High-precision temperature control and stabilization using a cryocooler

We describe a method for precisely controlling temperature using a Gifford-McMahon (GM) cryocooler that involves inserting fiber-reinforced-plastic dampers into a conventional cryosystem. Temperature fluctuations in a GM cryocooler without a large heat bath or a stainless-steel damper at 4.2 K are typically of the order of 200 mK. It is particularly difficult to control the temperature of a GM cryocooler at low temperatures. The fiber-reinforced-plastic dampers enabled us to dramatically reduce temperature fluctuations at low temperatures. A standard deviation of the temperature fluctuations of 0.21 mK could be achieved when the temperature was controlled at 4.200?0 K using a feedback temperature control system with two heaters. Adding the dampers increased the minimum achievable temperature from 3.2 to 3.3 K. Precise temperature control between 4.200?0 and 300.000 K was attained using the GM cryocooler, and the standard deviation of the temperature fluctuations was less than 1.2 mK even at 300 K. This technique makes it possible to control and stabilize the temperature using a GM cryocooler.     

Low temperature embedding with Lowicryl resins: two new formulations and some applications

Lowicryl K4M and HM20 are methacrylate/acrylate based low temperature embedding resins for biological material which can be used in conjunction with either the progressive lowering of temperature (PLT) technique or with freeze-substitution. K4M and HM20 are applicable over a very extended temperature range, approximately 220 K to 340 K. With two new resins, K11M and HM23, one can reach even lower temperatures, c. 200 K. Freeze-substitution combined with low temperature embedding allows for very mild or no chemical fixation which seems to increase the sensitivity of immunocytochemical localization of antigens on sections.     

High temperature (1)H NMR probe

A furnace is described which is suitable for single coil proton magnetic resonance experiments from room temperature to 1100 K, and which will fit a 30 mm magnet gap. The temperature variation is less than +/- K at 800 K over a 27 mm-long sample.     

High precision Mössbauer furnace for 1100 K

Detailed designs are given for a high precision M?ssbauer furnace that may be used up to temperatures of 1100 K. With proper precautions the furnace designs described yield long-term temperature instability better than approximately 0.02 K and temperature inhomogeneity of better than 0.05 K.     

对称结构的半导体式光纤温度传感器

基于半导体吸收的光纤温度传感器具有电绝缘好、抗电磁干扰、无火花、能在易燃易爆的环境下使用等优点，非常适合组建电力设备、石油井下等环境下的温度监测系统，但它目前仍存在测量精度低、稳定性差等问题。提出了一种对称结构的半导体式温度传感系统的设计方案，详细分析了测温原理和系统结构，并构建了实验平台，进行了实验。实验表明：该系统在263～419K的温度范围内有1K的测量精确度和0．1K的分辨率，以及良好的线性度和反应时间，有效消除了光源和光探测器性能的不稳定和光纤耦合效率变动对测量精度的影响，提高系统的测量精度和稳定性。     

光纤位移传感器在低温装置中测量超导转子悬浮微位移的应用

介绍了一种补偿式光纤位移传感器,对比分析了该传感器在室温(293 K)下和液氮温度(77 K)下的传输特性。结果表明,该传感器能有效地消除外界环境的影响,可用于宽温度范围的位移测量。在液氦温度(4.2 K)下测量超导转子悬浮微位移的实验结果表明,该传感器可在低温下进行位移测量,测量分辨率达到10 μm。实验结果为光纤位移传感器在低温环境下的应用提供了参考。     

Temperature control in Lowicryl K4M and glycol methacrylate during polymerization: is there a low-temperature embedding method?

An apparatus for embedding tissues at resin temperatures down to 228 K is described. By placing thermocouples in the resin the temperature has been monitored during embedding at low temperature with glycol methacrylate (GMA) and Lowicryl K4M. Even in this apparatus with a liquid cooling bath the heat of polymerization is not dissipated and the resin temperature rises. This rise is directly proportional to the resin temperature at the onset of polymerization and is higher in Lowicryl K4M than GMA. The initial resin temperature also affects the time taken for polymerization. The time to the onset of the peak and its duration are both increased as the temperature is lowered. This effect is more pronounced with GMA than Lowicryl K4M and polymerization of GMA is inhibited at the lowest temperature used. When Lowicryl K4M, polymerized at low temperature, is warmed up to ambient a further exothermic reaction occurs, which causes the resin temperature to rise well above ambient. Both this temperature peak and that during polymerization are reduced, but not totally eliminated, by reducing the resin volume. Aircooled systems are inefficient compared with the low-temperature apparatus used here and the resin temperature rise is consequently greater and, even with small resin volumes, it can be very high. It is therefore unlikely for published methods that the temperature specified has been maintained in the resin during polymerization. The implications of these findings are discussed in relation to enzyme and antigen survival. Recommendations include use of very small volumes of resin, refrigerated liquid-bath rather than air-cooled systems and contact with a heat sink when specimens are warmed up to ambient temperature. Examples of enzyme reaction, antigen survival and structural preservation obtained with the method are presented.     

