Cryocooler System Research Articles

Design and Demonstration of a 5-Bit Flash-Type SFQ A/D Converter Integrated With Error Correction and Interleaving Circuits

We have designed a fully integrated 5-bit flash-type single-flux quantum (SFQ) analog-to-digital converter (ADC), in which an error correction and a bit-interleaving circuit are integrated with complementary quasi-one-junction SQUID (CQOS) comparators, and we verified its operation in experiments. Two types of look-back error correction circuits with different clock schemes were designed for the integrated ADCs to avoid the gray zone in comparators and to convert gray code to binary code. The interleaving circuit was also used in the ADC to add one extra bit. A binary 5-bit A/D converter was integrated into an IC chip. Then, input waveforms at low frequencies were successfully retrieved from the binary data of the A/D converter without any errors. We also confirmed that the A/D converter operated properly by conducting tests in our cryocooling system using a 4K-GM cryocooler after the chip was flip-chip bonded onto a multi-chip-module (MCM) carrier. We also used the beat frequency method to test and confirm that the CQOS comparator operated effectively at high frequency, i.e., 3 bits at 15 GHz in the binary code operation and 4 bits at 15 GHz in the gray code operation. Furthermore, operations at sampling frequencies of up to 32 and 50 GHz with a low-frequency analog input signal were experimentally confirmed for a 4-bit comparator circuit with a critical current density J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> of 2.5 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and 10 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , respectively.

High Temperature Superconducting Motor Cooled by On-Board Cryocooler

HTS (high temperature superconducting) motor that utilizes superconductor as the field winding has advantage of compactness, light weight and high efficiency, but it has an inherent disadvantage that the rotor must be cooled down at cryogenic temperature. Conventionally, HTS rotor was cooled by circulation of cryogenic fluid such as helium or neon, and the cooling system was installed outside of the motor to prevent it from being rotated. In this paper, however, the prototype of the HTS motor with an on-board cryocooler, is fabricated and tested. The experimental system is composed of the stator with conventional copper winding, the rotor with superconductor, and the rotating cryocooler as a novel concept of cooling system. The rotor is fabricated as the race-track coil with 2G, YBCO tape and situated in the 110 mm diameter cryostat. It is designed to minimize heat invasion from room temperature environment and be compatible with the coaxial structure of the cryocooler. The cryocooler is in physically and thermally contact with the HTS rotor while being rotated together. Two kinds of refrigerator, a Stirling refrigerator and an inline-type PTR (Pulse Tube Refrigerator) are used individually as the on-board cryocooler. The whole system is carefully integrated and fabricated for rotating stability. Several temperature sensors and voltage taps are installed to monitor the conditions of the HTS rotor and the cryocooler while their signals are acquired by the bluetooth data acquisition system during the operation. The HTS motor is successfully operated with 120 rpm of rotating speed. In the rotating test, 70 A current is supplied to the superconducting rotor. Further developmental design issues for on-board cryocooling system are addressed and discussed in this paper.

US effort on HTS power transformers

Waukesha Electric Systems has been working in HTS power transformers development program under the auspices of US Government Department of Energy since 1994. This presentation will describe various milestones for this program and program history along with the lessons learned along the way. Our motivations for working on this development program based on man benefits offered by HTS power transformers to power delivery systems will be discussed.Based on various issues encountered during execution of many HTS projects, DOE has set up an independent program review process that is lead by team of experts. This team reviews are integral part of all DOE HTS projects. Success of all projects would be greatly enhanced by identifying critical issues early in the program. Requiring appropriate actions to mitigate the issues before processing further will lead to proactive interrogation and incorporation of expert’s ideas in the project plans. Working of this review process will be also described in this presentation.Waukesha Electric Systems team including: Superpower-Inc, Oak Ridge National Laboratory, University of Houston Center for Superconductivity and Southern California Edison company was awarded a cost share grant by US Government in 2010 for development of a fault current limiting HTS power transformer. This multi year’s program will require design, manufacture, installation, and monitoring of a 28MVA tree phase transformer installed at Irvine CA. Smart Grid demonstration site.Transformer specifications along with requirements for fault current limiting and site requirement will be discussed. Design and development of various sub systems in support of this program including: HTS conductor performance specification, Dielectric system design approach, Dewar development for containing phase assemblies, cryo-cooling system design approach, etc. will be described.Finally; overall program schedule, critical milestone events, test plans and progress to date will be reported.

