Ultra High Vacuum Test Research Articles

Nonevaporable getter-MEMS for generating UHV conditions in small volumina

The industrial use of quantum sensors requires further miniaturization of the experimental peripherals, i.e., the high vacuum chamber, laser technology, and control electronics. A central part of the high vacuum chamber is the maintenance of vacuum conditions. For this purpose, a prototype of a compact, i.e., miniaturized, ultrahigh vacuum pump in the form of a nonevaporable getter (NEG) pump at a wafer level (MEMS), is developed within the scope of this work. With regard to the basic conditions of the functionality of the NEG, a miniaturized heating plate with temperature sensors is analytically and numerically developed, constructed, and characterized in an ultrahigh vacuum test stand. This is followed by the integration of the NEG into the existing system, which, in connection with the characterization of material-specific parameters, enables a first correlation of heat input and pumping power. Thus, performance data of the getter-MEMS under high-vacuum confinement confirm its usability for quantum sensors. In addition, optimization potentials are shown with regard to all partial aspects of the MEMS.

Optical resonance enhanced Cs activated nano-structured Ag photocathode

Metallic photocathodes have drawn attention due to their outstanding performances of ultrafast photoelectric response and long operational lifetime. However, due to their high work function and the large number of scattering events, metallic photocathodes typically are driven by ultraviolet laser pulses and characterized by low intrinsic quantum efficiency (QE). In this work, a new type of Mie-type silver (Ag) nano-sphere resonant structure fabricated on an Ag/ITO composite substrate is used to enhance the photocathode QE, where Mie scattering resonance is used to enhance the local density of optical state and then to improve the light absorption and electron transporting efficiency in Ag nano-spheres. The cesium (Cs) activation layer is also used to lower the electron work function and then to excite photoemission in the visible waveband for Ag photocathode. The optical characteristics of Ag nano-sphere arrays are analyzed by using finite difference time domain method. For the investigated Ag nano-sphere array, theoretical results show that Mie-type electric dipole resonance modes can be obtained over the 400–600 nm waveband by adjusting the sphere diameter, and the large resonance-enhanced absorption can be achieved in nanospheres at the resonance wavelength. The Ag nano-spheres are fabricated on the Ag/ITO substrate by magnetron sputtering and annealing process, then the Cs activation layer is deposited on surface, and finally QE is measured in an ultra-high vacuum test apparatus. Experimental results show that over 0.35% of QE is obtained for Ag nano-sphere particle (with a diameter of 150 nm) at a wavelength of 425 nm, and the wavelength positions of QE maxima are in agreement with Mie resonance for corresponding geometry predicted from the computational model. Given these unique optoelectronic properties, Ag nanophotonic resonance structured photocathodes represent a very promising alternative to photocathodes with flat surfaces that are widely used in many applications today.

ПОВЫШЕНИЕ КАЧЕСТВА УПЛОТНИТЕЛЬНЫХ ЭЛЕМЕНТОВ ИОННО-ПЛАЗМЕННЫМ НАПЫЛЕНИЕМ

The purpose of the work is to study the possibility of reducing leakages in the seals with metal O-rings (on example of a vacuum flange joint of the ConFlat standard) by ion-plasma sputtering deposition of a soft metal on the ring surface. The coating was applied using an original ion-plasma source with a liquid anode. The hermeticity of sealing o-rings of the CF40 joint was tested on an ultrahigh vacuum test bench with a XT-100M mass spectrometer quadrupole gas analyzer tuned to control the in-leakage of helium in the test bench vacuum chamber. Conducted experiments allowed to determine that the amount of in-leakage decreases under the reusing of a sealing ring sputtered with a copper coating. Ring surface micrographs were obtained using a scanning electron microscope. Sputtering deposition of a soft metal layer on the contact surfaces of a single-used metal ring restores surface sealing properties as well as reduces in-leakage as compared to a new liner. The effect is provided by the formation of a tight contact of the flange wedge solid metal with the surface of the plastic coating leveled along the entire circumference, which was restored by smoothing ring cavities formed during the previous tightening of the flange joint.

