Liquid Helium Level Research Articles

Optimization of Construction of the Balance Mechanism Axial Superconducting Antenna: Research of Methods Stabilizing the Degree of its Balance

Introduction. There are three main means of supression of electromagnetic interference that can reveal at the operation of SQUID magnetometers – spatial and frequency signal selection and digital processing. The spatial signal selection is the most effective means that allows to significantly improve the signal/interference ratio directly in the receiving superconducting antenna. To optimize the design of the balancing system of the receiving gradiometric antenna is an important task in the conditions of existence of high electromagnetic interference in the contemporary city. The purpose of the work is to justify and develop a new design of the balancing mechanism of superconducting gradiometric antenna of the SQUID magnetometer for operation in conditions of a high level electromagnetic interference. To develop an algorithm for balancing the antenna of such a SQUID magnetometer. Results. The paper considers the main implementations of gradiometric antennas and their balancing methods. As the main factor affecting the normal operation of the balancing system of the gradiometric antenna of the SQUID magnetometer over a long period of time (the time between refueling the cryostat with liquid helium), the decrease in the level of liquid helium in the cryostat was emphasized. Such a decrease in level leads to the deformation of individual elements of the balancing system. As an counteraction to this, it is proposed to place the mechanism for moving the gradiometer balancing elements directly in the antenna housing. In it the all parts of the mechanism are located below the level of liquid helium during the entire time the magnetometer is operating. The analysis of the resistance to temperature and mechanical effects of individual elements of the balancing system was carried out. The approach to choosing the optimal size of the balancing element is substantiated, this size influences at the degree of the balance of antenna. The output of the magnetometer on the field of Helmholtz coils during the movement of balancing elements of different sizes along the axis of the axial gradiometer was obtained experimentally. Experimental results were obtained for a superconducting antenna – the second-order gradiometer, with a diameter of 20 mm and base of 60 mm. Conclusions. The approach proposed by the authors to increase the efficiency of electromagnetic interference filtering with the help of superconducting gradiometric antennas made it possible to develop a new design of their balancing mechanism. Its advantage is the resistance to mechanical stresses of individual elements of the system, which arises as a result of the existence of significant temperature gradients during the evaporation of liquid helium. The proposed algorithm for balancing of the superconducting gradiometer can be applied to balance superconducting gradiometric antennas of any configuration and size. Keywords: superconductivity, SQUID-magnetometer, antenna balance, optimization.

Numerical and experimental investigation on NbTi superconducting liquid helium level sensor based on a resistance heating

A resistance-heated NbTi superconducting liquid helium level sensor based on the principle of thermal conduction is proposed. A heat transfer model for the sensor was established, and its mathematical model was characterized. The effects of temperature, current, heating resistance value, and superconducting wire diameter on the sensor performance were investigated. It indicates that the temperature of the sensor in the vapor phase is decreased linearly from high to low, and the voltage is decreased with the increase of the liquid level. And the 45 μm diameter superconducting wire has a minimum propagation current, a minimal heat input to the system, and a small measurement error. The variation of the sensor output voltage with a level height was studied experimentally. The linear correlation coefficients R2 of the 1 Ω, 5.1 Ω, and 10 Ω sensors are all greater than 0.999, which are almost identical to the simulation results. The sensor’s response time is all less than 1 s, the sensitivity is 8.7070 mV/mm, 8.0110 mV/mm, and 6.9660 mV/mm, respectively, and the accuracy is 0.8226%, 0.8611%, and 0.9030%.

Design of the Superconducting Magnet System for the New $g-2$/EDM Experiment in the J-PARC

A superconducting solenoid system has been designed for the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$g$</tex-math></inline-formula> -2/EDM experiment at the J-PARC, which is used to store muon beam of 0.3 GeV/c. High homogeneous magnetic field is required to be below <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 0.1 ppm at 3 T within a muon storage region of 33.3 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 1.5 cm in radius and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathbf {\pm }$</tex-math></inline-formula> 5 cm in height around the magnet center. The muon beam is spirally injected to the storage region from the top end of the magnet, therefore the magnetic field distribution is carefully designed in the region where the muon beam pass through. In order to achieve both requirements, NbTi superconducting coils are surrounded by an iron yoke with pole tips, which can optimize the field distribution by adjusting the shape and size. The superconducting coils are cooled by pool boiling in liquid helium, and the evaporated helium gas is re-condensed by GM cryocoolers to keep the liquid helium level for a long time. The main coils are operated in a persistent current mode to remove the magnetic field fluctuation with time caused by a power supply. This paper presents the current design of the magnet system for the experiment at the J-PARC.

