Cool-down Cycles Research Articles

Toward a high-fidelity tritium transport modeling for retention and permeation experiments

Tritium Migration Analysis Program version 8 (TMAP8), the latest version of TMAP, was developed within the framework of the Multiphysics Object-Oriented Simulation Environment (MOOSE). Created at Idaho National Laboratory (INL), MOOSE is an open-source, dimension-agnostic, fully coupled, and fully implicit multiphysics platform featuring massively parallel computation capabilities. Using TMAP8, tritium transport in a divertor monoblock was analyzed to elucidate the effects of pulsed operation (up to fifty 1,600 s plasma discharge and cool-down cycles) on the tritium in-vessel inventory source term and ex-vessel release term (i.e., tritium retention and permeation) for safety analysis. With its built-in Message Passing Interface capability, TMAP8 can, in under 2 h, simulate tritium transport in three different layered materials (i.e., tungsten, copper, and copper-chromium-zirconium alloy) in 2D geometry, using a single device/computer with 10 cores. The MOOSE-based TMAP8 code can leverage other MOOSE tools developed under the Nuclear Energy Advanced Modeling and Simulation program to perform tritium and thermal transport in complex geometries and multiphysics environments. And via its massively parallel computation, MOOSE will enable the fusion pilot plant designers to conduct high-fidelity multiphysics modeling for the design of the divertor and blanket systems as well as for the safety analysis.

Performance of first insert coil with REBCO CICC sub-size cable exceeding 6 kA at 21 T magnetic field

The Institute of Plasma Physics at the Chinese Academy of Sciences is developing the REBCO cable in conduit conductor (CICC) technology for applications in next-generation nuclear fusion devices. The aim is to develop a CICC comprised of six REBCO sub-cables to satisfy the requirements of operation with a current of around 40 kA and a peak field of up to 20 T. To qualify the performance of the sub-size REBCO cable to be used in the CICC, two 25-turn insert solenoids have been designed, manufactured and tested at a current exceeding 6 kA subjected in a background field supplied by a water-cooled resistive magnet. The insert solenoid, wound from a 11.5 m long REBCO CORC® cable, was designed to investigate its current carrying capacity under high field and electromagnetic (EM) load at 4.2 K. Tests were performed under a background magnetic field up to 18.5 T, resulting in a peak magnetic field on the innermost layer turns of around 21.1 T at an operating current of 6.3 kA. The effects of operation with cyclic EM loads were tested by repeated current ramps to around 95% of the critical current. Moreover, the V–I characteristics were measured at 77 K and the self-field, to check the effects from warm-up and cool-down (WUCD) cycles between room temperature and 77 K with liquid nitrogen. The results show no obvious degradation after dozens of high-current test cycles in background fields ranging from 10 T to 18.5 T. The insert solenoid demonstrates the stable operation of the REBCO sub-size cable for CICC with EM loads of about 90 kN m−1 and WUCD cycles between room temperature and 77 K. These promising results indicate the potential of this technology for further applicationsin particular, for full-size CICC for high-performance fusion magnets.

Finite-Element Analysis of Pipelines with Axial Walking and Lateral Buckling

A pipeline is prone to axial movement, called pipeline walking, under heat-up and cooldown cycles. The build-up of axial force along the pipeline can result in the phenomenon referred to as lateral buckling. Walking and lateral buckling can both influence pipeline movement performance and threaten the safety of pipeline systems. The numerical simulation method is adopted to study the pipeline movement laws under walking and buckling interactions. Walking and buckling interactions are classified into three types for different forms of seabed slopes, and corresponding mitigation methods are proposed. The effects of buckling number, route bend, sleeper spacing, and anchor position on the lateral displacement amplitude, axial displacement, and effective axial force (EAF) of the pipeline are analyzed. Criteria for the mitigation methods are proposed based on parameters such as the pipeline end expansion, buckling failure parameter, maximum anchor force, and minimum compressive EAF. The results show that the anchor position has a great influence on the intertransformation of pipeline buckling and walking. The difference in anchor force can reach 51.1% considering different anchor positions.

