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A transient enhancement of the central plasma parameters is observed in pulses where a pellet is injected early in the discharge prior to the occurrence of the q = 1 surface in the plasma and to the onset of a strong auxiliary heating. PEP discharges have been obtained in L- and H-modes at various plasma conditions; they are all characterised by very peaked density profiles. The TRANSP analysis shows that the energy transport of the PEP discharges is reduced in the central region relative to a no-PEP discharge and that chi(eff) is close to the neoclassical value in the core region. Central heating by ICRH leads to improved central electron and ion temperatures and enhanced fusion performance but chi(eff) remains unchanged. The reasons for the good central confinement remain unclear, but it could be associated with a negative shear region in the core of the plasma driven by a strong off-axis bootstrap current. This leads to the stabilisation of ballooning modes and access to the second stability region. The stabilisation of eta(i) mode by the peaked density profile or the correlation of chi(eff) with 1/n(e) are also possible explanations.

Additional information

Authors: BALET B ET AL., JET Joint Undertaking, Abingdon, Oxon. (GB)
Bibliographic Reference: Report: JET-P(93)71 EN (1993) 13 pp.
Availability: Available from the Publications Officer, JET Joint Undertaking, Abingdon, Oxon. OX14 3EA (GB)
Record Number: 199311384 / Last updated on: 1994-11-28
Original language: en
Available languages: en
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