Stable Pirani gauge for precision pressure measurements

Classified abstracts 432--441 nozzle design itself. Some experimental variations that have been used to study its rate and distribution are described. D L Stevenson, Trans 10 A V S Nat Vac Symp, MacMillan & Co, 1963, p 134. 21 432. Some characteristics of unitarily designed ultra-high vacuum pumping groups based on diffusion pumps. ( U S A ) A pumping group incorporating a " Z " cold trap, chevron thermoelectrically cooled baffle, mercury diffusion pump and "highbacking-pressure" backing diffusion pump exhausts into a backing capacity evacuated by sorb pumps. Unitary design avoids demountable joints from inlet flange to below pump top stage. Organic-free construction is possible. Very low pressures can be achieved and recovered, after trap failure, without rebaking. Great freedom from organic contamination is demonstrated. Investigation of the gases accumulating in the backing capacity indicates the progress of the bake and the nature of the gases released during baking. A similar group employing an oil pump is described. B D Power et al, Trans 10 A VS Nat Vac Symp, MacMillan & Co, 1963, p 147. 21 433. Development of diffusion pumps. ( U S A ) The total performance of a diffusion pump depends upon the interrelation of the performance characteristics of the individual stages. By means of curves representing speed and forepressure tolerance as functions of nozzle dimensions and power input, the characteristics of the individual stages are shown. The manner in which these separate characteristics combine to give the total characteristic is then shown for the speed curve and forepressure tolerance characteristic. In addition a modification of the normal method of pump operation is described which makes low untrapped ultimate pressures achievable without the use of a fractionating boiler. W Bachler et al, Trans 10 A VS Nat Vac Syrup, MacMillan & Co, 1963, p 153. 21 : 18 434. Alternative ion pump configurations derived from a more thorough understanding of the Penning discharge. ( U S A ) An investigation of the Penning discharge has revealed that a specific motion pattern of the electrons is essential to its maintenance. The electrons must be able to move freely along the magnetic lines of force from cathode to cathode, and to carry out simultaneously an uninterrupted E × B drift in a direction normal to the magnetic field and parallel to the anode surface. It has been observed that a similar motion pattern can exist in a wide choice of electrode geometries and that in each of them, a Penning-type discharge can be sustained. Several of the tested configurations hold promise for use in ion pumps. W Knauer and E R Stack, Trans 10 A VS Nat Vac Syrup, MacMillan & Co, 1963, p 180. 2l 435. A high efficiency magnetic field design for large ion pumps. (USA) A method for doubling the magnetic field over the usual field strengths obtained in large permanent magnet designs has been developed. It is well known that the ratios of weight to pumping speed and the volume to pumping speed for ion pumps are determined almost completely by the pumps' magnetic circuit. Maximizing these ratios enables the system designer to reduce the size, weight and cost of a given installation with specific speed requirements. A further consequence of increasing the magnetic field efficiency is the noticeable reduction in fringing field around the magnet. This paper discusses the design of high efficiency magnetic circuits, magnetizing methods, and the adaption of such high efficiency circuits to practical ion pumps. W J Kearus, Trans 10 A V S Nat Vac Symp, MacMillan & Co, 1963, p I91. 21 : 1 1 : 4 7 436. Design and performance of a 50,000 L/see pump combining cold cathode ion pumping and active film gettering. ( U S A ) Over two years ago, work was begun to combine the gettering action of a reactive-metal film with the pumping action of a coldcathode multiple-cellion pump. Many approaches were attempted, including studies and tests on methods of evaporation, choice of the reactive metal, and geometry of the pumping system. From

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these studies evolved the design of several systems, which produced pumpdown speeds for sealed systems of orders of magnitude better than had been previously experienced. The performance data from these systems were used in the design of the 50,000 1./sec pump described. Preliminary tests have confirmed the predicted results. C F Brothers et al, Trans 10 A VS Nat Vac Symp, MacMillan & Co, 1963, p 202.

22. Gauges 22 On uncertainties in calibration of vacuum gauges and the problem of traceability. See abstract number 408. 22 Gauge calibration in the ultra-high vacuum range. See abstract number 409. 22 An improved positive ion source for mass spectrometers. See abstract number 425. 22 437. Stable Pirani gauge for precision pressure measurements. (USA) The modification consists in fitting two extra electrodes to the heated filament. By this means it is possible to measure the change in resistance of a portion instead of the whole of the filament assembly. The modified type of gauge maintains stability of calibration over long periods and can be used as a precision gauge over the pressure range 1-10 torr. E J Hughes and A D McQnilian, Rev Sci lnstrum, 36 (2), Feb 1965, 177-178. 22:16 438. The dynamics of pumping and desorpfion in a Bayard-Alpert ionization gauge. ( U S A ) The pumping and desorption of nitrogen in a Bayard-Alpert ionization gauge, in the 10 6 to 10 ~7 torr range, was investigated. The desorption rate was measured during gauge operation, and its dependence on previous pumping history was evaluated. Sticking times were found to be between 500 and 1000 sec at 70°C for electronically pumped molecules. H I Smith, Jr, Trans 10 A VS Nat Vac Symp, MacMillan & Co, 1963, p 263. 22 : 34 439. Response of modified Redhead magnetron and Bayard-Alpert vacuum gauges aboard Explorer XVII. ( U S A ) Two Redhead and two Bayard-Alpert gauges were used to measure the density pressure, and temperature of the earth's upper atmosphere. Gauge pressures, from 10 -6 to 10 -1° torr, a function of satellite attitude, velocity, and atmospheric parameters, were measured over the altitude range from 260 to 900 kilometers. During the spin period of 0.67 sec, the gauges recorded pressure changes as large as a factor of 30 (e.g. from 3 × 10 6 to 8 × 10-s torr). Comparison of the independent gauge outputs yielded values in good agreement with kinetic theory predictions. G P Newton et al, Trans 10 A VS Nat Vac Syrup, MacMillan & Co, 1963, p 208. 22 440. The effect of filament impurities on the operation of BayardAlpert ionization gauges. ( U S A ) The operation of the Bayard-Alpert ionization gauge is studied for low emission currents at pressures below 10-8 tort. It is shown that the sodium or potassium impurities normally present in the filament are liberated by chemical etching of the filament or by diffusion. These impurities reach the grid where they are adsorbed. Subsequent bombardment of the grid by electrons releases these impurities as ions which reach the collector of the gauge and which produce an anomalous ion current directly related to the pressure. D R Deuison et al, Trans 10 A VS Nat Vac Syrup, MacMillan & Co, 1963, p 218. 22 441. Effects of electron-surface interaction in ionization gauges. (USA) Studies have been carried out to compare the readings of various gauges in the presence of molecular gases, particularly 02 and CO. Large anomalous effects originally reported by Ackley, Wheeler