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Papers by Koichi Matsumoto
TEION KOGAKU (Journal of Cryogenics and Superconductivity Society of Japan), 2011
Journal of Physics: Conference Series, 2017
Magnetic materials play a significant role in improvement of regenerative cryocooler performance,... more Magnetic materials play a significant role in improvement of regenerative cryocooler performance, because they have high volumetric specific heat at magnetic transition temperatures. Gadolinium oxysulfide (Gd 2 O 2 S, GOS) that has an antiferromagnetic transition at 5 K improved the cooling performance of cryocoolers when it was used in colder side of the second stage regenerator operating below 10 K. Small magnetic susceptibility and specific heat insensitive to magnetic field is important in order to reduce influence of magnetic field on the performance of cryocooler. We measured magnetization and specific heat of ceramic GOS in magnetic field up to 5 T. The magnetization of GOS represented typical temperature dependence for antiferromagnetic materials and no metamagnetic transition was observed. As for specific heat of GOS, peak temperature decreased from 5.5 to 5.0 K with increasing magnetic field from 0 to 5 T and the transitions remained sharp in magnetic fields. Thermal conductivity of GOS was observed to have very small magnetic field dependence.
Physical Review Letters, 2004
Physical Review Letters, 2011
PrIr 2 Zn 20. The measurements of specific heat and magnetization revealed the non-Kramers À 3 do... more PrIr 2 Zn 20. The measurements of specific heat and magnetization revealed the non-Kramers À 3 doublet ground state with the quadrupolar degrees of freedom. The specific heat exhibits a sharp peak at T Q ¼ 0:11 K. The increment of T Q in magnetic fields and the anisotropic B À T phase diagram are consistent with the antiferroquadrupolar ordered state below T Q. The entropy release at T Q is only 20% of R ln2, suggesting that the quadrupolar fluctuations play a role in the formation of the superconducting pairs below T c ¼ 0:05 K.
Physical Review Letters, 1997
Journal of the Physical Society of Japan, 2009
Journal of Physics and Chemistry of Solids, 2005
Superfluid transition and solidification of 4He in aerogel has been studied by longitudinal ultra... more Superfluid transition and solidification of 4He in aerogel has been studied by longitudinal ultrasound. The superfluid transition temperature was determined up to the solidification pressure. The superfluid transition temperature in aerogel which was identified as a sharp absorption peak was suppressed from that in bulk liquid. The magnitude of suppression in aerogel was a few milli-Kelvin from the saturated vapor pressure to the solidification pressure and was much smaller than that in other porous media. The onset of solidification of 4He in aerogel was identified as an increase in sound absorption. It was shown that the overpressure required to initiate solidification was 0.2–0.3MPa between 1.1 and 1.8K. Small hysteresis was observed at the solidification and melting.
Journal of Physics: Conference Series, 2009
In the present work we propose the explanation of the recently observed at temperatures about 1.7... more In the present work we propose the explanation of the recently observed at temperatures about 1.7 K anomalous ultrasound attenuation in high-porous aerogels filled in by liquid 4 He by means of 2D-3D roton transformations. The existence of so-called 2D rotons in the system "aerogel-liquid 4 He" has been found early in the experiments on inelastic neutron scattering T < 1.5 K where the spectrum of roton excitations is well-defined. The difference in energies of 3D-rotons and 2D-rotons at low temperatures exceeds the energy of acoustic phonons and the process of transformation of 2D-roton to 3D-roton is forbidden by energy conservation law. But with increasing temperature the 2D-roton and 3D-roton states begin to be broadened (the lifetime of excitations is decreasing) and possibility of the mutual transformation of rotons with the participation of a phonon appears. The further increasing of temperature leads to the essential decreasing of superfluid density and the efficiency of the proposed mechanism decreases too. Numerical simulations show the qualitative agreement of the proposed mechanism with the observed data.