The fabrication of a double-layer atom chip with through silicon vias for an ultra-high-vacuum cell

This study presents a double-layer atom chip that provides users with increased diversity in the design of the wire patterns and flexibility in the design of the magnetic field. It is more convenient for use in atomic physics experiments. A negative photoresist, SU-8, was used as the insulating layer between the upper and bottom copper wires. The electrical measurement results show that the upper and bottom wires with a width of 100 µm can sustain a 6 A current without burnout. Another focus of this study is the double-layer atom chips integrated with the through silicon via (TSV) technique, and anodically bonded to a Pyrex glass cell, which makes it a desired vacuum chamber for atomic physics experiments. Thus, the bonded glass cell not only significantly reduces the overall size of the ultra-high-vacuum (UHV) chamber but also conducts the high current from the backside to the front side of the atom chip via the TSV under UHV (9.5 × 10−10 Torr). The TSVs with a diameter of 70 µm were etched through by the inductively coupled plasma ion etching and filled by the bottom-up copper electroplating method. During the anodic bonding process, the electroplated copper wires and TSVs on atom chips also need to pass the examination of the required bonding temperature of 250 °C, under an applied voltage of 1000 V. Finally, the UHV test of the double-layer atom chips with TSVs at room temperature can be reached at 9.5 × 10−10 Torr, thus satisfying the requirements of atomic physics experiments under an UHV environment.

The development of an atom chip with through silicon vias for an ultra-high-vacuum cell

This paper describes the development, fabrication and examination of an atom chip through silicon vias (TSV), which is anodically bonded with a Pyrex glass cell to form an ultra-high-vacuum system for the application of Bose–Einstein condensation (BEC) experiments. The silicon via is etched by the inductively coupled plasma reactive ion etch and filled by copper plating technology. The metal wires on both sides of the atom chips are patterned by the lithography process. Three different sizes of TSV are made and tested by continuously applying a maximum current of 17 A under the vacuum (70 Torr) and in air. In addition, after the thermal cycling of an anodic bonding process (requested at 350 °C) and a high electric field of 1000 V m−1, the TSV on atom chips can still hold the ultra-high vacuum (UHV). The conductive and vacuum yields of the TSV improved from 50% to 100% and from 75% to 81.25%, respectively after the modification of the fabrication process. Finally, the UHV test of TSV on atom chips at room temperature can be reached at 8 × 10−10 Torr, thus satisfying the requirements of atomic physics experiments under the UHV environment.

Design and manufacturing of the antechamber for BEPCII storage rings

Antechamber which composes the arc vacuum chamber of storage rings is one of the key devices of BEPCII. It has the characteristic of various specifications, large size, complex structure, and high dimension accuracy. This paper gives a review on the structure features and the procedure of production, including the mechanical machining process, cleaning and welding process of high vacuum aluminum alloy, ultrahigh vacuum test and so on. In view of the occurrence of the concave deformation, the reasons are analyzed and the correction method developed is introduced too.

Ultra high vacuum test setup for electron gun

Ultra High Vacuum (UHV) test setup for electron gun testing has been developed. The development of next generation light sources and accelerators require development of klystron as a radio frequency power source, and in turn electron gun. This UHV electron gun test setup can be used to test the electron guns ranging from high average current, quasi-continuous wave to high peak current, single pulse etc. An electron gun has been designed, fabricated, assembled and tested for insulation up to 80 kV under the programme to develop high power klystron for future accelerators. Further testing includes the electron emission parameters characterization of the cathode, as it determines the development of a reliable and efficient electron gun with high electron emission current and high life time as well. This needs a clean ultra high vacuum to study these parameters particularly at high emission current. The cathode emission current, work function and vapour pressure of cathode surface material at high temperature studies will further help in design and development of high power electron gun The UHV electron gun test setup consists of Turbo Molecular Pump (TMP), Sputter Ion Pump (SIP), pressure gauge, high voltage and cathode power supplies, current measurement device, solenoid magnet and its power supply, residual gas analyser etc. The ultimate vacuum less than 2×10−9 mbar was achieved. This paper describes the UHV test setup for electron gun testing.

