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Experience with several quadrupole residual gas analysers
Abstracts
from the point ofview ofmass separation and resolution, also with high mass values (its response being non-linear and, consequently, peaks being sometimes difficult to locate); the instrument constant has also usually been determined. This instrument is used at present (for residual-gas analysis and purity determinations of testing gases) in a system for surface analysis by Auger spectrometry. The quadrupole mass spectrometer, being, additionally, easier to use, has been used in different experiences, some of them requiring preliminary calibration. A number of applications are mentioned here : leak detection with gases of a high atomic number; detection and quantitative determination of traces of substances (inert or not) in sealed standards; analysis of degassing substances from materials used for the construction of metrological standards. The quadrupole mass spectrometer was calibrated with gaseous mixtures containing known amounts of the substance under examination; its operational characteristics were studied in relation to a number of known parameters (electronic current, multiplier voltage, etc). The present main object is the applicatio’n of the dynamic expansion method to calibration, in particular of the quadrupole. Signal repeatability in different conditions of use of the instrument is also being studied at IMGC, and quantification of the interaction of the instrument with the measurement quantities involved is attempted. The results so far achieved in these investigations are discussed, together with the problems still open or unsolved, which prevent a correct use of an instrument such as the mass spectrometer (especially of the quadrupole-type), which has been so widely applied during the last 10 yr in vacuum technology and other sectors.
however, involves some formidable problems before statements about the relevant physical quantities can be made. The sensitivity of quadrupole gas analysers to magnetic fields necessitates a fairly long tubular vacuum connection up to the zone of the vacuum vessel from where data are to be gained. One may term such an arrangement a ‘flux convertor’ since the gas density actually measured in the ion source is a function of the gas flux at the tube inlet. Moreover, the diffusive character of gas flow within the connecting tube results in a complicated time response function, which has to be taken into account for the often fast gas dynamical effects of plasma discharges, in particular, when short gas puffs are utilized for studying special plasma effects. And above all looms the delicate problem of what is called transpiration in gas dynamics, since in plasma devices energetic particle fluxes are encountered..In view of the uncertamties imposed by all these difficulties, highly accurate calibration and stability of the mass spectrometers tends to play a somewhat secondary role. Most disturbing in this respect are hysteresis effects, as observed at pressure above 10e4 mbar of H,, which often render attempts to exceed an accuracy better than _t lo’/, futile. In practice, the burst of outgassing immediately after termination of each discharge, which usually causes a pressure transient over the range of interest, is utilized to check the relative performance stability of the several analysers in use, and the absolute calibration is frequently checked by comparison with a Baratron and occasionally a spinning rotor gauge. A divertor experiment like ASDEX, owing to its topography, is found to be an especially rewarding object for mass spectrometry, and so the diagnostic set-up comprises five quadrupole gas analysers. Performance and application are demonstrated by a number of examples.
Experience with several quadrupole residual gas analysers*
Multiple head RCA installation on an electron storage ring
H C Hseuh, 911 B Brookhaoen
Ron Reid, SERC
New York 11973
National
Laboratory,
Upton,
USA
Quadrupole type residual gas analysers from VG (Masstorr), ANAVAC, UT1 (lOOC), Leybold-Heraeus (4200) and Hiden Analytical (HALlSO) were tested in a gauge calibration set-up using the orifice method (constant pressure). These RGA’s were calibrated in lo-‘, 10m6 and 10m5 torr range with pure hydrogen, nitrogen, argon and a standard mixture of H,, He, Ne, N,, Ar, Kr and Xe. Preliminary results on relative sensitivities, cracking patterns, and transmission coefficients will be presented.
* Work performed
under the auspices
of the US Department
of Energy.
Warrington
Daresbury
WA4 4AD,
Laboratory,
UK
The microcomputer-controlled, multiple-head multiplexed RGA system installed on the Daresbury SRS Electron Storage Ring is described. The system is based on a standard, commercially available package. In using such a system, it is important to have some knowledge of the variability of properties such as sensitivity, mass discrimination and electron multiplier gain between the different gauge heads. The system and methods used to characterize the gauge heads are described, and the standard resolution criteria employed are discussed. The results described demonstrate considerable variability between gauge heads which are nominally identical, and indicate that caution needs to be observed when interpreting RGA spectra from such systems.
