Type Cryostat Research Articles

Ligand Modified and Light Switched On/Off Single-Chain Magnets of {Fe 2 Co} Coordination Polymers via Metal-to-Metal Charge Transfer

Ligand Modified and Light Switched On/Off Single-Chain Magnets of {Fe ₂ Co} Coordination Polymers via Metal-to-Metal Charge Transfer

Short review on cryostats with superconducting magnets

Modern accelerators typically include many components working at cryogenic temperatures, like superconducting (sc) magnets, sc cavities, cooled beam tube, sc undulators. In most of the cases, sc magnets or cavities are used. Sc magnets were intensively developed over the last 50 years, and it is possible to say that for some sc materials, like NbTi or Nb3Sn, the technology reached a maturity. The sc magnets could be installed either in liquid helium reservoirs or be mounted on metallic structures and passively cooled by the thermal conduction. Though there is a large variety of different types of cryostats, some general requirements posted on them by sc magnets, bus-bars or current leads could be seen. In the present paper a short review on cryostats with superconducting magnets is done as well as general design requirements on bus-bars and safety diodes are shortly mentioned. Two typical cryostat types used for scientific needs or industry applications are discussed. Cryostats with high-Tc current leads or magnets are also shortly mentioned.

A low-temperature scanning probe microscopy system with molecular beam epitaxy and optical access.

A low-temperature ultra-high vacuum scanning probe microscopy (SPM) system with molecular beam epitaxy (MBE) capability and optical access was conceived, built, and tested in our lab. The design of the whole system is discussed here, with special emphasis on some critical parts. The SPM scanner head takes a modified Pan-type design with improved rigidity and compatible configuration to optical access and can accommodate both scanning tunneling microscope (STM) tips and tuning-fork based qPlus sensors. In the system, the scanner head is enclosed by a double-layer cold room under a bath type cryostat. Two piezo-actuated focus-lens stages are mounted on both sides of the cold room to couple light in and out. The optical design ensures the system's forward compatibility to the development of photo-assisted STM techniques. To test the system's performance, we conducted STM and spectroscopy studies. The herringbone reconstruction and atomic structure of an Au(111) surface were clearly resolved. The dI/dV spectra of an Au(111) surface were obtained at 5 K. In addition, a periodic 2D tellurium (Te) structure was grown on the Au(111) surface using MBE and the atomic structure is clearly resolved by using STM.

Temperature controller for immersion type cryostat

The main difficulty of investigations in the vicinity of phase transitions associated with high system requirements for the temperature stabilization. Due to the limited range of observed phenomena (~0.1-0.5K) [1], the algorithm of temperature stabilization should provide accuracy better than 0,01 ÷ 0.001K without over-regulation. This requirement means the choice of automatic control law parameters according to the following requirement - in the process of temperature stabilization, the system is not passed through the phase transition. Note also substantial dependence of physical parameters (permittivity, electrical conductivity, etc.) from the rate of temperature change, especially in the case of semiconductor materials [2]. Most thermostats used in experimental practice [3] do not meet the above requirements, so the study of critical phenomena in ferroelectrics - semiconductors need the development of non-standard equipment. This paper describes an automated control system for immersion type cryostat, which allows measuring the temperature Т with an accuracy of 0.001 K, change it according to prescribed algorithm and stabilize the T with an accuracy of ± 0,002 K in the range of 80 - 480 K. The system is built with the use of modern element base. Controller works as follows: Input signal from the PT100 [4] thermoresistor through ultra-low noise amplifier is supplied to the input of 24 bit analog-to-digital converter. The resulting digital code corresponds to the value of intensified voltage drop on PT100. For its conversion into the temperature the spreadsheet method is used. In the computer шы stored the calibration table according to R → T with the increments of 1 K. The temperature, which falls in the interval between two points of the table, is determined by spline-based interpolation that passes through the ten neighboring points of calibration table (five points above and the five points below of the coincidence interval). The resulting value of T is compared with the required temperature. Using standard PID (proportional-integral-differential) algorithm the necessary power of heater is determined. The code, corresponding to a given power, through the USB bus is fed to the digital-to-analog converter. DAC output voltage is determine the current on heater. For the output stage, the standard current amplifier is used. Computer based systems for measuring and stabilization of temperature provides the following benefits: o Temperature sensor replacement require only changing of the calibration table; o Using statistical analysis of the measurements data, exist a possibility for the significant increase of accuracy (noise compensation and emissions); o Temperature stabilization algorithm can be modified according to the objectives; o PID regulator parameters can be determined automatically (Autotuning PID or Adaptive PID).

