We investigated the mechanical and microstructural responses of a high-strength equal-molar medium entropy FeCrNi alloy at 293 and 15 K by in situ neutron diffraction testing.At 293 K,the alloy had a very high yield s...We investigated the mechanical and microstructural responses of a high-strength equal-molar medium entropy FeCrNi alloy at 293 and 15 K by in situ neutron diffraction testing.At 293 K,the alloy had a very high yield strength of 651±12 MPa,with a total elongation of 48%±5%.At 15 K,the yield strength increased to 1092±22 MPa,but the total elongation dropped to 18%±1%.Via analyzing the neutron diffraction data,we determined the lattice strain evolution,single-crystal elastic constants,stacking fault probability,and estimated stacking fault energy of the alloy at both temperatures,which are the critical parameters to feed into and compare against our first-principles calculations and dislocation-based slip system modeling.The density functional theory calculations show that the alloy tends to form shortrange order at room temperatures.However,atom probe tomography and atomic-resolution transmission electron microscopy did not clearly identify the short-range order.Additionally,at 293 K,experimental measured single-crystal elastic constants did not agree with those determined by first-principles calculations with short-range order but agreed well with the values from the calculation with the disordered configuration at 2000 K.This suggests that the alloy is at a metastable state resulted from the fabrication methods.In view of the high yield strength of the alloy,we calculated the strengthening contribution to the yield strength from grain boundaries,dislocations,and lattice distortion.The lattice distortion contribution was based on the Varenne-Luque-Curtine strengthening theory for multi-component alloys,which was found to be 316 MPa at 293 K and increased to 629 MPa at 15 K,making a significant contribution to the high yield strength.Regarding plastic deformation,dislocation movement and multiplication were found to be the dominant hardening mechanism at both temperatures,whereas twinning and phase transformation were not prevalent.This is mainly due to the high stacking fault energy of the alloy as estimated t展开更多
During the tokamak operation, variation of the stored energy can cause internal perturbations of the plasma. These perturbations may develop into large-scale vertical movement of the whole column for the vertically el...During the tokamak operation, variation of the stored energy can cause internal perturbations of the plasma. These perturbations may develop into large-scale vertical movement of the whole column for the vertically elon- gated tokamak, eventually generating the hot vertical displacement event （VIDE,）. It will cause considerable damage to the machine. In this work, the hot VDE process due to stored energy perturbations is investigated by a mature non-linear time-evolution code DINA. The influence on the vertical instability, the displacement direction and the electromagnetic loads on in-vessel components during the hot VDE are analyzed. It is shown that a larger perturbation leads to faster development of the vertical instability. Meanwhile the variation of the Shafranov shift, due to the energy change, is related to the VDE direction. The vertical electromagnetic force on the vacuum vessel and the halo current flowing in the divertor baffle become larger in the case of VDE moving towards the X point.展开更多
A Michelson interferometer, on loan from EFDA-JET（Culham, United Kingdom）has recently been commissioned on the experimental advanced superconducting tokamak（EAST,ASIPP, Hefei, China）. Following a successful in-sit...A Michelson interferometer, on loan from EFDA-JET（Culham, United Kingdom）has recently been commissioned on the experimental advanced superconducting tokamak（EAST,ASIPP, Hefei, China）. Following a successful in-situ absolute calibration the instrument is able to measure the electron cyclotron emission（ECE） spectrum, from 80 GHz to 350 GHz in extraordinary mode（X-mode） polarization, with high accuracy. This allows the independent determination of the electron temperature profile from observation of the second harmonic ECE and the possible identification of non-Maxwellian features by comparing higher harmonic emission with numerical simulations. The in-situ calibration results are presented together with the initial measured temperature profiles. These measurements are then discussed and compared with other independent temperature profile measurements. This paper also describes the main hardware features of the diagnostic and the associated commissioning test results.展开更多
To produce fusion reactions efficiently,thermonuclear plasmas have to reach extremely high temperatures,which is incompatible with their coming into contact with material surfaces.Confinement of plasmas using magnetic...To produce fusion reactions efficiently,thermonuclear plasmas have to reach extremely high temperatures,which is incompatible with their coming into contact with material surfaces.Confinement of plasmas using magnetic fields has progressed significantly in the last years,particularly in the tokamak configuration.Unfortunately,all tokamak devices,and particularly metallic ones,are plagued by catastrophic events called disruptions.Many disruptions are preceded by anomalies in the radiation patterns,particularly in ITER-relevant scenarios.These specific forms of radiation emission either directly cause or reveal the approaching collapse of the configuration.Detecting the localization of these radiation anomalies in real time requires an innovative and specific elaboration of bolometric measurements,confirmed by visible cameras and the inversion of sophisticated tomographic algorithms.The information derived from these measurements can be interpreted in terms of local power balances,which suggest a new quantity,the radiated power divided by the plasma internal energy,to determine the criticality of the plasma state.Combined with robust indicators of the temperature profile shape,the identified anomalous radiation patterns allow determination of the sequence of macroscopic events leading to disruptions.A systematic analysis of JET campaigns at high power in deuterium,full tritium,and DT,for a total of almost 2000 discharges,proves the effectiveness of the approach.The warning times are such that,depending on the radiation anomaly and the available actuators,the control system of future devices is expected to provide enough notice to enable deployment of effective prevention and avoidance strategies.展开更多
