimizing the liquid source according to the intended applications of the bulk.

Enhanced performance of GdBCO bulk superconductors by doping a new kind of YGdBa4CuNbO y nanoparticles

In this work, a new kind of YGdBa4CuNbO y (YGdNb-11411) nano-particles was designed and sintered using a solid-state reaction method, whereas their impact on the performance of GdBCO bulks was investigated for the first time. From the acquired x-ray diffraction data and scanning electron microscopy imaging results, it was proved that the YGdNb-11411 particles were of excellent chemical stability and did not react with other phases during the crystal growth process. The YGdNb-11411 particles ranged from 80 to 130 nm and they were uniformly distributed in the well-textured GdBCO bulk superconductors. The maximum critical current density (J c-max) of the samples was enhanced from 3.48 × 104 A cm−2 to 8.63 × 104 A cm−2 (77 K) in the self-field as the doping amount increased from 0 wt% to 7 wt%. In addition, the GdBCO sample with YGdNb-11411 particles also showed an enhanced flux pinning force density and relatively high J c around the magnetic flux density range of 1 T–2 T (77 K). These results clearly indicated that the YGdNb-11411 particles could effectively enhance the properties of the GdBCO bulk superconductors.

Thermal-driven gigantic enhancement in critical current density of high-entropy alloy superconductors

The high-entropy alloy (HEA) superconductor, Ta1/6Nb2/6Hf1/6Zr1/6Ti1/6 (Ta–Nb–Hf–Zr–Ti), is systematically studied to examine changes in superconducting critical properties, critical temperature (Tc), critical current density (Jc), and upper critical field (Hc2), concerning thermal treatment conditions. Annealing condition affects Jc more significantly than Tc and Hc2, with a large improvement of flux pinning force density (Fp). The Jc of bare sample is reduced to 10 A cm–2 at an applied magnetic field of approximately 1.5 T, whereas the sample annealed at 550 °C for 12 h exhibits Jc > 100 kA cm–2 up to around 4 T. Furthermore, the Vickers hardness (HVIT) of the Ta–Nb–Hf–Zr–Ti HEA superconductor notably increases from ∼384 to 528 HVIT following a 24-h annealing at 500 °C. These results demonstrate that thermal annealing is a powerful process to optimize both the superconducting and mechanical properties of high-entropy alloy superconductors.

Effects of irradiation on superconducting properties of small-grained MgB2 thin films

We investigate the effect of ion irradiation on MgB2 thin films with small grains of approximately 122 nm and 140 nm. The flux pinning by grain boundaries is insignificant in the pristine MgB2 films due to good inter-grain connectivity, but is significantly improved after 120-keV Mn–ion irradiation. The scaling behavior of the flux pinning force density for the ion-irradiated MgB2 thin films with nanoscale grains demonstrates the predominance of pinning by grain boundaries, in contrast to the single-crystalline MgB2 films where normal point pinning was dominant after low-energy ion irradiation. These results suggest that irradiation-induced defects can accumulate near the grain boundaries in metallic MgB2 superconductors.

Effect of nano ZrO2 addition on the properties of Ca0.86Sr0.14CuO2 added Bi 2223 composites

Effect of introducing nano ZrO2 particles into (Ca,Sr)CuO2 added Bi 2223 superconductor composites is studied. Microstructures revealed that 20 mol. % (Ca,Sr)CuO2 phase added to Bi 2223 formed as micron sized particles among the Bi 2223 platelet shaped grains. Distribution of (Ca,Sr)CuO2 in Bi 2223 has enhanced the critical current density (Jc) and flux pinning force density (Fp ) substantially to fields up to 9 T at 20 K. Introduction of nano ZrO2 into the composite reacted with (Ca,Sr)CuO2 particles and formed additional secondary phases of increasing amount with a rise in ZrO2 content. This resulted in lowering of Jc(0) due to a gradual reduction in the fraction of superconducting phases, but retained the enhanced field range in which flux pinning was achieved. At 10 wt.% addition of ZrO2, Bi 2223 phase was suppressed, and Bi 2212 phase was promoted. Scaling behaviour of pinning force density has shown the dominant mechanism at low fields to be normal surface pinning due to interfacial defects. The fact that (Ca,Sr)CuO2 distributes itself as fine spherical particles in Bi 2223, without causing degradation of the superconducting matrix material, is of significance and opens up a scope to optimize the microstructures further for enhancement of flux pinning.

