Indium Seal Research Articles

Performance of cryogenic demountable indium seal at high pressures.

An essential challenge in seal designis to provide an ultra-low leak rate at cryogenic temperatures and high pressures. In this paper, the performance of demountable indium seals under a charging pressure of 8.5 MPa A and at cryogenic temperatures down to -190°C was investigated. Three indium seal structures with a diameter of 30mm were specifically designed and tested. All three structures went through both room temperature and cryogenic temperature tests in cycles with a pressure of up to 8.5 MPa A. In addition, leak rate experiments regarding the creep relaxation effect of the indium ring were conducted. The results showed that the leak rates of all three structures were lower than 1 × 10-10 Pa m3s-1 at both room temperature and cryogenic temperature with the pressure up to 8.5 MPa A when the torque was 8 or 12 N m. It was concluded that the linear loads for achieving a successful indium seal were 163, 171, and 220 N mm-1 alongside its circumference for the 2mm indium M-T structure, the 3mm indium M-T structure, and the Z-shaped seal structure, respectively. Furthermore, although the torque slightly dropped after the assembly due to the creep relaxation effect, the leak rates of the structure were still lower than 1 × 10-10 Pa m3s-1 three days after the assembly. The present work is helpful for designing ultra-low leak rate demountable indium seals at cryogenic temperatures and high pressures.

Anti-reflection coated vacuum window for the Primordial Inflation Polarization ExploreR (PIPER) balloon-borne instrument.

Measuring the faint polarization signal of the cosmic microwave background (CMB) not only requires high optical throughput and instrument sensitivity but also control over systematic effects. Polarimetric cameras or receivers used in this setting often employ dielectric vacuum windows, filters, or lenses to appropriately prepare light for detection by cooled sensor arrays. These elements in the optical chain are typically designed to minimize reflective losses and hence improve sensitivity while minimizing potential imaging artifacts such as glint and ghosting. The Primordial Inflation Polarization ExploreR (PIPER) is a balloon-borne instrument designed to measure the polarization of the CMB radiation at the largest angular scales and characterize astrophysical dust foregrounds. PIPER's twin telescopes and detector systems are submerged in an open-aperture liquid helium bucket dewar. A fused-silica window anti-reflection (AR) coated with polytetrafluoroethylene is installed on the vacuum cryostat that houses the cryogenic detector arrays. Light passes from the skyward portions of the telescope to the detector arrays through this window, which utilizes an indium seal to prevent superfluid helium leaks into the vacuum cryostat volume. The AR coating implemented reduces reflections from each interface to <1% compared to ∼10% from an uncoated window surface. The AR coating procedure and room temperature optical measurements of the window are presented. The indium vacuum sealing process is also described in detail, and test results characterizing its integrity to superfluid helium leaks are provided.

Leakage analysis and ground tests of knife edge indium seal to lunar sample return devices

This work deals with the lunar sample return project, which requires lunar samples to be returned back to the ground without contamination. In this paper, a knife edge indium seal is proposed as a primary sealing form, where indium–silver alloy is welded into an annular groove of a cylindrical container firstly and then extruded by an annular knife edge of a cylindrical lid. The analysis of the leakage and sealing reliability of knife edge indium seal is the main aim of this paper. Firstly, the pretreatment of knife edge indium seal is discussed. Key techniques on indium welding are studied to evaluate its sealing reliability, with the tensile strength and welding void ratio mainly being discussed. Secondly, by means of “Roth” leakage theory, mathematical models on the leak rate for knife edge seal are established. By means of the finite element analysis, the knife edge geometry is optimized with minimum pressing force required. The results justify that the knife edge seal demands much lower pressing force to achieve a considerable sealing performance, which is suitable for low-powered operation. Finally, the ground tests are carried out to evaluate the feasibility of the indium welding and to measure the leak rate of the knife edge indium seal. Experimental results demonstrate the indium welding onto the stainless steel container is feasible, and the leak rate at room temperature is 3.0 × 10−10 Pa·m3/s, which is much lower than the rubber O-type ring seal. The knife edge indium seal is suitable for lunar sample return devices.

