An investigation of the factors affecting the performance of the quadrupole mass spectrometer with particular reference to residual gas analysis

The results of an experimental investigation into the factors limiting the performance of a conventional quadrupole mass filter are presented. The number of cycles of the rf field which the ions experience in travelling the length of the quadrupole is shown to be the factor limiting resolution under any given set of operating conditions. The design of an RGA is discussed in detail and it is shown that an analyzer only 2 in. long is adequate to achieve the required resolution giving at the same time a high sensitivity. This enables a small mass spectrometer to be designed capable of being fitted into a vacuum system as easily as an ionization gauge. This instrument will resolve perfectly individual peaks up to 50 amu with a limit to the detection of partial pressure of better than 10⁻¹¹ torr.     

A viscosity gauge for pressure measurement in the range 10 to 10 torr

In this paper a direct reading molecular damping gauge for pressure measurement in vacuum system is described. By making an oscillating vane (of aluminium foil 9 × 5 cm) one element of a closed loop servo system the amplitude of swing is maintained constant independent of pressure, the power fed into the system just balancing the losses due to gas damping. The power input is monitored and taken as a measure of gas damping and hence pressure. Experiment shows there to be a linear relation between power input and pressure over the whole useful working range 10⁻⁶ to 10⁻³ torr. By taking account of such secondary factors as the influence of the finite size of the vacuum vessel on the damping forces good agreement between theory and experiment can be reported. The relative unimportance of accomodation coefficient on the behaviour of the gauge is discussed. The prediction that sensitivity is proportional to the square root of the molecular weight of the gas in the vacuum system has been checked and found correct to ± 4 percent over the range 4–350 amu. This gauge can therefore be recommended as a useful secondary calibration standard for vapours where more conventional calibrating techniques are difficult to apply.     

A new reference ionization gauge for vacuum pressure measurement in the range 10−5 to 1 Pa

A new type of reference ionization gauge is described. This gauge is similar to the triode type ionization gauge but has a smaller residual current and better high pressure performance. One version of the new gauge has a nitrogen sensitivity of 0.073 Pa^?1, which is constant to within 1% at pressures up to 0.3 Pa, and a nitrogen pressure equivalent to its residual current of 10^?6 Pa. The long term behaviour of its sensitivity was compared with Bayard-Alpert and triode type ionization gauges over several hundred operating hours. The sensitivity of the new type of gauge changed by less than 0.1% per 100 h while under similar conditions the triodes drifted at rates of up to 0.45% per 100 h and the Bayard-Alpert gauge sensitivities drifted unpredictably, sometimes changing sharply by several percent. A second version of the new gauge showed similar long term behaviour to the triode with a residual current equivalent to a pressure of potentially less than 10^?7 Pa.     

Grundlagenuntersuchungen zum Betriebsverhalten eines „Stabil Ion Gauge”︁

Summary The fundamental characteristics of a commercial “Stabil Ion Gauge” [1] as well as its x-ray limit and the influence of desorption effects on the collector current at the lower limit of pressure measurement were investigated. A strange shape of the diode characteristics of the gauge was observed. By means of two-dimensional calculations of the electrical field with the simulation program “SIMION” [2] an emission of the backside of the ribbon cathodes was determined to be the reason for that behaviour. The agreement of these calculations and the experimentally observed curves supports this thesis. The decreasing tendency of the sensitivity vs electron space charge within the anode volume with increasing electron current. This effect is intensified by the directed electron beam which originates from the ribbon cathodes. The x-ray limit was determined by the Alpert-method to 1.9.10^?10 mbar and by the comparison method to 1.8.10^?10 mbar. The test gauge showed larger desorption effects than the reference gauge IE414 (Leybold) which is due to the installation of a big grounded shield surrounding the whole electrode structure. In agreement with experiences the desorption effects were largest for chemical active gases like oxygen and hydrogen. Summarizing one can state that the constant potential relations within the “Stabil Ion Gauge” which are essential for stability and reproducibility of the sensitivity of ionization gauges have been achieved at the costs of a disturbing desorption effects at lower pressures and a relatively high x-ray limit.     

