Knowledge Base

The KATRIN superconducting magnets: overview and first performance results

The KATRIN experiment aims for the determination of the effective electron antineutrino mass from the tritium beta-decay with an unprecedented sub-eV sensitivity. The strong magnetic fields, designed for up to 6 T, adiabatically guide β-electrons from the source to the detector within a magnetic flux of 191 Tcm. A chain of ten single solenoid magnets and two larger superconducting magnet systems have been designed, constructed, and installed in the 70m-long KATRIN beam line. The beam diameter for the magnetic flux varies from 0.064 m to 9 m, depending on the magnetic flux density along the beam line. Two transport and tritium pumping sections are assembled with chicane beam tubes to avoid direct “line-of-sight” molecular beaming effect of gaseous tritium molecules into the next beam sections. The sophisticated beam alignment has been successfully cross-checked by electron sources. In addition, magnet safety systems were developed to protect the complex magnet systems against coil quenches or other system failures. The main functionality of the magnet safety systems has been successfully tested with the two large magnet systems. The complete chain of the magnets was operated for several weeks at 70% of the design fields for the first test measurements with radioactive krypton gas. The stability of the magnetic fields of the source magnets has been shown to be better than 0.01% per month at 70% of the design fields. This paper gives an overview of the KATRIN superconducting magnets and
reports on the first performance results of the magnets.

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The influence of aspect ratio on the thermal performance of a cryogenic pulsating heat pipe

Pulsating heat pipes (PHPs) are expected to serve as a significant design component for the thermal management of superconducting magnets and various cryogenic space applications, including cryogen storage tanks and low temperature detectors on telescopes. A growing body of data is accumulating regarding the performance of cryogenic PHPs, including operation with helium, hydrogen, neon, and nitrogen, and the notable dependence on their orientation with respect to gravity. However, in view of the expectation that the thermal path between a low temperature heat source and the corresponding cryocooler will involve a convoluted route including vertical, horizontal, and sloping segments, we have begun a systematic study regarding the influence of the vertical-to-horizontal aspect ratio of a PHP on its thermal performance.

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A Dual 5T Superconducting Magnet System for the Brookhaven National Lab Electron Beam Ion Source

Cryomagnetics has delivered an upgraded magnet system to the Brookhaven National Laboratory’s RHIC Electron Beam Ion Source (EBIS) project. This consists of two 2.25 meter long, 215 mm room temperature bore 5T Solenoids separated by 20 cm. The system features a zero boil off system design with optional shield cooler. An overview of the magnet design parameters, cryogenic design, and test results will be presented.

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Qualification of the Joints for the ITER Central Solenoid

The ITER Central Solenoid has 36 interpancake joints, 12 bus joints, and 12 feeder joints in the magnet. The joints are required to have resistance below 4 nOhm at 45 kA at 4.5 K. The US ITER Project Office developed two different types of interpancake joints with some variations in details in order to find a better design, qualify the joints, and establish a fabrication process. We built and tested four samples of the sintered joints and two samples with butt-bonded joints (a total of eight joints). Both designs met the specifications. Results of the joint development, test results, and selection of the baseline design are presented and discussed in the paper.

Design and test results of a BSCCO-2223 magnet for gyrotron application

A program is currently under way to develop a compact, power-efficient, robust gyrotron. Gyrotrons require a very precise magnetic field, typically generated by a NbTi superconducting magnet, to form the environment necessary for the microwave power generation. The use of high-temperature superconductor (HTS) material for a liquid cryogen-free gyrotron magnet will significantly reduce the input power requirements for the cryocooler compressor and the overall size of the magnet system. Cryomagnetics has designed, built and successfully tested a magnet wound with BSCCO-2223 tape to be used in the gyrotron. The HTS magnet was designed such that it can replace the current LTS (NbTi) cryogen-free gyrotron magnet in form, fit and function. The HTS magnet consists of 11 double-pancakes and provides stable 3.57 T operation at 37 K with a current of 120 A. Magnetic field shape, which is extremely important in gyrotron applications, was a considerable challenge since NbTi operating at 4.2 K is capable of a much higher current density than BSCCO operating at 37 K. Overall refrigeration requirements were reduced from ∼8 kW in the LTS system to ∼4 kW in the HTS system. A single-stage GM cryocooler was used to cool the HTS magnet. Comprehensive tests of the HTS magnet, including operation with the gyrotron tube, have been successfully completed.

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High-frequency pulse tubes can’t always be tipped

High frequency (>30 Hz) ‘pulse tube’ coolers are often observed to perform well even when the ‘pulse tube,’ or thermal buffer tube, is in an orientation other than cold-end down, counter to the intuition that a column of gas with the colder, denser region above the warmer region is not convectively stable. In a recent paper, Swift and Backhaus advance a theory to explain this phenomenon, and offer some guidelines for a ‘tip-safe’ design. The present work offers some tipped vs. vertical data for a number of different sized pulse tube coolers, and compares the results to the theory of Swift and Backhaus. In general it is found that the results are in qualitative agreement with their theory, but that the ‘safety factor’ in a pulse tube design must be several times higher than their work suggests, to ensure orientation independence.