As JET is developing and testing operational scenarios for higher fusion performance,an increase in pulse disruptivity is being observed.On a deeper analysis,we find that several radiative phenomena play an active rol...As JET is developing and testing operational scenarios for higher fusion performance,an increase in pulse disruptivity is being observed.On a deeper analysis,we find that several radiative phenomena play an active role in determining the outcome of the pulse.The analysis is enabled by the use of real-time tomography based on the bolometer diagnostic.Even though plasma tomography is an inverse problem,we use machine learning to train a forward model that provides the radiation profile directly,based on a single matrix multiplication step.This model is used to investigate radiative phenomena including sawtooth crashes,ELMs and MARFE,and their relationship to the radiated power in different regions of interest.In particular,we use realtime tomography to monitor the core region,and to throw an alarm whenever core radiation exceeds a certain threshold.Our results suggest that this measure alone can anticipate a significant fraction of disruptions in the JET baseline scenario.展开更多
基金supported by the City U grant 9360161 and RGC grant 25202719funding from the Euratom research and training programs 2014–2018 and 2019–2020 under Grant Agreement No.633053+4 种基金the RCUK Energy Programme[Grant No.EP/T012250/1]funding from the European Research Council(ERC)under the European Union’s Horizon 2020 research and innovation program(grant agreement No.714697)support from high-performing computing facility MARCONI(Bologna,Italy)provided by EUROfusiona part of an international project co-financed from the funds of the program of the Polish Minister of Science and Higher Education entitled"PMW"in 2019,Agreement No.5018/H2020-Euratom/2019/2support of the Interdisciplinary center for Mathematical and Computational Modeling(ICM),University of Warsaw,under grant No.GB79–6。
文摘We investigated the mechanical and microstructural responses of a high-strength equal-molar medium entropy FeCrNi alloy at 293 and 15 K by in situ neutron diffraction testing.At 293 K,the alloy had a very high yield strength of 651±12 MPa,with a total elongation of 48%±5%.At 15 K,the yield strength increased to 1092±22 MPa,but the total elongation dropped to 18%±1%.Via analyzing the neutron diffraction data,we determined the lattice strain evolution,single-crystal elastic constants,stacking fault probability,and estimated stacking fault energy of the alloy at both temperatures,which are the critical parameters to feed into and compare against our first-principles calculations and dislocation-based slip system modeling.The density functional theory calculations show that the alloy tends to form shortrange order at room temperatures.However,atom probe tomography and atomic-resolution transmission electron microscopy did not clearly identify the short-range order.Additionally,at 293 K,experimental measured single-crystal elastic constants did not agree with those determined by first-principles calculations with short-range order but agreed well with the values from the calculation with the disordered configuration at 2000 K.This suggests that the alloy is at a metastable state resulted from the fabrication methods.In view of the high yield strength of the alloy,we calculated the strengthening contribution to the yield strength from grain boundaries,dislocations,and lattice distortion.The lattice distortion contribution was based on the Varenne-Luque-Curtine strengthening theory for multi-component alloys,which was found to be 316 MPa at 293 K and increased to 629 MPa at 15 K,making a significant contribution to the high yield strength.Regarding plastic deformation,dislocation movement and multiplication were found to be the dominant hardening mechanism at both temperatures,whereas twinning and phase transformation were not prevalent.This is mainly due to the high stacking fault energy of the alloy as estimated t
基金Supported by the Chinese ITER Plan Project Foundation under Grant Nos 2013GB113001 and 2015GB105001the National Natural Science Foundation of China under Grant No 11575056
文摘During the tokamak operation, variation of the stored energy can cause internal perturbations of the plasma. These perturbations may develop into large-scale vertical movement of the whole column for the vertically elon- gated tokamak, eventually generating the hot vertical displacement event （VIDE,）. It will cause considerable damage to the machine. In this work, the hot VDE process due to stored energy perturbations is investigated by a mature non-linear time-evolution code DINA. The influence on the vertical instability, the displacement direction and the electromagnetic loads on in-vessel components during the hot VDE are analyzed. It is shown that a larger perturbation leads to faster development of the vertical instability. Meanwhile the variation of the Shafranov shift, due to the energy change, is related to the VDE direction. The vertical electromagnetic force on the vacuum vessel and the halo current flowing in the divertor baffle become larger in the case of VDE moving towards the X point.
