1 - Nuclear Sciences and Applications - IAEA

108 OKABAYASHI et al.
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Time (ms)
FIG. 8. Raw signals from two Mirnov coils showing the change in broadband activity across the
H-mode transition. The top trace is from a Mimov coil on an upper passive plate near the x-point, and
the lower trace is from a coil situated in the midplane.
mode plasmas must be investigated as the injected power is increased in the
near future.
VI) Summary and Conclusions
Even these early results from PBX-M at low- and moderate-p have
produced tantalizing suggestions of the effects of the close fitting passive
plates. The overall MHD properties in PBX-M plasmas appear to be improved
from those in PBX in that operation in the present device routinely extends to
such lower q-values at moderate indentations (15%) without strong current
ramps. Other indications of this are the long period sawteeth, seen in PBX-M
without current ramps, while the long period sawteeth seen in PBX could be
produced only with strong current ramps. Additionally, the power threshold to
the H-mode has been reduced by about a factor of two going from PBX to
PBX-M. While currents induced on the passive plates by n = 1 magnetic
perturbations are indeed comparable in strength to those seen by the nearby
Mimov coils, these fluctuations are nevertheless still seen in the plasma core on