The Road to Vibration-free Refrigeration

The vibration-free cryocooler remains one of the key components in the Large-scale Cryogenic Gravitational wave Telescope (LCGT). Accordingly, reviewing the design and results of the vibration-free cryocooler for the Cryogenic Laser Interferometer Observatory (CLIO) (prototype of the LCGT) would be useful for development of the LCGT. At the same time, the development of the pulse-tube cryocooler is now progressing to a stage where it is more powerful with less vibration. In this paper, the past development of the vibration-free cryocooler system for CLIO, and new technologies of the vibration-free cryocooler are presented.

A magnetic resonance (MR) microscopy system using a microfluidically cryo-cooled planar coil.

We present the development of a microfluidically cryo-cooled planar coil for magnetic resonance (MR) microscopy. Cryogenically cooling radiofrequency (RF) coils for magnetic resonance imaging (MRI) can improve the signal to noise ratio (SNR) of the experiment. Conventional cryostats typically use a vacuum gap to keep samples to be imaged, especially biological samples, at or near room temperature during cryo-cooling. This limits how close a cryo-cooled coil can be placed to the sample. At the same time, a small coil-to-sample distance significantly improves the MR imaging capability due to the limited imaging depth of planar MR microcoils. These two conflicting requirements pose challenges to the use of cryo-cooling in MR microcoils. The use of a microfluidic based cryostat for localized cryo-cooling of MR microcoils is a step towards eliminating these constraints. The system presented here consists of planar receive-only coils with integrated cryo-cooling microfluidic channels underneath, and an imaging surface on top of the planar coils separated by a thin nitrogen gas gap. Polymer microfluidic channel structures fabricated through soft lithography processes were used to flow liquid nitrogen under the coils in order to cryo-cool the planar coils to liquid nitrogen temperature (-196 °C). Two unique features of the cryo-cooling system minimize the distance between the coil and the sample: (1) the small dimension of the polymer microfluidic channel enables localized cooling of the planar coils, while minimizing thermal effects on the nearby imaging surface. (2) The imaging surface is separated from the cryo-cooled planar coil by a thin gap through which nitrogen gas flows to thermally insulate the imaging surface, keeping it above 0 °C and preventing potential damage to biological samples. The localized cooling effect was validated by simulations, bench testing, and MR imaging experiments. Using this cryo-cooled planar coil system inside a 4.7 Tesla MR system resulted in an average image SNR enhancement of 1.47 ± 0.11 times relative to similar room-temperature coils.

Largely improved Jc at low temperatures observed in Y123 single crystals with chemically introduced point defects

Most of studies on pinning properties and relating vortex nature of the RE123 system were performed at high temperatures around 77 K. However, the pinning characteristics of RE123 at low temperatures have not been well understood yet, while extensive applications using the cryocooling system are also strongly expected. In the present study, the Jc-H-T properties have been studied for Gd123 single crystal with a low level Gd substitution for Ba and Y123 single crystals substituted by small amount of impurity ions, such as Sr and Co, which improve Jc properties accompanying huge peak effect in their Jc-H curves. It was found that the increase in Fp with decreasing temperature of the impurity doped Y123 samples were much larger than that of the Gd123 sample, while the Gd123 sample exhibited higher Jc than these Y123 samples above 77 K. The Jc performance below 50 K of the Gd123 sample was even lower than that of the undoped Y123 sample. This result strongly indicates that the RE123 with RE/Ba substitution does not appropriate for low temperature applications, such as high field magnets despite their good Jc performance at high temperatures e.g. 77 K.

