Kiyohide Kokubun

A bending and stretching mode crystal oscillator as a friction vacuum gauge

Abstract The pressure dependences of the electric impedances of quartz oscillators are analysed theoretically. A simple model of the quartz oscillator is proposed. Based on this model, the equations of fluid mechanics are analytically solved. The results calculated show good agreement with the experimental data. Especially, this theory succeeds in explaining the behaviour that the impedance of the quartz oscillator is proportional to the square root of the pressure in the higher pressure region. This relation cannot be understood as an effect of turbulent flow or the effect of emission of sound. This theory gives the gas species dependences of the impedance which are also verified experimentally.

Unified formula describing the impedance dependence of a quartz oscillator on gas pressure

The impedance dependence of a tuning‐fork‐shaped quartz oscillator on gas pressure is theoretically analyzed on the basis of a string‐of‐beads model of the quartz oscillator. The theoretical results are numerically compared with experimental data. The analysis has been already carried out in molecular flow and viscous flow region. In this paper, the impedance behavior in the intermediate flow region is formulated by making use of the theory of slip effect. Furthermore, by the formal extension of this formula to the molecular flow region, a single formula describing the impedance dependence on gas pressure over the whole pressure region is obtained. This formula is found to be in good agreement with experimental data. However, there is still a slight discrepancy (<20%) between the two in the intermediate flow region. This shows the limit of the slip theory. For this reason, the Millikan’s empirical formula is adopted in the intermediate flow region. The unified formula obtained thusly is in numerical agree...

Size effect of a quartz oscillator on its characteristics as a friction vacuum gauge

As the technical basis of the friction vacuum gauge using a quartz oscillator, the electric impedance of various types and sizes of quartz oscillators was measured as a function of pressure from 10−2 Pa to atmospheric pressure. Among the oscillators, the tuning fork showed the highest impedance change of about tenfold in the pressure range. The impedance was a linear function of the pressure in the lower pressure range and was proportional to the square root of the pressure in the higher range. This pressure dependence showed good agreement with the result of theoretical analysis by the authors. In this report, the relation between the change in impedance and the size of the tuning fork was studied experimentally in order to have design data for a gauge of high performance. A semiempirical formula concerning the size effect on the sensitivity was obtained. The formula predicted that an oscillator of a long length and of a small width and thickness has higher sensitivity as a gauge. A few of these oscillat...

Quartz friction vacuum gauge for pressure range from 0.001 to 1000 Torr

A quartz friction vacuum gauge (QF gauge) is based on the fact that the resonance impedance of a quartz oscillator is proportional to the frictional force of ambient gas. The first model of the QF gauge, which was developed by the authors as a wide range pressure monitor, has the minimum measuring pressure of 0.01 Torr with an accuracy of the order of 10%. To lower the minimum measurable pressure, we developed a sensing head consisting of a tuning fork oscillator with higher sensitivity fixed on a temperature‐stabilized metal rod and a digital readout circuit. The performance of the gauge was evaluated from results of measurement of pressure dependence, temperature variations, and fluctuations of the gauge output, which is proportional to the resonance current of the oscillator. It was confirmed that an error in measurement by the gauge is within ±10% for pressure from 0.001 to 1000 Torr.

Possibility and current status of absolute XHV measurement by laser ionization

Abstract The current status and possibility of XHV measurement by laser ionization using second harmonics of a picosecond YAG laser are discussed. Under the condition that incident laser energy was 30 mJ/pulse and the laser beam was focused with a spherical lens (focal length f = 250 mm) to a power density sufficient for the saturation of H 2 ionization at the focal point, the minimum pressure in an XHV chamber was measured. From the minimum pressure estimated by extrapolation (5 × 10 −11 Pa) and the ion counting rate at that pressure (one count during 500 laser shots), the volume of the ionization region was expected to be 1.7 × 10 −4 mm 3 . The ionization region was then measured experimentally under the same laser beam conditions. It was found that the ionization region has a spindle shape with maximum diameter of 45 μm and the length of 1.2 mm. The estimated volume is larger than the expected volume by a factor between 4 and 12. The ion detection efficiency of the electron multiplier is one of the major factors affecting the difference, and it can be reduced to within a factor of 3. On the basis of the results, the possibility of absolute measurement of XHV pressure by laser ionization is discussed.

