Wüest M. 51 Wykes M. 82 Yamaguchi M. 17 Ybarra G. 129 Yubero F ...

JUNE 26 MONDAY MORNING
WS-18-MoM-OR.3 NEUTRAL PRESSURE MEASUREMENTS IN TJ-II PLASMAS.
F.L Tabarés, D. Tafalla and J.A. Ferreira. Laboratorio Nacional de Fusión por Confinamiento
Magnético, CIEMAT, Avda Complutense 22, Madrid
The density of neutral species in the periphery of a hot plasma, such as in those generated for Fusion
research, represents a net particle source, ideally in equilibrium with the recycling flux of particles
escaping the plasmas due to limited magnetic confinement. Its measurement in Fusion plasmas is of
crucial interest in particular when divertors are used for the control of the particle and power outflux,
and several concepts have been put forth for its recording (1). In limiter devices, however, its
measurement has always been rather problematic. This is mostly due to the difficulty in defining the
concept of pressure itself under such anomalous conditions, i.e., in the region between the hot plasma
and the walls, where strongly non-thermal equilibrium conditions prevail. Even so, the recording of
the manometer readings during the plasma production can provide very useful information about the
particle confinement and recycling. In the TJ-II stellarator (2), a set of manometers, including
Bayard-Alpert gauges and baratrons, is routinely used for the control of the particle fluxes injected
into the plasma. Recently, the direct reading of the pressure evolution during the plasma shot at regions
away from the gas injection ports has also become available. Neutral pressures values in the
order of 10 -5 -10 -4 mbar have been recorded, depending on plasma heating and wall recycling conditions.
In this work, the technique of measurement and the interpretation of the readings will be described.
The implications for the density control of the plasma and the possible improvements for future
analysis of the particle out-flux will be also discussed.
1. H.F. Dylla. J. Vac. Sci. Tech. 20 (1982) 119
2. F.L Tabarés, A. García, J. Botija, 45 Vacuum (1994) 1059
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