The design of YBCO binary current leads and its electromagnetic-thermal coupling analysis based on PEEC and finite volume method

A superconducting magnet system is developed for the application of high-frequency gyrotrons at Wuhan National High Magnetic Field Center, China. The operating cost for the magnet is dominated by refrigeration power. To reduce the heat load for cryogenic systems, a pair of YBCO binary current leads is designed by consideration of the industrial concentration of type II high-temperature superconducting YBCO material. In this paper, a simulation model is proposed to perform the electromagnetic-thermal coupling analysis of these YBCO binary leads under different operating conditions by combining a partial element equivalent circuit method and finite volume method. The simulation code can improve computational efficiency and enable high-accuracy coupling between the electromagnetic field and heat transfer process. In the steady state, the heat leakage at the 4.2 K cold end of the YBCO binary leads depends mainly on the geometric parameters of the YBCO tape, especially the cross-sectional area of the copper layer in the YBCO tape. The cooling mode and liquid helium level also have a significant impact on the heat leakage level. The optimal outer diameter of the normal copper section is identified, and the optimum value is largely influenced by the effective cooling power imposed on the cold end of the normal copper section. In the transient state, simulations for the charging process and the loss of cooling accident are performed, along with a detailed analysis of the electromagnetic-thermal response features of the leads under these conditions. The results indicate that the YBCO binary current leads possess high thermal stability and an ample time margin for the magnet system to be demagnetized.

Liquid helium level regulation improvement in the LHC electrical distribution feedboxes

An important cryogenic equipment of the Large Hadron Collider (LHC) consists in the electrical distribution feedboxes (DFBs) which are used to power the superconducting magnets of the accelerator. These feedboxes contain the current leads achieving the electrical transition between the copper cables at ambient temperature to the Niobium-Titanium wires at cryogenic temperature, immersed in a liquid helium bath at 4.5 K. This liquid helium bath must be regulated at a defined level to allow the powering of the LHC, and this regulation often caused non-availabilities in the past. This paper presents the development of a new control scheme, coupled to the existing PID level controller, significantly improving this regulation, and rejecting disturbances in a highly efficient manner. First, a dynamic model of the DFBs was developed in the EcosimPro software using the CRYOLIB library to reproduce in simulation the regulation issues. In a second step, the new proposed regulation modes were tested and validated in simulation. Finally, the paper will present the results obtained in 2021 on a real DFBs operation in the LHC, validating the new control approach prior its massive deployment all around the LHC cryogenics.

Design and test of a liquid helium cryostat with automatic level control for cooling a superconductive single-flux-quantum circuit chip

A small-scale liquid helium cryogenic system has been designed for cooling the superconductive single-flux-quantum circuits. With a special double inner cylinders structure and a PID control system, automaticcontrolof the liquid helium level could be achieved. The cooling capacity recovered structure was added to the cold shield of the system in order to reduce the heat leakage of the system. Besides, A special composite magnetic shielding structure was designed to ensure the circuits working in an extremely low magnetic environment. Experiments were conducted to test the thermal performance and the magnetic shielding efficiency of the liquid helium cryogenic system. The results show that the storage time of the liquid helium is about 2 days with about 110 coaxial cables and the magnetic flux density at the chip location is below 5 nT at the temperature of 4.2 K.

Use of superconducting liquid helium level sensor as a temperature sensor and its applications

A superconducting liquid helium level sensor has been used as a temperature sensor to monitor cooldown and warmup of the holding device. Temperature dependent resistance of NbTi wire is utilised for measuring surrounding gas space temperature (300 K-5 K) during the transition time. Theoretical calculation for the system revealed that during passage of current, temperature rise of the wire will be restricted to safe limits due to generation of high natural convection gas flow around the sensor, initiated by the its heating. Actionable decisions can be started based on this measurement for controlling cooldown and warm up process of the system. Depending on helium temperature, a dual use electronics meter has been proposed which can measure either gas temperature or liquid helium level using the same sensor. Utilising this principle any existing LHe level sensor can also be operated as a temperature sensor during thermal transition process.

Stable operation of cryogenic system at 2K during the RF or magnet power variations

In the last 40 years several large laboratories, e.g. CERN, DESY, TJNAF, constructed the accelerators with large number of superconducting (sc) cavities or sc magnets operating at 2 or 4 K temperature levels. The sc cavity operation requires more stringent ranges of pressure variation than ones of sc magnets. In comparison to small testing benches or single cavities modules, for large accelerators a complicated controlling of refrigerator and cryogenic system is required. In the present paper, a review of controlling principles and loops, typically applied for the controlling of liquid helium (LHe) level and pressure for large accelerators is presented. Other possible control loops, e.g. cascade control or multivariable feed-back (or with feed-forward option), are discussed. Activities related to the commissioning of control loops and some supporting measurements are mentioned. Experimental data on investigation of gas/liquid thermal equilibrium are also presented.

