Measurement of the neutral gas fluxes into the divertor region, pumping duct, and the outside midplane in the presence of strong magnetic fields

[Detectors, Diagnostic Method]
Linear tetrode with hot cathode
(similar to the usual ionization gauges)
Chopping emission current to pick up the minute ion current
(related to the concept of lock-in amplifier)
Installed eleven gauges in the vacuum vessel

Measurable range : from ultra high vacuum to several Pascal
Vessel temperature : up to 400C
Magnetic fields : up to 5.4 Tesla
Time response : 3 - 4 ms (determined by conductance)
Chevron in front of gauge head
: to avoid plasma exposure
: to provide thermalization of particles

We would like to thank Dr. G. Haas at ASDEX, and Dr. J. Ehrenberg at JET for their discussion at the occasion of introducing the fast ionization gauges.