Ionization gauges

Ionization gauges Ionization potentials Ionizing radiation... 

INSIGHT INTO Gas Sensors Capacitance Manometer Thermocouple Gauge Ionization Gauge... 

In the experiment, the back pressure of H2 (or HD, D2) gas source is 2 atm. The speed of 99.999 % pure H2, HD, and D2 (HSG) after supersonic expansion is about 1.38, 1.24, and 1.03 km/s, respectively. The H atoms are generated by vacuum gauge ionization from H2 and then blown by the molecular beam into the scattering chamber. The molecular beam speed is determined using the Rydberg tagging time-of-flight technique. 

Vacuum gauge, ionization cold cathode gauge A vacuum gauge that uses an ion current formed by electron-atom collisions as an indicator of the gas pressure (density). The electrons are formed as secondary electrons from ion bombardment. 

Penmman-Zoph process Penning discharge Penning gauge Penning ionization... 

Hot-Cathode Ionization Gauges. For pressures below approximately lO " Pa, it is not possible, except under carehiUy controlled conditions, to detect the minute forces that result from the coUision of gas molecules with a soHd wall. The operation of the ion gauge is based on ionisa tion of gas molecules as a result of coUisions with electrons. These ions are then subsequendy collected by an ion collector. Ionisa tion gauges, used almost exclusively for pressure measurement in high, very high, ultrahigh, and extreme ultrahigh vacuums, measure molecular density or particle dux, not pressure itself. 

Diffusion Pump System. After the pump line and trap have been shut off, a large valve is opened slowly enough that the mass flow of gas from the chamber through the valve into the od-diffusion pump system does not dismpt the top jet of the diffusion pump (DP) (Fig. 4). When the Hquid nitrogen is replenished after the trap has been operated for some time, release of previously trapped gas must be avoided. The so-caded ionization-gauge response pips at the start of the Hquid-nitrogen replenishment are an indication of trap ineffectiveness. 

In practice, it is often necessary to take readings from hot-filament ionization gauges or other devices. Figure 5 gives pump-down curves for six different types of pumping equipment on the same vacuum chamber (23). The shape of curve 1 indicates that a real leak could be responsible for the zero slope demonstrated by the Bayard-Alpert gauge (BAG). The shape of the other curves could result from a combination of real and virtual leaks. 

Gauges. Because there is no way to measure and/or distinguish molecular vacuum environment except in terms of its use, readings related to gas-phase concentration ate provided by diaphragm, McCleod, thermocouple, Pitani gauges, and hot and cold cathode ionization gauges (manometers). 

The role, design, and maintenance of creepproof barriers in traps, especially those in oil DPs, remain to be fully explored. In general, uncracked oil from a DP is completely inhibited from creeping by a surface temperature of <223 K. On the other hand, a cold trap, to perform effectively in an ordinary vacuum system, must be <173 K because of the vapor pressure of water, and <78 K because of the vapor pressure of CO2. For ultracontroUed vacuum environments, LN temperature or lower is required. CO2 accumulation on the trap surface must be less than one monolayer. The effectiveness of a LN trap can be observed by the absence of pressure pips on an ionization gauge when LN is replenished in the reservoir. 

If the pressure in the system is measured by an ionization gauge, the pumping speed SG of this gauge must be added to the pumping speed of the pump. In some cases it is necessary to take into account also the pumping speed Sw = —Fw w hich is due to the adsorption on the system walls and can even differentiate to some extent between the individual components. At the beginning of an experiment F0 = St and Fa0 = StP t/Pt. 

The s-wave contribution to the photo ionization from the 3a3p level is plotted in figure 3 and shows a quite satisfactory gauge invariance. Its peak value is in excellent agreement with that yielded by our previous STOCOS ealeulations, 346 Mb (3). 

Varnerin jr., L. J., and White Ultimate vacuum in a vacuum enclosed ionization gauge. J. appl. Physics 25, 1207—1208 (1954). 

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