查看更多>>摘要：In the framework of JT-60SA Tokamak commissioning (Japan， 2021)， all coils have to be cooled with supercritical helium forced-flow at the temperature of 4。5 K in order to reach superconducting state before energization。 An important issue is to predict the Joule energy dissipated in Cable-In-Conduit Conductors (CICC) and the maximal temperature reached in case of an incidental quench occurrence。 Therefore， quench simulations were performed on the Toroidal Field Coil (TFC) with the STREAM (Superconductor Thermal hydraulic and Resistive Electrical Analytical Model) code and with the SuperMagnet code (CryoSoft)， coupling THEA (thermal hydraulic and electrical 1-D CICC model) and Flower (thermal hydraulic network model)。 The quench event was simulated for one TFC at nominal conditions of tokamak operation。 External energy deposition over each pancake's first turn of the coil at the peak magnetic field location was applied for initiating the resistive transition。 This way， the computed Joule energy dissipated by one TFC is conservatively evaluated to be 5。65 MJ。 The Joule energy dissipation depends strongly on quench initiation conditions and on the number of fully and rapidly quenched pancakes (maximal quench propagation velocity of 19。5 m/s)。 Some further analyses were performed on the acceptance quench test realized at the Cold Test Facility (CEA Saclay， 2018) on TFC02。 The different calculation results (helium temperature， mass flow rate in upstream and downstream manifolds， normal length propagation) are presented in the following study and are consistent with the measurements。 This analysis brings information on the limits and the ability of STREAM code to model quench behaviour in CICC coils cooled by forced flow of supercritical helium。 This tool could be useful for tokamak magnets protection during quench event and safe operation， notably thanks to its fast computing time。
查看更多>>摘要：Thermal-hydraulic analyses of forced-flow cooled superconducting conductors designed for fusion magnets are typically based on 1-D mathematical models， which demand reliable predictive correlations for the transverse mass-， momentum- and energy transport processes occurring between different conductor components。 Friction factor correlations， derived from pressure drop tests or Computational Fluid Dynamics (CFD) simulations of conductor samples， describe momentum transfer。 High Temperature Superconductors (HTS) are promising materials to be applied in future fusion magnets， since they offer operating magnets at higher magnetic fields or higher temperatures as compared to the current conductors made of Low Temperature Superconductors (LTS)。 Various concepts of HTS cables for fusion applications are being developed， characterized and analysed。 Recently three concepts of triplet HTS subsize-conductors for a quench experiment have been proposed by KIT。 Each of them consists of three twisted CrossConductor (CroCo) strands enclosed in a stainless steel jacket， but they feature different copper stabilizer geometry。 In the Option 1 and 2 conductors CroCo strands are contained in copper sheaths of different thickness， whereas in the Option 3 they are embedded in copper profiles with larger contact area。 Hydraulic characteristics of such conductors were unknown。 Three dedicated short dummy conductors with the geometry identical to Option 1-3 conductors were prepared by KIT to be tested for pressure drop。 Option 1 and 2 samples were prepared and characterized earlier。 In the present study we report the results of the hydraulic test of the Option 3 conductor， performed using demineralized water at different temperatures， as well as the outcomes of the CFD simulations using the ANSYS FLUENT commercial code。 It was observed that the experimental values of friction factor in the turbulent regime are small (close to the respective values predicted by the smooth tube correlation)。 The friction factors obtained by the CFD simulations agreed with the experimental data within the range of measurement uncertainty。 Based on experimental and simulation results we developed a friction factor correlation valid in a very wide range of Reynolds number which could be used in thermal-hydraulic analyses of similar HTS cables。
查看更多>>摘要：Piston offset in the helium valved linear compressor (VLC) deteriorates the cooling performance and operating life of Joule-Thomson (JT) refrigerators， especially in aerospace applications。 To clarify the influence of piston offset on the VLC performance， an experimental investigation was carried out。 Based on a laboratory developed VLC， the effects of piston offset on the suction and discharge pressure， pressure ratio， mass flow rate， motor efficiency， volume efficiency and adiabatic efficiency are systematically studied under two piston motion states (fixed piston displacements and full strokes)。 The results show that when the piston stroke is constant， the offset will increase the discharge pressure and mass flow rate， and decrease suction pressure。 When the piston moves at full stroke， the offset will reduce the discharge pressure and mass flow rate， and increase suction pressure。 Regardless of the working conditions， the existence of offset will affect the efficiency of the compressor， hence increasing the power consumption。