Mechanical Tests, Analysis, and Validation of the Support Structure of the eRMC and RMM Magnets of the FCC R&D at CERN

The enhanced racetrack model coil and racetrack model magnet constitute the current R&D Nb3Sn magnets under development at CERN aiming to achieve dipole fields of 16-18 T, the design baseline of the Future Circular Collider (FCC). This article reports the mechanical behavior of their common support structure, which underwent three different levels of room-temperature preload (with the bladders and key method) and two cooldown cycles to 80 K. The structure was mounted using aluminum dummy blocks in lieu of the actual Nb3Sn coils. Strain gauges were placed in the external aluminum shell, tie-rods, and dummy coils. The measurements agree well with the results of the finite-element models (FEM). This work validates the FEM and a support structure for testing Nb3Sn accelerator magnets in the 16-T regime.

Research on mechanical properties of high-performance cable-in-conduit conductors with different design

The China Fusion Engineering Test Reactor (CFETR) is a new tokamak fusion reactor under preliminary design, where the toroidal field (TF) coil has been designed to create a magnetic field of over 14.3 T. The TF conductors need to operate stably at 14.3 T, requiring the exclusion of conductor performance degradation from thermal and electromagnetic loading as much as possible. The maximum Lorentz force will reach about 1200 kN m−1, which is much higher than that of ITER conductors. In previous research, performance degradation was found during electromagnetic cycles and warm-up–cool-down cycles. A correlation was found between a conductor’s degradation and its mechanical properties. According to the analysis, a conductor with a short twist pitch (STP) scheme or a copper wound superconducting strand (CWS) design has large stiffness, which enables significant performance improvement in terms of the electromagnetic and thermal load cycling. The cable stiffness is closely related to the number of inter-strand contact points inside the conductor. Based on this concept, four types of prototype cable-in-conduit conductor samples with STP and CWS design were manufactured. The number of inter-strand contact points was analyzed, and mechanical transverse load testing was performed at 77 K. The results show that the conductors with more contact points per unit length exhibit a higher stiffness. However, the cable designed with high cable stiffness caused strand indentation, which was also investigated. In this paper, the conductor design and experimental results are discussed and compared with ITER TF and central solenoid conductors.

Stability study of SOFC using layered perovskite oxide La1·85Sr0·15CuO4 mixed with ionic conductor as membrane

Long-term stability is of significant importance to energy conversion devices including solid oxide fuel cell (SOFC). In this work, we apply a layered perovskite oxide La1·85Sr0·15CuO4 (LSCO4) mixing with ionic conductor Ce0.8Sm0.2O2-δ (SDC) to get an ionic and electronic conductor composite (IECC) membrane SOFC for the sake of achieving a stable cell. The addition of proper ratio of LSCO4 in the membrane improves cell performance. The IECC fuel cell reaches a stability of over 75 h at 550 °C under 100 mAcm−2 and can resist multiple times of rapid heat-up and cool-down cycles. The factors that influence cell stability are investigated. The covalence states of the IECC are found to change firstly but stabilize after several hours of test. Resulting from anode Ni0·8Co0·15Al0·05LiO2-δ (NCAL) reduction, Li+ is found to migrate to the IECC membrane, leading to IECC membrane densifying and resultantly protecting the IECC from further reduction by hydrogen. However, the continuous online reaction of NCAL electrodes leads to the increase of charge transfer resistance as well as the decrease of gas diffusion pores in the electrode. This study provides important reference for designing stable IECC membrane fuel cell.