Journal of Physics: Conference Series, 2009
Journal of Low Temperature Physics, 2007
We have studied the acoustic properties of liquid helium filled in various aerogels. The longitud... more We have studied the acoustic properties of liquid helium filled in various aerogels. The longitudinal ultrasound velocity and attenuation were measured at the frequency of 10 MHz with aerogels that had porosity from 92 to 97%. The mode intermediate between first and fourth sound was observed. The attenuation of this mode decreased with decreasing temperature for dense aerogels. However, an attenuation maximum was observed around 1.6 K for 97% open aerogel at various liquid pressures. In the present work, we discuss the possibility of the sound modes conversion between first, second sound in superfluid and aerogel sound mode in this composite system.
Journal of Low Temperature Physics, 2009
Journal of Experimental and Theoretical Physics Letters, 2004
Cryogenics, 2014
Nuclear demagnetization is one of the most successful methods of cooling an appreciable amount of... more Nuclear demagnetization is one of the most successful methods of cooling an appreciable amount of matter to the lowest temperatures. The principle of nuclear demagnetization is the same as that of the adiabatic demagnetization of a paramagnetic salt; however, there is a significant difference in practice. This article focuses on nuclear demagnetization refrigeration used in experiments at millikelvin and much lower temperatures. After a brief overview of the basic principle and methods, typical requirements of the refrigerants are described from the view point of experiments. The heat switch and thermometry used in nuclear demagnetization experiments are also discussed.
Cryogenics, 2014
The magnetocaloric effect is the thermal response of a material to an external magnetic field. Th... more The magnetocaloric effect is the thermal response of a material to an external magnetic field. This manuscript focuses on the physics and the properties of materials which are commonly used for magnetic refrigeration at cryogenic temperatures. After a brief overview of the magnetocaloric effect and associated thermodynamics, typical requirements on refrigerants are discussed from a standpoint of cooling power density optimization. Finally, a compilation of the most important properties of several common magnetocaloric materials is presented.
Cryogenics, 2014
This paper reviews the development status of magnetic refrigeration system for hydrogen liquefact... more This paper reviews the development status of magnetic refrigeration system for hydrogen liquefaction. There is no doubt that hydrogen is one of most important energy sources in the near future. In particular, liquid hydrogen can be utilized for infrastructure construction consisting of storage and transportation. Liquid hydrogen is in cryogenic temperatures and therefore high efficient liquefaction method must be studied. Magnetic refrigeration which uses the magneto-caloric effect has potential to realize not only the higher liquefaction efficiency > 50 %, but also to be environmentally friendly and cost effective. Our hydrogen magnetic refrigeration system consists of Carnot cycle for liquefaction stage and AMR (active magnetic regenerator) cycle for precooling stages. For the Carnot cycle, we develop the high efficient system > 80 % liquefaction efficiency by using the heat pipe. For the AMR cycle, we studied two kinds of displacer systems, which transferred the working fluid. We confirmed the AMR effect with the cooling temperature span of 12 K for 1.8 T of the magnetic field and 6 second of the cycle. By using the simulation, we estimate the total efficiency of the hydrogen liquefaction plant for 10 kg/day. A FOM of 0.47 is obtained in the magnetic refrigeration system operation temperature between 20 K and 77 K including LN 2 work input.
Cryogenics, 2011
AMRR cycle Layered bed Gd Àx Tb 1Àx alloys Gd Àx Dy 1Àx alloys a b s t r a c t Magnetic refrigera... more AMRR cycle Layered bed Gd Àx Tb 1Àx alloys Gd Àx Dy 1Àx alloys a b s t r a c t Magnetic refrigeration is an emerging technology based on the magnetocaloric effect in solid-state refrigerants. The active magnetic regenerative refrigeration (AMRR) cycle is a special kind of regenerator for the magnetic refrigerator, in which the magnetic material matrix works both as a refrigerating medium and as a heat regenerating medium, while the fluid flowing in the porous matrix works as a heat transfer medium. The performance of an AMRR cycle depends strongly on the behaviour of the adiabatic magnetization temperature change as a function of material temperature in the flow direction of the regenerator. In the present paper, a practical model for predicting the performance and efficiency of an AMRR cycle has been developed. The model simulates both the ferromagnetic material and the entire cycle of an AMRR operating in conformity with a Brayton regenerative cycle. The model simulates different kinds of layered regenerators operating at their optimal operation point. The program study the Gd Àx Tb 1Àx alloys as constituent materials for the regenerator over the temperature range 275-295 K, and Gd x Dy 1Àx alloys in the temperature range 260-280 K. With this model, the refrigeration capacity, the power consumption and consequently the coefficient of performance can be predicted. The results show a greater COP for the refrigerator based on the magnetocaloric technology compared with the COP of a classical vapour compression plant working between the same thermal levels.