The Internet of Things in the Life Sciences Laboratory.

The Internet of Things in the Life Sciences Laboratory.

Arduino-Based Novel Hardware Design for Liquid Helium Level Measurement.

Liquid helium (LHe) is used as a cryogen in a variety of applications involving superconductivity and is routinely monitored for conducting low-temperature experiments. Thermoacoustic oscillations, which are inevitably present inside closed LHe containers, are utilized for level detection by sensing the vibrations at the warm end of a thin capillary tube inserted into the Dewar. The position of the capillary tube at which a sudden change occurs in these oscillations is manually sensed to identify the liquid level. The present work proposes a novel hardware design to identify the thermoacoustic oscillations in a reliable way using an accelerometer driven by an Arduino microcontroller. Further, an automated approach has been devised to quantify the rate of change of these helium oscillations to measure the LHe level. The proposed method has been tested during several trials on a 120 L and 100 L capacity Dewar using the proposed hardware, and the mean error in measuring the LHe level was calculated to be less than 1 cm in comparison with the gold standard niobium-titanium level sensor. The results encourage the use of the proposed method to evolve as a cost-effective alternative to the widely used superconducting level sensors in measuring LHe level.

A fast response, low heat generating activation method for LHe level sensors.

A superconducting liquid helium (LHe) level sensor of length 300 mm has been fabricated based on the principle of differential heat transfer characteristic in helium gas compared to that in liquid. The sensor wire used has a diameter of 38 μm, and the wire was obtained from a pack of multifilament wires. A full thermo-electrical characterisation of the sensor was carried out in a dedicated setup. Its dynamic thermal response was also studied to understand its timing characteristics at different liquid levels and excitation currents. Based on the sensor characterisation, a new level measurement technique is evaluated which can reduce the heat load going to LHe during sensor activation without compromising on its sensitivity or accuracy. The timing response with this technique will make the level detection faster compared to the conventional techniques.

Cryogenic upgrade of the low heat load liquid helium cryostat used to house the Cryogenic Current Comparator in the Antiproton Decelerator at CERN

The Cryogenic Current Comparator (CCC) and its purpose built cryostat were installed in the low-energy Antiproton Decelerator (AD) at CERN in 2015. A pulse-tube cryocooler recondenses evaporated helium to liquid at 4.2 K filling the helium vessel of the cryostat at an equivalent cooling power of 0.69 W. To reduce the transmission of vibration to the highly sensitive CCC, the titanium support systems of the cryostat were optimized to be as stiff as possible while limiting the transmission of heat to the liquid helium vessel. During operation the liquid helium level in the cryostat was seen to reduce, indicating that heat load was higher than intended. To verify the reason for this additional heat load and improve the cryogenic performance of the cryostat, an upgrade was undertaken during the 2016 technical stop of the AD. This article presents the studies undertaken to understand the thermal performance of the cryostat and details the improvements made to reduce heat load on the liquid helium vessel. Also discussed are the procedures used to reduce the diffusion of helium to the vacuum space through ceramic insulators. Finally the upgraded cryogenic performance of the cryostat is presented.

Investigation of thermal acoustic oscillations in a superconducting linac cryogenic system

During the commissioning stage of a superconducting linear accelerator (linac) three major cryogenic systems were seen to generate thermal acoustic oscillations (TAO): the cryostat liquid helium level sensor interface, the pre-cooling line and the cryogenic distribution valve box with associated transfer tube. By using Rott’s stability curves, published by other researchers elsewhere, an approximate map of the oscillations in the cryogenic systems under investigation was created for both straight and U-shaped tubes. This investigation confirmed that all systems under consideration fall within the critical range and that damping of TAO would be needed to achieve stable operation conditions. The geometry and hence the temperature distribution within the cryogenic system of the accelerator facility could not be altered arbitrarily. Possible TAO damping techniques were narrowed to two options: (a) adding restrictions at the cold end and (b) control of the helium gas pressure. In all systems, before modifications, pressure oscillations were clearly observed within the frequency range 0.25–47Hz. In two systems TAO were observed with no liquid helium present at the cold end. The TAO investigations provided solutions that resulted in a substantial improvement in the performance of the linac cryogenic and RF stabilization systems, under test.

