1 - Nuclear Sciences and Applications - IAEA

IAEA-CN-50/A-I-1 13
poloidal field system [2]. The shape is defined by a matrix converting the magnetic
field measurements at the first wall into flux values at eight points of the desired
plasma surface. The control loop equalizes these eight fluxes. The plasma boundary
is modified by changing the matrix coefficients. The operation of the real time poloidal
feedback loop is schematically shown in Fig. 3. The loop cycle time is 1 ms.
2.3. First wall conditioning
As in all tokamaks, conditioning of the plasma vessel is a prerequisite for
obtaining good plasmas; we have, therefore, tried to reach the following goals [3]:
(a) desorption of water vapour and hydrocarbons by permanently baking the vessel
at 210°C;
(b) creation of an adequate metal surface (in particular, oxide free metal), on which
a carbonization layer could be deposited.
VESSEL
TEMPERATURE —
1 2 3 t 5 6 7 8 9 10 11 12 13 14 15 16 17 18
time (day)
FIG. 4. Time evolution of various partial pressures during first wall conditioning.