基金supported by National Natural Science Foundation of China(Nos.11405211,11275233)the National Magnetic Confinement Fusion Science Program of China(Nos.2013GB106002,2015GB101000)+1 种基金the RCUK Energy Programme(No.EP/I501045)partly supported by the JSPS-NRF-NSFC A3 Foresight Program in the Field of Plasma Physics(NSFC:No.11261140328)
文摘A Michelson interferometer, on loan from EFDA-JET（Culham, United Kingdom）has recently been commissioned on the experimental advanced superconducting tokamak（EAST,ASIPP, Hefei, China）. Following a successful in-situ absolute calibration the instrument is able to measure the electron cyclotron emission（ECE） spectrum, from 80 GHz to 350 GHz in extraordinary mode（X-mode） polarization, with high accuracy. This allows the independent determination of the electron temperature profile from observation of the second harmonic ECE and the possible identification of non-Maxwellian features by comparing higher harmonic emission with numerical simulations. The in-situ calibration results are presented together with the initial measured temperature profiles. These measurements are then discussed and compared with other independent temperature profile measurements. This paper also describes the main hardware features of the diagnostic and the associated commissioning test results.
文摘To produce fusion reactions efficiently,thermonuclear plasmas have to reach extremely high temperatures,which is incompatible with their coming into contact with material surfaces.Confinement of plasmas using magnetic fields has progressed significantly in the last years,particularly in the tokamak configuration.Unfortunately,all tokamak devices,and particularly metallic ones,are plagued by catastrophic events called disruptions.Many disruptions are preceded by anomalies in the radiation patterns,particularly in ITER-relevant scenarios.These specific forms of radiation emission either directly cause or reveal the approaching collapse of the configuration.Detecting the localization of these radiation anomalies in real time requires an innovative and specific elaboration of bolometric measurements,confirmed by visible cameras and the inversion of sophisticated tomographic algorithms.The information derived from these measurements can be interpreted in terms of local power balances,which suggest a new quantity,the radiated power divided by the plasma internal energy,to determine the criticality of the plasma state.Combined with robust indicators of the temperature profile shape,the identified anomalous radiation patterns allow determination of the sequence of macroscopic events leading to disruptions.A systematic analysis of JET campaigns at high power in deuterium,full tritium,and DT,for a total of almost 2000 discharges,proves the effectiveness of the approach.The warning times are such that,depending on the radiation anomaly and the available actuators,the control system of future devices is expected to provide enough notice to enable deployment of effective prevention and avoidance strategies.
基金This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 and 2019-2020 under grant agreement No.633053.The views and opinions expressed herein do not necessarily reflect those of the European Commission.IPFN(Instituto de Plasmas e Fusão Nuclear)received financial support from FCT(Fundação para a Ciência e a Tecnologia)through projects UIDB/50010/2020 and UIDP/50010/2020.The authors are thankful for the granted use of computational resources provided by CCFE/UKAEA at Culham,UK.
文摘As JET is developing and testing operational scenarios for higher fusion performance,an increase in pulse disruptivity is being observed.On a deeper analysis,we find that several radiative phenomena play an active role in determining the outcome of the pulse.The analysis is enabled by the use of real-time tomography based on the bolometer diagnostic.Even though plasma tomography is an inverse problem,we use machine learning to train a forward model that provides the radiation profile directly,based on a single matrix multiplication step.This model is used to investigate radiative phenomena including sawtooth crashes,ELMs and MARFE,and their relationship to the radiated power in different regions of interest.In particular,we use realtime tomography to monitor the core region,and to throw an alarm whenever core radiation exceeds a certain threshold.Our results suggest that this measure alone can anticipate a significant fraction of disruptions in the JET baseline scenario.