Early Calibration and Performance Assessments of NOAA-20 VIIRS Thermal Emissive Bands

The Visible Infrared Imaging Radiometer Suite (VIIRS) sensor aboard the NOAA-20 (previously JPSS-1) spacecraft has successfully operated since its launch in November, 2017. Similar to the first VIIRS instrument on the Suomi-National Polar-orbiting Partnership (SNPP) spacecraft, the data are collected in 22 spectral bands that are calibrated by a set of onboard calibrators. This paper provides an overview of the NOAA-20 VIIRS on-orbit operation and calibration, with a particular focus on the thermal emissive bands (TEBs). The results presented in this paper include the on-orbit changes in the TEB spectral band responses, detector noise characterization, and key calibration parameters, such as the nonlinear coefficients derived from the blackbody warm-up cool-down cycles. Other issues, such as the early mission long-wave infrared (LWIR) response degradation due to icing on the dewar window, and their impact on sensor calibration are also discussed. Since launch, the VIIRS instrument temperature has been stable to within ±0.8 K and the cold focal plane temperatures are well controlled with variations less than 40 mK. With the exception of the early degradation observed in the LWIR bands, the TEB gains have been stable to within 0.04% (except I5 at 0.07%). Based on the current performance, VIIRS is expected to meet its calibration requirements throughout its design lifetime.

Beam-based alignment of SRF cavities in an electron injector linac

Proper alignment of accelerating cavities is an important issue concerning beam quality of linear rf-accelerators. In particular, SRF cavities of injector linacs using high accelerating gradients on low-velocity electron beams can deteriorate the beam quality significantly when not aligned sufficiently. On the other hand, knowing the exact position of every cavity after several cool-down cycles of a cryomodule can be difficult depending on the particular module design. We will report on operational experience on the SC injector of the Darmstadt superconducting recirculating linac and ERL (S-DALINAC) showing unwanted effects on beam dynamics and beam quality due to cavity misalignment, such as transverse beam deflections by changing accelerating phases and a growth of transverse emittance. These effects could already be observed at small beam currents of a few nA, so space-charge effects were eliminated to be the reason for these observations. In this work we will report on the possibility to realign SRF cavities after cool-down by measuring the transverse deflection of the beam and compare results with beam dynamics simulations.

Contact resistance between two REBCO tapes: the effects of cyclic loading and surface coating

No-insulation (NI) superconducting REBCO magnets have advantages of self-quench-protection, a very high engineering current density and high mechanical strength, and the potential to reach very high magnetic fields. However, NI REBCO magnets have drawbacks of a long magnet charging time and high field ramp losses. These can be mitigated by controlling the turn-to-turn contact resistivity (Rc). In an effort to control Rc, we consider two approaches. One is coating a REBCO conductor with various resistive thin films, and the other is to use a stainless steel (SS) tape as an interlayer which is also coated with different metallic films. We present experimental results of Rc of an as-received sample under cyclic contact pressure of 2.5–25 MPa up to 30 000 cycles. After an initial increase in Rc for the first 10–20 cycles, Rc decreases to about one tenth of its initial value after a few hundred cycles. A warm-up and cool-down thermal cycle does not significantly change the low Rc resulting from a previously high number of load cycles. We also studied Rc of REBCO tapes that are coated with different resistive layers and interlayers. In order to increase Rc, we experimented with electro- and electroless plating of Ni, Cr, and Ni–P. We also measured Rc with a thin metallic interlayer as a coil co-winding material which included Cu, SS, and SS plated with Ni and Cu. A SS interlayer increases Rc by about three orders of magnitude; while the Cu plated SS interlayer only increases Rc by one order of magnitude. Finally, we treated the as-received REBCO surface by oxidation using an Ebonol® C solution. This controlled oxidation allowed the Rc to be controlled over a wide range.

Qualification of the U.S. Conductors for ITER TF Magnet System

The U.S. Domestic Agency is one of the six suppliers of the toroidal field (TF) conductor for ITER. To qualify conductors per ITER requirements, we prepared or provided to the Swiss Plasma Center (SPC) eight test articles, sixteen conductors total, that were tested in the SULTAN facility at SPC in the ITER relevant conditions. The strands that were used in these SULTAN samples were fully characterized in the laboratories. In this paper, we report both test results and analysis of the conductors’ performance against expected strand performance. The U.S. TF conductors showed a slightly better than average current sharing temperature and a relatively low sensitivity to warm up-cooldown cycles in comparison with other suppliers’ conductors. However, the trend in current sharing temperature versus cycles and warm ups did not saturate, which means a continuing slow degradation of the conductor performance if the number of warm up and cooldown cycles will be significantly higher than expected. The ac losses in the U.S. TF conductors are in line with losses in the other TF conductor suppliers.

