Warm-up Cycles Research Articles

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.

Visually Quantifiable Test Piece for Five-Axis Machine Tools Thermal Effects

Abstract Thermal deviation induced by ambient temperature changes and heat generated during machine operations influences the accuracy of machine tools. A thermal test is essential to evaluate the influence of thermal deviation. ISO 230-3 provides displacement sensor-based thermal tests for machine tools. This paper proposes a machining test that enables a user to visually, by the naked eye, observe the integrated thermal influence on the tool trajectory's displacement in the direction normal to the test piece surface from the length of the machined slots. The proposed test consists of the machining of the five surfaces to observe the thermal influence of the tool position with respect to the test piece in X, Y, and Z directions, as well as the position of two rotary axes with respect to the tool position. The advantages of the proposed test include that it requires no measuring instrument to quantitatively evaluate the thermal error in all directions. And since the thermal influence is evaluated by observing the position where the cutting tool leaves the test piece surface, where the cutting force is zero, the influence of the cutting force on the test results can be ignored. Thermal influences of a five-axis machine tool during the warm-up cycle are investigated by experiment to validate the feasibility of the proposed method. Results show that 150 min is needed for sufficient warm-up for the selected machine tool if permissible tolerance for thermal deviation is 2.5 µm for all the errors.

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.

Selecting of FBG Coatings for Quench Detection in HTS Coils

Fiber Bragg grating (FBG) temperature sensors are now regarded as a relatively mature sensing technology for temperature measurement in ambient conditions, and may offer potential as a cryogenic temperature sensor for quench detection. In this paper, the temperature response of three different coated FBG sensors from 77 to 293 K was studied; bare (silica) FBG, acrylic coated, and polyimide coated FBG sensors. We examine the effect of fiber coatings on the temperature sensitivity of an embedded FBG sensor down to cryogenic temperatures. Measurements were repeated with sensors from two FBG suppliers. The measured temperature response was then compared and contrasted with the predicted sensor response. In order to assess the sensor sensitivity, repeatability, and any hysteresis, these sensors were then subjected to repeated cool-down / warm-up cycles (77–293 K). The effect of epoxy resin impregnation on the temperature response characteristics was analyzed by comparing the sensor response characteristics before and after embedding into a 10 mm × 2 mm × 4 mm epoxy block. We compare this to the uncoated fiber for embedment in HTS coils. Finally, we recommend the optimum low-cost sensor construction for use in quench detection in coils.

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.

Application of the adaptive Monte Carlo method in a five-axis machine tool calibration uncertainty estimation including the thermal behavior

Calibration of the geometry of five-axis machine tools needs to be performed periodically since the machine accuracy has a direct impact on machined parts. Because mechanical adjustment and a software correction may be done using calibration results, the measurement results must be evaluated. In this paper, the scale and master ball artefact (SAMBA) method is evaluated through the estimation of the uncertainty of the identified machine geometric error parameters. This approach has the multi-input multi-output (MIMO) model and an iterative solution that makes it challenging to apply commonly used uncertainty calculation methods The Guide to the Expression of Uncertainty in Measurement Supplement 2 (GUM S2) gives the opportunity to estimate the uncertainty of a MIMO model through the adaptive Monte Carlo method (MCM). In order to include all the uncertainty sources, the input uncertainty is estimated from the repeated calibration tests performed in different thermal conditions (with and without the warm-up cycle). The uncertainty is calculated for each of the identified machine geometric error parameters along with their covariance. The correlation between the output variables and the impact of the machine state, before and during the repeated calibration, are analyzed. The results demonstrate that the machine tool geometry variations occur even without the warm-up cycle performed before the calibration. Moreover, machine performance has an impact the calibration results.

On the Exploitation of Automated Planning for Reducing Machine Tools Energy Consumption between Manufacturing Operations

There has recently been an increased emphasis on reducing energy consumption in manufacturing, driven by the fluctuations in energy costs and the growing importance given to environmental impact of manufactured goods. Lots of attention has been given to the reduction of machine tools energy consumption, as they require large amounts of energy to perform manufacturing tasks. One area that has received relatively little interest, yet could harness great potential, is reducing energy consumption by planning machine activities between manufacturing operations, while the machine is not in use. The intuitive option --which is currently exploited in manufacturing-- is to leave the machine in a normal operating state in anticipation of the next manufacturing job. However, this is far from optimal due to the thermal deformation phenomenon, which usually require an energy-intensive warm-up cycle in order to bring all the components (e.g. spindle motor) into a suitable (stable) state for actual machining. Evidently, the use of this strategy comes with the associated commercial and environmental repercussions. In this paper, we investigate the exploitability of automated planning techniques for planning machine activities between manufacturing operations. We present a PDDL 2.2 formulation of the task that considers energy consumption, thermal deformation, and accuracy. We then demonstrate the effectiveness of the proposed approach using a case study which considers real-world data.