Mass spectrometry as a quantitative diagnostic for plasma discharges in fusion research W P Poschenrieder, Max-Planck-lnstitut D-8046
Garching,
fiir Plasmaphysik,
Vacuum compatibility criteria used at SURF-II, the NBS Electron Storage Ring
West Germany
Lanny R Hughey, National The application of mass spectrometry to fusion experiments can yield important information about transport behaviour in the plasma edge and recycling phenomena at the wall. The interpretation of mass spectrometric data, as obtained during a discharge,
MD 20899,
Bureau
of Standards,
Gaithersburg,
USA
One of the vacuum compatibility criteria used with our ultra-high vacuum electron storage ring is that the total pressures near the 633
from the point ofview ofmass separation and resolution, also with high mass values (its response being non-linear and, consequently, peaks being sometimes difficult to locate); the instrument constant has also usually been determined. This instrument is used at present (for residual-gas analysis and purity determinations of testing gases) in a system for surface analysis by Auger spectrometry. The quadrupole mass spectrometer, being, additionally, easier to use, has been used in different experiences, some of them requiring preliminary calibration. A number of applications are mentioned here : leak detection with gases of a high atomic number; detection and quantitative determination of traces of substances (inert or not) in sealed standards; analysis of degassing substances from materials used for the construction of metrological standards. The quadrupole mass spectrometer was calibrated with gaseous mixtures containing known amounts of the substance under examination; its operational characteristics were studied in relation to a number of known parameters (electronic current, multiplier voltage, etc). The present main object is the applicatio’n of the dynamic expansion method to calibration, in particular of the quadrupole. Signal repeatability in different conditions of use of the instrument is also being studied at IMGC, and quantification of the interaction of the instrument with the measurement quantities involved is attempted. The results so far achieved in these investigations are discussed, together with the problems still open or unsolved, which prevent a correct use of an instrument such as the mass spectrometer (especially of the quadrupole-type), which has been so widely applied during the last 10 yr in vacuum technology and other sectors.
however, involves some formidable problems before statements about the relevant physical quantities can be made. The sensitivity of quadrupole gas analysers to magnetic fields necessitates a fairly long tubular vacuum connection up to the zone of the vacuum vessel from where data are to be gained. One may term such an arrangement a ‘flux convertor’ since the gas density actually measured in the ion source is a function of the gas flux at the tube inlet. Moreover, the diffusive character of gas flow within the connecting tube results in a complicated time response function, which has to be taken into account for the often fast gas dynamical effects of plasma discharges, in particular, when short gas puffs are utilized for studying special plasma effects. And above all looms the delicate problem of what is called transpiration in gas dynamics, since in plasma devices energetic particle fluxes are encountered..In view of the uncertamties imposed by all these difficulties, highly accurate calibration and stability of the mass spectrometers tends to play a somewhat secondary role. Most disturbing in this respect are hysteresis effects, as observed at pressure above 10e4 mbar of H,, which often render attempts to exceed an accuracy better than _t lo’/, futile. In practice, the burst of outgassing immediately after termination of each discharge, which usually causes a pressure transient over the range of interest, is utilized to check the relative performance stability of the several analysers in use, and the absolute calibration is frequently checked by comparison with a Baratron and occasionally a spinning rotor gauge. A divertor experiment like ASDEX, owing to its topography, is found to be an especially rewarding object for mass spectrometry, and so the diagnostic set-up comprises five quadrupole gas analysers. Performance and application are demonstrated by a number of examples.
Experience with several quadrupole residual gas analysers*
Multiple head RCA installation on an electron storage ring
H C Hseuh, 911 B Brookhaoen
Ron Reid, SERC
New York 11973
National
Laboratory,
Upton,
USA
Quadrupole type residual gas analysers from VG (Masstorr), ANAVAC, UT1 (lOOC), Leybold-Heraeus (4200) and Hiden Analytical (HALlSO) were tested in a gauge calibration set-up using the orifice method (constant pressure). These RGA’s were calibrated in lo-‘, 10m6 and 10m5 torr range with pure hydrogen, nitrogen, argon and a standard mixture of H,, He, Ne, N,, Ar, Kr and Xe. Preliminary results on relative sensitivities, cracking patterns, and transmission coefficients will be presented.
* Work performed
under the auspices
of the US Department
of Energy.
Warrington
Daresbury
WA4 4AD,
Laboratory,
UK
The microcomputer-controlled, multiple-head multiplexed RGA system installed on the Daresbury SRS Electron Storage Ring is described. The system is based on a standard, commercially available package. In using such a system, it is important to have some knowledge of the variability of properties such as sensitivity, mass discrimination and electron multiplier gain between the different gauge heads. The system and methods used to characterize the gauge heads are described, and the standard resolution criteria employed are discussed. The results described demonstrate considerable variability between gauge heads which are nominally identical, and indicate that caution needs to be observed when interpreting RGA spectra from such systems.
Mass spectrometry as a quantitative diagnostic for plasma discharges in fusion research W P Poschenrieder, Max-Planck-lnstitut D-8046
Garching,
fiir Plasmaphysik,
Vacuum compatibility criteria used at SURF-II, the NBS Electron Storage Ring
West Germany
Lanny R Hughey, National The application of mass spectrometry to fusion experiments can yield important information about transport behaviour in the plasma edge and recycling phenomena at the wall. The interpretation of mass spectrometric data, as obtained during a discharge,
MD 20899,
Bureau
of Standards,
Gaithersburg,
USA
One of the vacuum compatibility criteria used with our ultra-high vacuum electron storage ring is that the total pressures near the 633