Speaker
Dr
Hiroshi Saeki
(JAPAN SYNCHROTRON RADIATION RESEARCH INSTITUTE)
Description
It is well-known that ionization gauges mis-read due to an influx of photoelectrons
flowing from an external environment. In the SPring-8 storage ring, some of hot-
cathode-ionization gauges (B-A gauges) have indicated abnormally-low pressures (on
the order of 10-9 Pa) or negative pressures (from -2 x 10-9 Pa to -2 x 10-7 Pa) at
stored-electron-beam conditions due to the same cause, although elbows and permanent
magnets are set in front of these gauge heads. On the other hand, cold-cathode-
ionization gauges (Inverted magnetron gauges) at RF cavities in the ring have been
thought to indicate actual pressures. The effect on a cold-cathode-ionization gauge
caused by photoelectrons from an external environment has not been reported.
Therefore, a simulated experiment for pressure-measurement errors in a cold-cathode-
ionization gauge caused by electrons from an external-electron source, was carried
out. As the results, the indicated pressure with the cold-cathode-ionization gauge
was higher by about two orders of magnitude from the actual pressure. It also showed
that electrons with several eV from the external-electron source were effective in
this pressure-measurement error. Using a precise current-measurement system which
could measure a current of the order less than 10-9 A under an applied high voltage
to the anode of the gauge head, an actual current detected at the anode was also
measured. Furthermore, in the New SUBARU electron storage ring (the beam energy of 1
GeV) at a stored-electron-beam current less than 350 mA, the same environment of
excess photoelectrons in the SPring-8 storage ring was roughly reproduced and the
vacuum gauge was tested, using a gauge tube with metal meshes set in front of the
gauge head. As the result, it was found that the cold-cathode-ionization gauge with
the gauge tube was not influenced by the strong reflected light of synchrotron
radiation at all, in the pressure range of 10-8 Pa.
Author
Dr
Hiroshi Saeki
(JAPAN SYNCHROTRON RADIATION RESEARCH INSTITUTE)
Co-authors
Prof.
Ainosuke Ando
(LASTI, University of Hyogo)
Dr
Satoshi Hashimoto
(LASTI, University of Hyogo)
Prof.
Takashi Momose
(Miyagi National College of Technology)
Dr
Tamotsu Magome
(Japan Synchrotron Radiation Research Institute)
Mr
Tsuyoshi Aoki
(Japan Synchrotron Radiation Research Institute)
Dr
Yoshihiko Shoji
(LASTI, University of Hyogo)