Cryogenic system of China Dark matter Experiment (CDEX-10)

Dark matter is a type of matter hypothesized in astronomy and cosmology to account for a large part of the mass that appears to be missing from the universe. China Dark matter EXperiment (CDEX) is a direct detection system of dark matter. A cryogenic system for CDEX-10 has been designed and constructed. This note describes the cryogenic system of the CDEX-10, theoretical predictions of the heat loads to the cryostat, and measured heat loads at operation. The cryostat is an argon cooled bath type cryostat. Two pulse tube refrigerators are used for argon liquefying. The dark matter detecting needs a very quiet condition, so a special thermal shield is designed to reduce the radiation heat leakage.

Triple-Point Temperature and the Isotopic Composition of Three Commercial Neon Gases

The triple-point temperature of neon, \(T_{\mathrm{tp-Ne}}\), is known to have dependence on the isotopic composition. Recently, the Technical Annex for the International Temperature Scale of 1990 was updated to specify the method of correction for the isotopic reference ratio of neon. In this study, to confirm this correction in the Technical Annex independently, the effects of the isotopic composition of neon on \(T_{\mathrm{tp-Ne}}\) for three commercial neon gas sources were studied. For the measurement of the isotopic composition, a gas mass spectrometer was used to compare the sample gases with a reference neon gas whose isotopic composition was known with high precision by a gravimetric method. For the measurement of \(T_{\mathrm{tp-Ne}}\), an open-cell type cryostat for the realization of low-temperature fixed points was used. The physical cell and the thermal environment around it remained very similar for all \(T_{\mathrm{tp-Ne}}\) measurements with the neon gases due to the nature of the open-cell type system. Therefore, the difference in \(T_{\mathrm{tp-Ne}}\) among different samples could be measured with a relatively low uncertainty, canceling many systematic effects that are common to all measurements. Our result was consistent with the correction in the Technical Annex. Furthermore, because one of the commercial neon gases was the bottle that was used for KRISS measurements in the international comparison CCT-K2, it is now possible to correct the measurement for the reference isotopic ratio and compare it with other measurements for which isotopic composition data are available.

Development of a zero boil-off helium cryostat for superconducting magnets

This paper describes a horizontal type cryostat of a superconducting magnet with a 300mm room temperature bore. The magnet, with the diameter of 400mm and length of 815mm, is immersed in 30 liter liquid helium. Design consideration, including thermal staging of the silver/Bisco current leads, low thermal conduction mechanical support structure, and the theoretical calculation of heat load to the cryostat are discussed. And only a helium recondensing G-M cooler(40W at 50K, 1.5W at 4.2K) is used to achieve zero boil-off.

Tests of 3 T Superconducting Electromagnetic Iron Separator

A 3 T central field Superconducting Electromagnetic Iron Separator (SEIS) has been designed, fabricated and tested at Institute of High Energy Physics (IHEP) of China. The SEIS system is deliberately designed to separate small pieces of hazardous ferromagnetic materials, such as detonators, from coal to achieve high purity and good yield. The SEIS system mainly consists of a NbTi superconducting magnet, a LHe recondensation type cryostat with two GM cryocoolers (31 W/40 K, 1 W/4.2 K), a pair of binary current leads (CL). The 1 ton cold mass was located in the cryostat of the system with 630 mm room temperature bore. The system is powered with a 250 A/50 V power supply, and has charging time and discharging time of 15 minutes and 20 minutes, respectively. It took 10 days for SEIS magnet to cool down from 300 K to 4.2 K and 6 days to accumulate LHe at designed level 360 mm. The SEIS magnet suffered no quench to reach its designed current, and operated stably during many experiments afterwards. The experiment research of the SEIS system is detailedly presented in this paper.

Thermal Design and Experiment of Superconducting Electromagnet Iron Remover

A prototype of a Superconducting Electromagnet Iron Remover (SEIR) system with a 3 tesla (T) central field has been designed and manufactured at the Institute of High Energy Physics (IHEP) of China. The SEIR system is deliberately designed to separate small pieces of hazardous ferromagnetic materials, such as detonators, from coal to achieve high purity and good yield. The SEIR system consists of a NbTi superconducting magnet, a LHe recondensation type cryostat with two GM cryocoolers (31 W/40 K, 1 W/4.2 K), and a pair of binary current leads (CLs), etc. This paper presents the thermal analysis and experimental results of the SEIR system. A three-dimensional (3D) model of calculation for the magnet system was built. The heat load and the temperature distribution of the magnet system were analyzed using a finite element method. With regard to the heat load of the system, the finite element analysis (FEA) simulation results were quite close to the experimental results.

Steady and Transient State Analysis on Three Phase-in One Enclosure Type HTS Cable

This paper suggests an improved technique to establish the modeling regarding steady and transient state on three phase-in one cryostat type HTS(High Temperature Superconducting) cable. The proposed modeling is established using EMTP/ATPDraw and TACS and MODELS provided by that. It has higher accuracy than the conventional method, as the actual HTS cable is modelled. Steady and transient state analysis performed by EMTP/ATPDraw calculate the current of conductor, shield and former, respectively. In case of the transient state modeled quench state occurred by a single line-to-ground fault, current of conductor shield and former are also calculated, respectively. Especially, various fault resistances and angles are considered to improve the reliability during transient state analysis. Analysis results reveal that the proposed technique improves the accuracy of modeling.