Cryogenics, 1997
We investigated a layered structural regenerator (multilayer regenerator) with magnetic regenerat... more We investigated a layered structural regenerator (multilayer regenerator) with magnetic regenerator materials using a two-stage GM refrigerator. In this study we used Er0.75Gd0.25Ni which was expected to be placed in the high temperature part of the second regenerator. To confirm the effect of Er0.75Gd,,25Ni, the heat-exchange efficiency of the regenerator (regenerator efficiency) with Er0.75Gd0.25Ni, Er,Co and ErO.sYbO.,Ni, which were in the volumetric ratio x: (0.5-x): 0.5 (0 zz x I 0.5) was calculated as a function of x by computer simulation. We found that the regenerator efficiency increased when x (i.e. the amount of Er0.75 Gd,,25Ni) was increased and an optimum value of x was-0.25. We then made two kinds of second regenerator: a triple layer regenerator with Er0.75 Gd,,25Ni, Er,Co and ErO,gYb,.,Ni, which were in the volumetric ratio 0.25:0.25:0.5, and a double layer regenerator with Er,Co and
Cryogenics, 2011
ABSTRACT Considering the unignorable factors in practice, a new time independent, 2-dimensional p... more ABSTRACT Considering the unignorable factors in practice, a new time independent, 2-dimensional porous media model of room-temperature Active Magnetic Regenerative Refrigeration (AMRR) has been proposed. The 2-D model improved the existing 1-dimensional model by introducing the influence of heat transfer effect though the regenerator wall and conduction for y-axis inside the regenerator. This study compared the previous 1-D model with the 2-D model and concluded that the system can lose 22% of cooling capacity caused by air convection and the conduction loss in y can reach to 10% of cooling capacity. It is concluded that the new model will be useful to predict the performance of room AMRR for more practical conditions.
TEION KOGAKU (Journal of Cryogenics and Superconductivity Society of Japan), 2011
Journal of Physics: Conference Series, 2017
Magnetic materials play a significant role in improvement of regenerative cryocooler performance,... more Magnetic materials play a significant role in improvement of regenerative cryocooler performance, because they have high volumetric specific heat at magnetic transition temperatures. Gadolinium oxysulfide (Gd 2 O 2 S, GOS) that has an antiferromagnetic transition at 5 K improved the cooling performance of cryocoolers when it was used in colder side of the second stage regenerator operating below 10 K. Small magnetic susceptibility and specific heat insensitive to magnetic field is important in order to reduce influence of magnetic field on the performance of cryocooler. We measured magnetization and specific heat of ceramic GOS in magnetic field up to 5 T. The magnetization of GOS represented typical temperature dependence for antiferromagnetic materials and no metamagnetic transition was observed. As for specific heat of GOS, peak temperature decreased from 5.5 to 5.0 K with increasing magnetic field from 0 to 5 T and the transitions remained sharp in magnetic fields. Thermal conductivity of GOS was observed to have very small magnetic field dependence.
Physical Review Letters, 2004
Physical Review Letters, 2011
PrIr 2 Zn 20. The measurements of specific heat and magnetization revealed the non-Kramers À 3 do... more PrIr 2 Zn 20. The measurements of specific heat and magnetization revealed the non-Kramers À 3 doublet ground state with the quadrupolar degrees of freedom. The specific heat exhibits a sharp peak at T Q ¼ 0:11 K. The increment of T Q in magnetic fields and the anisotropic B À T phase diagram are consistent with the antiferroquadrupolar ordered state below T Q. The entropy release at T Q is only 20% of R ln2, suggesting that the quadrupolar fluctuations play a role in the formation of the superconducting pairs below T c ¼ 0:05 K.