查看更多>>摘要：A numerical model is established to calculate the temperature and pressure distributions of the 3 km long high temperature superconducting (HTS) power cable。 The model assumes that the configuration of HTS power cable is three phase co-axial shape with counter-flow cooling method。 In the numerical model， the circulating nitrogen enters the inner channel of the HTS power cable for cooling at the one end， flows to the other terminal， returns through the outer channel， and exits from the HTS power cable。 The numerical model considers the mass， the momentum， and the energy balances of nitrogen， and the heat diffusion inside the HTS layer to obtain the realistic temperature and pressure distributions of the cable。 When the long HTS cable is cooled by subcooled liquid nitrogen， the result shows that the maximum temperature of the compact HTS layer cannot be kept under 80 K even though the subcooled liquid nitrogen is supplied at the melting temperature。 In order to supply nitrogen with lower enthalpy for ensuring sufficient cooling through the whole cable region， we suggest using slush nitrogen， and analyze it in the detailed numerical model。 Thermo-hydraulic equations for slush nitrogen are incorporated in the numerical model。 The results show that the maximum temperature of the HTS layer decreases by 6。4 K when slush nitrogen with solid volume fraction of 30% is supplied to the HTS cable。 The effect of the inlet enthalpy of nitrogen and the heat transfer characteristics to the temperature distribution is discussed and further elucidated in this paper。
查看更多>>摘要：The pre-conceptual design phase of the EU DEMO magnet system relies on mechanical， electromagnetic and thermal-hydraulic analyses of different conductor designs for the Toroidal Field (TF) coils， the Poloidal Field (PF) coils and the Central Solenoid (CS) magnet。 The cryo-magnetic system includes the superconducting magnets cooled by forced flow of supercritical helium at about 4。5 K， the cryo-distribution lines and valve boxes， and the cryogenic system with several cold boxes。 The present analysis focuses on the cooling requirement of the TF coils with three winding pack options for the cable in conduit conductors based on 2015 DEMO baseline， featuring pancake or layer winding approaches。 This analysis methodology would be further developed with the latest conductor designs and more complete heat load assumptions for the future conductor design studies and the specification of the cooling requirements。 Parametric studies on the cold source temperature and on the supercritical helium mass flow rate have been performed on the three conductor designs in order to identify for each one the impact of the cooling conditions onto the temperature margin with respect to the current sharing temperature。 In this study， the heat load contribution have been limited to the estimation of the neutron heating and some joint resistance heat loads when available。 In addition， Simcryogenics， a dynamic modelling tool developed by CEA， is used to model supercritical helium loops for cooling different conductor designs。 An algorithm has been developed to optimize both the cold source temperature and the supercritical helium mass flow， in order to minimize refrigeration power for each conductor design。 Optimization studies are analyzed and compared in order to estimate for each TF winding pack design， the impact on refrigeration power。 The interest of such quick cross-check analyses is to identify design improvements for the conductors and the cryodistribution， keeping acceptable temperature margins and minimizing the refrigeration power。
查看更多>>摘要：A cooling system using a cryocooler and boil-off gas was proposed for cryogenic propellant storage on the lunar surface。 The cryogenic tank was covered with an advanced non-interlayer-contact multi-layer-insulation and coolant from the cryocooler and boil-off gas flow in the layers to remove the heat load。 The proposed system included optimization factors for fluid tubes location， cryocooler temperature， and flow rate。 A simple uniformtemperature thermal model was developed to optimize boil-off rates and system weights， and the results revealed a Pareto front。 A three-dimensional model was developed to discuss the effect of temperature nonuniformity。 Finally， the proposed concept was compared to other candidates。 The results showed that the proposed system offered a well-balanced system in terms of boil-off rate， system mass， and electric power consumption， which drastically reduced the boil-off rate when compared to only multi-layer insulations， which reduced the weight and power consumptions as compared to zero-boil-off systems。