Effects of Sn-ion irradiation on local structure and flux pinning properties of MgB2 thin films

We studied the effects of tin (Sn) ion irradiation on the local structure and flux pinning properties of 412-nm-thick MgB2 thin films. Ions with 2 MeV incident energy were irradiated onto MgB2 thin films at room temperature and various dose levels from 2 × 1012 to 7 × 1013 atoms/cm2. X-ray diffraction and extended X-ray absorption fine-structure results confirmed extended average bond lengths and increased mean-square relative displacement that correlated with crystalline disorder serving as artificial pinning centers induced by ion irradiation. While the superconducting transition temperature (Tc) exhibited a decreasing trend, the magnetization Jc (H) of the irradiated films measured at both 5 K and 20 K were remarkably enhanced compared to that of pristine films at high applied magnetic fields. The decreases in exponent β from 1.1 and 1.13 to 0.69 and 0.62 after irradiation at 5 K and 20 K, respectively, as the dose increased to 5 × 1013 atoms/cm2 indicates a shift in the pinning mechanism from weak collective pinning to strong plastic pinning according to collective pinning theory. In addition, the scaling behavior of the flux pinning force density (Fp) in the irradiated MgB2 films showed a crossover from surface pinning to normal point pinning. These results suggest that intermediate-energy irradiation by heavy ions such as Sn generates effective pinning sources for improving Jc(H) in MgB2 superconductors.

Enhanced flux pinning by magnetic CrB2 nanoparticle in MgB2 superconductor

Different from the non-magnetic pinning centers, the magnetic pinning centers have stronger flux pinning force due to the direct magnetic interaction between the magnetic pinning centers and the magnetic vortices, thus have been widely used to enhance the critical current density of various superconductors. In this article, nanoparticles of antiferromagnet CrB2 were introduced as magnetic pinning center to improve the flux pinning force density (Fp), irreversible field (Hirr), and critical current density (Jc) of MgB2. Compared to the pristine sample, the CrB2 doped MgB2 with low doping levels shows a significantly improved Jc and Fp, especially in the high field region. Hirr is also substantially enhanced. It is revealed that the magnetic flux pinning behavior of CrB2 doped samples obviously deviates from the surface pinning law followed by most pure MgB2. Through theoretical analysis and curve fitting, an extra pinning force superimposed on the surface pinning background is separated and identified, which follows the rule of point pinning. Such a pinning scenario is supported by the microstructure analyses which demonstrate that CrB2 nanoparticles are highly dispersed and embedded in MgB2 matrix, acting as effective pinning centers.

Improvement of bulk superconducting current capability of MgB2 films using surface degradation

The MgB2 films with the degraded MgB2 (SD) surface layer from the Cu ion bombardment show a large improvement in the field performance of critical current density (Jc) and a significant enhancement of the flux pinning force density (Fp). When the SD layer thickness is approximately 11% of the film thickness, the critical field corresponding to Jc = 105 A/cm2, a benchmark for large-scale practical applications, increases from 14.8 kOe at 5 K for the pristine film to 25 kOe. Being markedly different from the widely used chemical doping, the degradation of the small surface region does not lead to the suppression of the superconducting transition temperature (Tc) and low-field Jc. These results demonstrate that the formation of the small active area in MgB2 films is an effective way to improve their superconducting properties, thus paving the way for designing the geometry of flux pinning sites in MgB2.