Stability tests of ionization gauges using two-stage flow-dividing system

Stability tests of four ionization gauges (a BA gauge, an extractor gauge, an AT gauge, and a BA gauge with a heating electrode) were performed using a two-stage flow-dividing system from four viewpoints: (1) the fluctuation and drift of pressure readings, (2) the repeatability of pressure readings, (3) the change in sensitivity owing to prior conditions of use and (4) long-term stability. These tests were performed at pressures from 8 × 10⁻⁶ Pa to 8 × 10⁻⁴ Pa using N₂ gas under tightly controlled conditions.The fluctuation and drift of the four IGs were within 1% over 1 h. Their repeatability was also within 1% during eight cycles with an interval of 1 h between each cycle. Although changes in sensitivity of several percent owing to prior conditions of use were observed, the sensitivity was recovered to within 1% of its original values after operation in ultrahigh vacuum for one day. The result of a long-term stability test over a year showed that the sensitivity of the four IGs tended to decrease by 2.6-5.4% due to aging, depending on the gauge.     

The design and operation of a new extractor gauge for UHV pressure measurements

The design of a new extractor gauge is described for ultra high vacuum pressure measurements. which employs a separate extractor electrode external to the grid. The advantages to be gained by the use of this system, the importance of providing an adequate ion extraction field and also of preventing the flow of electrons into the collector region, are discussed. A method is described of reducing the effect on the residual current of X-rays reflected onto the collector. This allows a residual current of 10^?14 A, at 1 mA electron current, to be achieved. For a gauge sensitivity of 10 torr^?1 this is equivalent to a residual pressure of 1 × 10^?12 torr. The addition of a modulator has been found to give a high modulation factor of 0.95 which should enable the low pressure limit to be extended to below 10^?14 torr.     

Development of a miniature magnetic sector mass spectrometer

A miniaturized magnetic sector mass spectrometer has been developed and tested. The instrument was designed the number two filament in ion source, in order to avoid failure of the number one filament. It has a 90° magnetic sector-field analyzer with double trajectory, which has a magnetic flux density of 0.65 T. Two special trajectories are selected to cover the mass ranges, 1-12 amu and 6-50 amu. The mass spectrometer’s overall size, including the magnet assembly, is 250 mm wide, 250 mm long and 160 mm tall, it weighs 2.5 kg, and its power consumption was measured to be 15 W. It was able to attain a mass resolution of 56 at full-width at half-maximum and a sensitivity of 7.7 × 10⁻⁵ A/Pa. The resulting design is small, lightweight, and has low power consumption. All these characteristics make this miniature mass spectrometer suitable for space applications and chemical analysis and also for field applications on earth.     

Drift-tube linac geometry optimization at 108 and 216 MHz

Drift-tube linear accelerator geometries at 108 and 216 MHz have been studied using the computer code SUPERFISH with the aim of optimizing the effective shunt impedance, ZT². Optimum ZT² curves for particle velocities, β = v/c, ranging from 0.061 (1.75 MeV/amu) to 0.567 (200 MeV/amu) have been generated from over 2500 computer runs with SUPERFISH. These curves, although derived primarily for a high current electronuclear breeder accelerator, have general application for other proton or heavy ion linear accelerators.     