Tail Component Qualification For the EU ITER PF Coils

The ITER poloidal field (PF) magnet system is composed of six circular coils, consisting of winding packs (WP) made up from a stack of double pancakes (DP) wound of NbTi cable-in-conduit superconductor. The largest coil has a diameter of 24 m, the heaviest weighs 400 ton, and they are designed to produce a total magnetic energy of 4 Giga Joules at a maximum magnetic field of 6 T for 30 000 inductively driven plasma pulses. The ends of the conductors (in the outer-most coil turns) of the top and bottom DP are coil terminations, which are connected to the superconducting bus bars of the feeders, these conductors exit being one of the weakest structural points of the coils. The main function of the tail is to reinforce this region by linking the outer-most termination to the last-but-one turn, thus guaranteeing the transfer of longitudinal tensile force, through an electrically insulated mechanical connection featuring a fiberglass strap. The PF coils are subject to electromagnetic forces induced from their own magnetic field and the magnetic field generated from the rest of the ITER magnet system, the thermal stresses during cooldown and warmup cycles and dc/ac high-voltage levels. Therefore, the tail components shall withstand these conditions while staying within the geometrical boundaries imposed by the conductor dimensions, in order to avoid any protrusion on the WP surface. This paper aims to describe the adopted solution throughout its lifecycle, from the design validation, by the electromagnetic and mechanical analyses, to the design qualification of the set of imposed requirements through the manufacture, and testing of a set of full-size mock-ups.

Impact of Blackbody Warm-Up Cool-Down Cycle on the Calibration of Aqua MODIS and S-NPP VIIRS Thermal Emissive Bands

This paper evaluates the calibration quality during the blackbody (BB) warm-up cool-down cycle for thermal emissive bands onboard Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) and Suomi National Polar-orbiting Partnership (S-NPP) Visible Infrared Imaging Radiometer Suite (VIIRS). This evaluation utilizes data from Aqua MODIS Collection 6 Level-1B products and VIIRS Sensor Data Records in 6-min granule format provided by the NASA Land Science Investigator-led Processing System. Nearly simultaneous hyperspectral measurements from the Aqua Atmospheric Infrared Sounder (AIRS) and the S-NPP Cross-track Infrared Sounder (CrIS) are used as references for MODIS and VIIRS, respectively. Each AIRS footprint of 13.5 km is co-located with multiple MODIS pixels while each CrIS field of view of 14 km is co-located with multiple VIIRS pixels. The corresponding AIRS-simulated MODIS and CrIS-simulated VIIRS radiances are derived by convolutions based on sensor-dependent relative spectral response functions. In this paper, the analysis mainly focuses on the bands that are used in sea surface temperature products. The results show that there is virtually no impact for MODIS bands 22 and 23 and bands 31 and 32 for a BB temperature below 290 K; however, when the BB temperature increases above 290 K, the impact is up to 0.3 K for bands 22 and 23 and 0.05 K for bands 31 and 32, respectively. For VIIRS, BB temperature-dependent drifts are observed in M15 and M16, which can reach 0.15 and 0.1 K, respectively, over the operational BB temperature range and the VIIRS brightness temperature range.

Flux trapping in multi-loop SQUIDs and its impact on SQUID-based absolute magnetometry

The effect of flux trapping on the flux-voltage characteristics of multi-loop SQUID magnetometers was investigated by means of repeated cool-down cycles in a stepwise increased magnetic background field. For a SQUID with N parallel loops, N different flux offsets, each separated by were observed even in zero magnetic field. These flux offsets further split into a so called fine structure, which can be explained by minor asymmetries in the SQUID design. The observed results are discussed with particular regard to their impact on the previously presented absolute SQUID cascade vector magnetometer.