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Design and Results of a YBCO Magnet for a 95 GHz Gyrotron Application

The use of high-temperature superconductors (HTS) for cryogen-free gyrotron magnets will greatly reduce the power requirement and overall physical size of the system. Because some gyrotron systems are mounted on a vehicle and need to be mobile, the refrigeration system must be as lightweight and compact as possible. Cryomagnetics previously built a BSCCO magnet based on the design of a NbTi magnet. The limiting factors with this magnet were the cost of the BSCCO material and the excessive weight due to the necessity of field-shaping iron. Since it is projected that the cost of 2G YBCO tape will become significantly lower than BSCCO, and the critical current will also increase, the next generation of these magnets will mitigate those problems. The first objective was to study quench behavior in HTS coils. Cryomagnetics has also designed, built and successfully tested a 3.57 T magnet wound with 2G YBCO tape. This is the first full-scale magnet of its kind built using 2G YBCO tape. It consists of 10 double-pancakes operating at 140 A and 20 K. A single-stage cryocooler is used to cool the magnet. Because the performance of YBCO material is improving quickly, future magnets will be able to operate at lower current, higher temperature and will be lighter weight.

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Novel Integration of a 6T Cryogen-free Magneto-Optical System With a Variable Temperature Sample Using a Single Cryocooler

Cryomagnetics’ new “C-Mag Optical” Magneto-Optic Property Measurement System is a versatile materials and device characterization system that allows the researcher to simultaneously control the applied magnetic field and temperature of a sample while studying its electrical and optic properties. The system integrates a totally liquid cryogen-free 6T superconducting split-pair magnet with a variable temperature sample space, both cooled using a single 4.2K pulse tube refrigerator. To avoid warming the magnet when operating a sample at elevated temperatures, a novel heat switch was developed. The heat switch allows the sample temperature to be varied from 10K to 300K while maintaining the magnet at 4.2K or below. In this paper, the design and performance of the overall magnet system and the heat switch will be presented. New concepts for the next generation system will also be discussed.

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Superconductivity in Pristine 2H_α-MoS₂ at Ultrahigh Pressure

Zhenhua Chi,¹  Xuliang Chen,² Fei Yen,¹ Feng Peng,³ Yonghui Zhou,² Jinlong Zhu,⁴ Yijin Zhang,⁵ Xiaodi Liu,¹ Chuanlong Lin,⁶  Shengqi Chu,⁷  Yanchun Li,^7,*  Jinggeng Zhao,^8,9,†  Tomoko Kagayama,¹⁰ Yanming Ma,¹¹  and Zhaorong Yang^1,2,12,‡

Abstract:

As a follow-up of our previous work on pressure-induced metallization of the 2H_c -MoS₂  [Chi et al., Phys. Rev. Lett. 113, 036802 (2014)], here we extend pressure beyond the megabar range to seek after superconductivity via electrical transport measurements. We found that superconductivity emerges in the 2H_α -MoS₂  with an onset critical temperature T_c  of ca. 3 K at ca. 90 GPa. Upon further increasing the pressure, T_c is rapidly enhanced beyond 10 K and stabilized at ca. 12 K over a wide pressure range up to 220 GPa. Synchrotron x-ray diffraction measurements evidenced no further structural phase transition, decomposition, and  amorphization up  to  155  GPa,  implying  an  intrinsic  superconductivity  in  the 2H_α -MoS₂ .  DFT  calculations suggest  that  the  emergence of  pressure-induced superconductivity is intimately linked to the emergence of a new flat Fermi pocket in the electronic structure. Our finding represents an alternative strategy for achieving superconductivity in 2H-MoS₂  in addition to chemical intercalation and electrostatic gating.

DOI: 10.1103/PhysRevLett.120.037002

¹Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031, People’s Republic of China

²Anhui Province Key Laboratory of Condensed Matter Physics at Extreme Conditions, High Magnetic Field Laboratory, Chinese Academy of Sciences, Hefei 230031, People’s Republic of China

³College of Physics and Electronic Information, Luoyang Normal University, Luoyang 471022, People’s Republic of China

⁴Center for High Pressure Science and Technology Advanced Research (HPSTAR), Beijing 100094, People’s Republic of China

⁵Max Planck Institute for Solid State Research, Stuttgart 70569, Germany

⁶Center for High Pressure Science and Technology Advanced Research (HPSTAR), Shanghai 201203, People’s Republic of China

⁷Multidiscipline Research Center, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, People’s Republic of China

⁸Department of Physics, Harbin Institute of Technology, Harbin 150080, People’s Republic of China

⁹Natural Science Research Center, Academy of Fundamental and Interdisciplinary Sciences, Harbin Institute of Technology, Harbin 150080, People’s Republic of China

¹⁰KYOKUGEN, Center for Science and Technology under Extreme Conditions, Graduate  School of Engineering Science, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japan

¹¹State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012, People’s Republic of China

¹²Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, People’s Republic of China

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