Compact, ultra-low vibration, closed-cycle helium recycler for uninterrupted operation of MEG with SQUID magnetometers

A closed-cycle helium recycler was developed for continuous uninterrupted operation for magnetometer-based whole-head magnetoencephalography (MEG) systems. The recycler consists of a two stage 4K pulse-tube cryocooler and is mounted on the roof of a magnetically shielded room (MSR). A flexible liquid helium (LHe) return line on the recycler is inserted into the fill port of the MEG system in the MSR through a slotted opening in the ceiling. The helium vapor is captured through a line that returns the gas to the top of the recycler assembly. A high-purity helium gas cylinder connected to the recycler assembly supplies the gas, which, after it is liquefied, increases the level of LHe in the MEG system during the start-up phase. No storage tank for evaporated helium gas nor a helium gas purifier is used. The recycler is capable of liquefying helium with a rate of ∼17L/d after precooling the MEG system. It has provided a fully maintenance-free operation under computer control for 7months without refill of helium. Although the recycler is used for single-orientation operation at this initial testing site, it is designed to operate at ±20° orientations, allowing the MEG system to be tilted for supine and reclining positions. Vibration of the recycler is dampened to an ultra-low level by using several vibration isolation methods, which enables uninterrupted operation during MEG measurements. Recyclers similar to this system may be quite useful even for MEG systems with 100% magnetometers.

Programmable System-on-Chip (PSoC) Embedded Readout Designs for Liquid Helium Level Sensors

This article reports the development of programmable system-on-chip (PSoC)-based embedded readout designs for liquid helium level sensors using resistive liquid vapor discriminators. The system has been built for the measurement of liquid helium level in a concave-bottomed, helmet-shaped, fiber-reinforced plastic cryostat for magnetoencephalography. This design incorporates three carbon resistors as cost-effective sensors, which are mounted at desired heights inside the cryostat and were used to infer the liquid helium level by measuring their temperature-dependent resistance. Localized electrical heating of the carbon resistors was used to discriminate whether the resistor is immersed in liquid helium or its vapor by exploiting the difference in the heat transfer rates in the two environments. This report describes a single PSoC chip for the design and development of a constant current source to drive the three carbon resistors, a multiplexer to route the sensor outputs to the analog-to-digital converter (ADC), a buffer to avoid loading of the sensors, an ADC for digitizing the data, and a display using liquid crystal display cum light-emitting diode modules. The level sensor readout designed with a single PSoC chip enables cost-effective and reliable measurement system design.

Liquid nitrogen level meter for high-temperature superconductor (HTS)

Many kinds of high temperature superconductor (HTS) power machines such as HTS cable, HTS fault current limiter and HTS magnet are cooled by liquid nitrogen. The level of liquid nitrogen should be monitored and controlled to ensure the thermal stability and the dielectric strength as well. To measure the level, capacitance method and differential pressure method are usually used. However, each method has installation difficulties and measurement errors for unsteady state operation with varying system pressure. A new liquid level meter using a 2G HTS conductor is described, which has similar structure with the liquid helium level meter with NbTi filament. The level meter is fabricated with a parallel connected heater, which helps the separation of the superconducting region and normal region, considering the critical temperature, large heat capacity of conductor and cooling characteristics. The level of liquid nitrogen can be obtained from the measured voltage signal along the 2G HTS conductor. Design, fabrication and test results of the new liquid nitrogen level meter are presented.

Development of Superconducting Level Sensor for Liquid Helium Level Measurements

Liquid helium storage and transport Dewars of different types and different storage capacities are used in laboratories for experimental measurements at low temperatures. Liquid helium is used as a cryogen for cooling the sample to a temperature of 4.2 Kelvin. To measure the level of the liquid helium in the experimental cryostat or Dewar, imported superconducting level sensors are presently being used but are relatively expensive. In view of this, experimental work related to design and development of the superconducting level sensor based on NbTi superconducting wire was undertaken. This work includes the fabrication, characterization and calibration of the superconducting level sensor. The characterization work involves the measurement of the resistance of the level sensor at different levels of liquid helium in the Dewar for different values of excitation current to determine the optimum excitation current with a view to establish a single valued relationship between the measured resistance and the liquid helium level. A program has been written by using LABVIEW software to automate the characterization process. Based on the measurements, display system is being developed to display the level of liquid helium in the Dewar.

超伝導重力計連続観測に対する液体ヘリウムレベル変化の影響―南極・昭和基地での観測例―

超伝導重力計連続観測に対する液体ヘリウムレベル変化の影響―南極・昭和基地での観測例―

25 TESLA HTS MAGNET INSERT COIL IN ZERO BOIL OFF CRYOSTAT

25 TESLA HTS MAGNET INSERT COIL IN ZERO BOIL OFF CRYOSTAT

Electronic states above a helium film suspended on a ring-shaped substrate

We derived a nonlinear differential equation that describes the profile of a suspended helium film over a ring-shaped substrate in the presence of a perpendicular external electric field. The profile of the helium film was calculated as a function of the bulk liquid helium level and for several values of the external radius of the ring. The one electron surface states were calculated in the presence of external electric and magnetic fields. The electron energy levels increase with electric field as well as with the height of bulk helium. Aharonov-Bohm oscillations were observed in this system under appropriate conditions.