An improved ion gauge with gold coated electrodes for reliable operation in reactive gases and for use as reference standard

The ion gauge described here eliminates sources of error which cannot be removed with the grid-type ion gauge, for example, variation of the grid electron transparency, unstable mean ionization path length of the electrons, and losses of ions by exterior electrostatic fields and by ion pumping. In the pressure range from 10^?7 to 10^?1 Pa the response of the new ion gauge shows a high reliability. The gauge is operable in hydrogen without problems. The latter aspect is of interest for pressure measurement in equipment used for charged particle acceleration and storage, and for fusion experiments. The ionization gauge, in the form of a nearly closed system with pure gold layers on the electrodes, shows the following remarkable advantages with respect to grid-type gauges. (a) Shielded volume for effective ion formation, no influence of exterior electric fields. (b) Well defined and limited ionization path length for electrons. (c) Controlled heating of the gold plated electrode system during the operation at 250°C which diminishes disturbing effects by adsorbable gases and provides the same gauge coefficients in immersed or tubulated position—reduced variation of transpiration effects by changes of filament heating power. (d) A stable work function on the gold ion collector surface secures good long term stability of gauge coefficient. (e) V-shaped ion collector combines extension of linearity at high pressures by reducing space charges with a low X-ray limit. (f) Negligible ion pumping; undisturbed operation with hydrogen. Noteworthy and new, the grid is insulated from the anode cylinder. Thereby the interfering effects of the usual large variations in the grid electron transparency on the ionizing current may be eliminated. This results in high accuracy and stability of the gauge coefficient over nearly 5 pressure decades. The X-ray limit p_x is approximately 2 × 10^?7 Pa (H₂). Construction and operation mode of the new screened ion gauge has been presented already in Gentsch and Messer, Proc 8th Int Vac Congr, Cannes 1980, p. 203; the version described here was improved by the use of tungsten as supporting material instead of platinum-iridium alloy.     

Ein neues hochgenaues und zuverlässiges Ionisationsvakuummeter

A new highly accurate and reliable ionization vacuum meter – Permanent relative gas sensitivity sets new standard for manufacturers and users A novel ionization vacuum meter offers a solution to the previously insufficient stability of commercially available devices and enables predictable sensitivities. This is made possible by straight-line guidance of the ionizing electrons as they travel through the ionization space. The new high vacuum gauge is suitable for applications as a reference gauge and in process plants where high reproducibility is required. Even without calibration, the instrument offers a measurement uncertainty of less than 5%, making it commercially interesting for both manufacturers and users.     

Thle Monopole?A New Instrument for Measuring Partial Pressures

Design parameters appropriate to the construction of a monopole type mass spectrometer suitable for use as an ultra-high vacuum partial pressure analyzer are developed and elaborated. Performance results of an instrument built to these parameters are presented. Results indicate a usable mass range of 300 amu, with unit resolution over the whole range. Ultimate sensitivity is in the 10-2 Torr partial pressure range.     

The effect of ambient temperature on the sensitivity of hot-cathode ionization gauges

We measured the sensitivities of five hot-cathode ionization gauges for ambient laboratory temperatures between 23 and 31 °C. All of the ionization gauges exhibited very similar behavior, and the sensitivity could be adequately modeled with a linear function of temperature. The slopes of the fits were smaller than one would expect due to changes in the calibration chamber number density. The thermal transpiration effect, due to local heating of the gauge structures, can account for this, and a characteristic gauge tube temperature can be inferred from the temperature dependence of the sensitivity. A recent comparison of the high vacuum standards of several National Metrology Institutes (NMIs) was performed over the range of 10⁻⁶-10⁻³ Pa using hot-cathode and spinning rotor gauges as transfer standards. Among the participants, laboratory temperatures varied by as much as 5 °C. It is necessary to know how laboratory temperature affects the sensitivity of the hot-cathode transfer standards (spinning rotor gauges explicitly account for the gas temperature) so that individual laboratory results can be corrected to a common temperature.     