查看更多>>摘要：The second-stage regenerators of pulse tube refrigerators (PTRs) are routinely used to intercept heat loads without disturbing cooling at their base temperatures， often near 4 K。 Gifford-McMahon cryocoolers (GMCs) have not yet demonstrated a similar capability to provide regenerator cooling， possibly because of the thermal resistance between their regenerator shell and core。 Here we show that GMCs do have capacity to provide regenerator cooling when heat loads are applied directly on the outer regenerator shell， although to a lesser extent compared to PTRs of similar cooling capacity。 For example， we intercepted a 900 mW heat load at 21。6 K using the second-stage regenerator of a GMC while only giving up 10 mW of cooling at 3 K (out of 270 mW)。 This performance may possibly be improved by optimizing heat exchange between heat source and regenerator shell。 We provide detailed temperature profile measurements from both a GMC and a PTR while applying heat to the regenerators， showing distinct behavior between the two。 We also show that for GMCs， the optimal location of heat injection should be farther from the cold end than for PTRs。 Although the physical source of regenerator cooling is less clear for GMCs than it is for PTRs， a useful amount of cooling is available and warrants further study。
Savaskan, BurcuKantar, Gunay KayaGuner, Sait Baris
7页
查看更多>>摘要：The effect of bis oxalate (C22H22O6) addition on critical current density (J(c))， lattice parameters， microstructure， superconducting temperature (T-c)， magnetic levitation force (F-z) and lateral force (F-x) properties of bulk MgB2 has been studied for the first time in this study。 Bulk MgB2 samples containing x wt% C22H22O6;(x ranging from 0， 1。5， 3， 4。5， 6 and 9 wt%) were fabricated with by in-situ solid state sintering technique at 775 degrees C。 F-z and F-x measurements at 25 K and 30 K were made under zero-field-cooled (ZFC) and field-cooled (FC) regimes。 The analysis of XRD and SEM points out a drop in lattice parameters and grain size of bis oxalate added samples and endorses C replacement in B sites in MgB2 lattice。 It was observed that the bis oxalate addition has a progressive effect on magnetic levitation performance of MgB2。 Whereas the maximum F-z and F-x values of undoped sample show 16。91 N and 7。10 N at 25 K， the maximum force values of the 3 wt% (BO) added sample correspond to 18。62 N and 8。49 N at 25 K。 Furthermore， the (BO) addition meaningfully rises the critical current density (J(c)) values of MgB2。 The Jc values observed as 57 kA/cm(2) and 70 kA/cm(2) in self-field at 25 K for pure and 3 wt% (BO) doped MgB2 sample。 The experimental results reveal that C22H22O6， as an example of carbohydrate， is an effective C-containing additive for the enhancement of the superconducting and magnetic levitation capacities of MgB2。
查看更多>>摘要：A cryogenic capsule is the key component of the inertial confinement fusion device and has gained increasing attention in the world。 The solid hydrogen-isotope fuel inside the capsule is required to have a uniformity greater than 99% for a successful ignition。 This study is concerned with the growing characteristics of the fuel layer。 A numerical model has been established， and the predicted results are in good agreement with the experimental data。 The investigation results indicate that during the growing process， the DT ice layer gets thicker with a decreasing growth speed， and this is accompanied by a dramatical increase in the amplitudes of low modes， especially for mode 1。 The uniformity of the fuel layer can be improved by the means of reducing the maximum temperature difference along the capsule， increasing the mass of the fusion fuel inside the capsule， and using the higher-tritium fusion fuel。 For the content of tritium of the fuel， the modes amplitudes of the fuel layer decrease with the contents of tritium， and no obvious change is observed when the volume fraction of tritium becomes greater than 50%。
查看更多>>摘要：Under extreme conditions such as cryogenic temperatures， the application of optical fiber sensors inevitably encounters significant challenges， which include the calibrations associated with the thermal problems of sensor placement and heat sinking and the nonlinear dependence of cryogenic temperatures。 Thus， fundamental investigations involving high-precision calibrations of the strain and temperature at cryogenic temperatures are essential。 To this end， in this study， the thermo-optic coefficient， temperature and strain sensitivity coefficients for a Rayleigh-scattering-based distributed optical fiber sensor (DOFS) were calibrated。 This experiment was implemented using a self-built low-temperature test device， and the calibration study was conducted over a large cryogenic temperature range， from 77 K to room temperature。 The results indicated that the strain sensitivity coefficient of the Rayleigh-scattering-based DOFS is temperature-independent， whereas the temperature sensitivity coefficient has a significantly nonlinear temperature dependence and is associated with the coating polymer layers of the fiber。 The coefficients and fitting functions were obtained over a large range of cryogenic temperatures， which indicated the invaluable properties of optical fibers in practice。 Furthermore， the strain and temperature of an aluminum beam under thermal and bending loads were measured。 The results indicated good agreement between the optical fibers and strain gauges， which verified the availability and reliability of Rayleigh-scattering-based distributed optical fibers in cryogenic environments。
NSTL
Elsevier