Two-Stage Cryocooling Design for Hybrid Superconducting Fault Current Limiter

New concept of two-stage cryogenic cooling system for full-scale hybrid superconducting fault current limiter (SFCL) is proposed and designed with an objective to significantly reduce the capital and operational costs. Even though we have developed and successfully tested a cryocooling system for 300 A level, it is not easy to scale up the same technology to 3¿/22.9 kV/2.5 kA level, mainly because of the heavy cost of GM or Stirling cycle coolers to cover the increased thermal load. It is proposed in this study to employ a large capacity of JT cooler for heat intercept at an intermediate location of current leads. The JT coolers with mixed refrigerant are very reliable and commercially available at an inexpensive price. Detailed cryogenic design of cryostat and heat intercept components is carried out in consideration of thermal characteristics of cryocoolers and electrical insulation. It may be concluded that the two-stage cooling with a JT cooler at 130 K and a GM cooler at 77 K is feasible in practice, and can significantly reduce the capital cost and power consumption.

Dynamic Thermal Characteristics of HTS Coil for Conduction-Cooled SMES

In this paper, we investigate the thermal runaway characteristics of a BSCCO HTS single pancake coil conduction-cooled with a 4 K-GM cryo-cooler system. We also evaluate the static and dynamic characteristics of the HTS coil by measuring the temporal evolution of the temperature and the voltage for steady current and the typical current patterns of the load fluctuation compensation at different ambient temperatures T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> in the range of 20-50 K. Moreover, we experimentally discuss the criterion for monitoring the conduction-cooled HTS SMES system during compensating operation for load fluctuations.

Conducted EMI Reduction on the Pulse Tube Cryocooler

Pulse tube (PT) cryocoolers can be used to cool SQUIDs, however their electromagnetic interference (EMI) through the conducted high frequency noise currents are normally too large to operate SQUIDs. In this paper, high frequency noise currents of a pulse tube cryocooler system are simultaneously observed at several critical points to analyze conducting paths of the noise currents and to find a solution for this problem. High frequency noise currents are detected by current sensors consisting of a current transformer and a terminating resistor at the secondary side. By covering three-phase power lines and a neutral line connecting the valve motor to the inverter with a copper mesh, and by using it as an additional neutral line, conducted EMI (noise currents) to the cryostat has bee reduced by one fifth. With this treatment, SQUIDs have been operated normally.

40 Gbit/s operation of superconductive single flux quantum digital integrated circuit with optical data input

A superconductive single flux quantum (SFQ) digital integrated circuit with an optical data input has been demonstrated at the system level of 40 Gbit/s for the first time. A uni travelling carrier photodiode (UTC-PD) and an SFQ circuit chip, on which 40 Gbit/s I/O interfaces were integrated, were packaged on a cold stage (4–6 K) of a cryocooler system. The UTC-PD&apos;s output was connected to an input port of the SFQ circuit with a Cu coaxial cable. From room temperature, a 40 GHz clock was supplied to the SFQ circuit while 40 Gbit/s optical data were supplied to the UTC-PD. The SFQ circuit operated correctly with the optical 40 Gbit/s data. The measured bit error rate was less than 10−13 for 1.2 mW optical PRBS 7 input at 40 Gbit/s.

A Compact Cryocooling System With Subcooled Liquid Nitrogen for Small HTS Magnets

A compact cryogenic cooling system is developed for small HTS magnets to be continuously refrigerated in subcooled liquid nitrogen at temperatures below 77 K by a cryocooler. This thermal design is particularly useful when electrical insulation and compactness are significant at the same time. HTS elements are immersed in a cylindrical liquid-nitrogen vessel, and a copper band is brazed around the exterior sidewall of the cylinder at vertical location just under the liquid level in order to achieve peripherally uniform cooling with a GM cryocooler. The vapor space above liquid nitrogen in the vessel provides a fully open room for current leads and mechanical supports to the magnets. Heat is removed from the HTS magnets by natural convection of subcooled liquid nitrogen to the cold sidewall. The key components are designed based on heat transfer analysis. A prototype is fabricated, and it is successfully demonstrated that the thermal load is effectively removed and temperature is spatially uniform.