Neural network modelling of cold-cathode gauge parameters

This article describes modelling of the operating characteristics of a cold-cathode ionisation gauge (CCG). The gauge characteristics were measured on a gauge comparison UHV calibration system with a test chamber, an extractor gauge, a spinning rotor gauge, and a gas manifold with a precise leak valve. Discharge intensity was measured vs. anode voltage at different pressures selected in the range from 1×10⁻⁹ to 1×10⁻⁵ mbar, and vs. pressure at different operating voltages ranging from 1.2 to 9 kV. In all cases the magnetic flux density was the same and amounted to about 0.13 T. The CCG exhibits an extremely low thermal outgassing rate and a low measurement limit. Therefore, it is suitable for pressure measurements in the ultrahigh vacuum range; however, it has a significant disadvantage. The discharge current vs. the pressure characteristic is non-linear and, in some cases, even discontinuous.The measured CCG characteristics were used as an input for the artificial neural network, which was used to generate a non-linear CCG input-output function used for linearisation purposes. It is generally known and strictly proven that neural networks are capable of learning and building any kind of real and non-polynomial input-output function. Furthermore, it was also mathematically proven that the single hidden neural layer system can learn any function. Other authors have reported that the learned function characteristics are not always continuous.In our experimental work, no mapping discontinuities in the formed model were detected. Despite the fact that learning of the input-output characteristics can be obtained by the neural networks with only one hidden layer, we have used the multilayer neural networks that exhibit a faster convergent and smoother learning process. The neural networks were trained to perform the transfer function between the input gauge parameters and the pressure. The neural networks are a suitable solution for CCG characteristics modelling and thus offer the possibility to overcome the disadvantages of the CCG.     

Application of CLTD’s for High Resolution Mass Identification and for Stopping Power Measurements of Heavy Ions

An array of calorimetric low temperature detectors (CLTD’s) for energy sensitive detection of heavy ions was combined with time-of-flight (TOF) detectors to obtain a detector system for high resolution mass identification of low energy heavy ions. In addition the same setup was used to prove the ability of CLTD’s to be used in electronic stopping power measurements for heavy ions in matter. Experiments with 50?MeV ⁶³Cu and ⁶⁵Cu ions at the tandem accelerator at the MPI at Heidelberg, and with 25 to 250?MeV ²³⁸U ions at the UNILAC accelerator at GSI at Darmstadt have been performed. For ^63,65Cu at 50?MeV a mass resolution of Δm(FWHM)=0.9?amu, and for ²³⁸U in an energy range of 65 to 150?MeV a resolution of Δm(FWHM)=1.28?amu, was obtained. The results for stopping powers of ²³⁸U in carbon and gold are presented and compared with theoretical predictions and data from the literature.     

Development of high sensitivity oxide based strain gauges and pressure sensors

Strain gauges and pressure sensors are necessary tools for automotive, aerospace and biomedical monitoring applications. Of the various types of material, which can be used in their fabrication, oxides allow a degree of flexibility in their design. Furthermore, these devices are more rugged and cost effective than semiconductor sensors and have a higher sensitivity than metal-foil gauges. In this paper, the development of thin and thick film sensors based on oxides such as V₂O₅, CeO₂, Bi₂O₃, In₂O₃, RuO₂, TiO₂, MgO and Nb₂O₅ is discussed. The devices are evaluated in terms of their sensitivity or gauge factor, linearity, hysteresis and long term stability. Furthermore, different device configurations, planar and sandwich are compared. It is found that the devices presented in this work have sensitivity comparable to that of semiconductor gauges, with good long-term stability. This is particularly true of the sandwich devices. It is observed that oxide based strain gauges may offer an alternative to existing commercial gauges, for example, in applications involving load cells, torque wrenches and limb implants.     

Stress-strain properties of structural steel at strain rates of up to 105 per second at sub-zero,room and high temperatures

A testing technique and method of processing the displacement-time data have been developed following which the stress-strain characteristics of structural steel at strain rates between 10³ to 10⁵ per second over a strain of about 50% and at different temperatures have been determined. The steel under present test condition within this strain rate range showed a strong strain rate sensitivity. The material inertia and temperature rise during high speed deformation were found to have mutually cancelling effect on the deduced flow stress. In determining the results, appropriate friction correction was also made and the results presented in this paper are all converted to those under frictionless condition. Finally, a constitutive equation has been proposed for the steel incorporating the effects of work-hardening and strain rate sensitivity of the material.     