Temperature dependence of the mechanical properties of melt-processed Dy–Ba–Cu–O bulksuperconductors evaluated by three point bending tests

Dy–Ba–Cu–O bulk superconductor has an excellent capability of trapping magnetic fluxand lower heat conductivity at cryogenic temperatures as compared with Y–Ba–Cu–O bulksuperconductor. The Young’s modulus and the bending strength in the range from roomtemperature to 7 K were measured by the three-point bending tests using specimens cutfrom a melt-processed Dy–Ba–Cu–O bulk superconductor. They were tested in a heliumgas flow type cryostat at Forschungszentrum Karlsruhe and in a liquid nitrogen bath atIwate University. The Young’s modulus was calculated by either the slope of stress–straincurve or that of the load–deflection curve of the specimen. Although the bendingstrength measured in the two institutes coincided well, there was a significantdiscrepancy in the Young’s modulus. The Young’s modulus and bending strengthincreased with decrease of temperature down to 7 K. The amount of increasein the Young’s modulus and the bending strength were about 32% and 36% ofthose at room temperature, respectively. The scatter of data for each run wassignificant and did not depend on temperature. The temperature dependence ofthe Young’s modulus coincided with that in Y–Ba–Cu–O obtained by ultrasonicvelocity. The temperature dependence of the Young’s modulus and the bendingstrength was discussed from the view point of interatomic distance of the bulkcrystal.

可視化法による液体3Heの沸騰観測

The behaviors of bubble nucleation and growth in liquid 3He were investigated visually using the shadowgraph method. We have constructed two types of cryostats and sample cells for measurements between 0.5 and 1K. The 3He bubble that formed on the heated copper surface was spheroid-like due to a low surface tension and small buoyancy force. The time for required for the bubble to grow and separate from the surface was 14ms at a heat flux of q = 8=10-5 W/cm2 and bulk liquid 3He temperature of 0.7K. This means that the bubble growth rate is high as compared to other low-temperature liquids. The bubble size, number of bubbles separating from the heated surface in a specific time and the rising velocity of the bubbles were analyzed using photographs obtained from a high-speed camera as a function of heat flux and liquid 3He temperature. In the region of large heat flux, large bubbles formed by bubble accumulation covered the copper surface and the increase in bubble number as q increased became insignificant. In this region, the amount of heat flux carried by bubbles as latent vaporization heat was approximately 60% of the applied heat flux. The characteristic heat transfer curve of liquid 3He measured previously by our group could be explained qualitatively by these boiling behaviors.

Cryogenic system of the MAX-Wiggler

A novel insertion device for electron storage rings called the MAX-Wiggler has been constructed and commissioned at MAX-lab. The MAX-Wiggler is a cold bore superconducting wiggler magnet with 47 3.5 T poles and a period length of 61 mm aimed for the production of X-rays at the 1.5 GeV electron storage ring MAX-II at MAX-lab. This note describes the cryogenic system of the MAX-Wiggler, theoretical predictions of the heat loads to the cryostat, and measured heat loads at operation. The cryostat is a helium cooled bath type cryostat. The design criterion for the cryostat was to have a liquid He boil-off less than 3 l/h, which corresponds to a heat load of 2.1 W. The theoretical calculations predicted a heat load of 0.87 W to the liquid He bath. Of the 0.87 W predicted heat load, 0.17 W was predicted to be induced by the stored beam in MAX-II, 0.12 W from synchrotron radiation and 0.05 W from image currents. The measured heat load to the liquid He bath is larger than predicted from the theoretical calculations and at nominal working conditions it is 1.7 W. The measured contribution to the total heat load from the stored beam of 200 mA in MAX-II is 0.86 W, 0.59 W from image currents and 0.26 W from synchrotron radiation. The measured contribution from the image current is 0.59 W, about 10 times larger than expected from the theoretical calculations, which is assumed to depend on that the Cu plating of the inner surfaces of the cold bore has a lower electrical conductivity than foreseen. The higher than expected heat load from synchrotron radiation is assumed to come from a positioning error of the upstream absorber for synchrotron radiation. There is no observable increase of the heat load with the wiggler at full field. Even though the heat loads are higher than expected, the design criterion of obtaining a cryostat with a liquid He boil-off inferior to 3 l/h with 200 mA of stored current in MAX-II has been met.