Design Improvement and Bias Voltage Optimization of Glass-Body Microchannel Plate Picosecond Photodetector

Microchannel plate photodetectors, capable of picosecond time resolution and sub-mm spatial resolution, are a perfect candidate for the next generation of photodetectors for precision timing measurements. Argonne National Laboratory is producing low-cost, all-glass body, planar photodetectors with an indium seal. The design and fabrication of 6-cm square photodetectors has been well demonstrated in an ultra-high vacuum system. Recently, a new design was developed to optimize the photodetector bias voltage. This design offers an improved configuration and allows external control of the bias voltage for each internal detector component. Design and measurements of the new independently biased devices are described in this paper. We performed a systematic study on the bias voltage and achieved a gain on the order of $10^{{\mathbf {7}}}$ , a time resolution better than 35 ps, and a spatial resolution better than 1 mm.

Comparative research on indium seal process for transmission-mode GaAs photocathodes

For night vision devices and other applications, the transmission-mode photocathodes must be sealed to tube by indium seal process (ISP) in practical application. But in early research, the integral sensitivity has large drop to about 30% amplitude after ISP process than after activation process. In order to well study the influence of ISP on surface barriers of activated GaAs photocathodes, we used the comparative research method by surface photovoltage spectroscopy (SPS) and spectral response current (SRC). Through fitting calculation, we can find that the impurity gas sources by micro channel plate and fluorescent screen have deep influence on the amplitude and width of surface barriers which lead to the large drop on SRC curves before and after ISP process. This on-line comparative research method can help to optimize ISP technique and vacuum degree optimization for transmission-mode GaAs photocathodes in the future.

20 cm Sealed Tube Photon Counting Detectors with Novel Microchannel Plates for Imaging and Timing Applications

As part of a collaborative program between University of California, Berkeley, the Argonne National Laboratory, University of Chicago, and several commercial companies, a 20cm square sealed tube microchannel plate detector scheme with a proximity focused bialkali photocathode is being developed. Sealed tube microchannel plate deviceshave good imaging and timing characteristics, but large areas have been previously unavailable. We have madeb considerable progress in fabricating large size microchannel plates. A key feature is the novel implementation of low cost microchannel plates using borosilicate micro-capillary arrays with hollow core tubes. The resistive and secondary electron emissive surfaces are then applied by atomic layer deposition, eliminating the wet etch and thermal reduction processes for normal glass microchannel plates. Initial results with 33 mm format microchannel plates for gain, pulse width, imaging performance and lifetime are comparable to conventional MCPs. Large 20 cm square microchannel plate prototypes with 20 μm and 40 μm pores have been fabricated and initial tests show operational gain. Design and fabrication of a 20 cm sealed tube assembly is well advanced and comprises a borosilicate entrance window, a proximity focused bialkali photocathode, a pair of microchannel plates and a stripline readout anode. The design employs a brazed ceramic walled enclosure and a transfer tube type photocathode with an indium seal. We have adopted a baseline bialkali photocathode to match the anticipated input spectrum, and have made a number of test cathodes with >20% peak quantum efficiency on borofloat-33 window material. Stripline anodes are also being developed which will give less than 1 mm spatial resolution using custom ASIC amplification and timing electronics.

Note: Mounting ultra-high vacuum windows with low stress-induced birefringence

We have developed a way to mount ultra-high vacuum windows onto standard ConFlat(®) vacuum systems with very low stress-induced birefringence. Each window is sealed to a stainless steel flange with a compressed indium wire, and that flange is connected to a vacuum chamber with another indium seal. We find that deformation of a standard ConFlat flange during indium sealing dominates the stress on the window, so an extra-rigid flange is needed for minimal birefringence. With this mounting scheme, the typical residual birefringence is Δn = 2.3 × 10(-7) and is unchanged by a 120 °C bake.

Stresses in vacuum glazing fabricated at low temperature

This paper reports an experimental and theoretical study of the stresses in and durability of vacuum glazing fabricated at low temperature using an indium based edge seal. For the first time a finite-element model with support pillars incorporated directly, enabled the stresses in the whole structure to be explicitly calculated. Experimental validations of the finite element model predictions were undertaken. Modelling results are presented for a case with American Society of Testing and Materials standard winter boundary conditions. It was found that, for the particular system studied, the predicted stress level in the structure is essentially the same for indium sealed and solder glass sealed vacuum glazing, and the magnitude of stress values in the indium seal is comparable with that dictated by the indium strength characteristics.