Physical Review Letters, 1997
Journal of the Physical Society of Japan, 2009
Journal of Physics and Chemistry of Solids, 2005
Superfluid transition and solidification of 4He in aerogel has been studied by longitudinal ultra... more Superfluid transition and solidification of 4He in aerogel has been studied by longitudinal ultrasound. The superfluid transition temperature was determined up to the solidification pressure. The superfluid transition temperature in aerogel which was identified as a sharp absorption peak was suppressed from that in bulk liquid. The magnitude of suppression in aerogel was a few milli-Kelvin from the saturated vapor pressure to the solidification pressure and was much smaller than that in other porous media. The onset of solidification of 4He in aerogel was identified as an increase in sound absorption. It was shown that the overpressure required to initiate solidification was 0.2–0.3MPa between 1.1 and 1.8K. Small hysteresis was observed at the solidification and melting.
Journal of Physics: Conference Series, 2009
In the present work we propose the explanation of the recently observed at temperatures about 1.7... more In the present work we propose the explanation of the recently observed at temperatures about 1.7 K anomalous ultrasound attenuation in high-porous aerogels filled in by liquid 4 He by means of 2D-3D roton transformations. The existence of so-called 2D rotons in the system "aerogel-liquid 4 He" has been found early in the experiments on inelastic neutron scattering T < 1.5 K where the spectrum of roton excitations is well-defined. The difference in energies of 3D-rotons and 2D-rotons at low temperatures exceeds the energy of acoustic phonons and the process of transformation of 2D-roton to 3D-roton is forbidden by energy conservation law. But with increasing temperature the 2D-roton and 3D-roton states begin to be broadened (the lifetime of excitations is decreasing) and possibility of the mutual transformation of rotons with the participation of a phonon appears. The further increasing of temperature leads to the essential decreasing of superfluid density and the efficiency of the proposed mechanism decreases too. Numerical simulations show the qualitative agreement of the proposed mechanism with the observed data.
Journal of Physics: Conference Series, 2009
Journal of Low Temperature Physics, 2007
We have studied the acoustic properties of liquid helium filled in various aerogels. The longitud... more We have studied the acoustic properties of liquid helium filled in various aerogels. The longitudinal ultrasound velocity and attenuation were measured at the frequency of 10 MHz with aerogels that had porosity from 92 to 97%. The mode intermediate between first and fourth sound was observed. The attenuation of this mode decreased with decreasing temperature for dense aerogels. However, an attenuation maximum was observed around 1.6 K for 97% open aerogel at various liquid pressures. In the present work, we discuss the possibility of the sound modes conversion between first, second sound in superfluid and aerogel sound mode in this composite system.
Journal of Low Temperature Physics, 2009
Journal of Experimental and Theoretical Physics Letters, 2004
Cryogenics, 2014
Nuclear demagnetization is one of the most successful methods of cooling an appreciable amount of... more Nuclear demagnetization is one of the most successful methods of cooling an appreciable amount of matter to the lowest temperatures. The principle of nuclear demagnetization is the same as that of the adiabatic demagnetization of a paramagnetic salt; however, there is a significant difference in practice. This article focuses on nuclear demagnetization refrigeration used in experiments at millikelvin and much lower temperatures. After a brief overview of the basic principle and methods, typical requirements of the refrigerants are described from the view point of experiments. The heat switch and thermometry used in nuclear demagnetization experiments are also discussed.
Cryogenics, 2014
The magnetocaloric effect is the thermal response of a material to an external magnetic field. Th... more The magnetocaloric effect is the thermal response of a material to an external magnetic field. This manuscript focuses on the physics and the properties of materials which are commonly used for magnetic refrigeration at cryogenic temperatures. After a brief overview of the magnetocaloric effect and associated thermodynamics, typical requirements on refrigerants are discussed from a standpoint of cooling power density optimization. Finally, a compilation of the most important properties of several common magnetocaloric materials is presented.
