Evaporation Rate Of Liquid Helium Research Articles

FRP Dewar for measurements in high pulsed magnetic fields

We describe a liquid helium glass-fibre reinforced plastic (G-FRP) Dewar which we designed, fabricated and tested for excitation spectrum measurements in high pulsed magnetic fields of up to 50 T. The sensitivity of high-resolution magnetic measurements carried out at low temperatures in such high fields is limited inevitably by magnetic and electric properties of the structural Dewar materials involved. Magnetic properties of various G-FRP Dewar-purpose materials are explored with a χ -meter furnished with a RF SQUID magnetometer. The Dewar materials and multilayer insulation effects contributing to the magnetic response signal are analyzed. It has also been discovered that field noise caused by the magnetization of the Dewar materials can be suppressed substantially by using special glass–epoxy technologies. The liquid helium evaporation rate is 3.8 l/day while the hold time is 27 h, the influencing factors are discussed.

Liquid helium cryopumps with low‐emissivity Al film coatings and low helium consumption

Liquid helium storage‐type cryopumps made in Russia with a special surface treatment were experimentally studied. Pressures of the order of 10−9 Pa were obtained 19.5 h after the pump was filled with liquid helium. The ultimate pressure obtained was 2×10−10 Pa, with no baking, after about 58 days. The temperature of the cryosurface was 4.2 K. The evaporation rate of liquid helium was 8.7×10−10 m3/s (3.1 ml/h). The volume for liquid helium in the pump is about 7 l. The total inner surface area of the cryopump is about 0.23 m2. The Al film coating has an emissivity of 2×10−3 for liquid helium temperature to liquid nitrogen temperature. Its grain size is 2 to 3 μm, with a thickness of no less than 1 μm and a roughness of about 0.16 μm. The 7 l of liquid helium lasted for about three months.

Development of a biomagnetic measurement system for brain research

The tail of the dewar of the authors' system has a special shape that makes it possible to measure the brain activity of anyone lying on a bed regardless of head shape or size. It allows the parietal, one side of the temporal and the occipital regions to be measured simultaneously. In the system, 128 axial first-order gradiometers are mounted at intervals of about 26 mm. The diameter and baseline length of the pickup coil are 14 mm and 50 mm, respectively. The authors use square-shaped double-washer DC-SQUIDs with additional positive feedback to improve the flux resolution. System reliability is improved by hermetically sealing the SQUID in a ceramic package and including a heater resistor to eliminate trapped flux. To decrease the liquid helium evaporation rate, output cables are made with flexible printed circuits. The read-out electronics are based on the Direct Offset Integration Technique, which is a highly simplified feedback method. The white noise level measured in a magnetically shielded room is less than 10 fT//spl radic/Hz above 5 Hz. This system has successfully been applied to measuring auditory evoked fields. >

Development of the 19 T high field magnet system

A high field magnet system, up to 19 tesla at 1.8K, with magnet bore of 75mm was developed. The magnet consists of Nb/sub 3/Sn solenoids (3 sections) and NbTi solenoids (2 sections). A liquid helium vessel is divided into two parts (4.2K upper part and 1.8K lower part) by a fiberglass reinforced plastics separator. The central field is 17 tesla at 4.2K with normal liquid helium and 19 tesla at 1.8K with pressurized superfluid helium. This magnet can be operated in persistent mode and the field stability at that time is less than 10ppm/hour. The field homogeneity is better than 0.1% at 50 mm sphere volume. The stored energy is about 3MJ. A small refrigerator was installed on the top flange of the cryostat to reduce the evaporation rate of liquid helium and to maintain the superconducting magnet at low temperature while pausing. This system is used for the measurement of critical current and other physical properties of superconducting wire and other materials such as high T/sub c/ superconductors. >

Operation of 17.5 T superconducting magnet system in the last 8 years

A 17.5 T hybrid superconducting magnet with an outer Nb 3 Sn section and an inner V 3 Ga section was installed at National Research Institute for Metals (Japan) at the beginning of 1976. Since then the magnet system has been successfully operated about 60 times without any trouble. The magnet still generates the world-highest field in the superconducting state. Ordinarily, it is cooled from room temperature down to about 15 K using two helium refrigerators with a total refrigeration power of 750 W at 20 K. For one day operation, about 120 liters of liquid is transfered into the cryostat. It requires about 2 hours to induce the magnetic field from 0 to 17.5 T. The liquid helium evaporation rate is about 4.5 liters/hr when the magnet is in full operation. To suppress the instability due to the tape movement, it was necessary to refasten tie-rods between the upper and lower flanges of the magnet during the first few years after the installation. The magnet has been effectively used to measure the critical current of newly developed high-field superconductors.