Pressure measurement method using laser ionization for xhv

Abstract A pressure measurement method for xhv using laser ionization has been developed. By means of nonresonant multiphonon ionization, the proportional relation between the amount of laser-generated ions and the gas pressure is experimentally verified in the range 1 × 10−3−2 × 10−8 Pa. Also, a nonresonant 4-photon ionization of the He atom, which has the highest ionization potential of all atoms and molecules, and saturations of ionization for Xe, Kr, O2 and especially for H2, which is a main residual molecule in uhv and xhv, are successfully observed. In addition, a high-sensitivity ion-detection system for the exact measurement of several atoms and molecules in xhv is prepared. Noise due to scattered laser light is discussed.

Design and testing of a quartz friction vacuum gauge using a self‐oscillating circuit

A quartz friction vacuum gauge (QF gauge) is based on the fact that the change in resonance impedance of a quartz oscillator is proportional to the frictional force of ambient gas. The QF gauge adopting a self‐oscillating circuit has been developed in order to obtain quick response and high resolution. The sensor head is the tuning fork shaped (33 kHz) quartz oscillator, which is kept at about 50 °C by a temperature controller. The driving circuit consists of a phase shifter, a zero‐cross detector, and analog switches connected to constant voltage suppliers, which send the quartz oscillator 200 mV peak‐to‐peak square‐wave voltage. The I/V converter transforms the current through the quartz oscillator into the voltage. And the voltage is sent to the phase shifter and a meter driver. The testing results of the QF gauge are as follows. Measurable pressure range 10−1–105 Pa, pressure resolution 5×10−3 Pa at 10−1 Pa, stability 1.3×10−3 Pa, response time 0.2 s at the transition from 10−4 to 105 Pa.

Detection of Sputtered Neutral Atoms by Nonresonant Multiphoton Ionization

A nonresonant multiphoton ionization method was applied for the detection of sputtered neutrals using a time-of-flight mass spectrometer. The preliminary results for Cu, Ni and Cu-Ni alloy samples are reported from the viewpoint of a semiquantitative surface analysis. Photoions from pure elements were a reflection of their sputtering yield ratios. The estimated composition of an alloy during sputtering at room temperature is almost the same as that of bulk. On the other hand, anomalous copper-enriched flux was detected at 800 K, and the result was explained by the enhanced segregation and diffusion of copper through the ion-damaged surface layer.

Pressure measurement by laser ionization: Direct counting of generated ions by imaging of their spatial distribution

The spatial distribution of ions generated by nonresonant multiphoton ionization of Xe and H2 with second harmonics of a picosecond YAG laser was imaged with a new detection system. Ions were observed as bright spots on a microchannel plate (MCP) intensifier, and they appeared on a straight line, reflecting the ion generation along a laser beam path. The size of the ionization region, which has a spindle shape, was estimated from the image. The maximum diameter of the ionization region was ∼60 μm, and the length was 3.6 mm for a Xe gas pressure of 5×10−5 Pa and an incident laser energy of 10 mJ/pulse for our measurement system. The size depended on the incident laser energy, and on the lens assembly used for the focusing of the laser beam. The possibility of relative pressure measurement by counting of the bright spot on the MCP intensifier was also investigated.

Multiphoton Ionization of Xe and Kr Atoms by an ArF Excimer Laser

The dependence of ionization signals of Xe and Kr atoms on the laser intensity has been studied using an ArF excimer laser. For both atoms, we observe a slope of 2 in the log-log plot of the ionization signal versus laser intensity, and saturation of ionization at laser pulse energies higher than about 100 mJ (1.7?1010 W/cm2). The ionization of Kr can be interpreted as a 2-photon-resonant, 3-photon (2+1) ionization.