Flux-Pinning Properties of BaHfO3-Doped EuBCO-Coated Conductors Fabricated by Hot-Wall PLD

REBa2Cu3Ox (REBCO, RE = rare earth) coated conductors (CCs) are promising as superconducting wires for high-field magnets because of their high in-field critical current density (Jc) performance and high tensile tolerance. Fujikura, Ltd., has been developing BaHfO3 (BHO)-doped EuBa2Cu3Ox (EuBCO, Eu = Europium) CCs using a hot-wall-type pulsed-laser deposition (PLD) in order to further improve the in-field performance. Although a high deposition rate in the PLD process is necessary for mass production, it has been found that the in-field performance greatly differ depending on the deposition rate. In this study, flux pinning properties of BHO-doped EuBCO CCs fabricated with different deposition rates by the hot-wall PLD on IBAD substrates were investigated in detail. From the scaling characteristics of the flux-pinning force density (Fp) curve, the BHO precipitates in a fast deposition rate REBCO film appeared to behave like random pinning centers, which was almost consistent with a result of transmission electron microscope observation. On the other hand, from a decrease of anisotropy in the magnetic field angle dependence of Jc, it was also confirmed that BHO precipitates were not completely random pinning centers, that is, it has some kind of anisotropy. Considering the critical current value per production time, it was also found that the fast deposition rate is advantageous since the REBCO layer could be thicker.

Comparative study of hot and cold press and their effect on superconducting properties of coronene added bulk MgB2

In this study, the superconducting properties of 4 wt% coronene (C24H12) added polycrystalline bulk MgB2 samples prepared by hot pressing and cold pressing, were reported in detail. The results were compared to determine one of which pressing methods is more useful to substitute of carbon released from C24H12 into MgB2 structure and to increase the superconducting properties of MgB2. The lattice strain, crystallite size, residual resistivity, superconducting transition temperature (Tc), critical current density (Jc), flux pinning force density (Fp) and vertical/lateral levitation force (Fz, Fx) were analysed for the hot and cold pressed samples. The a-lattice parameter and Tc value reduced sharply for 4 wt% C24H12 added cold pressed sample, resulting in a notable decrease of increment ratio of Jc and Fp values, while the depressing of Tc is lower for 4 wt% C24H12 added hot pressed sample. The cold pressing strongly increased the lattice strain, confirming more C substitution, while the hot pressing ensured smaller crystallite size. The Jc and Fp values were respectively found as 4.6 × 103 A/cm2, 1.3 × 104 A/cm2, 5.8 × 103 A/cm2 and 1.8 × 108 N/m3, 5.1 × 108 N/m3, 2.3 × 108 N/m3 for the pure sample and, 4 wt% C24H12 added hot and cold pressed samples at 20 K, 4 T. The maximum repulsive and attractive levitation force values at 20 K in ZFC and FC regimes were obtained for the 4 wt% C24H12 added hot pressed sample. Finally, the hot pressing provides an effective way to substitute C into MgB2 lattice without a remarkable decrease of Tc value, ensuring more homogenous and compacted structure, more electron–phonon interaction and strong flux pinning force.

Influence of coronene addition on some superconducting properties of bulk MgB2

This study reports the effect of coronene (C24H12) addition on some superconducting properties such as critical temperature (Tc), critical current density (Jc), flux pinning force density (Fp), irreversibility field (Hirr), upper critical magnetic field (Hc2), and activation energy (U0), of bulk MgB2 superconductor by means of magnetisation and magnetoresistivity measurements. Disk-shaped polycrystalline MgB2 samples with varying C24H12 contents of 0, 2, 4, 6, 8, 10 wt%, were produced at 850 °C in Ar atmosphere. The obtained results show an increase in field-Jc values at 10 and 20 K resulting from the strengthened flux pinning, and a decrease in critical temperature (Tc) because of C substitution into MgB2 lattice, with increasing amount of C24H12 powder. The Hc2(0) and Hirr(0) values are respectively found as 144, 181, 172 kOe, and 128, 161, 145 kOe for pure, 4 wt% and 10 wt% C24H12 added samples. The U0 depending on the magnetic field curves were plotted using thermally activated flux flow model. The maximum U0 values are respectively obtained as 0.20, 0.23 and 0.12 eV at 30 kOe for pure, 4 wt% and 10 wt% C24H12 added samples. As a result, the superconducting properties of bulk MgB2 at high fields was improved using C24H12, active carbon source addition, because of the presence of uniformly dispersed C particles with nanometer order of magnitude, and acting as effective pinning centres in MgB2 structure.