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.

Comparison of the Measurement Performance of High Precision Multi-axis Metal Cutting Machine Tools

High precision manufacturers continuously seek out disruptive technologies to improve the quality, cost, and delivery of their products. With the advancement of machine tool and measurement technology many companies are ready to capitalise on the opportunity of on-machine measurement (OMM). Coupled with business case, manufacturing engineers are now questioning whether OMM can soon eliminate the need for post-process inspection systems. Metrologists will however argue that the machining environment is too hostile and that there are numerous process variables which need consideration before traceable measurement on-the-machine can be achieved. In this paper we test the measurement capability of five new multi-axis machine tools enabled as OMM systems via on-machine probing. All systems are tested under various operating conditions in order to better understand the effects of potentially significant variables. This investigation has found that key process variables such as machine tool warm-up and tool-change cycles can have an effect on machine tool measurement repeatability. New data presented here is important to many manufacturers whom are considering utilising their high precision multi-axis machine tools for both the creation and verification of their products.

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.

Effect of Thermal Loading on ${\rm Nb}_{3}{\rm Sn}$ CICC Performance

The ITER CICC will undergo a number of cool-down and warm-up cycles over the lifetime of the plant. The standard SULTAN based ITER conductor qualification test normally includes one thermal cycle in the test sequence. In many samples a performance degradation was observed following this thermal loading. In order to investigate the effect of multiple thermal cycles on the TF conductor short sample, additional repeated thermal cycles to liquid nitrogen temperature were carried out on the left leg of the CNTF3 sample and the JATF5 sample. Thermal cycles using SULTAN are very time consuming, about four days, with a corresponding cost of around 32 kEuro. Ten thermal cycles will give an estimation of the degradation upon repeated thermal loading, but would require a prohibitive amount of time in SULTAN, and therefore cause a significant delay in the testing of other time critical samples. As a large fraction of the change in thermal contraction occurs between room temperature and liquid nitrogen temperature, a purpose made facility and program was developed. This ad-hoc facility allowed faster, more cost effective thermal cycles that crucially did not interfere with SULTAN's ongoing test program. Cooling and heating was provided by means of forced flow nitrogen. The sample was contained within a vacuum to pre- vent the formation of moisture or ice. During warm-up, a heater distributed around the CNTF3A was also used. These cycles were performed both before and after electromagnetic loading. The results of these tests indicated that thermal loading before the first electromagnetic load cycle did not result in a worsening of the conductor performance. The tests following repeated thermal cycling after electromagnetic loading show a thermal cycle causes a performance degradation but a large number of consecutive thermal cycles do not appear to have a significant effect.

Temperature and humidity effects on superhydrophobicity of nanocomposite coatings

This work investigates temperature and humidity effects on the superhydrophobicity of polyurethane/organoclay nanocomposites. Previous reports of superhydrophobic degradation at decreasing surface temperatures for both low and high humidity were generally conducted in open environments. However, the present setup allows a thermally homogeneous environment, i.e., the temperature of the nanocomposite, air and water droplet are equal with no spatial temperature gradients. In such conditions, results showed stable retention of superhydrophobicity for both low humidity (RH < 20%) cool-down and warm-up cycles (20 °C to −3 °C to 20 °C). Similar performance was also observed for a high humidity (RH > 80%) cool-down cycle, though superhydrophobicity degraded during the warm-up cycle, which was attributed to dew condensation.

Model for transient behavior of pulse tube cryocooler

This article describes an investigation of the transient behavior of a small (2.0 W at 85 K) pulse tube cryocooler operating at 120 Hz with an average pressure of 3.5 MPa, capable of relatively fast cool-down from ambient to about 60 K. In a series of experiments, the cold end temperature was measured as a function of time in a complete cool-down and subsequent warm-up cycle, with no heat load and different quantities of excess mass at the cold end. A transient heat transfer model was developed, that considers the effects of the cooling power extracted at the cold end and that of the heat gain at the warm end on the cool-down time. The heat gain factor was calculated from warm-up data, and found to be approximately the same for all experiments. Using the same model with cool-down data enables a determination of both the gross and net cooling power as functions of time, but more importantly – as functions of the cold end temperature. An expression was derived for the cold end temperature as a function of time for any amount of excess mass, including zero. The cool-down time of the “lean” cryocooler (with no excess mass) was found to be less than 50 s. This cool-down/warm-up method for evaluating the cooling power of a cryocooler seems simpler than steady-state experiments with a heater simulating load at the cold end. Use of the heat transfer model with data from one or two good experiments conducted in the above manner, can yield both the gross and net cooling powers of a cryocooler as functions of the cold end temperature, and allow the determination of cool-down time with any amount of excess thermal mass. While the net cooling power during cool-down differs somewhat from that under steady-state operation, the former can serve as a good measure for the latter.