Experimental de-stratification and heat loss in a storage tank containing different thermal oils

Simplified experimental de-stratification and heat loss characteristics of three thermal oils in a small storage tank are presented during 24-h low-temperature and medium-temperature cool-down cycles. Sunflower Oil, Shell Thermia C and Shell Thermia B are characterized experimentally during cool-down cycles. Temperature, stratification number and heat loss factor profiles are evaluated during low- and medium-temperature cool-down cycles. For low-temperature cool-down, Sunflower Oil shows the best performance with the lowest heat loss factor due its larger thermal mass as a result of its larger density. The best stratification distribution is obtained with Shell Thermia B which has the lowest density. For medium-temperature cool-down cycles, Sunflower Oil shows the best overall thermal performance with less heat losses due to its larger thermal mass which slows the rate of natural convection. Shell Thermia C has greater values of the stratification number for most of the medium-temperature cool-down cycle possibly due to its higher initial TES temperatures. Temperature profiles for medium-temperature thermal energy retention show a different behavior from the low-temperature behavior. Heat loss factor values for both low- and medium-temperature cool-down cycles are comparable suggesting that heat losses are similar.

Planar Indium Tin Oxide Heater for Improved Thermal Distribution for Metal Oxide Micromachined Gas Sensors.

Metal oxide gas sensors with integrated micro-hotplate structures are widely used in the industry and they are still being investigated and developed. Metal oxide gas sensors have the advantage of being sensitive to a wide range of organic and inorganic volatile compounds, although they lack selectivity. To introduce selectivity, the operating temperature of a single sensor is swept, and the measurements are fed to a discriminating algorithm. The efficiency of those data processing methods strongly depends on temperature uniformity across the active area of the sensor. To achieve this, hot plate structures with complex resistor geometries have been designed and additional heat-spreading structures have been introduced. In this work we designed and fabricated a metal oxide gas sensor integrated with a simple square planar indium tin oxide (ITO) heating element, by using conventional micromachining and thin-film deposition techniques. Power consumption–dependent surface temperature measurements were performed. A 420 °C working temperature was achieved at 120 mW power consumption. Temperature distribution uniformity was measured and a 17 °C difference between the hottest and the coldest points of the sensor at an operating temperature of 290 °C was achieved. Transient heat-up and cool-down cycle durations are measured as 40 ms and 20 ms, respectively.

Test of the MF-CICC Conductor Designed for the 12-T Outsert Coil of the HFML 45-T Hybrid Magnet

A 45-T hybrid magnet is being built at the High Field Magnet Laboratory of the Radboud University in Nijmegen, The Netherlands. The hybrid magnet consists of a 12-T cable-in- conduit-conductor (CICC) Nb 3Sn superconducting outsert and a 33-T resistive insert magnet. To verify the CICC design, a thorough testing has been completed in the SULTAN facility at Swiss Plasma Center, EPFL in Villigen (Switzerland) for the medium- grade conductor of the outsert. In two test campaigns, the dc cable performance (current-sharing temperature, critical current), the ac loss, and the conductor's performance stability during cyclic loading and after one warmup and cooldown cycle have been investigated. Two different cable layouts were tested—one with a very short twist pitch (STP) and the second one with a long twist pitch (LTP) cabling pattern. As both conductors were made of the same Nb 3Sn strand and underwent the same heat treatment and sample preparation procedure, the effect of the twist pitch on the ac loss and on the dc performance with respect to cyclic loading could be reliably evaluated. The test results show that both cable layouts are actually very robust. The cable could withstand 2000 load cycles and the warmup and cooldown cycle without any significant degradation of the dc performance, and even the overloading at BI product (field multiplied by current) approximately two times larger than those foreseen during magnet operation did not lead to a big performance change. Small differences between the STP and LTP options have been observed, indicating that the STP conductor withstands high electromagnetic loads better than the LTP one.