Ultrahigh critical current densities, the vortex phase diagram, and the effect of granularity of the stoichiometric high- Tc superconductor CaKFe4As4

We present a comprehensive study of the critical current densities and the superconducting vortex phase diagram in the stoichiometric superconductor ${\mathrm{CaKFe}}_{4}{\mathrm{As}}_{4}$ which has a critical temperature of $\ensuremath{\sim}35\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. We performed detailed magnetization measurements both of high quality single crystals for different orientations in an applied magnetic field up to 16 T and for a powder sample. We find an extremely large critical current density, ${J}_{c}$, up to ${10}^{8}\phantom{\rule{0.28em}{0ex}}\mathrm{A}/{\mathrm{cm}}^{2}$ for single crystals when $H\ensuremath{\parallel}(ab)$ at $5\phantom{\rule{0.28em}{0ex}}\mathrm{K}$, which remains robust in fields up to $16\phantom{\rule{0.28em}{0ex}}\mathrm{T}$, being the largest of any other iron-based superconductor. The critical current density is reduced by a factor 10 in single crystals when $H\ensuremath{\parallel}c$ at 5 K and significantly suppressed by the presence of grain boundaries in the powder sample. We also observe the presence of the fishtail effect in the magnetic hysteresis loops of single crystals when $H\ensuremath{\parallel}c$. The flux pinning force density and the pinning parameters suggest that the large critical current could be linked to the existence of point core and surface pinning. Based on the vortex phase diagram and the large critical current densities, ${\mathrm{CaKFe}}_{4}{\mathrm{As}}_{4}$ is now established as a potential iron-based superconductor candidate for practical applications.

Improved Flux Pinning for High-Field Applications in BaHfO3-Doped SmBa2Cu3 Oy-Coated Conductors With High Density of Random Pinning Centers Induced by BaHfO 3 Nanorods

The critical current performance of REBa 2 Cu 3 Oy-coated conductors must be isotropically improved for use in high-field coil-based applications operated at low temperatures less than 50 K. The high and isotropic critical current densities (Jc) with respect to the directions of the magnetic field under these operating conditions were achieved by a 3.8 vol.% BaHfO3 (BHO)-doped SmBa 2 Cu 3 Oy (SmBCO) film on a metallic substrate deposited with low-temperature growth (L-BHO film). In particular, the L-BHO film attained a high flux pinning force density over 1.5 TN/m 3 at a temperature of 4.2 K. From the anisotropic scaling approach based on the effective mass model, a high density of random pinning centers in the L-BHO film plays an important role in achieving the high J c performance at 4.2 K. In order to reveal the reason why the L-BHO film includes high density of random pinning centers, we compared the flux pinning properties and the dominant flux pinning centers between the L-BHO film and the other two samples: a 3.8 vol.% BHO-doped SmBCO film fabricated with relatively high-temperature growth, and a nondoped SmBCO film fabricated with low-temperature growth. From the comparison, it is revealed that the random pinning centers are induced by BHO nanorods.

Enhanced critical current density of MgB2 thin films deposited at low temperatures by ZnO seed impurity

We report a facile method to enhance the critical current density (Jc) of superconducting MgB2 thin films. MgB2 thin films were deposited on zinc acetate dehydrate (Zn(CH3COO)22H2O) spin-coated Al2O3 (000l) substrates by using a hybrid physical-chemical vapor deposition system at low temperatures. Synthesis of MgB2 at low temperatures can reduce the substitution of Zn into the Mg site, hence avoiding the reduction of superconducting critical temperature. MgB2 thin films grown on ZnO-buffered layers showed a significant enhancement of Jc in the magnetic field due to the creation of additional pinning sources, namely point defects and grain boundaries. Broad peaks were observed in the magnetic field dependence of the flux pinning force density, indicating competition of different pinning sources.