Performance Test of 100 m HTS Power Cable System

In order to meet the needs of economical and stable power supply and high current density cable with compact size, several countries carry out researches on high temperature superconducting (HTS) cables. Korea Electric Power Corporation (KEPCO) established the HTS cable test center and installed 22.9 kV, 1250 A, 50 MVA, 100 m class HTS cable system to investigate the performances and application possibility in real power grids. The HTS cable system went through seven cool down and warm-up cycles and also many kinds of performance tests for 3 years. Rated voltage-current tests, over voltage tests, and measurements of heat loss and AC loss with various currents have been examined. Moreover, DC critical current tests were performed for checking conductor degradation before warming up or after cooling down. Through the performance tests of the HTS cable system, the overall efficiency and loss factors are estimated and compared with conventional power cables in this paper. We conclude the present status of HTS cable system and application possibility in the real power grid.

Mechanical properties of the ITER central solenoid model coil insulation under static and dynamic load after reactor irradiation

The candidate insulation system for the central solenoid (CS) model coil of the International Thermonuclear Experimental Reactor (ITER) is CTD-112P, an epoxy with a two-dimensionally woven S-glass-fiber reinforcement. Because of the pulsed operation of ITER, both the static and the fatigue behavior of the material have to be assessed under the actual operating conditions, including the appropriate radiation environment at the magnet location. To obtain information on the radiation-induced material degradation, the material was irradiated at ambient and low temperatures to neutron fluences of 5 × 10 22 m −2 ( E > 0.1 MeV). After measurements of swelling and weight loss, all experiments were carried out at 77 K. Half of the 5 K irradiated samples were subjected to a warm-up cycle to room temperature before testing. Tensile and short-beam-shear tests characterize the material in tension and interlaminar shear. Stress–lifetime diagrams of tensile and double-lap-shear specimens were assessed under tension–tension fatigue load up to 10 6 cycles.

Influence of temperature on the behaviour of INTEGRAL n-type HPGe detectors irradiated with fast neutrons

Several INTEGRAL n-type HPGe detectors have been irradiated by fast neutrons at different temperatures and their performances have been evaluated. Their behaviour during warm-up and cool-down cycles following the irradiations show evidence for irreversible temperature effects above 100 K. The detectors recovery after annealing was also studied.

Raman studies of the isotopic effect in solid and matrix-isolated oxygen

The Raman spectra of oxygen with different isotope compositions were investigated in the solid state and in argon and nitrogen matrices at 15 K. The fundamental vibration of the isotopomers 16O17O, 16O18O and 17O17O reveal a doublet of lines, each separated by 2.2 cm-1, in solid oxygen and in nitrogen matrices. The isotopic effect is independent of isotope composition and can be annealed by a warm-up cycle. © 1997 John Wiley & Sons, Ltd.

Low-temperature interlaminar shear strength of reactor irradiated glass-fibre-reinforced laminates

Glass-fibre-reinforced plastics (GFRPs) are candidate insulating materials for superconducting magnet coils in future fusion reactors. Therefore, the influence of radiation damage (gamma and fast neutrons) especially on the interlaminar shear behaviour of these materials has to be investigated carefully. Different types of GFRP laminate (two-dimensional E- or S-glass fibre reinforcements, epoxy or polyimide resins) have been irradiated at room temperature in the TRIGA reactor (Vienna, Austria) and at 5 K in the FRM Munich (Garching, Germany) up to a neutron fluence of 5 × 10 22m −2 ( E > 0.1 MeV) prior to short-beam-shear (SBS) testing at 77 K. After low-temperature irradiation, half of the samples were subjected to a warm-up cycle to room temperature before testing at 77 K. Results on the influence of different radiation sources, irradiation temperatures and annealing cycles as well as the boron content of some laminates on the interlaminar shear strength (ILSS) are compared and discussed, together with microstructural observations made with a scanning electron microscope.