ITER Central Solenoid Insert Test Results

The ITER central solenoid (CS) is a highly stressed magnet that must provide 30 000 plasma cycles under the ITER prescribed maximum operating conditions. To verify the performance of the ITER CS conductor in conditions close to those for the ITER CS, the CS insert was built under a USA-Japan collaboration. The insert was tested in the aperture of the CSMC facility in Naka, Japan, during the first half of 2015. A magnetic field of up to 13 T and a transport current of up to 60 kA provided a wide range of parameters to characterize the conductor. The CS insert has been tested under direct and reverse charges, which allowed a wide range of strain variation and provided valuable data for characterization of the CS conductor performance at different strain levels. The CS insert test program had several important goals as follows. 1) Measure the temperature margin of the CS conductor at the relevant ITER CS operational conditions. 2) Study the effects of electromagnetic forces and strain in the cable on the CS conductor performance. 3) Study the effects of the warmup and cooldown cycles on the CS conductor performance. 4) Compare the conductor performance in the CS insert with the performance of the CS conductor in a straight hairpin configuration (hoop strain free) tested in the SULTAN facility. 5) Measure the maximum temperature rise of the cable as a result of quench. The main results of the CS insert testing are presented and discussed.

S-NPP VIIRS thermal emissive bands on-orbit calibration and performance

Presented is an assessment of the on-orbit radiometric performance of the thermal emissive bands (TEB) of the Suomi National Polar-orbiting Partnership (S-NPP) Visible Infrared Imaging Radiometer Suite (VIIRS) instrument based on data from the first 2 years of operations—from 20 January 2012 to 20 January 2014. The VIIRS TEB are calibrated on orbit using a V-grooved blackbody (BB) as a radiance source. Performance characteristics trended over the life of the mission include the F factor—a measure of the gain change of the TEB detectors; the Noise Equivalent differential Temperature (NEdT)—a measure of the detector noise; and the detector offset and nonlinear terms trended at the quarterly performed BB warm-up cool-down cycles. We find that the BB temperature is well controlled and stable within the 30mK requirement. The F factor trends are very stable and showing little degradation (within 0.8%). The offsets and nonlinearity terms are also without noticeable drifts. NEdT is stable and does not show any trend. Other TEB radiometric calibration-related activities discussed include the on-orbit assessment of the response versus scan-angle functions and an approach to improve the M13 low-gain calibration using onboard lunar measurements. We conclude that all the assessed parameters comply with the requirements, and the TEB provide radiometric measurements with the required accuracy.

Development of atomic layer deposition-activated microchannel plates for single particle detection at cryogenic temperatures

Atomic layer deposition (ALD) technology is used to nanoengineer functional films inside the pores of microchannel plate (MCP) electron multipliers, enabling a novel MCP manufacturing technology that substantially improves performance and opens novel applications. The authors have developed custom tools and recipes for the growth of conformal films, with optimized conductance and secondary electron emission inside very long channels (∼6–20 μm diameter and >600 μm length, with tens of millions of channels per single MCP) by ALD. The unique ability to tune the characteristics of these ALD films enables their optimization to applications where time-resolved single particle imaging can be performed in extreme conditions, such as high counting rates at cryogenic temperatures. Adhesion of the conductive and emissive nanofilms to the 20 μm pore MCP glass substrates and their mechanical stability over a very wide range of temperatures (10–700 K) were confirmed experimentally. Resistance of ALD MCPs was reproducible during multiple cool-down cycles with no film degradation observed. Optimizing resistance of novel MCPs for operation at cryogenic temperature should enable high count rate event detection at temperatures below 20 K.

Protective atmosphere induction heating

Induction heating is used for a wide range of industrial applications. This energy efficient process converts up to 90% of the energy used into useful heat. Since start-up is virtually instantaneous induction requires no warm-up or cool-down cycle and stand-by heat losses are reduced to a bare minimum. However, it is usually associated with poor surface quality particularly oxidation and surface roughness that requires further energy intensive processing. The use of protective atmospheres eliminates this step, further improving the energy efficiency of the process route. This paper describes some practical applications of protective atmosphere induction heating from a broad spectrum of heat treatment processes.