Efficiency and behavior of textured high emissivity metallic coatings at high temperature

Three metallic coatings with textured surfaces, made of rhenium, tungsten and molybdenum, were studied in the frame of the Solar Probe Plus mission (NASA) as candidate materials. The role of these coatings is to dissipate a maximum of energy from a hot instrument facing the Sun, by the mean of their high total hemispherical emissivity. The total hemispherical emissivity of the three coatings was measured in the temperature range 1100–1900 K, as well as over time in order to study their high temperature stability. Various emissivity levels were obtained depending on the surface texture. The highest total hemispherical emissivity was obtained on a rhenium coating, with an emissivity of 0.8 in the temperature range 1300–1700 K. However, this rhenium coating with a fine, sharp surface texture, presented an instability at high temperature, which might limit its optimal operating temperature to about 1500 K. As for the tungsten coating, the total hemispherical emissivity was increased by a factor 2 due to the enhanced surface texturation and its great stability over the whole temperature range was shown.     

Absolute isotopic composition and atomic weight of commercial zinc using inductively coupled plasma mass spectrometry

Inductively coupled plasma mass spectrometry is introduced as a method for determining the absolute isotopic composition of zinc. The high ionization efficiency and time-independent characteristics of the mass spectrometry permit the absolute isotopic composition of high ionization potential elements. The mass discrimination of the instrument is calibrated by synthetic isotope mixtures prepared from highly enriched isotopes of zinc. The resulting isotope ratios yield atomic percents of 64Zn, 49.188 +/- 0.030; 66Zn, 27.792 +/- 0.041; 67Zn, 4.041 +/- 0.009; 68Zn, 18.378 +/- 0.050; and 70Zn, 0.600 +/- 0.003. This isotopic composition is different from those of conventional mass spectrometric measurements. Their differences depend on the mass differences about 0.8-1.2%/amu with enhancement of heavier isotopes. The atomic weight calculated from our isotopic composition is 65.3756 +/- 0.0040. The obtained atomic weight is fully consistent with that of a precise coulometric measurement in contrast to the previous mass spectrometric measurements. An isotopic variation of commercial zinc reagents has been investigated. A mass-dependent fractionation of 0.12%/amu is observed in a high-purity metal zinc, NIST-SRM 682, among five reagents. This mass dependence is probably inherited through their purification process.     

Quantitative measurement of oxygen content in Si targets

Enriched self-supporting targets of ^28,29,30Si are often used in the field of high resolution nuclear physics experiments. The Si targets were prepared by the thermal evaporation deposition or reduction-deposition methods. The targets, however, are always contaminated by oxygen as Si-material is easily oxidised. These contaminated targets lead to poor data with low S/N ratio. Thus it is very useful if one can estimate the amount of oxygen in the target quantitatively before experiments.In this work we have developed a method to estimate the amount of oxygen in the Si target. We used α-ray and β-ray thickness gauges, which have different sensitivity to oxygen atoms. Namely, the α-ray gauge is more sensitive to light elements such as oxygen compared to the β-ray gauge. Thus one can deduce the amount of oxygen by comparing the oxygen thickness measured by α-ray gauge with that of the β-ray gauge.Accuracy of a few percents can be obtained for the oxygen content in Si targets with a thickness of 1 mg/cm². The present method can also be applied to heavy elements such as Ta₂O₅.     

A wide‐g range silicon piezoresistive accelerometer

Abstract

In this paper, a high‐performance silicon piezoresistive accelerometer, fabricated by bulk micromachining with an almost linear I/O (acceleration / voltage) relationship from 0 to 90g over a 400Hz bandwidth suitable for vehicle's safety system, is described. This accelerometer is composed of two glass cover caps and a Si sensing structure. The size of the sensing structure is 3.3mm × 2.05 mm × 0.15 mm. It consisted of a “mass”, a “frame”, and 4 thin beam “bridges”. The sensitivity of the accelerometer was found to be 9.6 × 10^‐8 (sec²/m) and a gauge factor of 18 was deduced from this value.