Formation of qualified BaHfO3 doped Y0.5Gd0.5Ba2Cu3O7−δ film on CeO2 buffered IBAD-MgO tape by self-seeding pulsed laser deposition

Improvement in the in-filed transport properties of REBa2Cu3O7−δ (RE = rare earth elements, REBCO) coated conductor is needed to meet the performance requirements for various practical applications, which can be accomplished by introducing artificial pinning centers (APCs), such as second phase dopant. However, with increasing dopant level the critical current density Jc at 77 K in zero applied magnetic field decreases. In this paper, in order to improve Jc we propose a seed layer technique. 5 mol% BaHfO3 (BHO) doped Y0.5Gd0.5Ba2Cu3O7−δ (YGBCO) epilayer with an inserted seed layer was grown on CeO2 buffered ion beam assisted deposition MgO (IBAD-MgO) tape by pulsed laser deposition. The effect of the conditions employed to prepare the seed layer, including tape moving speed and chemical composition, on the quality of 5 mol% BHO doped YGBCO epilayer was systematically investigated by X-ray diffraction (XRD) measurements and scanning electron microscopy (SEM) observations. It was found that all the samples with seed layer have higher Jc (77 K, self-field) than the 5 mol% BHO doped YGBCO film without seed layer. The seed layer could inhibit deterioration of the Jc at 77 K and self-filed. Especially, the self-seed layer (5 mol% BHO doped YGBCO seed layer) was more effective in improving the crystal quality, surface morphology and superconducting performance. At 4.2 K, the 5 mol% BHO doped YGBCO film with 4 nm thick self-seed layer had a very high flux pinning force density Fp of 860 GN/m3 for B//c under a 9 T field, and more importantly, the peak of the Fp curve was not observed.

Strongly enhanced irreversibility field and flux pinning force density in SmBa2Cu3Oy-coated conductors with well-aligned BaHfO3 nanorods

A high flux pinning performance was obtained for a 3.8 vol % BaHfO3-doped SmBa2Cu3Oy superconducting film on a metallic substrate. At a temperature of 77.3 K, an irreversibility field of 16.8 T and the maximum flux pinning force density of 32.5 GN/m3 in fields applied parallel to the c-axis of the film were achieved, which are the highest values reported thus far for REBa2Cu3Oy films, to our knowledge. The introduction of well-aligned BaHfO3 nanorods with a high number density into REBa2Cu3Oy films with little or no degradation of the critical temperature is an effective method for improving the flux pinning performance.

Flux pinning landscape up to 25 T in SmBa2Cu3Oy films with BaHfO3 nanorods fabricated by low-temperature growth technique

REBa2Cu3Oy superconducting tapes are appropriate for high field magnet applications at low temperatures (i.e. below liquid nitrogen temperature). To clarify the morphology and the volume of the effective pinning center at low temperatures, we used a low-temperature growth technique to fabricate SmBa2Cu3Oy (SmBCO) films with various amounts of BaHfO3 (BHO) nanorods onto MgO-buffered metal substrates produced by ion-beam-assisted deposition; we investigated their flux pinning properties using a 25 T cryogen-free superconducting magnet that was recently developed at Tohoku University. According to the microstructural analysis using transmission electron microscopy, the BHO nanorods have a content-dependent morphology and are aligned for the higher content. The inclined and discontinuous BHO nanorods were observed in SmBCO films with BHO contents up to 3.8 vol%; they show an excellent flux pinning force density (1.5 TN m−3 at 21 T and 4.2 K) even when the magnetic field is perpendicular to the films. Based on the effective mass model for the flux pinning, the random pinning centers are dominant at low temperatures. The correlated flux pinning is stronger for aligned nanorods; however, the random pinning center becomes weaker in the 4.5 vol% BHO-doped films. Therefore, the optimal BHO doping level is approximately 3.8 vol% in terms of the amplitude of the critical current density and the anisotropy from 4.2 K to 20 K because this provides the best mixture of correlated and random flux pinning centers.