PdPtAu alloys for low-temperature precision resistors

Palladium-rich PdPt and PdAu alloys exhibit a resistance-temperature behavior characterized by flat minima even after eliminating the Kondo effect by oxidation of the impurities. The opposite signs of their thermoelectric potentials against a superconductor permit the preparation of ternary PdPtAu alloys free of a thermoelectric power. The measurements resulted in a nomogram suitable for determining the composition of the alloy necessary for a resistivity minimum at a given temperature between 1.5 and 4.2 K. Alloys manufactured in this way have a temperature coefficient of resistivity of less than 10(-6)/K within a temperature interval of 0.5 K and a thermoelectric power against a superconductor of less than 1 nV/K.     

Friction of molybdenum disulfide-titanium films under cryogenic vacuum conditions

The tribological behavior of steel and sapphire sliding on a sputtered MoS₂+Ti coating was studied in ultra-high vacuum as a function of temperature over the range of 4-300 K. The coefficient of kinetic friction for the steel/moly interface was determined to be approximately 0.05 from room temperature to 240 K, and increased monotonically to 0.125 at 4 K. The sapphire/moly friction coefficient was measured to be 0.15±0.05 at room temperature and increased monotonically to 0.25 at 4 K. We also analyze in detail the flash temperature due to frictional heating at the sliding contacts. Flash heating is a particularly strong effect at cryogenic temperatures.     

Thermal contact conductance of demountable in vacuum copper-copper joint between 14 and 100 K

Thermal contact conductance (TCC) at material interfaces has a great impact upon the efficiency of cooling in cryogenic instruments, and is thus a crucial design parameter. Lack of reliable numerical data for demountable in vacuum bare (uncoated, dry, and without interposers) copper-copper joints prompted us to carry out systematic studies of TCC over the temperature range 14-100 K. We measured TCC as function of applied force for the contacts with surface roughness R(a) = 0.2, 1.6, and 3.2 μm. It is seen that with increasing temperature, the TCC of bare Cu-Cu contact initially rises following a generic power law dependency T(γ) with γ = 1.25 ± 0.02, reaching a maximum value at 40-50 K. TCC then decreases as temperature continues to rise towards 100 K. We show results that match those in the literature from low (4-20 K) and high (100-300 K) temperature domains, resulting in a unified smooth curve of temperature dependency of TCC for bare Cu-Cu joints. Temperature dependence is then described in a phenomenological model, accounting for the effects of changes in bulk conductivity and surface hardness with temperature. This model consistently explains the observed power law dependence of TCC as function of applied force and changes caused by roughness of contact surfaces.     

Note: cryogenic low-noise dc-coupled wideband differential amplifier based on SiGe heterojunction bipolar transistors

Silicon-germanium heterojunction bipolar transistors can be used to construct low-noise cryogenic amplifiers. We present a dc-coupled differential amplifier capable of operating down to 10 K. In this temperature regime it has bandwidth of 15 MHz and noise temperature as low as 1.3 K. When operated at liquid nitrogen temperature of 77 K, the measured noise temperature is lower than 3 K. The amplifier is based on the commercially available transistors NESG3031 and operational amplifier OPA836 and is capable of standalone operation without any additional stages at room temperature.     

Friction of molybdenum disulfide–titanium films under cryogenic vacuum conditions

The tribological behavior of steel and sapphire sliding on a sputtered MoS₂+Ti coating was studied in ultra-high vacuum as a function of temperature over the range of 4–300 K. The coefficient of kinetic friction for the steel/moly interface was determined to be approximately 0.05 from room temperature to 240 K, and increased monotonically to 0.125 at 4 K. The sapphire/moly friction coefficient was measured to be 0.15±0.05 at room temperature and increased monotonically to 0.25 at 4 K. We also analyze in detail the flash temperature due to frictional heating at the sliding contacts. Flash heating is a particularly strong effect at cryogenic temperatures.     