Ultra-low-vibration pulse-tube cryocooler system – cooling capacity and vibration

This report describes the development of low-vibration cooling systems with pulse-tube (PT) cryocoolers. Generally, PT cryocoolers have the advantage of lower vibrations in comparison to those of GM cryocoolers. However, cooling systems for the cryogenic laser interferometer observatory (CLIO), which is a gravitational wave detector, require an operational vibration that is sufficiently lower than that of a commercial PT cryocooler. The required specification for the vibration amplitude in cold stages is less than ±1 μm. Therefore, during the development of low-vibration cooling systems for the CLIO, we introduced advanced countermeasures for commercial PT cryocoolers. The cooling performance and the vibration amplitude were evaluated. The results revealed that 4 K and 80 K PT cooling systems with a vibration amplitude of less than ±1 μm and cooling performance of 4.5 K and 70 K at heat loads of 0.5 W and 50 W, respectively, were developed successfully.

Compact cryocooling system for HTS sampler

This paper describes a compact cooling system using a single-stage stirling-type cryocooler for a practical HTS sampler. The system was designed to cool down an HTS sampler module below 50K, enabling a bandwidth of the chip more than 100GHz. The system measures 150mm in width, 140mm in height and 310mm in depth, and weighs 5kg. Semi-rigid coaxial cables made of brass with a silver coated inner conductor were adopted for a signal to be measured and a trigger pulse. The loss for the signal line was less than 1.5dB at 50GHz with relatively small thermal inflow. Thermal inflows from low frequency lines, IF signal lines for control/output of the sampler and dc bias lines, were minimized by choosing proper wires. A new sampler module with reduced weight was placed on the cold stage, which was surrounded by double magnetic shields. The module was successfully cooled down to less than 50K with cooling time of 1h in the system. We have also succeeded in observing sinusoidal waveforms with the HTS sampler cooled by the compact cooling system.

Preparation of conduction-cooled HTS coils using Y-123 coated conductors by IBAD/PLD process

We have developed a long Y-123 coated conductors by ion-beam-assisted deposition (IBAD) and pulsed-laser-deposition (PLD) method. Now, we can routinely obtained 100m class Y-123 tapes with over 100A at 77K. For power applications using Y-123 conductors, coiling and cooling techniques are important elements. From 2004, we have developed and demonstrated a solenoid type coil that is the most suitable for practical application because it has advantage such as (1) uniformity of magnetic field (2) no joint. In this paper, we describe the development of conduction-cooled HTS test coil that has 14 turn×22 layers using 100m Y-123 conductors. In order to use the conduction cooling system, the Y-123 conductors were stabilized for 0.1mm thick Cu tapes and spacers between the layers consisted of aluminum nitride in the coils. In the demonstration of this coil at 30K, 40K, 50K, 60K and 77K by cryo-cooling system, the good cooling and superconducting performances were observed. The central magnetic fields of over 1T were successfully obtained with operating currents of over 400A and under 40K. Furthermore, this coil was operated on additional magnetic fields of 3T by combination of LTS magnets. The central magnetic fields of 0.5T were generated from the cooled HTS coils with operating current of 190A on additional magnetic fields of 3T by LTS magnets at 30K. Total magnetic fields were exceeded 3.5T at 30K.

Thermal Runaway Characteristics of Bi2212 Coil for Conduction-Cooled SMES

In this paper, we investigated the thermal runaway characteristics of a conduction-cooled Bi2212 HTS coil with a 4 K-GM cryocooler system under compensating operation for load fluctuations. We measured the temporal evolutions of temperature and voltage distributions of the HTS solenoidal coil for typical current patterns of load fluctuation compensation at different ambient temperatures. On the basis of these experimental results, we constructed a thermal analysis model, and analysed the thermal runaway characteristics during and after the load fluctuation compensation. Based on the results of our experiments and the numerical simulations, we proposed criterion for the monitoring of an HTS SMES system during compensating operation for load fluctuations.

Development of Calpain-specific Inactivators by Screening of Positional Scanning Epoxide Libraries