Strong flux pinning at 4.2 K in SmBa2Cu3Oy coated conductors with BaHfO3 nanorods controlled by low growth temperature

In order to apply REBa2Cu3Oy (REBCO, RE = rare earth elements or Y) coated conductors in high magnetic field, coil-based applications, the isotropic improvement of their critical current performance with respect to the directions of the magnetic field under these operating conditions is required. Most applications operate at temperatures lower than 50 K and magnetic fields over 2 T. In this study, the improvement of critical current density (Jc) performance for various applied magnetic field directions was achieved by controlling the nanostructure of the BaHfO3 (BHO)-doped SmBa2Cu3Oy (SmBCO) films on metallic substrates. The corresponding minimum Jc value of the films at 40 K under an applied 3 T field was 5.2 MA cm−2, which is over ten times higher than that of a fully optimized Nb–Ti wire at 4.2 K. At 4.2 K, under a 17.5 T field, a flux pinning force density of 1.4 TN m−3 for B//c was realized; this value is among the highest values reported for REBCO films to date. More importantly, the Fp for B//c corresponds to the minimum value for various applied magnetic field directions. We investigated the dominant flux pinning centers of films at 4.2 K using the anisotropic scaling approach based on the effective mass model. The dominant flux pinning centers are random pinning centers at 4.2 K, i.e., a high pinning performance was achieved by the high number density of random pins in the matrix of the BHO-doped SmBCO films.

Improvement of Flux Pinning Properties for Hafnium-Doped Gd123 Thin Films Fabricated by a Fluorine-Free MOD Method

In order to enhance the flux pinning force density $F_{p}$ in magnetic fields for REBa2Cu3O $_{y}$ (RE123)-coated conductors, Hf and Zr doping are the very valid way of introducing the perovskite nanostructure as artificial pinning centers (APCs) into the superconductors. However, the studies for Hf-doped RE123 thin films fabricated by the fluorine-free metal organic deposition (FF-MOD), which is the easiest production process, have not been done yet. In this study, we have successfully fabricated Hf-doped FF-MOD GdBa2 Cu3O $_{y}$ (Gd123) thin films on LaAlO3 substrates and investigated their flux pinning properties. Critical temperature for Gd123 thin films indicated around 92 K, and $T_{c}$ varied little by Hf doping. Hf 10 mol% doped film achieved high critical current densities of 2.72 mA⋅cm −2 at 77.3 K under 0 T, and 0.27 mA⋅cm−2 at 77.3 K under 1 T. With increasing Hf-doping amount, $F_{p}$ gradually increased, and the peak of $F_{p}$ shifted to the high magnetic field side. The elementary pinning force and the effective pinning center density also increased. We believe that effective APCs, probably BaHfO3 are introduced into FF-MOD Gd123 thin films by Hf doping.

Delocalization of vortex in SmBa2Cu3O7−δ superconducting films with BaHfO3 nano-rods

Transport measurements revealed flux pinning properties and vortex phases in SmBa2Cu3O7−δ (Sm123) superconducting films with BaHfO3 nano-rods on LaAlO3 substrates. The films have large matching fields BΦ up to 9.9 T, nano-rod diameters of ∼6 nm, and a slight Tc degradation with Tc ∼ 91.8 K by using the low temperature growth technique. According to the transport results, a small critical exponent ∼4 indicates the presence of a Bose-glass phase in the films. Double peaks of the flux pinning force density are unexpectedly observed at high temperatures over 80 K, which is accompanied by steep drops of the crossover magnetic fields between the single vortex pinning and the collective pinning states. The drops are explained by the delocalization of the vortex where the vortex is pinned by many nano-rods in the single vortex pinning state. From the viewpoint of the vortex delocalization, we conclude that BΦ should be less than 11 T for applications at liquid nitrogen temperature.