Results of preliminary testing of Blip and cancellation coils for the samsung superconductor test facility (SSTF)

The background magnet system of SSTF (Samsung Superconductor Test Facility) for KSTAR (Korea Superconducting Tokamak Advanced Research) will be equipped with a pair of main coils (MC) and a pair of blip coils (BC). The main goal of the BC is to simulate electromagnetic disturbances (1 T amplitude and 20 T/s discharge rate), expected from the KSTAR operation. The coupling losses and magnetic interaction between MC and BC will be decreased by resistive cancellation coils (CC) wound onto a fiberglass bobbin. The BC is wound with a cable in conduit conductor (CICC) packed with Nb/sub 3/Sn strands. A set of BC and CC was tested in an open type cryostat. The BC is cooled with both boiling LHe in a container and pressurized helium passing through the CICC. The BC was charged up to 6.7 kA and discharged in 50 ms. During the discharge, the maximum field variation rate corresponds to 28 T/s in the BC center and 53 T/s on the BC conductor. No quench was observed and the BC was recharged in less than 1 minute. The measured shielding current in the CC is in a good agreement with the calculated value.

THz-ESR System by Using Single Shot and Repeating Pulsed Magnetic Fields

A THz-ESR system has been developed by using both a single shot pulsed magnetic field system and a repeating pulsed magnetic field system. A single shot system has been used to generate high fields up to 40 T. The temperature of specimen can be changed between 450 K and 400 mK by using a gas-flow type cryostat, 3 He and 4 He cryostat systems. A repeating pulsed field system has been also used. The system is capable of generating 30 T every 2 seconds. A signal to noise ratio of the ESR spectrum has been improved more than one order of magnitude by the signal averaging. This technique provides a new way to improve the sensitivity of high frequency ESR system. Several recent examples on the application of the THz-ESR system are reported.

The fabrication of superconducting magnet for MRI

The fabrication and the test results of the superconducting magnet for a whole body MRI are presented. The magnet consists of a main coil with six solenoids, a shielding coil with two solenoids, and six sets of cryogenic shim coil. The ferromagnetic shim assembly is installed on the inside wall of the room temperature bore to compensate the inhomogeneous field components that originated in insufficient tolerances, installation misalignments, and external ferromagnetic materials near the magnet. In addition, the magnet is enclosed by a horizontal type cryostat with the room temperature bore of 80 cm. According to the test of the MRI magnet, the central field of the magnet is 1.5 T with a field homogeneity of 9.3 ppm on 40 cm DSV (the diameter of spherical volume). Some magnetic resonance images for human body have been achieved by employing this magnet.

Quench performance and mechanical behavior of the first Fermilab-built prototype high gradient quadrupole for the LHC interaction regions

As part of the US LHC program to provide high gradient superconducting quadrupoles for the LHC interaction regions, a 5.5 meter long prototype magnet has been built and tested horizontally in a production type cryostat at Fermilab. This prototype magnet was used to validate the mechanical and magnetic design, production fabrication and assembly tooling. The first prototype magnet has met the LHC requirements of operating at 215 T/m with excellent magnetic field harmonics. This paper summarizes the test results of this magnet, including quench tests and mechanical behavior over several thermal cycles.

Optimum design of superconducting magnet coil for a micro SMES unit

The paper outlines a systematic procedure for the design of a solenoidal coil to obtain maximum stored energy for a given length of normal conductor and superconductor. In case of normal conductor, it would suffice if we design the coil to obtain maximum inductance. For superconducting coil, it is essential to maximize (1/2Li/sup 2/) as a whole since the value of allowable current depends on flux density which in turn is linked with L. This results in the design of a coil, whose inductance is much lower than the maximum possible value and has relatively large diameter as compared to its length and radial thickness. Since such a coil requires a cryostat of unusually large neck, one may choose a sub-optimal design based on commercially available drum type cryostat for transportable micro SMES units. The paper concludes with the dimensions of a solenoidal coil for optimum and sub-optimum designs using superconducting (Nb-Ti) wire of 8 km length and 1 mm diameter.

Science as a Craft Industry

Science as a Craft Industry

Design and construction of a superconducting magnet system for an Electron Cyclotron Resonance (ECR) ion source

The cyclotron accelerator at Laboratorio Nazionale del Sud in Catania, Italy will be equipped with a high-performance ECR ion source. This source which is presently under construction comprises a so-called Minimum-B magnetic bottle of 130 mm diameter and 480 mm length. The specified magnetic field values are 2.7 T, 1.6 T and 0.37 T respectively for the axial component at the two ends and at the center. The transverse field component is required to reach 1.4 T at the cylindrical boundary. The complex field configuration is produced by means of a compound superconducting coil system whose essential parts are an approximately 800 mm long sextupole and three coaxial solenoids surrounding the sextupole. All windings will be made from NbTi composite conductors and impregnated with epoxy resins. Bath cooling at 4.5 K for all coils will be provided by a warm-bore type cryostat with horizontal axis. The paper presents design and construction of the coil system, its support structure and the cryostat.