Operating a triple stack microchannel plate-phosphor assembly for single particle counting in the 12-300 K temperature range

An assembly consisting of a stack of three microchannel plates (MCPs) and a phosphor screen anode has been operated over the temperature range from 300 to 12 K. We report on measurements at 6.4 kHz (using an alpha source) and with dark counts only (15 Hz). Without any particle source, the MCP bias current decreased by a factor of 2.1 x 10(3) when the temperature was lowered from 300 to 12 K. Using the alpha source, and a photomultiplier tube (PMT) to monitor the phosphor screen anode, we first observed an increase in the decay time of the phosphor from 12 to 45 mus when the temperature was decreased from 300 to 100 K while the decay time then decreased and reached a value of 5 mus at 12 K. The pulse height distribution from the PMT was measured between 300 and 12 K and shows a spectrum typical for a MCP phosphor setup at 300 K and 12 K but is strongly degraded for intermediate temperatures. We conclude that the present MCP-phosphor detector assembly is well suited for position-sensitive particle counting operation at temperatures down to at least 12 K even for count rates beyond 6 kHz. This result is crucial and an important part of ongoing developments of new instrumentation for investigations of, e.g., interactions involving complex molecular ions with internal quantum state control.     

A programmed controlled temperature microscope stage

The construction, and testing, of a programmed controlled temperature stage for optical microscopy is described. The stage is shown to be capable of attaining temperatures between 160 K and 373 K, and of providing repeatable heating and cooling rates up to, and in excess of 100 K min^?1. It is also capable of providing stable temperature holds.     

A Temperature-Controlled System for Optical Microscopy in the Temperature Range 40–800 K

A system with temperature control over a range of 40–800 K is designed for examining materials by the optical microscopy and spectral analysis methods. Liquid helium (control range, 40–400 K) or liquid nitrogen (control range, 80–800 K) is used as a cryoagent. The temperature in the system is stabilized over the entire range of temperatures with an accuracy of ±0.3 K.     

A cryosystem for cooling samples in a secondary-ion mass spectrometer with a static analyzer

A cryogenic system for cooling samples in an IMS-4F secondary-ion mass spectrometer with a static analyzer is described. The cryogenic system allows maintenance of the sample temperature with an accuracy of ±1 K in a temperature range of 60–420 K by combining heating and cooling (by using liquid helium or nitrogen). The effect of the sample temperature (300 and 110 K) on the secondary-ion mass spectra of Si and GaAs samples is considered.     

Modeling temperature effects on a Coriolis mass flowmeter

Coriolis mass flowmeters are used for many applications, including as transfer standards for proficiency testing and liquified natural gas (LNG) custody transfer. We developed a model to explain the temperature dependence of a Coriolis meter down to cryogenic temperatures. As a first step, we tested our model over the narrow temperature range of 285 K to 318 K in this work. The temperature dependence predicted by the model agrees with experimental data within ± 0.08 %; the model uncertainty is 0.16 % (95 % confidence level) over the temperature range of this work.Here, basic concepts of Coriolis flowmeters will be presented, and correction coefficients will be proposed that are valid down to 5 K based on literature values of material properties.     

Effects of Temperature on the Microscale Adhesion Behavior of Thermoplastic Polymer Film

Adhesion tests were carried out under various temperature conditions to investigate the effects of temperature on adhesion behavior between a fused silica lens and a poly(methylmethacrylate) (PMMA) film, materials used for molds and as thermoplastic polymer films in nanoimprint lithography (NIL). The pull-off force and the contact area were measured as the temperature of the PMMA film was increased from 300 to 443 K, and as it was decreased back to 300 K. As the temperature increased, the PMMA film changed from a glassy state to a viscous flow state, and the adhesion behavior showed significant variation corresponding to this change in state. In the glassy state (below 363 K), the pull-off force did not change noticeably as the temperature increased. In the rubbery state (383–413 K), the pull-off force increased significantly as the temperature increased. In addition, the contact area was enlarged. In the viscous state (above 423 K), fingering instability was observed in the contact area and the pull-off force decreased, while the contact area increased, as the temperature increased. The adhesion behavior was also found to vary markedly with thermal history of the PMMA film. The causes of these changes are discussed.     

Effects of materials and solution temperatures on cavitation erosion of pure titanium and titanium alloy in seawater

Cavitation erosion was studied for various pure titanium and titanium alloy samples using a rotating disk method in seawater at 303, 318, and 333 K. Their respective erosion resistances were evaluated in terms of Vickers hardness (HV). The resistance increased in order with increasing hardness: pure titanium samples of first, second, and third types, and titanium alloy (Ti–6Al–4V). The relative temperature was defined as 273 K for freezing temperature and 373 K for boiling temperature under pressurized water. The volume loss rate of test specimens increased with rising seawater temperature of 289–316 K of the relative temperature, as well as in cases using cavitating liquid jet and vibratory apparatuses.     

A versatile light microscope heating stage for biological temperatures

A light microscope heating stage suitable for biological temperatures is described. A novel feature of the design is the use of cupro-nickel foil heaters (0.1 mm thick). With a temperature sensor mounted on the slide clip and a temperature controller unit, this apparatus maintains a temperature of 310 K with a precision of 0.1 K. The apparatus is inexpensive, reliable, not confined to use with one microscope and does not interfere significantly with the stage movement or optical alignment.