Calpains are calcium-dependent proteases that are required for numerous intracellular processes but also play an important role in the development of pathologies such as ischemic injury and neurodegeneration. Many current small molecule calpain inhibitors also inhibit other cysteine proteases, including cathepsins, and need improved selectivity. The specificity of inhibition of several calpains and papain was profiled using synthetic positional scanning libraries of epoxide-based compounds that target the active-site cysteine. These peptidomimetic libraries probe the P4, P3, and P2 positions, display (S,S)- or (R,R)-epoxide stereochemistries, and incorporate both natural and non-natural amino acids. To facilitate library screening, an SDS-PAGE assay that measures the extent of hydrolysis of an inactive recombinant m-calpain was developed. Individual epoxide inhibitors were synthesized guided by calpain-specific preferences observed from the profiles and tested for inhibition against calpain. The most potent compounds were assayed for specificity against cathepsins B, L, and K. Several compounds demonstrated high inhibition specificity for calpains over cathepsins. The best of these inhibitors, WRH(R,R), irreversibly inactivates m- and mu-calpain rapidly (k(2)/K(i) = 131,000 and 16,500 m(-1) s(-1), respectively) but behaves exclusively as a reversible and less potent inhibitor toward the cathepsins. X-ray crystallography of the proteolytic core of rat mu-calpain inactivated by the epoxide compounds WR gamma-cyano-alpha-aminobutyric acid (S,S) and WR allylglycine (R,R) reveals that the stereochemistry of the epoxide influences positioning and orientation of the P2 residue, facilitating alternate interactions within the S2 pocket. Moreover, the WR gamma-cyano-alpha-aminobutyric acid (S,S)-complexed structure defines a novel hydrogen-bonding site within the S2 pocket of calpains.

Electrical and thermal characteristics of Bi2212/Ag HTS coils for conduction-cooled SMES

In this paper, we investigated the electrical and thermal performance of conduction-cooled Bi2212/Ag HTS coils with 4K-GM cryocooler system. First, we measured the critical current Ic for different ambient temperatures T0 at 4.2 K - 40 K. Experimental results revealed that Ic increased with the decrease in T0 and was saturated at T0 < 10 K. We carried out thermal analysis considering heat generation, conduction and transfer under conduction-cooling condition, and reproduced the electrical and thermal characteristics of the conduction-cooled HTS coil, taking account of temperature dependence of specific heat and thermal conductivity of the materials. We also measured the temperature rise of Bi2212/Ag HTS coil for different continuous current levels at T0 = 4.8 K. Experimental results revealed the criterion of thermal runaway, which was discussed in terms of heat generation and propagation in the test coil.

SMALL VIBRATION CRYOCOOLER SYSTEM FOR CRYOGENIC GRAVITATIONAL WAVE INTERFEROMETER

An ultra-small vibration cryocooler system for a cryogenic interferometric gravitational wave detector has been developed. The system consists of a pulse tube cryocooler and a vibration-reduction system. Its vibration level was about 50 nm for the vertical direction at 1 Hz, which was three orders of magnitude smaller than that of an original pulse tube cryocooler.

Performance of the HTS bulk magnet in cryocooler system with cyclic temperature variation

We have proposed a new cryocooler system for the high temperature superconducting (HTS) bulk magnet. In this system, the cyclic temperature variations are generated. A change of magnetic trapped flux under the cyclic temperature variation is examined in detail. As a result, it has been found that the trapped flux mainly deteriorates at the first temperature rise, but it has been kept almost constant after the first temperature descent and following thermal cycles when the bulk is excited at 100 mT. Moreover it has been found that the change of the trapped flux at the excitation of 130 mT becomes same as the case of 100 mT. The deterioration at the first temperature rise can be explained by the Bean model, but we can find a difference between calculated results by the Bean model and experimental trapped flux distributions near the center of the bulk. Therefore, we take into consideration a two dimensional invasion of the magnetic field to explain the difference. Consequently calculated distributions of the trapped flux become in goal accordance with experimental ones.

The design and fabrication of a reverse Brayton cycle cryocooler system for the high temperature superconductivity cable cooling

A high temperature superconductivity cable must be cooled below the nitrogen liquefaction temperature to apply the cable to power generation and transmission systems under superconducting state. To maintain the superconducting state, a reliable cryocooler system is also required. The design and fabrication of a cryocooler system have been performed with a reverse Brayton cycle using neon gas as a refrigerant. The system consists of a compressor, a recuperator, a cold-box, and control valves. The design of the system is made to have 1 kW cooling capacity. The heat loss through multilayer insulators is calculated. Conduction heat loss is about 7 W through valves and access ports and radiation heat loss is about 18 W on the surface of a cryocooler. The design factors are discussed in detail.