Cryogenics, 2014
This paper reviews the development status of magnetic refrigeration system for hydrogen liquefact... more This paper reviews the development status of magnetic refrigeration system for hydrogen liquefaction. There is no doubt that hydrogen is one of most important energy sources in the near future. In particular, liquid hydrogen can be utilized for infrastructure construction consisting of storage and transportation. Liquid hydrogen is in cryogenic temperatures and therefore high efficient liquefaction method must be studied. Magnetic refrigeration which uses the magneto-caloric effect has potential to realize not only the higher liquefaction efficiency > 50 %, but also to be environmentally friendly and cost effective. Our hydrogen magnetic refrigeration system consists of Carnot cycle for liquefaction stage and AMR (active magnetic regenerator) cycle for precooling stages. For the Carnot cycle, we develop the high efficient system > 80 % liquefaction efficiency by using the heat pipe. For the AMR cycle, we studied two kinds of displacer systems, which transferred the working fluid. We confirmed the AMR effect with the cooling temperature span of 12 K for 1.8 T of the magnetic field and 6 second of the cycle. By using the simulation, we estimate the total efficiency of the hydrogen liquefaction plant for 10 kg/day. A FOM of 0.47 is obtained in the magnetic refrigeration system operation temperature between 20 K and 77 K including LN 2 work input.
Cryogenics, 2011
AMRR cycle Layered bed Gd Àx Tb 1Àx alloys Gd Àx Dy 1Àx alloys a b s t r a c t Magnetic refrigera... more AMRR cycle Layered bed Gd Àx Tb 1Àx alloys Gd Àx Dy 1Àx alloys a b s t r a c t Magnetic refrigeration is an emerging technology based on the magnetocaloric effect in solid-state refrigerants. The active magnetic regenerative refrigeration (AMRR) cycle is a special kind of regenerator for the magnetic refrigerator, in which the magnetic material matrix works both as a refrigerating medium and as a heat regenerating medium, while the fluid flowing in the porous matrix works as a heat transfer medium. The performance of an AMRR cycle depends strongly on the behaviour of the adiabatic magnetization temperature change as a function of material temperature in the flow direction of the regenerator. In the present paper, a practical model for predicting the performance and efficiency of an AMRR cycle has been developed. The model simulates both the ferromagnetic material and the entire cycle of an AMRR operating in conformity with a Brayton regenerative cycle. The model simulates different kinds of layered regenerators operating at their optimal operation point. The program study the Gd Àx Tb 1Àx alloys as constituent materials for the regenerator over the temperature range 275-295 K, and Gd x Dy 1Àx alloys in the temperature range 260-280 K. With this model, the refrigeration capacity, the power consumption and consequently the coefficient of performance can be predicted. The results show a greater COP for the refrigerator based on the magnetocaloric technology compared with the COP of a classical vapour compression plant working between the same thermal levels.
Cryogenics, 1997
We investigated a layered structural regenerator (multilayer regenerator) with magnetic regenerat... more We investigated a layered structural regenerator (multilayer regenerator) with magnetic regenerator materials using a two-stage GM refrigerator. In this study we used Er0.75Gd0.25Ni which was expected to be placed in the high temperature part of the second regenerator. To confirm the effect of Er0.75Gd,,25Ni, the heat-exchange efficiency of the regenerator (regenerator efficiency) with Er0.75Gd0.25Ni, Er,Co and ErO.sYbO.,Ni, which were in the volumetric ratio x: (0.5-x): 0.5 (0 zz x I 0.5) was calculated as a function of x by computer simulation. We found that the regenerator efficiency increased when x (i.e. the amount of Er0.75 Gd,,25Ni) was increased and an optimum value of x was-0.25. We then made two kinds of second regenerator: a triple layer regenerator with Er0.75 Gd,,25Ni, Er,Co and ErO,gYb,.,Ni, which were in the volumetric ratio 0.25:0.25:0.5, and a double layer regenerator with Er,Co and
Cryogenics, 2011
ABSTRACT Considering the unignorable factors in practice, a new time independent, 2-dimensional p... more ABSTRACT Considering the unignorable factors in practice, a new time independent, 2-dimensional porous media model of room-temperature Active Magnetic Regenerative Refrigeration (AMRR) has been proposed. The 2-D model improved the existing 1-dimensional model by introducing the influence of heat transfer effect though the regenerator wall and conduction for y-axis inside the regenerator. This study compared the previous 1-D model with the 2-D model and concluded that the system can lose 22% of cooling capacity caused by air convection and the conduction loss in y can reach to 10% of cooling capacity. It is concluded that the new model will be useful to predict the performance of room AMRR for more practical conditions.