1 - Nuclear Sciences and Applications - IAEA

HEATING OF PEAKED DENSITY PROFILES
PRODUCED BY PELLET INJECTION IN JET
JET TEAM*
(Presented by G.L. Schmidt)
JET Joint Undertaking,
Abingdon, Oxfordshire,
United Kingdom
Abstract
IAEA-CN-50/A-IV-l
HEATING OF PEAKED DENSITY PROFILES PRODUCED BY PELLET INJECTION IN JET.
A transient enhancement in performance of JET limiter discharges has been obtained when a
peaked density profile formed by pellet injection is heated by using either ICRH alone or in combination
with NBI. Pellet ftielling is applied during the current rise. Heating follows the fuelling sequence and
must be localized predominantly within the plasma core. Electron density profiles are strongly peaked
immediately following the pellet injection sequence, ne(0)/vo| < 5, and retain a central peak while
decaying during the period of enhancement. At a power level of 19 MW (Prr = 12.5 MW,
Pnb = 5 MW and Poh = 1.5 MW) and a central density of 6 x 10 19 m~\ central ion and electron temperatures
of 10.5 and 12 keV are obtained in 3 MA, 3.1 T discharges. Global energy confinement
1.6 times the L-mode level has been obtained. Values of nd(0)Ti(0)TE(a) in the range from 1 to
2 x 10 20 rn" 3 -keV-s are achieved. Peak neutron rates can exceed those in similar, non-enhanced shots
by factors of three to five and increase strongly with heating power. Central ion and electron pressure
can be enhanced by a factor of two to three. Electron pressure can be > 1 bar with a gradient of
4 bar-m" 1 . Ballooning stability limits are approached within the plasma core. The period of enhanced
performance has extended up to 1.2 s into the heating pulse, terminating spontaneously. The longest
periods terminate with enhanced fluctuations and a strong and rapid decrease in central electron and ion
temperatures. Although MHD activity can be present during this period, no sawtooth activity appears.
1. Introduction
The combination of peaked density profiles produced by pellet fueling with strong,
central ICRF heating has been proposed as a means to enhance performance of limiter
discharges! 1,2,3]. Such experiments have begun on JET using a pellet injector system
jointly built as pan of the JET/USDOE collaboration on pellet fueling. The fueling
source is a multi-barrel, multiple pellet, pneumatic launcher developed at Oak Ridge
National Laboratory[4]. Initial results were reported previously[4,5,6,7]. Improved
performance has been obtained with peaked density profiles in previous ohmic and
NBI heated experiments[2,8,9,10,llj and recently with RF heating in divertor configuration
[12]. Experiments on TFTR[13] and JET[14], with high auxiliary heating
power, have demonstrated improved performance in limiter configurations at high
* See Appendix I to this paper.
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