A large dilution refrigerator forpolarized target experiments

The refrigerator for the SMC polarized target at CERN (NA47) is by farthe largest dilution refrigerator in operation for this purpose. The target is loaded cold, horizontally into the mixing chamber, which is sealed with a cold indium seal. In "frozen" mode a circulation of 30 mmol/s gives a base temperature of 30 mK. A proton target is polarized to 90 % at 300 mK with a circulation of 180 mmol/s.

Improved indium seal for LiF windows of resonance lamps for use at low temperatures

A method of attaching crystalline LiF windows to glass lamps has been developed. The resulting seals have good vacuum properties and can be cooled to cryogenic temperatures while maintaining their vacuum integrity. The technique uses dual, indium O rings to provide a vacuum seal for a LiF window on a resonance lamp. It is appropriate for resonance lamps that produce line spectra. LiF crystals must be cooled to transmit Lyman-β radiation that can optically pump atomic hydrogen. This indium seal has other applications such as windows for VUV lasers. Details of the construction, assembly, and performance of the seal are described. A discussion of the merits and applications of the window seal is presented.

Indium seals for low-temperature and moderate-pressure applications

Some ideas as to what the important factors are that will produce a reliable indium O-ring seal are discussed. Four novel indium seal designs which are based on these ideas are presented. Three of these seals have been incorporated in a Brillouin cell. They include a simple sapphire window seal, a filling line union, and a flange seal. All of them have withstood low temperatures down to 77 K and moderate pressures up to 177 bar. The fourth seal described is a Pyrex tube seal for a Raman cell.

A comparison of specimen stage surface temperature and the GA‐1 control unit reading in Balzer's Freeze fracture microtome cold stage

AbstractThe cold stage specimen surface in our Balzer's 300 Freeze‐etch instrument, averages 29–43°C warmer than the reading on the GA‐1 stage temperature control unit. By introduction of Indium foil seals above and below the stainless steel plug in the stage tower, the specimen cold stage surface temperatures were still 9–10°C warmer than the GA‐1 reading. After replacing the stainless steel plug with a copper plug and using Indium seals, the cold stage specimen surface was brought within 2.6°C of the GA‐1 temperature reading. In addition, the copper plug, Indium seal modified stage cools about two times faster in going from –100°C to –150°C than the normal stainless steel stage modified with Indium seals.

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A Test of Modified Indium Seal of a Window at Liquid Helium Temperature

A modified version of an indium seal with a very small loss area, in which pure In solder is used instead of pure In wire, has been tried for a glass window of 20mm in diameter. It has turned out that this seal is vacuum tight against the liquid helium at 4.2K.A seal of a 10mmφ sapphire window with STYCAST 2, 850GT was also successfully tested at 4.2K.

A low temperature indium seal

An indium seal is described which operates reliably without vacuum lubrication in superfluid helium due to the tightening of the screws after single cooling with liquid nitrogen. (auth)

A wide aperture, low temperature valve

A wide aperture valve, suitable for high vacuum work at liquid helium temperatures is discussed. The valve, utilizing a self-renewing indium seal, and the mechanism from a standard bellows sealed valve, was designed for use in conjunction with a fixed liquid helium cooled charcoal adsorption pump.

Microwave and Fast-Acting Valves and Vacuum Couplings for Accelerators

The high vacuum requirements of the Stanford Two-Mile Linear Electron Accelerator plus the radiation produced by electron acceleration have made it necessary to design special vacuum and isolation components. Two of these are special purpose valves capable of operating in a vacuum system at 10-8 torr, and the third is a group of quick-disconnect couplings used for component installation in the beam switchyard area of the accelerator. One valve is an all-metal, 50-megawatt, S-band microwave valve used to isolate an evacuated rectangular waveguide feed system from exposure to air during the replacement of a klystron drive tube for the accelerator. The valve is built with a remeltable indium seal which provides for leak rates on closure below 24 × 10-8 std. cc He/sec. The second valve is a fast-acting unit that was designed for beam axis application within the disk-loaded waveguide accelerator structure. This valve also has an indium seal that is remotely remeltable and has a measured closing time of nine milliseconds. The group of quick-disconnect couplings, which are 6, 10 and 12-inch pipe sizes, are remotely operable, non-elastomer couplings used in the vacuum chamber system of the beam switchyard. The radiation intensity in this area is sufficient to make elastomer seals impractical and to require that replacement of switchyard components be done quickly and remotely. Indium is also used as a reusable seal for these couplings and can be re-formed mechanically to extend seal life.