Large Heat Transport Due to Spontaneous Gas Oscillation Induced in a Tube With Steep Temperature Gradients

This paper describes experimental studies of heat transfer due to the oscillations of gas columns that are spontaneously induced in a tube with steep temperature gradients. The tube (∼3 m in length) is closed at both ends and bent into U-shaped form at the midpoint. The temperature distribution along the tube is step-functional and symmetrical with respect to the midpoint. The warm part (closed-end sides) is maintained at room temperature and the cold one is immersed in liquid helium (4.2 K). The heat transported from the warm part to the cold is estimated from the evaporation rate of liquid helium. The heat flux by the oscillations is proportional to the square of the pressure amplitude, and the effective heat conductivity can be several orders of magnitude larger than the molecular heat conductivity of gas. The experimental results are compared with the theory of the second-order heat flux proposed by Rott and are found to be in satisfactory agreement with this.

Cryostat design for efficient use of liquid helium

Abstract The evaporation rate of liquid helium from a large (8” neck) superinsulated dewar is measured for various cryostat baffle configurations and vent rates through vapor cooled magnet leads. The evaporation rate of helium is almost linearly dependent on baffle number, but no support for the practice of placing edge rings on these battles was found. The addition of large magnet leads provided the major heat leak. Vapor cooling of these leads in the case of zero current did little to diminish the evaporation rate.

Fiberglas insert to liquid helium Dewar

We present the design of a simple Fiberglas insert to the liquid helium space of a conventional metal Dewar that results in a considerable reduction in the liquid helium evaporation rate. The original purpose of this simple modification was to minimize the volume of liquid helium that is used for experiments not requiring the full volume available at low temperature.

極低温引張試験装置の試作

With the development of cryogenic equipments such as superconducting magnets in recent years, there has been an increased requirement for knowledge of mechanical properties of structural materials at cryogenic temperatures. Taking these circumstances into consideration, the authors designed and constructed an apparatus for tensile tests to perform in the temperature range from room temperature to −271°C. The apparatus consists of a universal testing machine,a cryostat, an automatic temperature controller, a supply system for the coolant (liquid helium), a recovery system for the helium gas and a vacuum system. Temperatures down to −269°C can be controlled by the power inputs both to the heater in the coolant and the heater wound around specimens. Temperatures below −269°C can be obtained by pumping the cryostat with a mechanical pump. The cryostat, the most important part of the apparatus, consists of a dewar and a testing device inserted into the dewar. Specimens are fastened between the lower ends of pull rods and the bottom plate of a cylinder. Padding of copper scraps was provided around the specimens to keep uniform temperature distribution in the specimen. After measuring the natural evaporation rate of liquid helium in the cryostat and examining uniformity of the temperature distribution in the specimens, actual tensile tests were performed at cryogenic temperatures with 18-8 stainless steel and copper specimens. Then the reproducibility of test results were studied. The variation in the values of ultimate tensile strength and yield strength were within ±6 kg/mm2 and those of elongation were within ±5%.The work was performed as part of a national project and supported by the Agency of Industrial Science and Technology.

Evaporation Rate of Liquid Helium. I

In connection with a study of the emissivity of metals at low temperatures, a quantitative analysis has been made of the factors involved in the design of storage containers for liquid helium. Experiments confirm the analysis, which has resulted in an exceedingly simple liquid-nitrogen-protected liquid helium container having a helium evaporation rate of 1 percent per day. The hemispherical emissivity of mechanically polished copper at 4.23°K was determined for blackbody radiation. For radiation corresponding to that emitted by a blackbody at 77.1°K and 297.1°K, the measured emissivities are 6.9×10−3 and 1.29×10−2, respectively. These data are discussed in relation to the recent theoretical work of Reuter and Sondheimer. The heat of vaporization of helium at 4.228°K was determined to be 4.93 cal g−1, in substantial agreement with the data of Dana and Kamerlingh Onnes. Kistemaker's thermodynamic considerations questioning the accuracy of these data are evaluated in terms of the new determination.