Light emission in XLPE subjected to HV in high vacuum and pressurized gas

The spectral and spatial resolution of electroluminescence, the light emitted from polymeric insulation subjected to high electric field, is studied in a test cell pressurized to 215 kPa with ultra high purity nitrogen gas. The paper also describes light emission from crosslinked polyethylene (XLPE) subjected to HV in an ultra high vacuum test cell. It is shown that the characteristics of light emitted from XLPE in the evacuated test cell are quite different from the light emitted when the test cell is pressurized. The mechanisms responsible for light emission under high vacuum condition are described and it is suggested that care should be taken when interpreting the light detected from polymeric insulation subjected to high electric fields.

Formation of Subgrains in Tungsten–Rhenium–Hafnium Carbide Alloys During Creep

Tungsten (W) has unique advantages for hightemperature applications such as having the highest melting point (3680 K) of all metals, a high modulus of elasticity (315 GPa at 2273 K) and a low selfdiffusion coef®cient. Its poor low-temperature ductility, however, has limited its applications. Extensive alloying studies have focused on tungsten to improve its low-temperature fabricability and high-temperature strength, and it was found that the addition of rhenium (Re) increased room-temperature ductility and the high-temperature creep strength of tungsten [1]. Strengthening tungsten with ®ne precipitates of second-phase particles is a very effective way of improving high-temperature tensile and creep properties at temperatures above 0.5 Tm (Tm is the melting temperature of tungsten in Kelvin). Among potential strengtheners, hafnium carbide (HfC) has the highest melting point, the highest thermodynamic stability and the lowest vapor pressure. Combining the low-temperature ductilizing effect of Re and the high-temperature strengthening effect of HfC makes W±Re±HfC alloy one of the candidate structural materials for use at service temperatures above 1500 K. Because creep is one of the major concerns for high-temperature materials, the creep behavior of W±Re±HfC alloy was studied in this research. The material used in this research was an arcmelted and swaged W±4 wt % Re±0.32 wt % HfC (W±4Re±0.32HfC), which was supplied by the National Aeronautics and Space Administration. As-received materials was in the form of 25.4 mm diameter rods. Plate-type specimens with a gage section of 12:7 mm 3 3:2 mm were prepared by electric discharge machining. The specimens were ®rst mechanically polished with abrasive papers and then lapped with alumina powders. After the mechanical polishing, the specimens were chemically polished in a 10% NaOH solution to ensure a smooth surface. Prior to testing, all the specimens were annealed at 2500 K for 1 h to produce recrystallized grains. The creep test in this research was conducted in a custom-built ultrahigh-temperature, ultrahigh-vacuum (UHV) creep test station. The specimens were tested under stresses from 40 to 70 MPa, with 10 MPa intervals, at 2200, 2300 and 2400 K. Specimens were heated by passing alternating current through them. A mechanical pump, a sorption pump and an ion pump ensured a vacuum level of less than 1:33 3 10y6 Pa (1 3 10y8 Torr) during the creep tests. The specimen temperature was measured by a micro-optical disappearing ®lament pyrometer that was calibrated with a standard tungsten ribbon ®lament lamp provided by the National Institute of Standards and Technology. Blackbody temperature of the specimen was veri®ed by high-temperature emissivity data from a sample with the same alloy composition. The maximum uncertainty of the measured temperature was 5 K for the entire temperature range used in this research. Load was applied to the specimen through stainless-steel bellows that were attached to the UHV chamber, and corrections were made for changes in the spring force of the bellows caused by extension of the load column. Specimen elongation was measured by a linear variable differential transformer interfaced with a data acquisition system, which made it possible to measure the creep strains with 0.03% accuracy. The specimens were examined before and after the creep test with a transmission electron microscope (TEM) to study the microstructures that developed during the high-temperature deformation. Samples for the TEM study were cut from the gage section of the post-test specimens, and the thicknesses of the samples were reduced to approximately 120 im. From these 120 im samples, disc-shaped blanks with a diameter of 3 mm were produced using an ultrasonic cutter, and both sides of the blanks were ground to a thickness of 70 im. The blanks were dimpled to a thickness of 30 im at the center using a 6 im diamond paste for 2 h and then were polished with a 1 im diamond paste for 5 min. After the mechanical thinning procedures were complete, the specimen blanks were ion milled at an angle of 15±208 for 10±15 h. The samples were then examined with a high-resolution TEM at magni®cations of 5000, 15 000, 30 000, 60 000 and 100 000 times at 200 kV. All specimens fractured at the center of the gage section. There were no changes to the composition after the tests. The results of the strain-time creep curve [2] showed three regions of a creep curve:

A test method for 50 Hz capability of vacuum interrupter materials

This investigation method allows an excellent comparison of the interruption behavior of contact materials in real vacuum tubes by using small cylindrical contact samples (12 mm diameter) in a special experimental setup. The described investigations were carried out with different CuCr materials in an ultrahigh vacuum test vessel. For the test an apparent current density similar to the stress in real switches is applied to the contact materials of reduced size. A high current circuit with a current of 10.7 kA peak is used for the interruption check. After current zero a Weil-Dobke voltage superposition circuit applies a transient recovery voltage (36 kV, 41 kHz) to the open gap to test the restrike behavior. From the measured data the percentage of successful interruptions of the total number of tests and the re-ignition times were taken as quality criteria. Compared to interruption capacity, measurements with real breakers the results of the developed test method show very similar rankings for different contact materials.

Vacuum system of the Dubna heavy ion storage ring facility K4-K10

The complex K4-K10 of two storage rings is intended to provide the beams of exotic neutron deficient and neutron excess nuclei ranging from He to Ni. High momentum resolution of cooled exotic beams ( δp/ p = 10 −5 −10 −6) and maximum energy of 150–200 MeV amu −1 are the purpose of this project. Interactions of heavy ions with the molecules of the important constituents of the residual gas are analysed. For a successful operation of the ring complex, the pressure in the vacuum chambers must not be less than 1 × 10 −8 Pa. The gas load sources are analysed and the vacuum technology of the initial preparation of the vacuum chamber materials and the procedure of reaching the desirable vacuum are defined. The structures of the vacuum systems and their different parts are described. An ultra high vacuum test bench for modelling works and examination of individual parts of the vacuum system is created.

The effect of silicon on the adhesion of noble metals

The effect of silicon on the adhesion of noble metals has been studied using a twist-compression bonding test and an ultrahigh vacuum test. The specimen surfaces were analysed using ion microprobe mass analysis and electron spectroscopy for chemical analysis. It was found that silicon, whether introduced on the surface as an impurity or present as an alloy component, was effective in preventing adhesion in air because of the formation of silicon oxide. The oxidation rate of silicon and metal-silicon alloy systems is qualitatively discussed considering changes in adhesion coefficient and contact resistance. Twist-compression bonding tests of noble-metal alloys containing an active additive such as silicon were found to be affected by the surrounding atmosphere.

Electrostatic Detection of Large Microparticles (> 10 μm) in a High-Voltage Vacuum Insulated Apparatus

Two electrostatic detectors are designed to search for the presence of microparticles of dimensions greater than 10 μm, in an ultrahigh-vacuum test gap (≈7 mm), when a high dc voltage (> 100 kV) is applied across the gap. The experiments with both the detectors revealed that such microparticles are not generated in detectable numbers, within the vacuum gap, prior to breakdown.

Device for the Measurement of Friction at Ultrahigh Vacuum

A friction measurement device has been developed which permits continuous measurement of static and kinetic coefficient of friction at ultrahigh vacuum. Sliding motion inside the vacuum chamber is accomplished by using a disk rotated by a zero-leakage, direct-drive rotary seal. The coefficient of friction is measured using a strain-gauge system which is compatible with the ultrahigh vacuum test environment. An example of the type of results obtained with the device is given. The apparatus has been continuously operated at pressures in the 10−10 Torr region.